Introduction
In plants, vacuoles play key roles in the plant
responses to any stress (Dietz et
al. 2001). The vacuole membrane H+-PPase (VM-PPase) and H+-ATPase
(VM-ATPase) are two major vacuole membrane proteins which have been extensively
researched. Drought stress affects food yield in the world, and the plant
response to drought stress has been widely studied (Farooq
et al. 2014; Avramova
et al. 2015; Zhu 2016). The relation
between drought stress and the activities of VM-PPase and VM-ATPase in vacuole
membrane have also been documented, however, the
results have revealed variable notions (Colombo
and Cerana 1993; Shantha et
al. 2001; Wang et al.
2001). It is reported (Shantha et
al. 2001) that osmotic stress treatment resulted in vacuolar
alkalinization and decreased the pH gradient across vacuole membrane in the
root cells of a maize cultivar relatively susceptive to osmotic stress, whereas
the root cells of a pear millet cultivar relatively tolerant to osmotic stress,
were able to keep the pH gradient across vacuole membrane and to inhibit the
vacuolar alkalinization. It was suggested that the tolerance of this cultivar
to stress should be attributed to maintaining the VM-ATPase activity. However, Wang et al. (2001) indicated
that the VM-ATPase activity in vacuole membrane isolated from Suaeda salsa
plants under PEG osmotic stress was almost same as the vacuole membrane
isolated from controls. The VM-PPase activity was unaffected in the vacuole
membrane isolated from the cell line of Dacus
carota under sorbitol osmotic stress (Colombo and Cerana
1993). Wang et al.
(2001) also showed that the activity of VM-PPase decreased 3-fold in the
vacuole membrane isolated from Suaeda salsa plants under PEG-osmotic
stress for 8 d. These results on the activities of VM-PPase and VM-ATPase in
vacuole membrane under water stress might be attributed to their playing
various physiological roles in various tissues at various growing and developing
stages. Therefore, the effects of water stress on the activities of VM-PPase
and VM-ATPase need to be further elucidated.
Polyamines (PAs) are long nitrogenous aliphatic
amines extensively prevalent in microorganism, animals and plants. In plants, they
are implicated closely in plant growth and development (Du et al. 2018; Guo et al.
2018; Cetinbas-Genc 2019). Furthermore, PAs are
related to many abiotic stresses containing water stress, salt stress, heavy metal,
and temperature stresses (Tang and Newton 2005; Farooq et al. 2009; Goyal and Asthir 2010; Do et al. 2013; Du et al. 2017; Taie et al.
2019). Spermine (Spm), spermidine (Spd) and putrescine (Put) are three main
PAs. Put converts into Spd via
linking up an aminopropyl moiety at either end, and into Spm
via linking up two aminopropyl moiety
at both ends. The key enzyme which catalyzes these conversions is S-adenosylmethionine
decarboxylase (SAMDC), and SAMDC is inhibited potently by methylglyoxyl bis
(guanyl hydrazone) (MGBG) (Slocum 1991). At physiological pH, PAs are naturally cationic (Kumer et al. 1997), and by ionic
bonding, PAs could interact with anionic macromolecules and form conjugated
non-covalently PAs (CN-PAs) in the membrane (Feuerstein and Martin 1989). By this, PAs function in
stabilizing the conformation of the bio-membrane (Galston and Kaur-Sawhney 1995; Du et al. 2015).
Besides CN-PAs mentioned above, PAs could covalently link to endo-glutamines of
proteins to transform into covalently conjugated PAs (C-PAs) by the enzyme
transglutaminase (Tgase).
Phenanthrolin (o-Phen) inhibits the Tgase activity (Del-Duca et
al. 1995; Serafini-Fracassini 1995). C-PAs in plasma membrane play
crucial roles in modifying protein and enhancing the wheat tolerance to drought
stress (Du et al. 2015). Del-Duca et al.
(1995) showed that C-PAs play crucial roles in cell chloroplasts.
However, to our knowledge, the relationship between the conjugated PAs (CN-PAs
and C-PAs) and the activities of VM-PPase and VM-ATPase in wheat embryo
vacuole membrane under drought stress remains to be elucidated.
In this study, the
effects of drought stress on the contents of CN-PAs and C-PAs, the activities
of VM-PPase and VM-ATPase, and their relationship were investigated.
Materials and Methods
Wheat cultivation
Two wheat (Triticum aestivum L.) cultivars
(Zhoumai No. 26 and Wenmai No. 10) were used as materials. Zhoumai 26 is
drought tolerant, whereas Wenmai 10 is drought susceptive. The seeds of the two
cultivars were surface-sterilized in 5% NaClO (w/v) for 10 min, rinsed with
distilled water, and then germinated in plastic pots (20 seeds/pot) (rim
diameter: bottom diameter: height: 45 cm: 35 cm: 55 cm), which contained water-normal
and nutrient-rich topsoil. After the seedlings vernalized, the pots with
seedlings were moved into greenhouse, in which a 25℃/15℃
(day/night) temperature and a 70% air humidity
were achieved and the cool-white fluorescent lamps were installed for supplying
16 h photoperiod at 600 μmol m-2 s-1 quantum flux density.
Experimental treatments
On the tenth day after fertilization, the developing
wheat plants were treated as followings: ① Control:
The roots of the materials for the control groups grew in water-normal soil
(soil water potential: -0.15 Mpa)
and the ear and flag leaf for the control groups were sprayed with distilled
water; ② Drought: Roots were treated with drought stress
(soil water potential: -1.0 Mpa)
and the ear and flag leaf were sprayed with distilled water; ③ drought + Spd: Roots were treated with drought stress (soil water
potential: -1.0 Mpa), and the
wheat ear and flag leaf were sprayed with Spd solution (
Determination of relative
increase rate of embryo dry weight (RIREDW)
RIREDW was calculated with the following formula:
GREDW = (W5 –
W0) / W0 (GREDW represents grow rate of embryo dry weight, W5
represents the embryo dry weight of all the material treated for 5 d and W0
represents the embryo dry weight of the material treated for 0 d). And then, to
counteract the diversity of different cultivar, RIREDW of every cultivar was calculated with the following
formula:
RIREDW (%) = (GREDW of treatment/GREDW of control) × 100
(In the formula,
the wheat materials of the treatment and the control were the same cultivar).
Determination of relative water content of embryo (RWCE)
RWCE was calculated with the following formula:
RWCE (%) = (FW
- DW) / (SW - DW) × 100 (SW, FW and DW represents the saturation weight,
fresh weight and dry weight of the embryo of the wheat materials treated for 5
d, respectively).
Purification of
vacuole membrane
Vacuole membrane was purified by the methods of Chen et al. (1999) and Suzuki and Kanayama (1999) with minor modifications.
Determination of the activities of VM-PPase and
VM-ATPase
The purity of the vacuole membrane was estimated by the
method of Widell and Larsson (1990), with three
inhibitors nitrate, vanadate and azide. The activity of vacuole membrane H+-ATPase
is inhibited by nitrate. In the present experiment, the activity of isolated
enzyme was inhibited by nitrate more than 75%, showing that the vacuole
membrane band at the down-layer/up-layer interface was vacuole
membrane-enriched. The activities of VM-PPase and VM-ATPase were detected by
the method of Zhang and Liu (2002)
with a little modification.
Conjugated PA determination
The vacuole membrane sample prepared above was added
into with 10% (v/v) of perchloric acid (PCA) stock solution until 5% terminal
PCA concentration. Then, CN-PAs and C-PAs were detected according to the method
of Du et al. (2015) by HPLC.
Statistical analysis
The experiments were repeated 3 times and 3 samples were
taken in every experiment. Every value was means (n=9) ± stand error (S.E.) of
3 independent tests. Data were analyzed by software of SPSS16.0 and Microsoft
Excel software.
%201258-1264_files/image002.png)
Fig. 1: The effects of drought, Spd, MGBG and o-Phen on RIREDW and RWC of embryos. Control–roots of
the materials for the control groups grew in water-normal soil (soil water
potential: -0.15 Mpa),
and the ear and flag leaf for the control groups were sprayed with distilled
water; Drought–roots were treated with drought stress (soil water potential:
-1.0 Mpa),
and the ear and flag leaf were sprayed with distilled water; Drought+Spd–roots were treated with drought stress (soil
water potential: -1.0 Mpa),
and the wheat ear and flag leaf were sprayed with Spd
solution (
Results
Changes in RIREDW and RWC
Treatment of wheat with drought stress for 5 d induced
decreases of RIREDW (Fig. 1A) and RWC (Fig. 1B) of wheat cultivars, Wenmai 10 (drought susceptive) and
Zhoumai 26 (drought tolerant), and the changes in the Wenmai 10 were more
obvious than in Zhoumai 26 (Fig. 1). Exogenous Spd inhibited markedly the
decreases of RIREDW and RWCE of the cultivar Wemai 10 under drought stress and the effects
on Zhoumai 26 were slight. Treatments of Zhoumai 26 with MGBG and o-Phen aggravated obviously the decreases
of RIREDW and RWCE of the cultivar under drought stress, and the effects of MGBG and o-Phen on those of Wenmai 10
were slight.
Changes in the activities of VM-PPase
and VM-ATPase
Under drought stress, the activities of VM-PPase (Fig.
2A) and VM-ATPase (Fig. 2B) in Wenmai 10 decreased by half approximately. However, in vacuole membrane of the drought
resistant cv. Zhoumai 26, both of the activities
of VM-PPase and VM-ATPase decreased less. Exogenous Spd retarded markedly decreases the activities of VM-PPase
and VM-ATPase of Wenmai
10 under drought stress, and the Spd treatment effects on Zhoumai 26 were
slight. Treatments of Zhoumai 26 with MGBG and o-Phen aggravated obviously the decreases of the activities of
VM-PPase and VM-ATPase of this
cultivar under drought stress, and the effects of MGBG and o-Phen on Wenmai 10 were
slight (Fig. 2).
Changes in the contents of CN-PAs
%201258-1264_files/image004.png)
Fig. 2: The effects of drought, Spd, MGBG and o-Phen on the activities of VM-PPase and VM-ATPase in embryo cells
%201258-1264_files/image006.png)
Fig. 3: The effects of drought, Spd and MGBG on the contents
of CN-PAs in vacuole membrane of embryo cells
%201258-1264_files/image008.png)
Fig. 4: The effects of
drought and o-Phen on the C-Put content in vacuole membrane of embryo cells
The contents of CN-Put and CN-Spd could be detected, but
the content of CN-Spm was not detected as the amount might be too little. Under
drought stress, the contents of CN-Put and CN-Spd rose in vacuole membrane of
the two cultivars. However, CN-Spd content in drought stress-treated Zhoumai 26 rose much more significantly than in drought stress-treated Wenmai 10. On the contrary, CN-Put content in drought treated Zhoumai 26 did not rise as much as in drought treated Wenmai 10 (Fig. 3). With Spd treatment, the content of CN-Spd
rose obviously in the embryo vacuole membrane from drought treated Wenmai 10. However, the increase was negligible in drought treated Zhoumai 26. MGBG treatment brought about a
marked reduction in the content of CN-Spd in drought treated Zhoumai 26.
Exogenous Spd or MGBG treatment affected the CN-Put level little in drought
treated wheat cultivars. With respect to the ratio of CN-Spd
to CN-Put showed clearly that exogenous Spd obviously raised the ratio in
drought treated Wenmai 10, but to a lesser extent, the treatment affected the
ratio in drought treated Zhoumai 26 (Fig. 3). Treatment with MGBG lowered the
ratio in drought treated Zhoumai 26 more significantly than in Wenmai 10.
Changes in the contents of C-PAs
Likely CN-PAs, the contents of the two C-PAs (C-Spd and
C-Put) were detected in vacuole membrane from drought treated wheat embryos.
However, the C-Spm content was not detected. Under drought stress, the C-Put
content in vacuole membrane from Zhoumai 26 increased more markedly than from
Wenmai 10. However, as to C-Spd, no obvious difference between the two
cultivars was detected. O-Phen treatment obviously inhibited the drought
induced increase of C-Put content in embryo vacuole membrane from Zhoumai 26
more markedly than Wenmai 10 (Fig. 4).
Growth inhibiting is the most susceptive physiological
reaction of plants to various stresses, and plant tolerance to drought stress
has been closely associated with water content and growth rate (Hsiao 1973; Schonfeld et al. 1988). Therefore,
wheat Zhoumai 26 was drought tolerant and Wenmai 10 was drought susceptive
(Fig. 1). Using the two diverse wheat cultivars elucidated the significance of
the activities of VM-PPase and VM-ATPase in embryo vacuole membrane under
drought stress.
%201258-1264_files/image009.png)
Fig. 5: The effects of
drought and o-Phen on the C-Put content in vacuole membrane of embryo cells
Under drought
stress, the activities of VM-PPase and VM-ATPase in drought tolerant Zhoumai 26
could be maintained in a higher level, whereas in drought susceptive Wenmai 10
the activities decreased obviously (Fig. 2). Thus, it could be concluded that
the maintenance of the activities of VM-PPase and VM-ATPase might enhance the
wheat tolerance to drought stress. Shantha et
al. (2001) on the roots of pear millet found that the cells of the
cultivar relatively tolerant to osmotic stress were able to keep the pH
gradient across vacuole membrane and to inhibit the vacuolar alkalinization, suggesting that the tolerance of this
cultivar to stress should be attributed to maintaining the VM-ATPase activity.
It is obvious that vacuolar water content and turgor are closely associated
with ion accumulation in vacuole, and ion accumulation might be attributed to
pH gradient across vacuole membrane and vacuolar acidification (Dietz et al. 2001).
Maintenance of pH gradient across vacuole membrane in turn is attributed to the
activities of VM-PPase and VM-ATPase. Hence, under drought stress, maintaining
activities of VM-PPase and VM-ATPase in vacuole membrane is of crucial
importance for plant tolerance to the stress.
It has been
reported that CN-Spd and C-Put in vacuole membrane purified from barley
seedlings were associated with the tolerance of the seedlings to salt stress
(Zhao et al. 2000; Sun et al. 2002).
Our previous study showed that conjugated polyamine contents in plasma membrane
purified from developing wheat embryos under short-time drought stress enhanced
the tolerance of wheat plants to the stress (Du et al. 2015). Under drought stress, in vacuole membrane of drought
tolerant Zhoumai 26, the content of CN-Spd was much more than in drought
susceptive Wenmai 10 (Fig. 3), which seems to imply that the wheat tolerance
might partly attribute to CN-Spd. Two further studies by using exogenous Spd
and inhibitor MGBG supported the hypothesis. Exogenous Spd treatment obviously
elevated not only the CN-Spd content in vacuole membrane of drought susceptive
Wenmai 10 (Fig. 3), but also the tolerance of the cultivar (Fig. 1). Inhibitor
MGBG treatment significantly reduced not only the CN-Spd content in vacuole
membrane of drought tolerant Zhoumai 26 (Fig. 3), but also the tolerance of the
cultivar (Fig. 1). As regard to the C-PAs in vacuole membrane, under drought
stress, the C-Put content of drought tolerant Zhoumai 26 increased substantially
(Fig. 4), which imply that the wheat tolerance might partly attribute to C-Put.
The experiment by using inhibitor o-Phen supported the notion. Exogenous o-Phen
treatment obviously reduced not only the C-Put content in vacuole membrane of
drought tolerant Zhoumai 26 (Fig. 4), but also the tolerance of the cultivar
(Fig. 1). In one word, the contents of CN-Spd and C-Put in embryo vacuole
membrane were associated with the wheat tolerance.
The relationship
between polyamines and ion channels has been reported (Williams 1997). The Dobrovinskaya et
al. (1999) indicated that the ion channels of vacuolar were
inhibited by polyamines. The Liu et al.
(2000) showed that polyamines could target the channels of KATl-like
in guard cells to modulate stomatal movements. These studies provided a link
among polyamines, membrane proteins and stress conditions. In the presented
study, an interesting fact found was that under drought stress contents of
CN-Spd (Fig. 3) and C-Put (Fig. 4) increased markedly in drought tolerant
Zhoumai 26, and simultaneously the activities of VM-PPase and VM-ATPase of the
cultivar were maintained in a higher level. These results were indicative of
possible involvement of the two conjugated PAs in the relationship with the
activities of VM-PPase and VM-ATPase in vacuole membrane. This hypothesis was
supported by using exogenous Spd, inhibitors MGBG and o-Phen (Fig.
2, 3 and 4). Furthermore, statistical analysis showed that there was positive
correlation between VM-PPase activity and the ratio CN-Spd/CN-Put (r0.05 =
0.95, n = 8), between VM-ATPase activity and the ratio CN-Spd/CN-Put (r0.05
= 0.96, n = 8), between VM-PPase activity and C-Put levels (r0.05 =
0.94, n = 4), and between VM-ATPase activity and C-Put levels (r0.05
= 0.91, n = 4).
The reason why CN-Spd, but not
CN-Put could promote the activities of VM-PPase and VM-ATPase in vacuole
membrane might be attributed to cationic nature (Sood and Nagar 2003). With
more positive charges, CN-Spd might modulate the enzyme activities
by binding to protein non-covalently to affect their conformations and
functions more easily than CN-Put. Besides that, CN-Spd might be associated
with the enzyme activities by conjugating non-covalently to membrane
phospholipids and affecting vacuole membrane physical state. Of course, the
changes in physical state of vacuole membrane are associated with the
activities of the enzymes. As to C-PAs, Del-Duca et al. (1995) reported that PAs played an important role in
chloroplasts by being conjugated covalently to CP24, CP26 and large subunit of
Rubisco, forming protein–Glu-PAs-protein and protein-Glu-PAs. It could be
inferred that under drought stress, C-Put might stabilize conformation and
function of VM-PPase and VM-ATPase by preventing the enzyme from denaturing,
and thus maintain the activities of these enzymes. Obviously, the
effects of conjugated-PAs on the activities of VM-PPase and VM-ATPase in
vacuole membrane are interesting and complex, which deserves further
elucidation.
Conclusion
The study elucidated that the induced CN-Spd and C-Put might enhance
the wheat resistance to drought stress via maintaining the activities of
VM-PPase and VM-ATPase in developing embryo vacuole membrane.
Acknowledgements
The research is supported by National Natural Science Foundation of
China (Grant No.31271627), Science and Technology Program of Henan Province
(Grant No.192102110135) and Key Scientific
Research Projects of Higher School in Henan Province (Grant
No.20A210032).
Author Contributions
HY Du and HP Liu, conceived and designed the experiments; HY
Du and HL Liu, performed the experiments; DX Liu, analyzed the data; HY Du, HP
Liu and R Kurtenbach, rote the paper
References
Avramova V, H AbdElgawad,
ZF Zhang, B Fotschki, R Casadevall,
L Vergauwen, D Knapen, E Taleisnik, Y Guisez, H Asard, GTS Beemster (2015).
Drought induces distinct growth response, protection, and recovery mechanisms
in the maize leaf growth zone. Plant Physiol 169:1382‒1396
Cetinbas-Genc A (2019). Putrescine modifies the pollen tube growth of tea (Camellia sinensis) by affecting actin organization and cell wall
structure. Protoplasma 257:89–101
Chen Q, WH Zhang, YL Liu (1999).
Effect of NaCl, glutathione and ascorbic acid on function of tonoplast vesicles
isolated from barley leaves. J Plant
Physiol 155:685‒690
Colombo R, R Cerana (1993). Enhanced activity of tonoplast
pyrophatase in NaCl-grown cells of Daucus
carota. J Plant Physiol 142:226‒229
Del-Duca S, S Beninati, D
Serafini-Fracassini (1995).
Polyamines in chloroplasts: Identification of their glutamyl
and acetyl derivatives. Biochem J
305:233‒237
Dietz KJ, N Tavakoli, C Kluge (2001). Significance of the V-ATPase for the
adaption to stressful growth conditions and its regulation on the molecular and
biochemical level. J Exp Bot 52:1969‒1980
Do PT, T Degenkolbe, A Erban, AG Heyer, J Kopka, KI Kohl, DK Hincha, E
Zuther (2013). Dissecting rice polyamine metabolism under
controlled long-term drought stress. PLoS One 8; Article e0060325
Dobrovinskaya OR, J Muñiz, II Pottosin (1999). Inhibition of vacuolar ion channels by polyamines. J Membr Biol 167:127‒140
Du HY, DX Liu, GT Liu, HP Liu, R Kurtenbach (2018). Relationship between polyamines and anaerobic respiration of wheat
seedling root under water-logging stress. Russ J Plant Physiol 65:874‒881
Du HY, XG Zhou, GT Liu, HP Liu, R Kurtenbach (2017).
Relationship between seed quality and changes in conjugated polyamine in plasma
membrane purified from wheat embryos during grain ripening. Russ J Plant Physiol 64:325‒332
Du HY, XG Zhou, QH Yang, HP Liu, R Kurtenbach (2015). Changes in H + - ATPase activity and conjugated
polyamine contents in plasma membrane purified from developing wheat embryos
under short-time drought stress. Plant
Growth Regul 75:1‒10
Farooq M, M Hussain, KHM Siddique (2014)
Drought stress in wheat during flowering and grain-filling periods. Crit Rev Plant Sci
33:331–349
Farooq M, A Wahid, N Kobayashi, D Fujita, SMA Basra
(2009) Plant drought stress: Effects, mechanisms and management. Agron Sustain Dev 29: 185‒212.
Feuerstein BG, LJ Martin (1989). Specificity and binding
in polyamine nucleic acid interactions. In:
The Physiology of Polyamines,
pp:109‒124. Bachroch U, YM Heimer (Eds.). CRC
Press, Boca Raton, Florida, USA
Galston AW, R Kaur-Sawhney
(1995). Polyamines as endogenous
growth regulators. In: Plant Hormones: Physiology, Biochemistry and
Molecular Biology, pp:158‒178. Davies
PJ (Ed.). Kluwer Academic Publishers, Dordrecht, The
Netherlands
Goyal M, B Asthir (2010). Polyamine catabolism influences antioxidative defense
mechanism in shoots and roots of five wheat genotypes under high temperature
stress. Plant Growth Regul 60:13‒25
Guo
J, S Wang, X Yu, R Dong, Y Li, X Mei, Y Shen (2018). Polyamines
regulate strawberry fruit ripening by ABA, IAA, and Ethylene. Plant Physiol
177:339‒351
Hsiao TC (1973). Plant responses to water stress. Annu Rev Plant Physiol
24:519‒570
Kumer A, T Altabella, MA Taylor, AF Tiburcio (1997).
Recent advances in polyamine research. Trends
Plant Sci 2:124‒130
Liu K, HH Fu, QX Bei, S Luan (2000). Inward
potassium channel in guard cells as a target for polyamine regulation of
stomatal movements. Plant Physiol
124:1315‒1325
Schonfeld MA, RC Johnson, BF Carver, DW
Mornhinwey (1988). Water relation in winter
wheat as drought resistance indicators. Crop Sci 28:526‒537
Serafini-Fracassini D (1995). Plant
transglutaminase. Phytochemestry
40:355‒365
Shantha N, C Dijkema, HV As, S Nagarajan, AH
Van (2001). Metabolic response of
roots to osmotic stress in sensitive and tolerant cereals qualitative in
vivo [31P] nuclear magnetic resonances study. Ind J Biochem Biophys 38:149‒152
Slocum RD (1991). Polyamine
biosynthesis in plant. In: Polyamines in Plants, pp:23–40. Slocum RD, HE Flores (Eds.). CRC Press, Florida, USA
Sood S, PK Nagar (2003). The effect of polyamines on leaf
senescence in two diverse rose species. Plant
Growth Regul 39:155‒160
Sun
C, YL Liu, WH Zhang (2002).
Mechanism of the effect of polyamines on the activity of tonoplast of barley
roots under salt stress. Acta Bot Sin
44:1167‒1172
Suzuki Y, Y Kanayama (1999). Vacuolar H+-pyrophosphatase
purified from pear fruit. Phytochemestry
50:535‒539
Taie HAA, MAS El-Yazal, SMA Ahmed, MM Rady (2019). Polyamines modulate growth,
antioxidant activity, and genomic DNA in heavy metal-stressed wheat plant. Environ Sci Pollut Res Intl 26:22338‒22350
Tang W, RJ Newton (2005). Polyamines
reduce salt-induced oxidative damage by increasing the activities of
antioxidant enzymes and decreasing lipid peroxidation in Virginia pine. Plant Growth Regul 46:31‒43
Wang BS, U Lüttge,
R Ratajczak (2001). Effect of salt treatment and osmotic
stress on V- ATPase and V-PPase in leaves of the halophyte Suaecla salsa. J Exp
Bot 52:2355‒2365
Widell S, C Larsson (1990). A critical
evaluation of markers used in plasma membrane purification. In: The Plant Plasma Membrane,
pp:16‒43. Larsson C, IM Moller (Eds.).
Springer Verlag, Berlin, Germany
Williams K (1997). Interactions of
polyamines with ion channels. Biochem J
325:289–297
Zhang WH, YL Liu (2002). Relationship between H+-ATPase activity, ion uptake and calcium in barley roots
under NaCl stress. Acta Bot Sin
44:667‒672
Zhao FG, C Sun, YL Liu, ZP Liu (2000).
Effect of salinity stress on the levels of covalently and noncovalently
conjugated polyamines in plasma membrane and tonoplast isolated from barley
seedlings. Acta Bot Sin 42:920‒926
Zhu JK (2016). Abiotic stress signaling and responses in plants. Cell 167:313‒324