Glat, Dobrenz, Palzkill
Stomatal
Characteristics of
Jojoba,
Simmondsia chinensis
(Link) Schneider
D. Glat, A. K. Dobrenz
and D. Palzkill
Department of Plant Science, University of Arizona
Jojoba
153
major dilemma that desert adapted species have to face is
how to reduce the amount of water vapor lost from the
leaves (transpiration) to a minimum while still maintaining some CO2 uptake (photosynthesis) required for the initial synthesis of all carbon compounds. The vast majority
(95 %) of the CO2 and water vapor exchange that occurs
between plants and the atmosphere is through small
orifices present on leaf surfaces called stomata (stoma,
singular). Stomata are openings that appear on the leaf
epidermis between two specialized cells called guard cells,
when these are filled with water. Thus, stomata opening
and closing are primarily dependent on the flow of water
to guard cells and on the general water status of the plants.
In the absence of water stress, however, stomata follow a
diurnal pattern of opening during the day and closing at
night. An interesting exception is the behavior of some
succulent desert species, which present the cransulacean
acid metabolism pathway of photosynthesis. Those
plants, contrarily of all others keep stomata closed during
the day to avoid any water loss, and open them at night to
uptake CO2.
Desert -adapted species present several other morpholog-
ical and physiological features that enable them to cope
with the adverse environmental conditions of their
natural habitat. Some of these features are small leaf size,
leaf hairs, thick leaf cuticle, long roots, photosynthesizing
stems, drought deciduous leaves, and short life cycle.
Some stomatal characteristics are also important to the
adaptations of plants to the desert. Most plants have their
stomata level or slightly above the leaf surface while some
desert adapted species present their stomata recessed, or
sunken below the leaf surface. Also, stomata of desert
plants are usually smaller than those of most mesophytic
plants (Zelich, 1963 ).
Other stomatal characteristics which influence the
water budget of plants, and which vary considerably between species, are stomata distribution over leaf surfaces,
and stomata density; for example, some dicotyledon trees
have stomata only on the lower surface, while water lily
and other aquatic plants have stomata on the upper surface exclusively (Northern, 1968).
Stomata densities between species range from less than
Introduction
Jojoba (Simmondsia chinensis (Link) Schneider) is an
evergreen desert shrub native to the Sonoran Desert of the
Southwestern United States and northwest Mexico. Its
seeds contain a liquid wax which is unique in the plant
kingdom and can replace whale sperm oil in many industrial processes. Presently, jojoba oil is being utilized by the
cosmetic industry in hair oil, shampoo, soap, and other
products. It can also be used in lubricants for high speed,
20 to more than 1000 stomata per mm2 of leaf surface
high temperature machines, in polishing waxes, plas-
trations between the atmosphere and the interior of
ticizers, and in other industrial products.
Jojoba is a true xerophyte, which can stand temperatures
as high as 115° -120 °F and very low levels of water in soil
leaves. The water vapor gradient present between these
sites is much steeper than that of CO2; also, the diffusion
without signs of major injury (Al -Ani, 1972). Being a
tion in stomata conductance caused by a decrease in
drought resistant species which produces a valuable product jojoba can possibly become an important crop for arid
and semiarid regions of the world where very few crops
can be grown profitably.
The most stressful factor limiting plant growth and development in the desert is the shortage of water. Thus a
stomata density, would decrease water loss proportionally
more than it would decrease CO2 uptake. This could definitely assist on the water -saving adaptations of drought tolerant species.
In this present study we decided to investigate the dif-
(Meidner, 1968). Stomata density also varies considerably
between individual plants of the same species, among
leaves of the same plant, and even among different parts of
the same leaf surface (Cole, 1970). Other factors being constant, the diffusion of CO2 in, and water vapor out of the
leaves are directly related to stomata density and distribution (Bidwell, 1979). The movement of these gases in and
out of leaves is a function of the difference in their concen-
coefficient for water is higher than for CO2. Thus a reduc-
ferences in stomata density among individual plants of
Desert Hants
154
1
jojoba and among ;.,.)ioba clones- ,V,TCATS
e plant
sur
were po.-..duced ir.-!ni
identical plaw:s
hetweeh
by vegetative 1);-,-.pf2-:)ri.
lace were also stu1.
were u.sed
phot.,,4 a; 'rlies
,istribution parassociated with
haracteTize
tr
shay,.
and ;.my
Autumn. 1981
s:.y of upper and lower leaf suafaces of leaves
Table
from
tilt apex. of 5 jujirba nlonc.s.
up
Clone
S t °Marl I11111-:'
A
98
131
117
123
84
126
sto.n..ta
D
A
10- S cm long ttq-n.kinal stem cut-
tirs
Wild
grwing in the
-.terri, After
i'..79 from lojoba. pia
using a M161:
117,1 in 1
.
fiylene con.e end vercutrIRgs Vere
tainen
of loam.
4.2:11 The
miculite in the
grown for six months in a
22 to
greenhouse in in which temperaY,lre:7--,
30°C, At the end of this gro.ng
!.
t..asz. IU new
iÇ
leayes15 nodes) had trued
Cellulose acc.t.q.te. was used to
fof:
stomata counilhg.
-watur
and Aristect dry, th .e1.1
acetate was pr:
cf7-:-Jr
:1. the 1.::i to one side of thc
1,9 r* n ia ior 3 v.o 5 min, the acei.3e
du"!
peeled
gias slJ and
fields 10.135
twk.z.7.y.rs,
,r,
coy
irn2
and the
,+..(:re count
mean of
coup?,
,,,ourits were made on
i.
ati,eai analysis.
of fully
or each
-
ler.vcs (3rd
111 A
7ants.
and
taken
surface of a 4
scanning elec
Mean
L9'
qaell value is tF
r
if
107
separation wittnn col
umns by Stu3en,..rn:,,-n:.2, a .Y12!'s
inch is an important Lcto:-
Stomata
trolling gas
..
ccrn-
c,...,y,:lbinatic.rn of the stornatal
density. From the picurts obtain&d,
we estimate the c.)joba stoma area to be afc,und
of
(9-10 u long and 2-3 u wide) deper.:iing ort the
pore area and st:.,m
opening. Assuming mean stomata
to
107
stainotaimm2 of leaf surface; we calculs.tte total p,we area
of Jojoba leaves to be around .8% of total leaf area. this
is close to values reported for other crops-3rof.m,,i
-(ZelitcL, )63); therefore, total pore area doesn't seem
to he a
factor influencing the drought tolerance
of jojoba.
Significan, differences were found in stomata derFly
bet:Al:ten 5 diqtrent clones from Arizona's nativ
1).
was a 30% ilì:ference in stomata derv* y
and Itiwr...st clonal means. The nagof t;-;_s ,Aatic1,.ynce could have important effects on
gas exchange of these clones.
The average ,tomata density for all leaf surface measured on the clonal study was 107 stomataimm2, This
i7z. not much diff,=nt than other major crops. It is
deso.r:1!ec.f;.,..i.3ove
CO:'
123i,
E
and AIi.11.3.,ds
3:7
Mean
LOWCT
IOW,. T. '.7n the avc.rrigc. of. several alfalfa varieties-around
200 sT».,:b.ata/nuri: (C)lc and Dubrenz, 1970), It is much
than that of tcrv:iAoes-I2-1.3 siomatalmm2 (Northern, i96:1) and similar to corr
,, .
(ZeUtch. 63).
Results and Di.,.cu,sion
jojoba
d on SE t present cha.r,
conserva!'ic. :7,nard cells at both
teristirs
Tarer [Figure. ft A
w the op
surfa e.
liar
density
these
f
....
roco!.a3.. dome
mottos in an cartie.i:
lc axe from
leaf, respectively.
deposition whh...;-.
iniTi.cate
served on Figure in
sun e Figure if This
seems to be abseni: on the
-
'
may be anothf-r adopt:.
foimd
d...ficien,,,.s in stomata (.1,.
-veer
and upper
had i
5 clones. On the
stwnata4nr.2
Sign if
stomo!.::'51n.)2, When 3
3rought
It is known tb at
the stomata or. upp,..r
:SU
wgi:er
2..
1.:-
to
ore 3i.:..q1.1::in
arnc.ag
'
-
This wax
"iV 2 tt'i.
tica
would he 'i"
to
¡,..i.dhlg off effe.cC
L',1Y
if., a hot; arid enYilronnun.
r
em we eon.Q
¡Nrthicn i95)8j
ane.
surf.
that these differences a-
aosed
mainly
stomata is illso
may be what
tric,-. on ti't'
10r:mge in stomata densh,,
s (Table 2). The
stC'in:ta
is 70% higher ola that of the k.p,vt. Since
grown in very similar envirc.ohlen!ai
A
iiejoba
also
am:my; tìe
w,-re
we also
ari r-ty more
been repotted
leaf sorfat:e also,
i.:.)cam, corn, tomati,,cL,
e arid to.bren7, 197N
-male and female flowers in epaian. d
pollinatcdb.v -wind.lhcrefort. populagrrat zrtettc vatiohtliz-y Experitions
uidicate thit ;eloba ern
ments at the T. Tni veIsity
,
Glat, Dobrenz, Palzkill
155
Jojoba
Table 2. Stomatal density of upper and lower leaf surfaces of 10 jojoba
seedlings.
Seedling
Upper
Surface
Lower
Surface
Mean
Stomata mm2
67'
1
63
2
3
4
84
72
5
101
6
7
87
83
91
88
8
9
10
Mean
60
79
84
82
99
85
110
87
92
102
91
69
89
75
72
91
78
106
87
87
96
89
62
94
yMean value in the mean of 21 separate counts on each of 3 leaves.
xMeans of upper surfaces was significantly less than that of adaxial
D rD ,D u H
A
surfaces of the 5% level by the Student Newman Keul Test.
be successfully propagated by cuttings, which allows for
the development of clones. Desirable characteristics can
thus be perpetuated by vegetative propagation of plants
presenting such characteristics. This procedure is especially important for jojoba because taking 3 -4 years to
produce seeds, it could take many years before actually
improved jojoba varieties could be developed by modern
breeding techniques. Results of this study show that there
are significant differences in stomata density between
B
00i
uH
jojoba clones and individual seedlings. Other researchers
have suggested that stomata density would be an important criterion for producing high -yielding wheats (Teare,
1971) or to influence yields of triticale under certain environmental conditions (Sapra, 1975). Further studies are
necessary to determine if a decrease in stomata density
would indeed increase yields or water use efficiency of
jojoba. If either of those factors can be determined experimentally then selection of jojoba clones with low stomata
density could result in plants still better adapted to lowwater agriculture.
Bibliography
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C
D10n0u
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Figure 1. Electron micrographs from Jojoba stomata on
the upper (1a and 1c) and lower surface (1b), of a fully
expanded leaf.
69 -80.
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664. The Connecticut Agricultural Experiment Station. New
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