eXtra Botany
Commentary
Speedy small stomata?
Key words: Carbonic anhydrase, efficiency, flashing light,
osmolarity, photoinhibition, rate, safety, stomata, zinc.
John A. Raven*,†
Introduction
School of Plant Biology, University of Western Australia, 35 Stirling
Hoghway, Crawley, WA 6009, Australia
Stomata have had, and continue to have, an important role
in the colonization of the land by embryophytes as part of
the mechanism of homoiohydry (Cowan, 1977; Cowan and
Farquhar, 1977; Raven, 1977, 1984a, 2002; Wong et al., 1979;
Willmer and Fricker, 1996; Edwards et al., 1998; Beerling and
Franks, 2009; Franks and Beerling, 2009; Berry et al., 2010;
Haworth et al., 2011; Chater et al., 2013; Vialet-Chabrand
et al., 2013; Raven and Edwards, 2014). There is also great
agricultural and horticultural interest in manipulating stomatal behaviour (Jones, 2004). As well as regulating the ratio
of transpiratory water loss to carbon dioxide assimilation
under varying conditions to allow some photosynthesis, the
closure of stomata maintains plant hydration and prevents a
catastrophic loss of xylem water conductance for periods varying with the plants and the environment under conditions of
restricted water availability from the soil and/or a large potential for transpiraton.
Stomatal structure and function has been the subject of
much research for well over three centuries (Meidner, 1987).
However, much still remains to be done, and Drake et al. (2013)
have made a significant contribution by suggesting, and testing, three hypotheses about stomatal function in five closely
related species of Banksia (Proteaceae). The first is that the
operating maximum stomatal conductance under standard
conditions is positively correlated with the minimum stomatal conductance just prior to dawn. The second is that stomatal size is negatively correlated with the operating maximum
stomatal conductance under standard conditions, and with
the maximum rate of opening of the stomata in response to
light. The third is that the operating maximum stomatal conductance under standard conditions is negatively correlated
with instantaneous water use efficiency, although there is a
positive correlation with the maximum rate of carboxylation
and of light-saturated electron transport. Drake et al. (2013)
found that all three of the hypotheses were in agreement with
their experimental results.
It is important to note that there are a number of other
implications for plant ecophysiology which relate to stomata
in their completely open state (Franks and Beerling, 2009).
One of these concerns the maximum gas conductance of the
leaf. The units are mol m–2 s–1 if the driving force for diffusion
* E-mail: [email protected]
† Permanent address: Division of Plant Science, University of Dundee at
the James Hutton Institute, Invergowrie, Dundee DD2 5DQ, UK.
Journal of Experimental Botany, Vol. 65, No. 6, pp. 1415–1424, 2014
doi:10.1093/jxb/eru032 Advance Access publication 7 March, 2014
Received 5 August 2013; Revised 9 December 2013; Accepted 9
January 2014
Abstract
Recent work has made progress in relating the size of stomata to stomatal functioning and, in particular, the speed
of opening and closing and its implications. Calculations
of the influence of stomatal size on the potential rate
of osmolarity increase, assuming size-independent ion
influx rate per unit area of guard cell plasmalemma set at
the value found in large (60 μm long) stomata, show that
10 μm long stomata could have at least a 6-fold higher
rate of osmolarity increase. There could be a corresponding decrease in the time taken in going from the closed
to the fully open state from about 1 h to about 10 min; this
is approximately the range found for stomata.. However,
there are no data on the rate of stomatal movement over a
sufficient size range to test this suggestion. Faster opening requires, assuming optimal allocation, a higher activity of the required enzymes per unit volume of guard cells.
This is explored for cytosolic carbonic anhydrase which
is needed in guard cells, at least in the light, for malic
acid synthesis which is involved in stomatal opening in
most stomata. Faster opening and closing of smaller than
of larger stomata could allow closer tracking of environmental (mainly light) variations, although the available
data are not adequate to determine if such a greater
tracking occurs. The range of speeds of stomatal movement is similar to that for photoinhibition-related phenomena, despite the very different mechanisms involved.
© The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved.
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1416 | Raven
is expressed as the difference in mol fraction of the gas. There
is a greater gas conductance (units of mol s–1 for a given pore
area per unit leaf area) for a leaf with many small pores than
for one with fewer large pores, the result of the shorter diffusion path through smaller pores (Franks and Beerling, 2009).
This greater maximum gas conductance, in turn, means that
the potential for overall photosynthesis (mol carbon dioxide
m–2 s–1) is greater for a leaf with more small stomata than for
a leaf with fewer large stomata with the same (fully open)
pore area per unit leaf area (Franks and Berling, 2009).
The present article focuses on the effect of the size of stomata, as well as more general features of stomata, on the
opening (and closing) rates. It first considers the constraints
on the observed phylogenetic range of sizes of stomata, continues with consideration of the range of stomatal movement
rates and constraints on the rate at which stomata can open
(and close) and how these can be related to stomatal size,
and ends with a consideration of how the rate of stomatal
movement relates to stomatal responses to environmental
variations at a higher frequency than that of the diel light–
dark cycle, and a comparison with the time course of the
diversity of mechanisms related to limiting photodamage in
photoinhibition. The rationale for this is the reversibility of
the photoprotection processes, limiting photodamage at high
irradiances while not limiting photon yield at low light, analogous to the role of stomata in restricting the catastrophic
loss of xylem hydraulic conductance while otherwise increasing the water use efficiency of carbon gain.
Evidence on the range of stomatal opening
rates and its relation to stomatal size and
constraints on stomatal size
The reported range of stomatal movement rates are given
in Table 1. There is a considerable range of movement rates.
However, there are not enough measurements, similarity in
experimental conditions, or ability to deal with possible phylogenetic bias, to permit investigation of the relation of the
range of rates with stomatal size.
Hetherington and Woodward (2003) suggested that smaller
stomata open and close faster, and this has been examined
for a relatively small stomatal size range by Drake et al.
(2013). Opening and closing speeds are not only influenced
by the size of the guard cells. Franks and Farquhar (2007)
list these other factors, i.e. guard cell geometry, osmotic shuttling, and variations in mechanical advantage. These factors
are discussed in more detail below and in Appendix 1, under
mechanistic constraints on the speed of stomatal opening
and closing.
The minimum size of cells, including stomatal guard cells,
is set, in part, by genome size (number of base pairs) and,
hence, nuclear size, and the relatively constant ratio of volumes of the nucleus and cytoplasm (Hodgson et al., 2010).
Over a wide range of genome sizes there is a significant positive correlation with the size of stomata (Masterson, 1994;
Beaulieu et al., 2008; Hodgson et al., 2010), with much
smaller phenotypic variation in guard cell size with environmental changes for a given genotype (Franks et al., 2009;
Lomax et al., 2009). The work of Drake et al. (2013) involved
five species of the genus Banksia (Proteaceae) with a range of
stomatal sizes and from different habitats. The close phylogenetic relationship of the species means that size could well
be the predominant factor determining the speed of stomatal
movement, although adaptation to different habitats could
also be a factor. No data are available for the genome size of
these five species.
Stomata are part of the homoiohydric apparatus, and there
is a lower limit of cell and organism size which permits homoiohydry to occur (Raven, 1999a,b; Boyce, 2008). The lower
limit on cell size permitting homoiohydry in vascular plants
seems to be smaller than is allowed by the smallest known
genome size (Raven et al., 2013). The smallest known stomata
are still large enough for diffusive fluxes through the stomatal
Table 1. Comparison of the rates of opening and closing of stomata with rates of increase and decrease of photoprotection by four
mechanisms
Protective mechanism
On and off rates
References
Stomata: balance of photosynthesis and transpiration, limitation of
water loss when evaporative demand exceeds supply
State transitions: attach antennae to PSII at low and moderate
PAR, detach at potentially very high PAR
Chloroplast phototaxis: chloroplasts occupy positions permitting
photon absorption at low incident PAR, move to positions of
minimum photon absorption at very high incident PAR
Non-photochemical quenching: dissipates excess excitation from
PSII other than by photochemistry. In the widespread variant
using a xanthophyll cycle, epoxidized forms of xanthophylls act as
quenchers, non-epoxidized forms do not quench and can act in
photon harvesting
Leaf folding: leaves fold in high PAR, limiting PAR absorption
(Oxalis oregana)
10 min to 1 h for both
opening and closing
Less than 10 min in each
direction
Less than 10 min in each
direction
Raschke and Humble (1973); Jinng (1988);
Franks and Farquhar (2007); Drake et al. (2013)
Mawson and Cumming (1986); Schubert et al.
(1995)
Jeong et al. (2002)
Less than, 20 min in each
direction
Härtel et al. (1996); Färber et al. (1997)
Closure in 2 min, opening in
36 min
Bjorkman and Powles (1981); Powles and
Bjorkmam (1981); Raven (1989)
Speedy small stomata | 1417
pore, predominantly by diffusion described by Fick’s law, as
in the case for larger stomata at more than minimal opening
(Hodgson et al., 2010). There is a very small role for Knudsen
diffusion, involving pores less wide that the mean free path of
the gases concerned, requiring very small stomatal apertures
which permit very little gas exchange, and so contribute very
little to total carbon assimilation and water loss (Hodgson
et al., 2010).
The possible mechanistic constraints on the speed of
stomatal movement for stomata of different sizes are considered in Appendix A1, while the possible constraints on
construction costs of stomata as a function of speed of
opening is considered in Appendix A2. Based on the work
of Drake et al. (2013) the influence of stomatal size on the
potential upper limit of the rate of osmolarity increase has
been calculated. This calculation assumes a constant flux
rate of ions (potassium, protons, chloride) per unit area
of plasmalemma at the value found in large (60 μm long)
stomata. These calculation show that 10 μm long stomata
could have a greater than a 6-fold higher rate of osmolarity increase than a 60 μm long stomata, if stomatal opening rate is limited by plasmalemma fluxes. There could be a
corresponding decrease in the time taken in going from the
closed to the fully open state from about 1 h to about 10 min.
Turning to the possible changes in construction costs for
stomata with different speeds of movement, independently
of whether or not the speed differences are a function of stomatal size, faster opening requires a higher catalytic activity
of enzymes and transporters per unit volume of guard cells
if the resources are optimally allocated. Calculations show
that carbonic anhydrase activity is needed to convert carbon
dioxide into the bicarbonate used in phosphoenolpyruvate
carboxylase. This produces the oxaloacetic acid and, hence,
the malic acid involved in stomatal opening in most plants,
and also that a higher activity is needed for faster opening,
with the zinc requirement for carbonic anhydrase predicting a slight increase in the zinc requirement for the whole
organism.
There is no obvious reason why there should be a difference in the energy costs per opening and closing cycle on a
leaf area basis for faster as opposed to slower stomatal opening and closing, assuming that the predominant control of
speed of stomatal movement is stomatal size. The argument
is that there is an inverse relationship between stomatal size
and stomatal density (number of stomata per unit leaf area)
(Franks and Beerling, 2009), so that the same numbers of
osmols have to be generated in guard cells per unit leaf area
during stomatal opening, and correspondingly removed during closing regardless of stomatal size. Even if there was no
difference in energy cost per cycle as a function of stomatal
opening and closing speeds, there could be greater energy
cost per leaf area for faster moving stomata in an environment of high variability of incident light. High variability
here means a frequency of alternation of high and low light
episodes which is so rapid that even the rapidly opening and
closing stomata could not achieve the degree of opening
appropriate for the steady-state at a particular instantaneous high or low irradiance in the time for which the high
or low irradiance occurs. Under such conditions, more rapid
opening and closing would have a greater rate of energy consumption per unit leaf area than would slower opening and
closing, even though the mean stomatal aperture might be
the same under each irradiance condition independently of
the rate of change of stomatal aperture (see Cowan, 1986,
for arguments on tracking versus averaging environmental
variations).
Tracking versus averaging, evolutionary
constraints on the use of very high speeds
of stomatal movement
Temporal tracking of environmental variations by changed
stomatal aperture is clearly not possible if the environmental fluctuations are faster than the rate at which the stomata
can response (fully closed–fully open–fully closed). There
have been several measurements of the effects of light–dark
alternations of shorter periodicities than the diel light–
dark cycle (Martin and Meidner, 1971; Woods and Turner,
1971; Kirschbaum et al., 1988; Gross et al., 1991; Kaiser
and Kappen, 1997), with systematic studies going back to
Gregory and Pearse (1937). Short-term light–dark alternations have influences on stomata which are superimposed
on the circadian rhythmicity of stomatal aperture (Gregory
and Pearse, 1937; Meidner and Mansfield, 1968; Martin and
Meidner, 1971; Kaiser and Kappen, 1997).
Gregory and Pearse (1937) investigated stomatal resistance in Pelargonium zonale leaves exposed to light–dark
alternations of 5, 10, 20, 45, 60, and 120 s for periods of
several hours and compared with the resistance in continuous light. The alternating:continuous ratios of stomatal
resistance was 1.3 at 5 s alternations, increased to 9.3 at 45
s and decreased to 3.5 at 120 s alternations. Kirschbaum
et al. (1988) examined the effect of light flecks (sunflecks) of
15 s to 5 min durations on the rainforest understorey plant
Alocasia macrorrhiza. Even the shortest light fleck caused
significant stomatal opening, with the maximum response,
in terms of stomatal aperture, attained about 20 min after
the end of the light fleck. Stomatal closing is slower than
opening in response to the light fleck (Woods and Turner,
1971; Kirschbaum et al., 1988). Kaiser and Kappen (1997)
examined Vicia faba stomatal conductance exposed to 5 min
dark and 5, 10, 25, and 55 min of light during the12 h photophase and during the 12 h scotophase. On the first days of
exposure, light–dark alternations in mid-photophase caused
an amplitude of change in stomatal pore area in each cycle
that was consistently about 3–6% of the total range of pore
areas, with increasing, reproducibly different, amplitude
with increasing light periods. The response is smaller near
dawn and dusk with no effect of the light–dark cycles in
the scotophase. The response of pore area to the alternating
light and dark periods decreased on subsequent days of the
treatments, i.e. there was an adjustment to the fluctuations
by decreasing the amplitude of the effect. Could this means
of dampening the response to fluctuating light be related to
an habituation to the fluctuations when they are repeated
1418 | Raven
for a long time? Is the evolutionary expectation that the
fluctuation will have a longer periodicity and that it takes
some time before the plant responds to the shorter than
expected fluctuations by the dampening effect? The variations in technique among these studies, and the absence of
focus on stomatal size, means that further work is needed
before any effect of size on opening speed in light flecks can
be determined.
Even when the environmental fluctuations occur over timescales permitting a significant response in terms of stomatal
opening and closing, there is the question of whether the cost
of tracking the environment in terms of energy consumed in
stomatal movement outweighs the gain in energy (as fixed
carbon) at the least cost of water transpired caused by the
stomatal movement. This point was raised, but not dealt with
quantitatively, by Cowan (1986). Stomatal function serves,
among other things, to avoid catastrophic xylem failure by
restricting transpiration, and, hence, photosynthetic carbon
gain, when water availability is low and/or the potential for
transpiratory water loss is high.
This role of stomata in protecting the plant from damage,
at a cost to carbon gain in photosynthesis (Cowan, 1977,
1986; Cowan and Farquhar, 1977; Raven, 1977; Wong et al.,
1979) has parallels in the various mechanisms of protecting
the photosynthetic system, and especially photosystem II,
from photodamage by high excitation relative to the potential
for use of the products of photochemistry. These mechanisms
restrict the rate of photosynthesis under subsequent lower
fluxes of PAR, and there is presumably a trade-off between
avoiding photodamage and maximizing the mean photosynthetic rate (Raven, 2011). Two examples are leaf movements
(Raven, 1989) and plastid taxes (Jeong et al., 2002) which
restrict the fraction of the incident PAR which is absorbed
by photosynthetic pigments. State transitions detach some
of the antenna pigments from photosystem II so that, while
PAR is absorbed at the same rate in a given radiation environment, a smaller fraction of it reached the reaction centre of
PSII (Raven, 2011). Finally, non-photochemical quenching
[including functioning of the xanthophyll cycle(s)] dissipates
some of the excitation energy arriving at the reaction centre
of PSII (Dimier et al., 2009; Raven, 2011). At the moment,
however, there is not enough information to allow a detailed
comparison of costs and benefits among the processes
(Raven, 2011).
Importantly, in the present context, maintenance of a
high photon yield of photosynthesis in lower light periods
between potentially photodamaging high irradiances require
the various photoprotective mechanisms which decrease
the photon yield per incident photon. These variations in
light supply involve, for example, the times between light
flecks in understorey species and in phytoplankton moving
through the vertical light gradient when entrained in the
vertical movement of water in Langmuir Cells in a wellmixed ocean surface (Dimier et al., 2009). Photoprotection
not only needs to be turned on in high irradiance but also
to be turned off in low irradiance. Photoprotection thus
involves both avoiding damage under potentially damaging conditions and maximizing photon yield under lower
irradiances. As suggested in the Introduction, this is, in a
general way, analogous to stomatal functioning in closing
in order to avoid damage to the hydraulic system under soil
water shortage relative to atmospheric demand, and varying
the aperture in balancing a high rate of carbon gain and a
high water use efficiency.
In considering the possibilities of tracking or averaging
environmental changes in their influence on stomatal processes and on light harvesting and photoprotection processes,
variation in electromagnetic radiation (clouds, light flecks for
understorey plants) is an obvious link. Table 1 shows that
there are overlapping time-scales for stomatal and various
other photoprotective processes, with stomatal movements
generally being slower. The range for stomata relates to phylogenetic factors (graminaceous as opposed to kidney-shaped;
possibly genome size) rather than different mechanisms as in
the case of the various means of photoprotection. However,
it is of interest that the time-scales for the different processes
are similar, despite the very different mechanisms involved
(Table 1), and further investigation of the reasons for this
apparent convergence of tine-scales is needed. A comparison
of the costs and benefits of the processes in Table 1 awaits
further information.
Conclusions
The work of Drake et al. (2013) has made progress in
relating stomatal size to stomatal functioning, including
the speed of opening and closing and its implications.
Prompted by this work, the influence of stomatal size on
the potential for the rate of osmolarity increase has been
calculated, assuming a constant flux rate of ions (potassium, protons, chloride) per unit area of plasmalemma at
the value found in large (60 μm long) stomata,. These calculation show that 10 μm long stomata could have a greater
than 6-fold higher rate of osmolarity increase than 60 μm
long stomata. There could be a corresponding decrease
in the time taken in going from the closed to the fully
open state from about 1 h to about 10 min. Faster opening
requires a higher activity per unit volume of guard cells if
resources are optimally allocated. Calculations show that
carbonic anhydrase activity is needed to convert carbon
dioxide into the bicarbonate used in phosphoenolpyruvate carboxylase which produced the oxaloacetic acid, and
hence the malic acid involved in stomatal opening in most
plants. This could marginally increase the whole organism zinc requirement, especially with faster opening of
stomata. Any faster opening and closing of smaller than
of larger stomata could allow closer tracking of environmental (mainly light) variations. The available data are not
adequate to determine if such a greater tracking occurs for
small stomata.
Acknowledgements
Discussions with David Beerling, William Challenor, Ian Cowan, Dianne
Edwards, Graham Farquhar, Alistair Hethrington, John Hodgson, Lyn
Speedy small stomata | 1419
Jones, Charlie Knight, Hans Lambers, Tracy Lawson, Stephen Long, Enid
MacRobbie, Jonathan Newman, Barry Osmond, Robert Pearcy, Imogen
Poole, Erik Veneklaas, Jonathan Weyers, and Ian Woodward have been
very helpful. The University of Dundee is a registered Scottish Charity, No
SC015096.
Appendix I. Mechanistic constraints on the
speed of stomatal opening and closing as a
function of stomata size
The speed of signal transduction is unlikely to cause a significant delay in opening or closing relative to constraints
imposed by the mechanisms of movement. After signal
transduction, in opening there is what Stålfelt (1927) terms
the ‘Spannungsphase’, in which preparatory reactions but
no movement occurs; this is followed by the ‘Motorphase’ in
which opening occurs. Franks and Farquhar (2007) discuss
the factors determining the speed of stomatal movement.
Guard cell geometry is a significant factor in the speed
of movement; for a given guard cell size, with the ‘dumbbell’-shaped guard cells of grasses giving faster movements
than ‘kidney-shaped’ guard cells found in many other stomata-bearing plants (Hetherington and Woodward, 2003;
Franks and Farquhar, 2007). Other factors determining
the speed of movement are osmotic shuttling (movement
of solutes between guard cells and other epidermal cells)
and the related manipulation of mechanical advantage,
i.e. the difference in osmotic, and hence turgor, pressures
between guard cells and adjacent epidermal cells (Franks
and Farquhar, 2007).
The most likely restriction on the rate of stomatal opening
(and closing) is the rate of production (and removal) of intracellular osmolarity. Willmer and Fricker (1996) point out that
not all of the osmolarity increase in the guard cells which is
required for stomatal opening is generated by the accumulation of potassium ions with an organic anion (mainly malate)
or an inorganic ion (mainly chloride), particularly at low
apertures and the early stages of opening (Allaway, 1973;
MacRobbie and Lettau, 1980; Talbott and Zeiger, 1996).
The additional solute is a neutral organic compound such as
sucrose (Talbott and Zeiger, 1996) derived from new photosynthate generated during opening in the guard cells or, at
least in part, from stored photosynthate. Generation of the
remaining osmolarity involves potassium malate and potassium chloride accumulation (Willmer and Fricker, 1996).
Constraints could involve limits on the rates of proton efflux,
potassium influx, and chloride influx, or of conversion of
new photosynthate or, more likely, organic carbon stored in
the guard cell, into malic acid.
There could be limitation of the rate of osmolarity generation by the activity of the enzymes involved in neutral
solute (e.g. sucrose) or organic acid (e.g. malic acid) production from starch. Starch breakdown to glucose-1-phosphate
allows the synthesis of sucrose, as well as malic acid, by glycolysis, phosphoenolpyruvate carboxylase, and NAD(P) malic
acid dehydrogenase. Even with adequate enzyme activity for
starch breakdown, there could be limitation by the surface
area of starch available for enzyme attack; this could be overcome by having smaller starch grains.
The rate at which potassium malate and potassium chloride can be accumulated could also be restricted by the rates
of potassium and chloride entry, or proton exit, at the plasmalemma. The required net fluxes can be computed from
the data in Table 8.1 in Willmer and Fricker (1996) on the
difference in potassium concentration of open and closed
(or nearly closed) stomatal guard cells of Commelina communis and Vicia faba for which there are, respectively, ten
and seven paired (open and closed) estimates of potassium
concentrations. There are large variations among data sets in
both cases; the means, and ranges, are 408 (181–814) and 169
(62–353) mol m–3 for open and closed Vicia faba guard cells,
and 421 (98–1170) and 155 (43–668) mol m–3 for open and
closed Commelina communis guard cells. There is no obvious relationship, from the limited data available, between
the potassium concentrations and the rate of opening and
closing, which is perhaps not surprising in view of the different techniques used. From these values, the mean increase in
potassium between closed and open stomata is, respectively,
239 and 266 mol m–3. These guard cells are at the large end
of the range for stomata, i.e. about 60 μm long and, 20 μm
in diameter (Lawson et al., 1998; Willmer and Fricker, 1996).
Assuming that the cells with these dimensions are cylindrical with hemispherical ends, the volume and surface area
per cell can be calculated. It is assumed that the guard cell
dimensions used refer to half-open stomata. The guard cell
volume and the mean potassium concentration in guard
cells allows the potassium content per cell to be calculated,
and hence, using the surface area per cell, the area-based
potassium flux per opening event. Assuming that complete
opening takes an hour (Raschke and Humble, 1973; Jinng,
1988; Willmer and Fricker, 1996) and that the potassium
influx rate is constant through the opening process, the net
potassium influx rate per unit of plasmalemma area can be
estimated. The results of these calculations give potassium
influxes of, respectively, 184 nmol m–2 s–1 and 211 nmol m–2
s–1 for the two species. These estimated influxes are toward
the high end of the range cited for tracer fluxes of potassium (as 42K+ and 86Rb+) and chloride (as 82Br-) influxes in
guard cells of these two plants (Fischer, 1972; Pallaghy and
Fischer, 1974; MacRobbie, 1981; Blatt and Clint, 1989; Clint
and Blatt, 1989; Brindley, 1990).
Using the range of potassium fluxes on a plasmalemma
area basis calculated for the large guard cells of Commelina
communis and Vicia faba, it is possible to estimate the rate
of osmolarity increase in a very small guard cell pairs relative to that in the large stomata. For guard cells 10 μm long
and with a radius 1.5 μm for the cylindrical portion and the
hemispherical ends, the volume per unit plasmalemma area
is 6.75 × 10–7 m3 m–2, compared with 6.46 × 10–6 m3 m–2 for
the 60 μm long guard cells. The smaller volume (by a factor
of 0.15) of guard cell which is supplied with potassium by 1
m2 of plasmalemma in the smaller than in the larger stomata
means that the rate of osmolarity increase in the small guard
cells is 6.6 times that in the large guard cells.. As a consequence, the rate of opening could be just over 6.6 times higher
for the smaller than the larger stomata, assuming the same
fluxes per plasmalemma area of potassium (and other ions)
1420 | Raven
in the smaller as in the larger stomata. Instead of an hour
for complete opening as in the lager stomata, with all other
things being equal the smallest stomata could open completely in about 9 min.
Comparing these estimates with other transport processes at the embryophyte or charophycean algal plasmalemma, the highest values for ion fluxes (other than
for action potentials) are for ammonium (see Table 7.7 in
Raven, 1984b). Ammonium enters through channels (Amt
gene product) which do not transport potassium but which,
like potassium transporters, can catalyse either cation uniport or cation:proton symport (=cotransport) (Britto and
Kronzucker, 2008; Ortiz-Ramirez et al., 2011). More relevant
to stomatal opening is active proton efflux, since the influx of
potassium and chloride are powered by the proton electrochemical potential difference across the plasmalemma. The
proton stoichiometries are two proton:one chloride in active
chloride influx and in potassium influx through uniport
channels; or one proton:one potassium occurs with potassium symport (Raven, 1984b; Blatt and Clint, 1989; Clint
and Blatt, 1989; Britto and Kronzucker, 2008). These ratios
involve two (potassium uniport) or three (potassium:proton
symport) protons exported per KCl accumulated; for malate
as the anion, the requirement is for one or two protons per
potassium ion and half a doubly charged malate accumulated. For Commelina communis the required active proton
efflux is, from these stoichiometries, 211–633 mol proton
m–2 s–1. We now discuss how these requirements relate to the
upper limits on proton efflux.
Active proton efflux at the plant cell plasmalemma involves
a P-type proton ATPase moving protons out of the cytosol.
This flux (mol transported m–2 membrane s–1) are the product
of the density of transporters in the membrane (mol transporter m–2 membrane) and the maximum specific reaction
rate of the transporter (mol transported substrate moved
mol–1 transporter s–1), as modulated by the concentration of
substrate on the uptake side and, for electrogenic transport,
the electrical potential difference. For the proton ATPase at
the plasmalemma, an upper limit on the transporter density
of 5.5 nmol m–2 and the ATP hydrolysis rate of 130 mol ATP
mol–1 ATPase s–1 (p.102 of Raven, 1984b) yields an ATP
hydrolysis rate of 715 nmol ATP m–2 s–1. With a proton:ATP
ratio of two for the ATPase the proton flux is 1430 nmol m–2
s–1, and with a proton:ATP ratio of one the flux is 715 nmol
m–2 s–1. (Raven, 1984b; Briskin and Reynolds-Nielman,
1991; Miedena and Prins, 1993). The lower estimate would
just be sufficient to support the fluxes calculated in the last
paragraph. Limitation of porter density per unit area of plasmalemma could be overcome, for a given cell wall area, by
cell wall and hence plasmalemma, invaginations. Such wall
invaginations have occasionally been reported for guard
cells (Thomson and De Journet, 1970; Louguet et al.1990),
but do not permit any correlation with guard cell size to be
established. Greater ion fluxes, including protons, are needed
if stomata open faster (Table 1) and a greater cell surface
area-based ion flux, while smaller stomata, with their greater
surface area per unit volume, could cope with rather faster
opening.
Table A1. Comparison of the in vivo rates of uncatalysed v=conversion of carbon dioxide to bicarbonate with the requirement for
bicarbonate as substrate for a range of metabolic processes.
Process
Rate of bicarbonate
production
(mol m–3 s–1)
References
Uncatalysed CO2 conversion with 1.7 mol m-3 CO2: ‘realistic’ option for a respiring bulky
non-photosynthetic tissue, or a leaf with closed stomata
Uncatalysed CO2 conversion with 5 mol m–3 CO2: ‘realistic’ option for a respiring bulky nonphotosynthetic tissue, or a leaf with closed stomata
Uncatalysed CO2 conversion with 10 mmol m–3 CO2: cytosol of a photosynthesizing
mesophyll cell with partially open stomata
PEPc activity in the cytosol of thermogenic spadices of Arum maculatum
0.063
PEPc in the cytosol of N2-fixing nodules of Glycine max)
0.028
PEPc in the cytosol of lipogenic tissue of Ricinus communis endosperm
0.035
Acetyl CoA carboxylase in the stroma of lipogenic tissue of Ricinus communis endosperm
0.035
PEPc in the cytosol of cluster roots of Hakea rostrata synthesizing and secreting citric acid
PEPc in the cytosol of mesophyll cells involved in generating carbon skeletons for N
assimilation and acid–base regulation related to nitrate assimilation in the light phase of a
light–dark cycle
PEPc in the cytosol of mesophyll cells involved in generating carbon skeletons for N
assimilation and acid–base regulation related to nitrate assimilationin the dark phase of a
light–dark cycle
0.017
0.040
Raven and
Newman (1994)
Raven and
Newman (1994)
Raven and
Newman (1994)
Raven and
Newman (1994)
Raven and
Newman (1994
Raven and
Newman (1994)
Raven and
Newman (1994)
See footnote (1)
See footnote (2)
0.040
See footnote (2)
0.185
0.00037
0.124
Speedy small stomata | 1421
Table A1. Continued
Process
Rate of bicarbonate
production
(mol m–3 s–1)
References
PEPc in the cytosol of guard cells in plants generating malate as two-thirds of the negative
charge in the ionic component of the osmolarity used in stomatal opening
0.055
See footnote (3)
(1) From the citrate synthesis rate in cluster roots (Shane et al., 2004), adjusted to 25 °C with a Q10 of 2, assuming that 10% of the cluster root
volume is cytosol and that all the secreted citrate is synthesized in the cluster roots rather than in the shoot, as in the case of non-cluster-rooted
Brassica napus (Hoffland et al., 1992). There would be a greater requirement for bicarbonate if all the glycolytic products used in respiration, as
well as for citrate efflux, entered mitochondria as malate requiring PEPc.
(2) Nitrate as the only nitrogen source, all nitrate reduced in the leaf mesophyll, equal rates in 12 h photophase and the 12h scotophase. Gross
photosynthetic carbon dioxide fixation rate:nitrate assimilation=50, mean carbon dioxide assimilation rate in the photophase, 2000 nmol m–2
mesophyll area s–1 (Raven and Glidewell, 1981), so nitrate assimilation rate in light and dark is 40 nmol m–2 s–1. In a mature leaf there is no net
requirement for organic nitrogen, so all the organic nitrogen is exported in the phloem. Assuming that nitrogen is exported as a mixture of amino
acids and their amides with one-third negative charge per N, which involved one-third of the nitrogen exported as asparagine and glutamine,
one-third as aspartate and glutamate, and one-third as amino acids whose synthesis does not involve PEPc, i.e. two-thirds bicarbonate are
required per N assimilated. Each nitrate assimilated into this suite of organic N compounds involves the production of 0.67 hydroxyl ions (Raven
and Smith, 1976). If the hydroxyl ions are neutralized by the production of dicarboxylic malic acid, half a bicarbonate is used per hydroxyl
generated, i.e. one-third bicarbonate per N assimilated. The total bicarbonate required is one per nitrate assimilated, so a 1 μm layer of cytosol
has a requirement of 0.04 mol bicarbonate m–3 s–1.
(3) Net potassium influx into guard cells during opening is 165 nmol m–2 guard cell plasmalemma s–1. Two-thirds of the anionic charge
balancing the potassium is dicarboxylic malate (Willmer and Fricker, 1996), i.e. one-third bicarbonate is needed for PEPc per potassium or
55 nmol m–2 guard cell plasmalemma s–1. For a 1 μm thick layer of cytosol in guard cells this corresponds to a need for 0.055 mol m–3 s–1.
Appendix 2. Would faster stomatal
opening mean greater construction
costs and greater operating costs per
opening–closing cycle?
Does rapid opening cost more resource in stomatal constructure, and per opening–closing cycle? Other things being
equal, faster opening needs more enzymes and transporters per unit rate of osmolarity increase (and hence stomatal aperture), regardless of whether faster opening involves
smaller stomata or stomata of the same size for all opening
rates. This means that there is a requirement for additional
energy, carbon, nitrogen, and (for RNA for protein synthesis) phosphorus for the synthesis of the catalytic machinery.
Any such requirement is unlikely to involve a measurable
additional content of carbon, nitrogen, and phosphorus on a
leaf basis, since stomata are a small fraction of the total leaf
biomass. Kubínova (1991) performed a stereological analysis
on leaves of Hordeum vulgare grown in high and low light; in
further calculations the mean of the two growth conditions is
used. The data give the total volume (excluding intercellular
gas spaces) of the leaf (115 mm2), and also the number of
stomata (74 000) per leaf. Assuming that the approximately
40 μm long stomata in this grass can be approximated by two
5 μm radius spheres connected by a cylinder, 20 μm long and
2.5 μm radius, this gives a total stomatal volume of 0.66 mm3
per leaf. The ratio of stomatal volume to leaf volume is thus
only 0.0063. It is likely that stomata have higher protein and
RNA contents per unit volume than some other leaf cell
types (epidermal cells, xylem parenchyma), so the stomata
only contribute about 0.01 to the leaf carbon, nitrogen, and
phosphorus budgets. The same is probably true of the next
element considered which is zinc.
There is also a need for more zinc if additional cytosolic
carbonic anhydrase is needed for a more rapid conversion
of carbon dioxide to bicarbonate to provide the inorganic
carbon substrate required for the additional phosphoenolpyryvate carboxylase activity needed for faster malic
acid synthesis. Carbonic anhydrase occurs in the cytosol of
leaves of C3 plants (Fett and Coleman, 1994; Ludwig, 2011).
This carbonic anhydrase is used to produce bicarbonate as
the substrate for phosphoenolpyruvate carboxylase that is
required for anaplerotic metabolism such as producing the
carbon skeletons for the assimilation of ammonium resulting from nitrate assimilation in mature leaves. These assimilation products are exported from mature leaves with no net
need for organic nitrogen. Phosphoenolpyruvte carboxylase
is also involved in producing the citric acid cycle organic
acids (e.g. malic and citric), as well as being involved in some
mechanism of oxalic acid; these organic acids are used in neutralizing the hydroxyl ions generated in nitrate assimilation
(Raven and Smith, 1976). There is a better-characterized role
of cytosolic CA in C4 photosynthesis, supplying bicarbonate
for PEPc in photosynthesis from the entering carbon dioxide (Ludwig, 2011). The cytosolic CA in C3 plants is probably also involved in facilitating carbon dioxide flux from the
inner side of the plasmalemma to the chloroplast envelope
by enlisting bicarbonate and buffered protons (Enns, 1967;
Raven and Glidewell, 1981; Cowan, 1986).
Willmer and Fricker (1996; Hu et al., 2010) point out that
CA occurs in Commelina communis guard cells with a rather
high activity on a cell chlorophyll basis than in mesophyll cells,
but with rather lower activity than in mesophyll cells on a
protein basis. No indication is given as to the compartment(s)
in which the carbonic anhydrase occurs. Most carbonic
anhydrase in the mesophyll of C3 leaves is apparently in the
1422 | Raven
plastids, i.e. not where phosphoenolpyruvate carboxylase
activity involved in malic acid synthesis occurs. Table A1
gives some calculations of carbonic anhydrase requirement
in supplying bicarbonate from carbon dioxide for a variety of
plant processes, including the production of malic acid in stomatal opening. The calculated values of carbonic anhydrase
requirement in non-photosynthesising tissues are generally of
a similar magnitude to the uncatalysed rate for the ‘realistic’
intracellular carbon dioxide concentrations, with only the
bicarbonate production rates required for the Arum spadix
exceeding the uncatalysed rate. By contrast, the required rates
of bicarbonate production are much larger than the uncatalysed rates for the photosynthesizing tissues, so CA in the
cytosol is clearly required in guard cells as well as in nitrateassimilating mesophyll cells. For the guard cells complete
stomatal closure at night, which is not invariably the case in
non-Crassulacean Acid Metabolism plants, could allow the
uncatalysed production of bicarbonate for malic acid synthesis in the guard cells at the start of the photophase, while the
carbon dioxide concentration inside the leaf was being drawn
down as the photosynthetic rate exceeded the respiratory rate.
Can a requirement for zinc for cytosolic carbonic anhydrase in guard cells be shown in the phenotype of zincdeficient plants? This may seem like a forlorn hope in view
of the absence of a decrease in photosynthetic rate in zincdeficient plants, despite decreased carbonic anhydrase activity (references in Sasaki et al., 1991).. This lack of effect is
perhaps to be expected in view of the multiple roles of zinc
in the cells of oxygenic photolithotrophs (Cooke et al., 2004;
see also Prask and Plock, 1971; Kitaguchi et al., 1987), and
the lack of a clear phenotypic effect on photosynthesis in C3
plants when chloroplastic carbonic anhydrase expression is
specifically decreased (Price et al.1994; Williams et al., 1996;
Ferreira et al., 2008). The phenotypic effect that is observed
for zinc deficiency or chloroplastic carbonic anhydrase downregulation is consistent with a slight decrease in the conductance of carbon dioxide from the atmosphere to Rubisco as a
result of decreased mesophyll diffusive conductance (Cowan,
1986; Raven and Glidewell, 1991; Sasaki et al., 1998) and/or
decreased stomatal conductance (Sharma et al., 1995; Khan
et al., 2004). This later effect could occur through a decrease
in the cytosolic carbonic anhydrase activity required for malic
acid synthesis.
Is there a difference in the construction costs of the cell
walls of stomata that open more rapidly? For stomata of
the same size, cell wall synthesis should have the same cost
for rapid and slow movement. If the faster-moving stomata
are smaller than the larger stomata, the fraction of the cell
mass occupied by cell walls should be the same regardless of
cell size, assuming the same wall composition and the same
mechanical safety factor (Laplace relationship; Raven, 1987).
If the faster-moving stomata are smaller, then the fraction of
the cell mass that is occupied by cell walls should be the same,
granted the assumptions mentioned above (Raven, 1987). If
there is an inverse relationship between stomatal density and
stomatal size, the same pore area as a fraction of leaf area
would involve the same mass of stomatal cell walls on a leaf
area basis. These arguments suggest that there is no obvious
reason why faster-moving stomata should have different wall
synthesis costs for a given maximum conductance of a leaf
of a given size.
There is no obvious reason why there should be a difference
in the energy costs per opening and closing cycle on a leaf area
basis for faster as opposed to slower stomatal opening and closing, assuming that the predominant control of speed of stomatal movement is stomatal size. The argument is that there is an
inverse relationship between stomatal size and stomatal density
(number of stomata per unit leaf area) (Franks and Beerling,
2009), so that the same numbers of osmols have to be generated
in guard cells per unit leaf area during stomatal opening, and
correspondingly removed during closing regardless of stomatal
size. Even if there was no difference in energy cost per cycle as
a function of stomatal opening and closing speeds, there could
be greater energy cost per leaf area for faster moving stomata in
an environment of high variability of incident light. High variability here means a frequency of alternation of high and low
light episodes which is so rapid that even the rapidly opening
and closing stomata could not achieve the degree of opening
appropriate for the steady-state at a particular instantaneous
high or low irradiance in the time for which the illumination
occurs. Under such conditions, more rapid opening and closing
would have a greater rate of energy consumption per unit leaf
area than would slower opening and closing, even though the
mean stomatal aperture might be the same under each irradiance condition independently of the rate of change of stomatal
aperture (see Cowan, 1986, for arguments on tracking versus
averaging environmental variations).
References
Allaway WG. 1973. Accumulation of malate in guard cells in guard cells of
Vicia faba during stomatal opening. Planta 110, 67–70.
Beaulieu JM, Leitch HJ, Patel S, Penharden A, Knight CA., 2008.
Genome size is a strong predictor of cell size and stomatal density in
angiosperms. New Phytologist 179, 975–986.
Beerling DJ, Franks PJ. 2009. Evolution of stomatal function in ‘lower’
land plants. New Phytologist 183, 921–925.
Berry JA, Berling DJ, Franks PJ. 2010. Stomata: key players in the
earth system, past and present. Current Opinion in Plant Biology 13,
223–240.
Bjorkman O, Powles SB. 1991. Leaf movement in the shade species
Oxalis oregana. I. Response to light level and light quantity. Role in
protection against injury by intense light. Carnegie Institute of Washington
Year Book 80, 59–62.
Blatt MR, Clint GM. 1989. Mechanism of fusicoccin action: kinetic
modification and inactivation of K+ channels in guard cells. Planta 178,
509–523.
Boyce CK. 2008. How green was Cooksonia: the importance of size
in understanding the early evolution of physiology in the vascular plant
lineage. Palaeobiology 34, 179–194.
Brindley HM. 1990. Fluxes of 86Rb+ in ‘isolated’ guard cells of Vicia faba
L. Planta 181, 432–439.
Briskin DP, Reynolds-Nielman I. 1991. Determination of the H+-ATP
stoichiometry for the plasma membrane H+-ATPase from red beet (Beta
vulgaris) storage tissue. Plant Physiology 93, 242–250.
Britto T, Kronzucker HJ. 2008. Cellular mechanism of potassium
transport in plants. Physiologia Plantarum 123, 637–650.
Chater C, Graham JE, Beerling DJ. 2013. Early evolutionary acquisition
of stomatal control and development gene signalling networks. Current
Opinion in Plant Biology 13, 233–240.
Speedy small stomata | 1423
Clint GM, Blatt MR. 1989. Mechanism of fusicoccin action: evidence
for concerted modulation of secondary K+ transport in a higher plant cell.
Planta 178, 495–508.
Cooke R, Hurd CL, Peake BM, Raven JA, Rees TAV, Lord M. 2004.
The occurrence and significance of spatial and temporal variations in
Fe and Zn content of Hormosira banksii in New Zealand. New Zealand
Journal of Marine and Freshwater Research 38, 73–85.
Cowan IR. 1977. Stomatal behaviour and environment. Advances in
Botanical Research 4, 117–228.
Cowan IR. 1986. Economics of carbon fixation in higher plants. In: Givnish
T, ed. 117–128. Cambridge, UK. Cambridge University Press, 421–493.
Cowan IR, Farquhar GD. 1977. Stomatal function in relation to leaf
metabolism and environment. Symposia of the Society for Current Biology
31, 471–505.
Dimier C, Tramontano F, Geider RD, Raven JA, Benoit C. 2009.
Growth and photoregulation dynamics of the picoeukaryote Pelagomonas
calceolata in fluctuating light. Limnology and Oceanography 53, 823–836.
Drake PL, Froend RH, Franks, PJ. 2013. Smaller, faster stomata:
scaling of stomatal size, rate of response, and stomatal conductances.
Journal of Experimental Botany 64, 495–505.
Edwards D, Kerp H, Haas H. 1998. Stomata of early land plants: an
anatomical and ecophysiological approach. Journal of Experimental
Botany 49, 255–278.
Enns T. 1967. Facilitation by carbonic anhydrase of carbon dioxide
transport. Science 155, 14–47.
Färber A, Young A, Ruban AV, Horton P, Jahns P. 1997. Dynamics
of xanthophyll-cycle activity in different antenna subcomplexes in the
photosynthetic membranes of higher plants. Plant Physiology 115,
1609–1618.
Ferreira FJ, Guo C, Coleman JR. 2008. Reduction of plastid-localized
carbonic anhydrase activity results in reduced Arabidopsis seedling
survivorship. Plant Physiology 147, 585–594.
Fett JP, Coleman JR. 1984. Characterization and expression of two
cDNAs encoding carbonic anhydrase in Arabidopsis thaliana. Plant
Physiology 105, 707–713.
Fischer RA. 1972. Aspects of potassium accumulation by stomata of
Vicia faba. Australian Journal of Biological Sciences 25, 1107–1123.
Franks PJ, Beerling DJ. 2009. Maximum leaf conductance driven
by CO2-effects on stomatal size and density over geological time.
Proceedings of the National Academy of Sciences, USA 106,
10343–10347.
Franks PJ, Drake PL, Beerling DJ. 2009. Plasticity in maximum
stomatal conductance constrained by negative correlation between
stomata size and density: an analysis using Eucalyptus glabrus. Plant, Cell
and Environment 32, 1737–1748.
Franks PJ, Farquhar GD. 2007. The mechanical diversity of stomata and
its significance in gas-exchange control. Plant Physiology 143, 78–87.
Gregory FG, Pearse H. 1937. The effect on the behaviour of stomata
of alternating periods of light and darkness of short duration. Annals of
Botany New Series 1, 3–10.
Gross LJ, Kirschbaum MIF, Pearcy RW. 1991. A dynamic model of
photosynthesis in varying light taking account of stomatal conductance,
C3-cycle intermediates, photorespiration and Rubisco activation. Plant,
Cell and Environment 14, 881–883.
Härtel H, Lokstein H, Grimm B, Rank B. 1996. Kinetic studies on the
xanthophyll cycle in barley leaves. Influence of antenna size and relations
to nonphotochemical chlorophyll fluorescence quenching. Plant Physiology
110, 471–482.
Haworth M, Elliott-Kingston C, McElwain JC. 2011. Stomatal
control as driver of plant evolution. Journal of Experimental Botany 62,
2414–2423.
Hetherington AH, Woodward FI. 2003. The role of stomata in sensing
and driving environmental change. Nature 424, 901–908.
Hodgson JG, Sharafi M, Jlili A, et al. 2010. Stomatal vs. genome size
in angiosperms: the somatic tail wagging the genome dog? Annals of
Botany 105, 573–584.
Hoffland E, van den Boogaard R, Nelemanns J, Findensegg
GR. 1992. Biosynthesis and root exudation of citric and malic acids in
phosphate-starved rape plants. New Phytologist 122, 675–680.
Hu H, Boisson-Dernier A, Israelsson-Nordstrδm M, Bδhmer M,
Xue S, Ries A, Godoski J, Kuhn JM. Schoeder JI. 2010. Carbonic
anhydrases are upstream regulators of CO2-controlled stomatal
movements in guard cells. Nature Cell Biology 12, 87–93.
Jeong WJ, Park Y-I, Suh K, Raven JA, Yoo O. Liu JR. 2002. A large
population of small chloroplasts in tobacco cells allows more effective
chloroplast movement than a few enlarged chloroplasts. Plant Physiology
129, 112–121.
Jinng N. 1988. Methionine induced stomatal opening in Commelina
communis. Scientific Bulletin of the Faculty of Education, Osaka University
39, 61–71.
Jones HG. 2004. Irrigation scheduling: advantages and pitfalls of plantbased methods. Journal of Experimental Botany 55, 2427–2436.
Kaiser H, Kappen L. 1997. In situ observations of stomatal movements
in different light–dark regimes: the influence of endogenous rhythmicity and
long-term adjustments. Journal of Experimental Botany 48, 1587–1589.
Khan HR, McDonald GK, Rengel Z. 2004. Zinc fertilization of water
stress affects plant water relations, stomatal conductance and osmotic
adjustment in chickpea (Cicer arietinum L.). Plant and Soil 267, 271–284.
Kirschbaum MUF, Gross LJ, Pearcy RW. 1988. Observed and modeled
responses to dynamic light environments in the shade plant Alocasia
macrorrhiza. Plant, Cell and Environment 11, 111–121.
Kitaguchi K, Obata H, Kondo T. 1987. Effect of zinc deficient on 80S
ribosome content of meristematic tissues of rice plant. Soil Science and
Plant Nutrition 33, 423–429.
Kubínova L. 1991. Stomata and mesophyll characteristics of barley leaf
as affected by light: stereological analysis. Journal of Experimental Botany
47, 995–1001.
Lawson T, James W, Weyers J. 1998. A surrogate measure of stomatal
aperture. Journal of Experimental Botany 49, 1397–1403.
Lomax BH, Woodward EI, Leitch IJ, Knight CA, Lake JA. 2009.
Genome size as a predictor of guard cell length in Arabidopsis thaliana is
independent of environmental conditions. New Phytologist 181, 311–314.
Louguet P, Coudret A, Couet-Castelier J, Lascene G. 1990. Structure
and evolution of stomata. Biochimie und Physlogie der Pflanzen 186,
273–287.
Ludwig M. 2011.The molecular evolution of β-carbonic anhydrase in
Flaveria. Journal of Experimental Botany 62, 3071–3081.
MacRobbie EAC. 1981. Ion fluxes in ‘isolated’ guard cells of Commelina
communis L. Journal of Experimental Botany 32, 545–562.
MacRobbie EAC, Lettau J. 1980. Potassium content and aperture in
‘intact’ stomatal and epidermal cells of Commelina communis L. Journal of
Membrane Biology 56, 249–256.
Martin ES, Meidner H. 1971. Endogenous stomatal movements in
Tradescantia virginiana. New Phytologist 70, 923–928.
Masterson J. 1994. Stomatal size in fossil plants: evidence for polyploidy
in majority of angiosperms. Science 264, 421–424.
Mawson BT, Cummings WR. 1986. The kinetics of in vivo state
transitions in mesophyll and guard cell chloroplasts monitored by 77 K
fluorescence emission spectra. Plant Physiology 82, 873–879.
Meidner H. 1987. Three hundred years of research into stomata. In:
Zeiger F, Farquhar GD, Cowan IR, eds. Stomatal function. Stamford, USA:
Stamford University Press, 7–27.
Meidner H, Mansfield TA. 1968. Physiology of stomata. Maidenhead,
UK: McGraw-Hill, xiii+179.
Miedena M, Prins HBA. 1993. Simulation of the light-induced oscillation
of the membrane potential in Potamogeton leaf cells. Journal of Membrane
Biology 133, 107–117.
Ortiz-Ramirez C, Mora SI, Trejo J, Pantoja O. 2011. PvAMT1:1,
a highly selective ammonium transporter that functions in H+/NH4+
symporter. Journal of Biological Chemistry 286, 31113–31122.
Pallaghy CR, Fischer RA. 1974. Metabolic aspects of stomatal
opening and ion accumulation by guard cells in Vicia faba. Zeitschrift für
Pflanzenphysiology 71, 332–344.
Powles SB, Bjorkman O. 1991. Leaf movement in the shade species
Oxalis oregana. II. Role in protection against injury by intense light.
Carnegie Institute of Washington Year Book 80, 63–66.
Prask JA, Plocke DJ. 1971. A role for zinc in the structural integrity of the
cytoplasmic ribosomes of Euglena gracilis. Plant Physiology 48, 150–155.
1424 | Raven
Price GD, von Cammerer S, Evans JR, Yu JW, Lloyd J, Oja V, Kell P,
Harrison K, Gallager A, Badger MR. 1994. Specific reduction of chloroplast
carbonic anhydrase activity by antisense RNA in transgenic tobacco has a
minor effect on photosynthetic CO2 assimilation. Planta 193, 331–340.
Raschke K, Humble GD. 1973. No uptake of anion required by opening
stomata of Vicia faba: guard cells release hydrogen ions. Planta 115, 47–57.
Raven JA. 1977. The evolution of vascular land plants in relation to
supracellular transport processes. Advances in Botanical Research 5,
153–219.
Raven JA. 1984a. Physiological correlates of the morphology of early
vascular plants. Botanical Journal of the Linnean Society 88, 105–126.
Raven JA. 1984b. Energetics and transport in aquatic plants. New York:
A.R. Liss, xi+587.
Raven JA. 1987. The role of vacuoles. New Phytologist 106, 357–422.
Raven JA. 1989. Fight or flight: the economics of repair and avoidance of
photoinhibition of photosynthesis. Functional Ecology 3, 5–19.
Raven JA. 1999a. The minimum size of seeds and spores in relation to
the ontogeny of homoiohydry. Functional Ecology 13, 5–14.
Raven JA. 1999b. The size of cells and organisms in relation to the
evolution of embryophytes. Plant Biology 1, 2–12.
Raven JA. 2002. Selection pressures on stomatal evolution. New
Phytologist 153, 371–386.
Raven JA. 2011. The cost of photoinhibition, Physiologia Plantarum 142,
87–104.
Raven JA, Beardall J, Larkum AWD, Sanchez-Baracaldo P. 2013.
Interaction of photosynthesis with genome size and function. Philosophical
Transactions of the Royal Society of London B. 368, 1–11. doi:2010264.
Raven JA, Edwards D. 2014. Photosynthesis in early land plants:
adapting to the terrestrial environments. In: Hanson DT, Rice SK, eds.
Photosynthesis of Bryophytes and early land plants. Dordrecht: SpringerVerlag, 29–58.
Raven JA, Glidewell SM. 1981. Processes limiting photosynthetic
conductance. In: Johnson CB, ed. Physiological processes limiting plant
productivity. London: Butterworths, 109–136.
Raven JA, Newman IR. 1994. Requirement f or carbonic anhydrase
activity in processes other than photosynthetic inorganic carbon
assimilation. Plant, Cell and Environmen.17, 123–130.
Raven JA, Smith FA. 1976. Nitrogen assimilation and transport in
vascular land plants in relation to intracellular pH regulation. New
Phytologist 76, 415–431.
Sasaki H, Hirose T, Watanabe Y, Ohsugi R. 1991. Carbonic anhydrase
activity and CO2-transfer resistance in Zn-deficient rice leaves. Plant
Physiology 118, 929–934.
Shane MW, Cramer MD, Funayama-Naguchi S, Cawthray GR, Millar
AH, Day DA, Lambers H. 2004. Developmental physiology of cluster
root carboxylate synthesis and exudation in harsh hakea expression of
phosphoenolpyruvate carboxylase and the alternative oxidase. Plant
Physiology 135, 549–560.
Schubert HS, Forster RM, Sagent S. 1996. In situ measurement of
state transitions in cynobacterial blooms: kinetics and extent of state
change in relation to underwater light and vertical mixing. Marine Ecology
Progress Series 128, 99–108.
Sharma ON, Tripathi A, Bist SS. 1995. Zinc requirement for stomatal
opening in cauliflower. Plant Physiology 107, 751–756.
Stålfelt MG. 1927. Die photischen Reaktionen im
Spaltoffnungsmechanisms. Flora 121, 236–272.
Talbott LD, Zeiger E. 1996. Central roles for potassium and sucrose in
guard-cell osmoregulation. Plant Physiology 111, 1051–1057.
Thomson WW, De Journet R. 1970. Studies on the ultrastructure of
guard cells of Opuntia. American Journal of Botany 574, 309–316.
Vialet-Chabrand S, Dreyer E, Brendl O. 2013. Performance of a
new dynamic model for predicting diurnal time-courses of stomatal
conductances at the leaf level. Plant, Cell and Environment 36,
1529–1546.
Williams TG, Flanagan LB, Coleman JR. 1996. Photosynthetic gas
exchange and discrimination against 13CO2 and C18O16O in tobacco plants
modified to have low chloroplastic carbonic anhydrase. Plant Physiology
112, 319–326.
Willmer C, Fricker M. 1996. Stomata, 2nd edn. London: Chapman and
Hall, xvi+375.
Wong SC, Cowan IR, Farquhar GD. 1979. Stomatal conductance
correlates with photosynthetic capacity. Nature 282, 424–426.
Woods DB, Turner NC. 1971. Stomatal response to change in light
by four tree species of various shade tolerance. New Phytologist 70,
72–84.