THE BASIC PLANT CELL STRUCTURE
Cell and vacuolar
membrane
Chloroplast with grana
Nucleus and
nucleoli
Mitochondrion
,
endoplaqmic
reticulum
chloroplast
Microtubules
<3.2
<1D1=1
'
...4
.
Nrt
Golgi apparatus
Golgi
apparatus
Coiled DNA in
protein
Starch grains
Enduplasmic
reticulum
chrorposome
nucleolus
nucleus
nuclear
membrane
riboeomes
vacuole
cell wall
plasma membrane
mitochondrion
leucoplast
Diagram showing the ultrastructure of a cell. Code: CP, chloro-
TABLE 4.2 The Parts of the Cella
Cell part
Plant cell, 1880
Primary cell wall, 1665
Cellulose microfibrils, 1948
Cellulose molecules, 1922 (x ray), 1949
Amorphous matrix
Middle lamella
Protoplast, 1846
Protoplasm, 1840
Cytoplasm, 1882, 1957
Chloroplast, 1702, 1953
Chromoplast, 1900, 1958
Dimension
2-5 p,
10-25 nm (indefinite length)
0.834 x 0.8 nm
Protection, strength
Mechanical strength
Strength
2p.
0.025-2 mm
Adhesion between cell walls
Homeostatic unit
Synthetic and developmental
reactions under direction of
nucleus
2-20
Photosynthesis
Accumulation of carotenes
and similar pigments
Starch storage
2-10p
Amyloplast, 1884, 1955
Leucoplast, 1883, 1957
Mitochondrion, 1897, 1947
Dictyosomes, 1927, 1956
Endoplasmic reticulum, 1957
Ribosomes, 1955
Sphaerosomes, 1919, 1967
Microbodies, 1965
2-25 ti
2-14
2 x 2-14
3
17 nm (indefinite length)
20 nm
2µ
0.1-2.0
Microfibrils, 1959
Tonoplast, 1877, 1960
28 nm (indefinite length)
8 nm
Plasmalemma, 1880(?), 1954
8 nm
Crystals, 1963
Plasmodesmata, 1879, 1957
Nucleus, 1831
Nuclear envelope, 1907, 1955
Function
2p,
5-30
25 nm
Respiration
Enzyme synthesis
Protein synthesis
Protein synthesis
Lipid synthesis (?)
Compartmentalization of various enzymes
Various functions
Regulation of exchange between vacuole and cytoplasm
Regulation of exchange between cytoplasm and external solution
Unclear,
possibly
protein
storage
Protoplasmic bridge between
cells
Contains genetic information
necessary for normal cell
development and activity
Separates nucleoplasm from
cytoplasm
Nucleoplasm, 1879
Chromatin, 1880
Nucleoproteins, 1869
(I3
Dimension
Cell part
Nucleic acids, 1889
DNA, 1924
DNA helix, 1953
Unit fibers, '1963
1.8 nm (indefinite length)
12.5 nm (indefinite length)
tJucleolus, 1882, 1958 (animal, 1952)
RNA
1-5 ti
Rihosomes, 1956
rSitosis, 1882, '1960
15 nm
Interphase, 1830
Chromosome, 1888, 1955
2-200,a
Kinetochore
Centromere 1925
Chromatid, 1900
Prophase
Metaphase, 1884
Anaphase, 1884
Telophase, 1894
Spindle, 1883, 1960
Fibers, 1881, 1960.
Microtubules, 1960
Cytokinesis, 1891, 1960
Equatorial plate, 1875, 1958
Vacuole, 1835, 1957
Water
Inorganic salts
Various organic solutes
Crystals
1-10,0
Various indefinite lengths
28 nm (indefinite length)
Various
Function
Carries genetic code
Encompasses DNA helix and
nucleoproteins
RNA synthesis
information
Transferal
of
from DNA to cytoplasm
Protein synthesis
Replication of DNA and distribution to daughter cells
Replication of DNA
Vehicle carrying DNA helix in
replication and distribution
Region of chromosome to
which spindle fibers are
attached
One-half of a chromosome
Stages or mitosis
inCytoplasmic structure
volved in moving chromosomes
During mitosis
Division of cytoplasm to
daughter cells, frequently
unequal
First stage in separation of
daughter cells
Various functions important
in water economy of cell
CELL GROWTH
B
(cD
ft
)
/
p
Diagrams to illustrate plant cell growth. A. By cell division.
B. By cell enlargement. C. By cell differentiation.
1\
s,A
T
G
C
P
PI
T
's
NP
s
A
,
P
The double helix of DNA. -->
—S'
Diagram of mitosis in a plant cell.
cell wall
nu cleus
A. Metabolic phase
chromosome
chromosome
B. Early prophase
chromatids
spindle
fiber
C. Late prophase
cell plate
forming
cell
plate
new cell wall
original double strand
A
F. Early telophase
G. Late telophase
or)
11.
H. New cells—metabolic phase
E. Anaphase
Replication of DNA.-- ->
H
Mitosis. Series of diagrams showing mitosis in a
cell with six chromosomes. A,
interphase; B, early prophase;
C, late prophase; D, metaphase;
E, anaphase; f, late anaphase
verging toward telophase; G,
late telophase; H, interphase.
new double strands
IIS
- —
SF Cie\vocc•
totel,"
• - '.‘
", '
' • -•
When seen close up; the supercoitrt
turns out to consist of coils withirr.:- .
coils. It looks like a tangled mess,Cr.:•
yet chromosomes make amazingly . : ---few errors in passing genetic inforrt
mation from parents to offspring.'
Half the chromosomal material
comes from one's mother and half
from one's father. Surprising as it
seems, researchers didn't prove until
1956 that the normal human has
46 chromosomes per cell.
A
A human cell contains a total of 46
chromosomes, the X-shaped objects
shown here . The "spindle" fibers
on both sides of the chromosomes•indicate the cell is about tb divide.
phosphate
group
sugar.
,
"41 •'
Xj
S
The "arms" of a chromosome are
thick, tightly coiled columns called
supercoilp. Zebra-like bands on an
arm are detected by staining it with a .
dye. Bands show where DNA and_
proteins are tightly packed.
cientists discovered DNA in the 1860$. However, few suspected
its monumental importance for many decades; most experts assumed
the genetic code was "written" on protein molecules, which were far
bigger than DNA. The turning point came in 1944, when O.T. Avery and
his colleagues at Rockefeller University in New York City conducted
experiments on mice that proved DNA, and DNA alone, transmits
hereditary information. Then in 1953, DNA's structure — a double helix
(see insets (G) and (H)) — was announced by James Watson and
Francis Crick in England. The paired bases (A, T, C and G) are the
"code" that controls cellular activity, in the following way: (1) A DNA ,
strand "unzips" down the middle; (2) a substance called RNA •
polymerase "transcribes" a "complementary" version of DNA — sort ,'
of like a wax mold — onto a strand of "messenger" RNA (ribonucleic
acid); (3) a chubby object called ribosome "reads" the instructions on .
a strand of messenger RNA (like a tape head reading a magnetic tape)
in order to assemble chains of amino acids — the building blocks of
proteins.
Source' 'Human Genebcs' by Sam Smger,
Freemanand Co., 1355
_•
,
•
••
—
.
,
H
Up close, DNA resembles a twisted
ladder. Its "rungs" are paired chemical bases; cytosine (C) always pairs s .
with guanine (G) and thymine (T)
always pairs with adenine (A). The
rungs are held in place by sugarphosphate bonds (on the left and
right sides of the structure) and by
weak hydrogen bonds (dotted lines).
DNA has a "double helix" shape,
similar to two intersecting staircases. Human DNA is six billion base
pairs in length.
This shows a supercoiled strand of
material called chromatin. Whenseen under the electron microscope,
chromatin resembles beads on a
string. The beads are called nucleosomes.
Up close, the nucleosomes turn out '3-0. 1
to be balls of protein called histones .surrounded by DNA. If stretched out
flat, the DNA would be about 200
base pairs in length.
•
Open Stomo
Closed Stomo
(111 :
it
li
l tii
ir:
i
Guord
Cells
/Guard
Cells
Subsidiary
Cells
E
Subsidiary
Cells
A diagrammatic representation of the mechanism of opening of stomata.
Stomata open when the extensible ends of the dumbell-shaped guard cells are expanded,
as in the figure on the right. The expansion is caused by an uptake of water, which itself
is an osmotic consequence of the uptake of potassium salts. Expansion is restricted to the
end regions of the guard cells since the cross-hatched areas are reinforced and relatively
inelastic. The increase in volume of the ends pushes the guard cells apart at the middle to
form an open pore.
F
Some types of tissues, showing only
the cell walls or cell outline, without contents.
A, parenchyma; B-D, epidermis; E, F, collenchyma.
Stomata in
open position
.E0)
(./
Diagram .showing stomata in
the opened and closed
positions.
Some types of
A-C,
sclerenchyma
cells.
cells, with the walls stippled: A, fibers; B, stone
cells; C, an idioblast; D, cork
cells; E, sieve tube and companion cells of phloem, the
sieve tube showing a welldeveloped sieve plate at the
end and some less well-developed lateral sieve areas.
Stomata in
closed position)
nr
SPECIALIZATION OF
PLANT CELLS
A
K
L
M
Xylem cells. A, fiber; B, tracheid; C,
D, vessel segments; E-C, ends of vessel segments,
with progressively less obstructed opening; H M,
types of secondary thickening of xylem cells; H,
annular; I, spiral; J, scalariform; K, reticulate;
L, reticulate-pitted; M, pitted.
-
DIAGRAMS OF BASIC PLANT STRUCTURE
hoof prinlotdia
thoot op. x
Terminal bud
001orylmoch
Primary
growing
zone of
shoot
flower shoot
Leaf
Lateral bud
Branch shoot
Node
Internodo
Stem
node
Internode
194
Node
phloem
cod.
;donna
I
cortex ondocionsis
round hoe
Soil surface
Tap root
Lateral root
xylem
Primary
growing
zone of
lateral root
branch roots
phloem
C
Rylom
Root hairs
opiclormit
Primary growing
zone of tap root
phloe m root apex
root cap
A. the principal
organs and tissues of the body
of a seed plant: B. cross-section
of stem: C, cross-section of
root.
Root cap
A
Typica/ external features and mode of growth of the shoot and root systems.
TRUNK
The cross section of a trunk, showing A, the heartwood, composed of dead
cells; B, the sapwood, which has mane living cells that conduct water and nutrients
upward; C, the annual rings composed of summer and spring wood; D, the medullary rays, which transfer water and food radially; E, the cambium from which are
formed xylem cells on the inside and phloem tissue on the outside; F, the phloem
cells, which conduct elaborated food downward; C, the cork cambium, which
produces cork cells to form the outer hark, H.
Bark
Phloem
Xylem
\ Annual Annual
ring
\ ring
Ray
Xylem
vessel
Cambium
Cor k
cambium
F
Cork: A. xylem ray, B. tangential surface, C. heanwood, D. radial surface, E. sapwood, F. vascular cambium, G. phloem ray. H. phloem (inner bark). I. cork (periderm).
Phloem
sieve tube
Diagram of part of a wood
stem showing two annual
rings. The large xylem vessels are formed in the early
spring.
1°\
PIERRE GALET
A Practical Ampelography
L4
GRAPEVINE IDENTIFICATION
TRANSLATED AND ADAPTED BY
LUCIE T. MORTON
FOREWORD BY
LEON D. ADAMS
Truncate
Reniform
Cordiform
Lt
Outline of a vine leaf
Convex
Orbicular
Pointed
Teeth forms, from nearly flat at
to very narrow at right
Cuneiform
Iry
Wine Grape Varieties
in the
San Joaquin Valley
Division of Agricultural Sciences
UNIVERSITY OF CALIFORNIA
Revised July 1980
Priced Publication 4009
Fig. 1. Typical vInIfera grape leaf with five lobes.
FIg. 2. Main features of the cane.
FIg. 4. Common grape cluster shapes.
.•.1 . 1f) (
Fig. 3. Structure of the grape cluster and Its
attachment to the cane.
Flg. 5. Grape berry shapes.
3
2_1
Bud
Tendril
tAl
.•
Lateral
Petrolar
Leal scar
vascular trace
COnCtuctrni:
fibers
- Internocte
- tqceti,
The cane
Diagrammatic representation of the morphology of the cane.
Abscission layer.
Diagrammatic transverse section through a compound bud (eye) of V.
labruscana (Concord) showing relative position of leaf scar (LS), lateral shoot (LAT),
and three dormant buds (1, 2, 3). Primary bud (1) in axil of prophyll (solid black)
of lateral shoot.
Compound bud and part.of the cane in longitudinal section.
Abbreviations: a — apical meristem of the shoot arising from the primary bud; b —
rudimentary leaf; c — rudimentary inflorescences; d — rudimentary tendril; ph —
phloem; x — xylem; pi - pith; d — diaphragm.
Development of summer lateral. The compound bud or winter eye (e) is
on the dorsal side, while the smaller bud, out of which summer lateral (0 arises, is
on the dorsal side of the shoot.
12_
RAVE 89
U.C. Davis
March 31, 1989
J.C. Morrison's Current Research
Bud Development and Vine Fruitfulness
We have identified four developmental stages that are critical in determining
grapevine fruitfulness. The first critical stage is the period when anlagen
(undifferentiated primordia) inside a developing bud differentiate into cluster primordia.
This occurs in late spring of the year preceeding bud break. Cluster differentiation is
thought to be regulated by plant hormones, but environmental factors can influence
whether anlagen differentiate into clusters or tendrils. Shoots developing in the shaded
interior of vigorous vines tend to differentiate fewer clusters and more tendrils than the
exposed shoots on the same vines.
The second critical stage is the period before the buds go dormant in midsummer.
During this period one or more of the three buds that make up the compound dormant
bud may die. The primary dormant bud is the one most often affected, and when the
primary bud dies, one of the less fruitful secondary buds will push the following spring,
leading to a reduction in crop. In chronically unfruitful vineyards more than 75% of the
primary dormant buds may die. High vine vigor, high nitrogen and shading within the
canopy all seem to be related to the problem of primary bud necrosis.
The third critical stage is the period of bud reactivation in the spring. We have
frequently observed the death of clusters in apparently healthy buds during the weeks
before bud break; this appears to explain why cluster counts from dormant buds are
usually higher than cluster counts after bloom. When cluster death occurs after bud
break, it is referred to as "early bunchstem necrosis". The symtoms of this disorder are
similar to waterberry, a disorder that occurs after veraison. Our work on waterberry
suggests that ammonia toxicity due to a metabolic disorder in the cluster may cause
rachis death; by analogy to the similar symptoms, this may also be involved in rachis
browning and cluster death in early bunchstem necrosis.
The fourth critical period is bloom and fruit set, when the number of berries per
cluster is determined. From 20% to 75% of the flowers on a cluster normally abscise
during this period, but even higher percentages may abscise under conditions of
environmental stress. The percentage of abscising flowers varies greatly with variety and
from year to year, and fruit set is highly unpredictable. The internal and external factors
controlling flower abscission in grapevines are not well understood.
Growth Stages of a Grape Berry
Fruit Growth
•
Stage I
Stage 11
Stage Ill
Size of berries
A
•
Blossom
A
Veraison
Time
Maturity
►
Stigma
Anther
Filament
Style
Ovary
Nectary
Calyptra (CAP)
a
b
Bloom sequence of grape flower: (a) calyptra attached,
(b) calyptra
separating, and (c) open flower.
•
Anther (4 microsporangia)
Pollen gr:
Style
Pollen ti
Stamen (microsporop}
Filament
Stigma
- Style —Pistil (meg,a6porophyll).-
Ovary
d Cametophyt
Ovule
In teitiM
9 Game tophy te
Megasi5orang
Micro
Longitudinal cross section of
grape berry.
1-
Ilecept
Sepal
eduncle
hermaphrodite flower
female flower
hermaphrodite flower physiologically
male by abortion
male flower
ANTI*.
STAMEN
STIGMA
E IlAm ENT-'.
STYLE
PISTIL
1
OVARY
ISUPERIOR).‘
•*- PET Al
O VULE
DORSAL CARP/LEARY
TRACE
VENTRAL CARIMARY
T R ACE
SEPAL
i - R ECEP TAM
The flower, the berry, and the seed. A. Unopened grape flower. B. Dehiscence of the flower and formation of the
calyptra. C. Perfect flower. D. Female or pistillate flower with reflex stamens. E. Male or staminate flower, no apparent
ovary. F. Physiologically male with a partially aborted ovary. G. Unopened flower cut longitudinally. H. Ovaries with 2 and 3
carpels cut transversely. I. Berry cut longitudinally. J. Berry cut transversely. K. Dorsal side of seed. L Ventral side of seed.
M. Seed of V. rotundifolia. N. Seed cut longitudinally. 0. Seed cut longitudinally. P. Seed cut transversely. C. Embryo (c,
cotyledon; h, hypocotyl; s, suspensor).
I O2
LEST
)
PEDICE
Longitudinal section of a grape flower (hermaphroditic) of 'Muscat
Hamburg' grape, showing vascularization.
Berry
Di ckwl eter
St age
Sto,r
Sta5e
Seeo
Form c■-i-► on
Ce11 1=h t a rr(qAt
gloom
Berr i
MAiu
Vera isevl
e rn ■ 5try
TPA
—
—20
o\ c \ck
— IS
—10
- so
5 1 00
Ve rssis Pn
1V1o\--4. 064 y
3
Comparative anatomy of one-year-old V. vinifera cane (A) and root (B):
transverse sections.
Although the internal structure of the secondary vascular cylinder (phloem, xylem
and pith) is similar in Vitis stems and roots, the relations of the various tissues in the
vascular cylinder differ considerably. Consequently, the anatomy of one-year-old
cane (A) can easily be distinguished from that of the one-year-old root (B) by:
(a) its strikingly larger pith;
(b) its very numerous and much narrower medullary rays;
(c) its narrower phloem section;
(d) the presence of perivascular fibres outside each phloem bundle;
(e) the presence of a thick dead bark, and
(f) its dorsiventral structure.
Abbreviations: rh — rhytidoma (dead bark); to — dead cortex; co — cambium;
pe — periderm; phf — phloem fibres; pefi — perivascular fibres; ph — phloem; x —
xylem:// — medullary ray of the first order; /2 — medullary ray of the second
order; /3 — medullary ray of the third order; px — residues of the primary xylem;
and pi — pith.
Fig. 3.2. Diagrammatic longitudinal section of the root tip of the vine, indicating
distribution of meristematic activity. (Meristem: tissue in which cell division predominates.
Abbreviations: pl — plerome, meristem forming the core of the axis composed of
the primary vascular tissues and associated ground tissue; pb — periblem, incristem
forming the cortex; pd — protoderm, meristematic tissue giving rise to the epidermis;
pli — plerome-initials; pbi — periblem-initials; dc — dermo-calyptrogen, mcristcm
giving rise to the root-cap; and c — calyptra.
Fig. 3.3. Primary structure of the root. Diagrammatic transverse section of the root
of the vine in the absorption zone.
Abbreviations: e — epidermis; many epidermal cells have elongated perpendicularly to the surface to form root-hairs, rh; the root-hairs soon die, and the root is
then covered by intercutis, i; c — cortex,which is distinguished by its well-developed
intercellular spaces. In the centre is the vascular bundle with two strands of xylem
and phloem respectively, enclosed by the endodermis. The number of vascular
bundles varies from 2 to 8, depending on species and root size
Grapevine Root systems
(- Ov rce.
()Kits" ug, v,)
Introduction
Roots are vital to overall vine growth and production, but relatively
little is known regarding their activity because of the difficulty in gaining
access to study root systems. The adage "out of sight, out of mind" has
always plagued our understanding of root systems.
Many of the findings covered in this presentation are from studies of
roots of mature fruiting vines growing in an underground root observation
chamber in Australia. It is important to study fruiting vines because of
the intimate relationship between growth of roots, shoots and fruits. This
makes it difficult to study vines in a laboratory because of the difficulty
of growing small fruiting vines. Digging a trench to study root growth has
its limitations because cutting roots, just like cutting shoots, will stimulate growth, particularly lateral growth.
Grapevines appear to be unique when compared with most cultivated fruit
plants, mainly due to two aspects of their root systems.
Firstly, vines apparently do not have root hairs. This is based on observations of vines grown in root chambers over a period of about 10 years. Root
hairs are elongated cells of the epidermis and should occur just behind the
growing tip. This is considered the zone of absorption and the lack of root
hairs greatly reduces the surface area of the root.
Secondly, vine root systems are sparse and have very low root densities
compared with other species, but this is compensated for by an extensive root
system which taps a large volume of soil. Thus vines are adaptable to a wide
range of soil types and can tolerate drought conditions. Vines will survive,
but not necessarily thrive in unfavorable conditions.
Root Functions
1) Anchor:
Vine root systems are like an uncontrolled, wild inverted vine without
leaves. There are main structural and, branching roots, as well as new
roots produced each year. This is very similar to the aerial arms of a vine
with new shoots being produced each year. One of the functions of the root
system is to hold the vine down and the weak part in the system is the trunk
above ground. Therefore, vines often will snap rather than blow over and be
uprooted.
2) Absoprtion:
The root system supplies the water and nutrients needed by the vine.
Water and nutrients are actively and selectively absorbed and then transported to the aerial parts of the vine. For example, roots have the ability
1LB
to selectively absorb potassium and reduce the amount of sodium absorbed.
The root system can also be used to store carbohydrate and nitrogen reserves
for the vine which may then be utilized during the period of rapid shoot
growth, budbreak and fruit ripening.
3) Metabolic activity:
This is an interesting and important function of root systems. The active
site for the metabolism is the root tip which regulates shoot growth, cluster,
flower and fruit development.
Developing buds have a group of cells known as primordia, which have the
potential to develop into clusters or tendrils. Recent information indicates
that the fate of these primordia, i.e. whether they become clusters or tendrils,
depends to a large extent on root produced hormones, particularly cytokinins.
Thus, cuttings have the potential to carry clusters, but rarely do because the
lack of an established root system indicates the level of cytokinin production is
very low. Also, young leaves are a greater sink for cytokinin than clusters,
and leaf growth is stimulated at the expense of cluster growth. However, it
is possible to develop clusters on cuttings by removing the leaves below the
cluster before they develop.
Shoot growth is
reduce shoot growth
shallow soil have a
vines grown in deep
correlated with root volume. A small root volume will
compared with a larger root volume. Thus, vines grown in
restricted root system and lower vigor compared with
soil with a larger root system.
Roots also produce hormones which apparently exert some control over the
numbers of seeds produced in grape berries. Experiments with tomatoes have
shown that restricting the root volume reduces the number of seeds produced in
the fruit, which in turn reduces the strength of the fruit as a sink for carbo
hydrate. This is best demonstrated by a pot-bound tomato plant which may be
very vigorous, but only produce small tomatoes that do not size up. Whether
a similar relationship occurs in grapes is not known.
Root Growth and Development
1) Development of roots:
Cuttings produce large numbers of fine white roots which radiate from the
cutting. The root tip contains the active meristem for cell division and is
protected by the root cap as it pushes through the soil. Behind the root tip,
the cells elongate and differentiate into the xylem and phloem and this is
called the absorption zone. This zone may be up to 20 cm long and depends on
the rate of root growth and browning, a process known as suberization. This
is the development of bark layers on the root surface and occurs more rapidly
when the roots are actively growing than in winter.
The roots may become permanent structural roots or lose their function and
die. What controls this phenomenon is not known. Most fine roots die within
a relatively short time.
Structural roots increase in size and may grow to 40 cm (16 inches) in
diameter. The thickness of a root at any one point is a function of its
age and cumulative activity of the branches beyond that point.
Vines, asexually propagated have no tap roots, and the main roots radiate
from the trunk and may be "spreaders" which grow horizontally and branch
frequently or plunging roots which grow downward and have few branches. Some
roots may shrivel and die and this favors the growth of new roots down the
originally formed root cavity. As many as three or four roots have been
observed growing in one old decayed root cavity. New growth can be a resumption of growth of the root tip or new laterals arising from the structural
roots.
2)
Periodicity of root growth:
In mature vines, root growth commences several weeks after budbreak and
there is a peak of root growth after shoot growth begins to slow down (see
Figure 1). Thus, root growth and aerial growth alternate; when shoots are
growing rapidly there is little root growth and vice versa. Generally,
root growth is most active immediately following the "grand" period of shoot
growth, and before rapid berry growth commences. During berry growth and
fruit ripening, root growth is suppressed. After harvest a second smaller
peak of root growth occurs (Figure 1).
-
In spring when shoots are growing rapidly, there are very few unsuberized
roots. Thus, both suberized and unsuberized roots must be able to absorb
water. The alternation in growth may be controlled by a two stage synthesis
of gibberellin; a gibberellin precursor may be produced in the leaves and then
translocated to the roots where it is transformed and moved to the top. However, this is only a hypothesis and must be verified experimentally.
3) Myccorhizae:
A myccorhizae is a fungus - root combination and the growth of vines is
aided by this symbiotic association. It has been shown that myccorhizae are
widespread in Australian grapevines. The fungal hyphae invade the cortical
tissue of grape roots and help the vines in a symbiotic manner. Myccorhizae
aid grapevines by increasing uptake of minerals, especially phosphorus, and
water. Thus, the presence of myccorhizae may. compensate for the lack of root
hairs in vines and help explain why grapevines are able to grow in relatively
low fertility soils.
Root Distribution
1)
Physical obstruction:
The distribution of the vine root system is most affected by the structure
of the soil profile. Dense layers or other physical barriers will limit root
growth. The majority of roots are concentrated in the top meter of soil
directly under the vine and usually few roots grow into the interrow space
mainly due to the compaction of the soil by tractor wheels. Roots proliferate
in zones that are favorable for growth, but some roots will penetrate unfavorable areas because of the extensive nature of the vine's.root system.
2) Soil oxygen and water:
The soil structure affects the soil oxygen content and soils low in oxygen
limit root growth. Dense soils limit root growth both by physical impedence
and lack of soil oxygen. Soil types most favorable for oxygen supply would
be ones with uniformly large pores that drain easily, e.g. a coarse sand. But,
a soil with large pores would be unfavorable with respect to water supply. An
ideal soil with regards to water supply would be one with relatively fine
pores, such as occurs in loamy soils. Thus, the ideal soil for root growth is
one with a mixture of large and small pores. The large pores would drain
quickly and ensure adequate oxygen supply, but the small pores would retain
water for the vines. Well structured lams or clay loams without sudden changes
in texture would be examples of soils favorable for promoting vine root growth.
The best viticulture soils in France are on slopes, partially because they are
free draining, and hence favorable for root growth.
Waterlogging leads to an oxygen deficiency which can be tolerated for a
relatively long time in winter, but a very short time in summer. The death
of vines in a waterlogged situation is a result of accumulation of anaerobic
respiration products, such as ethanol and malic acid as the uptake of excess
cations, particularly manganese
Water—&.t.ress-stops aerial cell expansion and division before photosynthesis.
Thus photosynthesis will continue after shoot growth has stopped and sugars
will continue to be translocated to the roots. The roots have a higher osmotically active solute content and hence are more turgid than the leaves and will
continue to grow after shoot growth has stopped.
3) Soil temperature:
Maximum root growth occurs between 20 and 30°C and higher temperatures
restrict growth. Roots are rarely found in the top 10 an of soil in exposed
areas due to the high temperature. Surface soil temperatures in some grape
growing areas may exceed 60°C, which are fatal for roots. High temperatures
(35°C) reduce root growth more than hoot growth. This is believed to be
associated with a decreased in cytokAnin and potassium levels in roots at
high temperatures.
Root System Management
1)
Shoot: root ratio:
The ratio of the amount of aerial growth to the amount of roots ir vines
tends to be constant. If part of the root system is removed, the vine will
re-establish an equivalent root system or shoot growth will be reduced to
maintain a nearly constant ratio between shoots and roots. Water stress can
increase the proportion of roots compared to shoots and high temperatures
will reduce the proportion of roots compared to shoots. There may be a
permanent change in the ratio if these conditions are maintained, but the
effects are unknown if the vine is returned to a more favorable environment.
This balance between the root and shoot system could be idealized as
follows: the shoot growth in spring compensates for the shoot growth that
is pruned off in winter and when the balance is restored, root growth
commences. The regulation of these mechanisms appears to be related'to
the relative amounts of hormones produced in the roots and shoots, especially
cytokinins and gibberellins.
2)
Cultivation:
Cutting a root will stimulate production of lateral roots and increases
overall root production so that the effect of cultivation may not be as
detrimental as it first seems. The practice of deep ripping or trenching,
deep ploughing and burying prunings with fertilizer has been extensively
practiced in many grape growing countires in the past. Through these
practices, vines would produce more root growth due to the stimulative
effect of root cutting, but also the improved aeration, water penetration
and nutrients would favor root growth. This practice may be beneficial if
soil compaction or other barriers within the root zone was restricting growth,
however, the response would not be immediate, but would take time to re-establish
the constant shoot-to-root ratio.
,
The root system is restricted by soil compaction by wheeled tractors and
other implements. Ripping of this zone usually improved the soil environment
for root growth by increasing aeriation and reducing physical obstructions.
It is often difficult to rip where the wheel tracks are located because most
large rippers are centrally mounted and there is not enough row space to
maneuver the ripper. The benefits of such practices are difficult to assess
because the soil is soon compacted again by wheeled traffic.
3)
Soil temperature:
Roots do not grow near the surface of exposed soils because of high lethal
temperatures, but will grow close to the soil surface under the vine canopy.
An insulating mulch will encourage the root system to grow near the surface.
This would be an advantage in sites where the size of the root zone is restricted or immobile fertilizer, such as phosphorus, is applied to the surface.
4)
Fertilizer application:
The greatest concentration of roots occurs under the vine canopy and thus
fertilizer should be applied under the vine canopy to maximize fertilizer
uptake.
Nitrogen fertilizers in California are generally applied in the fall or
winter after buds have gone into a state of rest or dormancy. There is some
information available that indicates that uptake of nitrogen is greater in
the fall (November and December) while the soil is still relatively warm.
At this time there is generally a new flush of root growth which should
benefit mineral uptake. Care must be taken not to apply nitrogen too
early in the fall since this may stimulate new shoot growth to occur. In
California, generally by mid-November, most buds are in a state of rest or
organic dormancy and nitrogen fertilization will not stimulate new growth.
Nitrogen fertilization near flowering time may cause a stimulation of shoot
growth and promote berry shatter. Therefore, fall or winter applications
are generally recommended, the exact timing depending on the amount of winter
rainfall that normally occurs in a given area.
Bud
Burst Flowering
140
Fruit
Maturity
i
Leaf
Fall
i
—700
SHOOT LENGTH
CUL TI VATED
120
100
NON-
_
600
N
500 Id
CULTIVATED
9. = 80
L.,
ROOT GROWTH
400 —
I-0
0
cc
300
0
cc
60
u) 40
200
20
100
SPRING
SUMMER
Periodicity of root growth for two
15-year-old Shiraz vines located in
Griffith, Australia. The amount of
number of new roots crossing a grid
intervals on a glass panel.
0
FALL
cultivated and two non-cultivated
the Root Observation Chamber at
root growth is indicated by the
of horizonal lines at one inch
Grape Vine Growth Chart
A
WINTER BUD
C
WOOLLY BUD
GREEN TIP
E
LEAF EKERGENCE
F
INFLORESCENCE
VISIBLE
LEAVES UNFOLDED
D
G
INFLORESCENCES
SEPARATED
H
FLOWERS SEPARATED
BUT NOT OPENED
FLOWERING
Practical Viticulture
Grapevine Physiology
Flowers Bloom
Set Fruit Bud Verasion and
Ripening
Fruit Maturity
FOR
FRUITING
IN
FOLLOWING
YEAR
FLOWER CLUSTER
INITIATION AND DEVELOPMENT
FRUIT SET
FRUITING
IN
CURRENT
YEAR
SHATTER
BLOOM
FLOWER
DEVELOPMENT
I
VEGETATIVE
GROWTH
IN CURRENT
YEAR
COLOR
CHANGE HARVEST
I
BUD BURST
ACTIVE GROWTH
LEAF FALL
I
QUIESCENCE
I
I
REST
I
I
I
I
I
I
I
I
I
JAN. FEB. MAR. APR. MAY. JUN. JUL. AUG. SEP. OCT. NOV. DEC.
Calendar showing when the stages in the growth and fruiting of a
vinifera grapevine occur in an average year. Heavy lines indicate the periods of
active growth. For emphasis, the events of shoot growth, flowering, and fruiting
for the current year, and flower cluster initiation for the following year are
shown on separate lines; actually many occur simultaneously in a mature vine.
initiation of a flower cluster
in the summer preceding its flowering
reproductive cycle
Annual life-cycle of the vine.
blooming/fruit set
Feb
bleeding
Mar-Apr
bud-breaking
May-Jun
July
veraison
maturation
Aug
Sept-Oct
active growth stops
Nov-Dec
leaf fall
ripening of the wood
accumulation of food reserves
most active growth
dormancy
rest
vegetative cycle
13L
STRUCTURE OF THE LEAF
Hair
Upper epidermis
Palisade layer
Upper surface
Cs Hs with c hloroplasts
Vein
Vascular bundle
Air space
Lower surface
Spongy mesophyil
St ornate
Vascular bundle
A t'.s sectinn
through
a
typical leaf.
Sub-stomatal cavity
Stomata
c)V 0 0
BUNDLE SHEATH
CUTICLE
UPPER EPIDERMIS
PALISADE
XYLEM
PHLOEM
SPONGY MESOPHYLL
AIR SPACE
LOWER EPIDERMIS
CORTEX
PHLOEM
XYLEM
PITH
Diagrammatic section of a stem and leaf, shoving (arrows) paths of movement of water molecules.
Veins in a small part of the leaf of
lime (Citrus aurantilolia), showing the fine network and blind ends of the smallest veins.
tvlesophyll in leaf cross section: A. cuticle. B. xylem, C. guard cell, D. bundle sheath,
H. palisade parenchyma, I. upper epidermis, J. spongy
iareischyma.
stoma, F. phloem, G. lower epidermis,
PHOTOSYNTHESIS
6 CO 2
light
+ 6 H2O
energy
> C 6 H 12 0 6 +
granum
r evk
d i D.X 412,
A71-eAr"
S
H
\ /
C
H
I
H—C
I
H
C
' ..5.,
HC
\
H
C
/
H —C—C
I
ii
6Ac
H
1
H —C— H
H
C
I
H
/ \ C // \C
\
Oxk,.,kl
H
I
CH
1
C
Chloroplast
k 14r-
6 02 t
N
(-i
\ /
C—Cc—ri
I
Isl
C/
I
1
\
H H
CH
hig,
N
N
H
C''*"
H
\
I
C—C— H
I II
\ C /cC /c\ C ,
4, 1
1
H
1
HC —C= 0
0=C-0
H
H
I
I
H
I
H
I
C
H — C—H
H
/ \
FI
H-- C —H H—C—H H—C—H H —C—H H —C — H
H
H..„ ......+1
I
H., ,...11
I
H.., ,,..H
H., ...-Fl
,.C.,.. .,C ,, ,,,C
C.,. c./ti .c,,,C .c,,,C ,..,, c ,,C,.. 0.,,C.....0
C H C
C li C
%1-1/\
H H
/\ HH
/\ HH
/\H H
1-1 /\ HH i\ NH
. Structural formula of chlorophyll
a, the porphyrin head at the right, the phytol
..
tail at the left.
Carbon dioxide in the atmosph'ere
enters through stomates.
Photosynthesis as a chemical
'factory. In chloroplasts (the.
Oxygen is released_
rectangular box), light energy, ar...
0
to
the atmosphere...is used by chlorophyll to
through stomates
split water to form molecular
Stomate
oxygen and hydrogen ions
$1111 111111111I lila gODZ MW
(H*). In a second set of light
reactions, chlorophyll is excited and the excitation energy is used to link
phosphate ions to form the
high-energy compound ATr_.
Both the H* and the ATP arc
Chlorophyll
then used in the dark reaca
tions to convert atmospheric
"Light
carbon dioxide into carbohyReaction"
drate. i
CV/10.,91414
Coo tonv
■■•■•
C.46.vOr
Sunlight
•
'4?
13B
Photosynthesis
14CO2
hv
Fifth edition
/Dark
Light
D. 0. Hall
Professor of Biology
King's College, University of London
14
C 0 2 + H 2O
2H
NADPH 2
Thylakoid membranes
K. K. Rao
I ATP
NADPH 2
ADP + Pi —0- ATP
NADP
and
Honorary Lecturer in Biology
King's College, University of London
[ 14 C H 2 0 ]
Stromal enzymes
Published in association with the Institute of Biology
CAMBRIDGE
UNIVERSITY PRESS
Photosynthetic Apparatus
+
Granum
Chlorophyll a
Chlorophyll b
Thylakoid
Chloroplost
envelope
Stroma
Stroma
lamellae
Grano
lamellae
Hydrogen
• Carbon
o Oxygen
® Nitrogen
Magnesium
Freeze fracture split
______
■
•I
Chlorophyll a and b structures.
Thylakoid
„or.. ' 41\101.1
Envelope membrane
Granum ( stacked )
Stroma lamella
\ s,
\ \\
\ \ 1
11 % I
Figure 7.13
Summary of the light reactions of
photosynthesis.
acceptor molecule
FRS
2 NADP
acceptor molecule
Q
4 e-
tte A
2 NADPH 2
2 ADP + 2 P,
non cyclic
photophosphorylation
electron•
carrier
4
02
4ecyclic
photophosphorylation
electron
carrier
2 ATP
4 H+
2 ADP + 2 P,
electron
carrier
electron
carrier
4e-
electron
carrier
electron
carrier
2 H2 O
4 e-
2 ATP
photosystem I
P682
P700
photosystem II
light -
Figure 7.14
Diagram of the Calvin cycle (dark
reactions) of photosynthesis.
6 NADP
Introductory Plant Biology
6 NADPH 2
Kingsley R. Stern
California State University. Chico
6 molecules
of PGAL
6 ADP
Second Edition
1 molecule
of PGAL
6 ATP
5 molecules
of PGAL
6 molecules
of PGA
3 ATP
3 molecules
of RuDP
3 ADP
3 molecules _got CO 2
L-W
LIGHT AND PHOTOSYNTHESIS
VISIBLE SPECTRUM
X - RAYS I
ULTRA-VIOLET
O
BLUE
3t-1
z
GREEN
10
0.01
390 430 470 500
295
INFRA-RED
RED
3
5
560 600
650
780
The spectrum of radiant energy; figures represent millimicrons (nm).
VIOLET
BLUE
But
GREEN_
YELL O W ORANGE
GREEN
RED
Action spectrum
of light in photosynthesis
(i.e., the relative rates of
photosynthesis in different
wavelengths of light of equal
250
200
150
intensity).
100
50
450
400
550
650
500
600
WAVELENGTHS IN MILLIMICRONS
700
750
LEAFLET 21231
How Does
a Grapevine
PRINTED JUNE1981
Division of Agricultural Sciences
UNIVERSITY OF CALIFORNIA
Make Sugar?
FULL
•
SUNLIGHT
10,000 FOOT CANDLES
-FIRST LAYER OF LEAVES
IS ABOVE LIGHT
SATURATION
20
-PHOTOSYNTHESIS
AT A MAXIMUM
0
15
IN
-0
1,000 FOOT CANDLES
E
)-
•
10
-SECOND LAYER OF
LEAVES IS AT ABOUT
1/3 LIGHT SATURATION
Sultana Field Vine
0 Sultana Shade House Vine
-PHOTOSYNTHESIS
AT ABOUT 1/4
MAXIMUM
0
■ Shiraz Field Vine
0
a_
w
z
100 FOOT CANDLES
-THIRD LAYER OF LEAVES
IS AT COMPENSATION POINT
5,000
10,000
LIGHT INTENSITY (Foot Candles)
15,000
- NO NET PHOTOSYNTHESIS,
LEAVES ACT AS PARASITES
Lh
10
Photosynthesis
,Re,piration
80
75
Re la tive ra le
100
e it
60
5
40
\ Plant growth
20
25
00
10
5
0
20
23
15
Temperature (SC)
30
35
Ellett of temperature on photosynthesis, resonation, and the net
accumulation 01 city matter by the plant.
How Does
Changes in rate of photosynthesis of Shiraz leaves with
increase in water stress. Net photosynthesis expressed in relative units where 100 - 17.5 mg CO 2drn• 2 hr. " 1 .
LEAFLET 21231
PRINTED JUNE1981
a Grapevine
Make Sugar?
—15
— 10
—5
LEAF WATER POTENTIAL (atm.)
Division of Agricultural Sciences
UNIVERSITY OF CALIFORNIA
Main direction of movement of photosynthate at different physiological stages of shoot and cluster development.
Cone, spur, arm,
or parent vine
a.
1st 2 to 3
weeks after
bud break
Leaf
Inflorescence
( flower cluster)
Movement of photosynthotes
20
b.
3 to 8 weeks
(until bloom)
after bud break
c.
Fruit-set
until veraison
0
E
15
>-
0
Fruit cluster
I- 10
11.1
z
d.
Veraison until
fruit maturity
S
0
10
20
30
40
50
60
70
LEAF AGE - DAYS FOLLOWING UNFOLDING
Relationship between leaf age and net photosynthesis of
Thompson Seedless vines.
e. Post - harvest
until leaf-fall
it 4
4 Sfili
PHOTOSYNTHESIS IN
GRAPEVINE LEAVES
In talking about climatic effects on grapevine
productivity, we are really talking about effects
on the photosynthetic efficiency of inchvicitiai
leaves, that is, on their aliility to fix COQ
convert it into sugar. The most direct mrthod for
studying photosynthesis is to measure the rat'.
at which carbon dioxide is used up by individual
leaves, and this can be followed in either of two
ways. One technique is to enclose a leaf, while
still attached to the plant, in an atr=stahere containing radioactive carbon dioxide. The il.dicactivity accumulated by the leaf gives a measuie c•f
its photosynthetic activity, while the occui ranee
of radioactivity in compounds extracted fi•oni the
fed leaf shows the chemical identity of fixation
products.
Another technique involves enclosing a leaf In
a glass chamber through which air can be or.tinuously pumped and then measuring the CO,
concentration in the air going into, and coming
out of, the chamber—the reduction in concentration represents the amount used by the leaf, Atmospheric COQ levels are surprisingly low. they
average around 0.032 p.c. of the total air volume,
so that instruments which measure CO4 consumption by individual leaves must be particularly
sensitive. One type of infra-red gas analyser widely used for this purpose can measure CO3 consumption down to as little as 1 volume of CO3
in one trillion volumes of air (i.e., .0001 p.c.). The
test gas is passed down long cells (60 cm) within
this instrument and changes in CON concentration are registered as alteration in absorption of
a beam of infra-red radiation—hence its name.
Leaf temperature moderate
All viticulture! produce, iirt:specties of whether
it ls fresh or dried fruit, wine or distilled alcohol (e.g., brandy), has its origin in the sugars
produced within vine leaves by a process known
as photosynthesis. When leaves "photosynthesise,"
they use solar energy to manufacture sugar out
of carbon dioxide (CO.) absorbed ftom the air,
and water drawn from the soli. Plants then use
the products of photosynthesis as starting material for all of their constituents, Since a vine's total
photosynthetic activity for the season determines
its yield, we are naturally Interest:kJ In climatic
factors which limit photosvntnesis. Titis article
prepared by Dr. P. E. Kriedemann. of the Merbein
Laboratory of the CSIRO Divivon of Horticultural Research summarises the findings of research
work carried out by officers of the Division of
Horticultural Research on photosynthetic responses of grapevines. Much of the work has been
undertaken by Dr. Kriedemann but a number of
other scientists of the Division have participated,
and in particular, Dr. B. R. Loveys, of the Division's Adelaide Laboratory.
Primary Mechanisms
Photosynthesis takes place in microscopic
bodies called chloroplasts, which are located within the cells of every green leaf (see fig. 1). These
chloroplasts contain chlorophyll (the green colouring material of plants) and are responsible for
trapping sunlight and then converting this energy
into biologically useful forms which can drive the
reaction shown below:
COg ♦ water -4- sunlight
\ sugar
(with chlorophyll)
This sugar, formed within the vine's foliage.
represents atmoapheric carbon dioxide which has
become fixed as carLoEydrate, and is now avail
able for vegetative growth or fruit production by
the grapevine.
* Leaf temperature high
‘s s, (,*are than 30QC)
heavy cloud
moderato cloud
bright sunshine
LIGHT INTENSITY
Figure 2—Vine leaf
intensify.
photosynthesis in relation to light
Throzighout all of these experiments the leaf
under test remains attached to the plant. Equipment has been developed for measuring photo-
synthesi of leaves on small test plants in the
laboratory and of leaves on vines in the field.
Under laboratory conditions, the temperature of
the leaf in the chamber can he changed, as can
the intensity of the light fulling on it from a
strong Lamp mounted above it. In the vineyard,
environmental conditions are variable and almost
impossible to control, so that changes in both
photosyc.thesis and external factors (light, temperature; moisture supply) have to be monitored.
Ugh( Late ruaty
The energy required for photosynthesis comes
from the sunlight which falls cn a plant. Photosynthesis is not possible in the dark and In fact
grapevine leaves show a net loss of CO3 at night
(they respire) and together with other parts ,:,1*
the vine-. which de not photosynthesise. the foli-
age loses a small part of the food produced during the previous day.
Laboratory experiments, where individual
grape leaves have been exposed to artificial light,
have shown that as light intensity increases, a
leaf's rate of photosynthesis builds up very rapidly and reaches a maximum at about the intensity
of light on an overcast day (fig. 2). In other
words, if a leaf is held at right angles to direct
sunlight around noon on a clear day, it will
encounter two to three times more energy that
can be usefully absorbed for photosynthesis.
At first sight, it might seem that bright sunlight is not used very effectively by the grapevine, but a vine canopy obviously represents far
more than a single layer of leaves. Such a canopy
does, in fact, offer a wide variety of leaf size,
shape and orientation. For one thing, only some
leaves on a grapevine are right out in the open:
many are partly shaded by other leaves, so that
very few leaves would be fully exposed during
the entire day,, virtually all leaves will be shaded
to some extent.
As the sun moves across the sky, patterns of
illumination and shading within the canopy will
vary continuously and whenever the wind moves
the leaves this whole pattern is subject to rapid
fluctuation. Photosynthesis by individual leaves
will vary accordingly, so we must now consider
the light climate experienced by leaves within a
vine canopy.
_I •
r
-
1.y,
,
f-;:1-- (1," I t
• 1- 4it
• r" -^‹ .1 •
,J
i
.• •
•
t
t
-
;.
,A
• • ••
'
.
•, *
•
•••••
N.,t
,'
r
7./
.•
•
)
•
I
•
•
;
•
":""
4•P
1
•
•
N....:"..- ,, ).•,!'fi' /.7'.` `j..• r .-, N,..: 11 •
• • tin
...
'4
1..,.
.6 1. v...4—.,
- i '1,,,... i • e ...
41,1k:1'
1
..... .....7.....w,........ •,,.. - e•-• • VA.,' . )
•
i . — 'e
•••
04.1
•
.
•
'I'
.4t
j
f( •1 •r1
)
•••
cam
I
— -'
..., ?••••...
.e.,
•";•
.‘;
:
• t,...,./..
,,- ...,-....
‘...
........,..,,,,.............
.,,,..
[
Figure I—Microscopic view of • section taken through
• mature vine leaf which emphasises the vertically
arranged cells underneath the leaf's upper surface,
and the Foos. assemblage of cells throughoUt other
parts of tile section.
Chloroplasts are visible within
individual cells. A heavy. accumulation of starch
within these tiny organelles has made them mor•
prominent.
Leaves completely shaded by the outermost layer
of leaves in a grapevine canopy receive very little
light directly through the leaves above them, but
they do get some diffuse light, Naturally enough.
the deeper the leaf is inside the canopy the less
diffuse light reaches it, and inside a very dense
Figure 3—iline leaf photosynthesis in relation to the
angle at
• which the sun shines cc she leaf.
Light can reach a leaf in a variety of ways—
either directly from the sun, by reflection from
adjacent surfaces, or as a diffuse light from the
sky and from surrounding objects, including other
leaves. This diffuse light is obviously not as bright
as direct sunlight; it represents less energy, but
is not necessarily less important, and results in
fig. 3 provide some indication.
Photosynthesis by single leaves on field vines
changes as the angle between the leaf surface
and the sun is varied. Typical results are given
in fig. 3. Photosynthetic rate was greatest when
the sun shone on to the leaf at right angles. As
the angle between the leaf and the rays from the
sun decreased from 90° there was at first little
change in photosynthesis, but below about 60'
the rate of photosynthesis decreased quite rapidly.
If however, a leaf experiences diffuse sky light
as well as direct sunlight, its rate of photosynthesis will remain quite high, even when the
direct light shines parallel to the leaf surface
Diffuse light, therefore, is very important to
grapevine leaves which are partly hidden from
direct sunlight or on which the sun is shining at
less than 90'. On bright cloudless days those
leaves fully exposed to the sun will not be fixing
more CO, than they would on a cloudy day, but
those partly obscured would be much better off
because the diffuse •-light:• would be stronger.
crowded canopy some leaves are essentially in
the dark; they give off more CO :., than they fix
and they then behave in a parasitic way. In this
event they tend to become yellow and die; it
seems like nature's way of eliminating the unproductive!
Nevertheless, many of theSe deeply buried
leaves 3naly still be able to survive and fix COs
if they receive enough "flecks" of sunlight
through chinks in the canopy, caused by movement of 'eaves by wind. Recent experiments have
attempted to measure the contribution of these
sunflecks to grapevine photosynthesis.
In the vineyard, wind speed and "gustiness"
will, of course, cause the size of sunflecks and
the time for which they shine on leaves to vary
enormously. Suntieck frequencies at windspeeds
between 3 and 48 km per hour were followed at
Merbein and results pooled over all wind speeds
showed that on average, sunflecks lasted 0.6 seconds with Intervals between sunflecks lasting 1.2
seconds.
Laboratory apparatus was then set up where
a perforated disc of green perspex was rotat( , i
between a light source and a photosynthesising
leaf which enabled measurements of photosynthesis in grapevine leaves which received regular
pulses of light resembling sunflecks. During intervals between "flecks" the leaf was illuminated by
the weak green light which penetrated the solid
sectors in the perspex disc; this was intended to
simulate the diffuse light shining on leaves inside a grapevine canopy.
These laboratory experiments suggested that
the energy of a sunfleck would be used more
efficiently by the leaf than a similar amount of
energy supplied by continuous white light (Table
1). It seems that during the intervals between
sunflecks the leaf has a chance to "recover"—
perhaps by being able to clear the build-up of
sugar produced within individual chloroplasts, or
by allowing replenishment of substances in the
leaves needed for absorbing light and driving the
photosynthetic machinery. Whatever the explanation, it is clear that grapevine leaves are very
efficient at using sunflecks. It was also possible
to show that a grapevine leaf in the dark started
to become a food producer when as little as 1 p.c.
of its surface was illuminated by sunflecks, so it's
now less of a puzzle that a grapevine manages
to retain so many leaves within its "gloomy" interior.
Sunfiecics, thdrefore, support the vine's photosynthetic activity in at lease two respects; they
make a direct contribution by enabling partly exposed leaves in outer layers of the canopy to
make more effective use of direct sunlight, and
they make an indirect contribution by aiding leaf
retention at lower levels within the foliage. These
inside leaves often become better exposed. and
are able to renew their photosynthetic contribution later in the growing season as the canopy
changes shape under the weight of a developing
crop.
Temperature and Water Relations
Water Relations of Cells
Grapevines, like other plants, have evolved with
a photosynthetic mechanism that works only in a
liquid medium. In a leaf, where the cells provide
a suitable environment for biochemical activity
such as photosynthesis, water represents 80-90
p.c. of the fresh weight. In furnishing the needs
of the chloroplasts for photosynthesis (light,
water, CO, and nutrients), a leaf encounters something of a dilemma: It needs to assimilate atmospheric CO5 but must, at the same time, minimise evaporative losses. Some regulatory system
is clearly needed and specialised pores at the leaf
surface, called stomata, fulfil this function.
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Figure 4—Stomata on the lower surface of a vine
leaf achieve close control over gas exchange. This
view at low magnification (x1150) under reflected
light emphasis's their ebundarsca.
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Figure 5—Dtutail of a single stomata (x1000) viewed
with transmit,t•d light. The guard cells with their
thickened inmer walls can be seem to surround the
stometal pore.
The low,rer surface of a vine leaf is occupied
by tens of thousands of these stomata over every
square centimetre (see figs. 4 and 5). Their elliptical openintgs measure on average 10-13 microns
(thousandths of a millimetre) in length and vary
up to 5 microns in width (fig. 5). Aperture is
influenced by expansion and contraction of individual cells within neighbouring epidermal tissue,
although two cells, called guard cells, which encompass each pore, provide the primary regulation. These guard cells have a heavily thickened
zone on thmir inside walls making this inner portion more resilient than remaining areas, so the
cell as a whole becomes distorted during volume
increase wad the stomatal pore dilates.
When a Leaf is illuminated and CO g concentration within the leaf is decreased by the photosynthetic activiity of adjacent cells, dissolved solids
are drawn halo the guard cells. These solutes, together with• sugars produced by guard cell photosynthesis, enable the guard cell to absorb additional water from surrounding tissues; pressure
builds up the guard cells become "turgid")
and the stomatal pore begins to open. Only a few
minutes are required for this opening process to
go to complietion. If, on the other hand, the leaf
is darkened,. or if water supply becomes limiting,
the guard cells lose their turgor and stomatal
pores close. Stomata, therefore, serve the needs
of photosynthesis by responding to CO g depletion
but contriburte to the maintenance of leaf moisture status by closing down when evaporative
demand excieeds water supply.
Regulating !Water Loss
Water ewaporates from leaves (transpires) because the relative humidity inside a leaf is higher
than the nitoisture level outside. Under natural
conditions, sunlit leaves are generally warmer
than their ambient atmosphere so that a gradient
in water vaspour pressure from leaf to air will
exist even diuring humid conditions. Under moderate envirconmental conditions (say 35% relative
humidity anal air temperature 25' C.) every litre
of air contaiiins about 8 milligrams of water vapour, A leaf int this same temperature would hold
within its sin- spaces almost 23 milligrams per
litre. This aim- erence in concentration occurs within a few millimetres of the leaf surface. A differ-
ence in water vapour concentration of this magnitude over such a short distance would favour
rapid transpiration, but a leaf does not behave
like a free water surface because the pathway of
water loss is mainly via' stomata, which regulate
transpiration. Despite this control, however, the
rate of loss of water vapour from the leaf is far
greater than the rate of COs assimilation into
the leaf, even on mild days.
cells most be able to absorb enough water to generate ir.ternal pressure for particular organs to
grow. Root elongation, shoot extension, lerif expansion and berry enlargement all rely on such
positive pressure (or turgor), but the system of
direct-concern for photosynthesis is stomata! behaviour. As mentioned previously, stor ata! open-
ing is a► consequence of guard cell turgnr; once
this pressure diminishes, stomatal eperture decrease& If evaporative demand causes heir transpiration to exceed water supply, a rnois;ure stress
develops-: within the foliage. \Vhen this rt-ess intensifies:. stomata may close completely. If euffielent su'ater is available, leaf water status might
then recover, particularly at night when evaporative dermand is low. If water supply iervains inadequatie. however. the vine eventunily wiltn. In
this event, stomatal function is temporarily impaired (because stomata then fail to
re - open
despite restoration of a favourable moisture status wlthiin the leaf. Same days can elapse before
)4
s.
E
stomata.1 function and photosynthesis are fully
restored".
E
2
4
IS
25
35
45
Leaf temperature 0C
Figure 4—Stylized diagram illustrating the effect of
leaf temperature on photosynthesis in grapevine leaves.
Temperature Effects
•
Leaf-temperature has a marked effect on both
transpiration and photosynthesis; water loss will
increase substantially with increased temperature,
but grapevine leaves show their best photosynthetic performance between 25 and 30° C. At
higher or lower temperatures they are less active,
and once leaf temperature exceeds 45* C., photosynthetic activity comes to a virtual standstill
(fig. 6).
In the field, leaves on well-watered vines
would rarely get more than 8' C, above air temperature, so that on hot humid days they would
still be fixing some COs provided their moisture
Status is favourable. However, if the soil dries out
to the point where roots are unable to take up
enough water to replace foliar losses and leaves
start to wilt, photosynthesis will decline to zero.
More often, however, it seems as though heatwave conditions reduce growth by causing leaf
damage through desiccation rather than via temperature alone. We have held leaves at 48-49' C.
for up to three hours under laboratory conditions
without obvious deterioration, provided leaf moisture content was maintained. Once temperatures
reach 50-55' C., the leaf dies because leaf proteins
start to lose their structure faster than the cell
can repair the damage.
Vine Response to Moisture Stress
During the process of photosynthesis (described
earlier) water combines biochemically with CO:
derived from the atmosphere, but this consumption of HaO represents less than one percent of
water absorbed by vine roots; the remainder is
loot in transpiration!
Despite this enormous loss, vine leaves need
to maintain a high moisture content (75 to 85
p.c. fresh weight) to remain viable, and individual
Chamber
(or
Scholander
Pressure
Figure T.—This
provides a measure of leaf moisture status.
"Bomb")
A leaf 14 cut off and immediately placed in the
chamber \whore its petiole protrudes through a rubber
gland in tihe lid. The gland is sealed on to the petiole
(comproused between a metal washer and a flange)
and gas its introduced from a cylinder of compressed
Preassure is allowed to build up steadily (5.10
air.
psi/sec) ,until sap appears at a freshly cut surface of
the protruding petiole. Chamber pressure at this point
serves an an index of leaf moisture status, and is
expressed) as bars II bar= 15 lb./sq. inch).
Vtrhem leaves lose water (due to transpiration)
faster than the vine can obtain moisture from
the soil,. tension develops within the plant's vascular sy.•stem. Measurement of leaf tension has
become at science in itself but can be conveniently estirmated in the vineyard with a pressure
chamber. (fig. 7).
The relationships between photosynthesis, stomatal binhaviour, and leaf tension (a measure of
water sttress). help to define conditions which
limit vime productivity and might, in turn, lead
to a better understanding of water requirement
and irrigation timing. One such set of relationships is shown in fig. 8. These results were obtained by measuring photosynthesis and leaf tenelan in "potted sultana vines growing in a shadehouse (610 p.c. full sun). Almost thirty inclividi
measurements of each of these factors were made
on the viines, which had been subjected to drought
conditions for varying periods thereby presenting
a wide range of leaf moisture status and photosynthetiic rates. The pooled data (hg. 8) revealed
a steady - decline in photosynthesis once n -wisture
tension exceeded 5 bars. Photosynthesis came to
a virtual standstill at tensions greater than .15
bars.
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