Comparative Analysis of Short- and Long-Term Changes in Gene Expression Caused by Low Water Potential in Potato (Solanum tuberosum) Cell-Suspension Cultures

To dissect the cellular response to water stress and compare changes induced as a generalized response with those involved in tolerance/acclimation mechanisms, we analyzed changes in two-dimensional electrophoretic patterns of in vivo [35S]methionine-labeled polypeptides of cultured potato (Solanum tuberosum) cells after gradual and long exposure to polyethylene glycol (PEG)- mediated low water potential versus those induced in cells abruptly exposed to the same stress intensity. Protein synthesis was not inhibited by gradual stress imposition, and the expression of 17 proteins was induced in adapted cells. Some polypeptides were inducible under mild stress conditions (5% PEG) and accumulated further when cells were exposed to a higher stress intensity (10 and 20% PEG). The synthesis of another set of polypeptides was up-regulated only when more severe water-stress conditions were applied, suggesting that plant cells were able to monitor different levels of stress intensity and modulate gene expression accordingly. In contrast, in potato cells abruptly exposed to 20% PEG, protein synthesis was strongly inhibited. Nevertheless, a large set of polypeptides was identified whose expression was increased. Most of these polypeptides were not induced in adapted cells, but many of them were common to those observed in abscisic acid (ABA)-treated cells. These data, along with the finding that cellular ABA content increased in PEG-shocked cells but not in PEG-adapted cells, suggested that this hormone is mainly involved in the rapid response to stress rather than long-term adaptation. A further group of proteins included those induced after long exposure to both water stress and shock. Western blot analysis revealed that osmotin was one protein belonging to this common group. This class may represent induced proteins that accumulate specifically in response to low water potential and that are putatively involved in the maintenance of cellular homeostasis under prolonged stress.     

A Comparison of the Effect of Salt on Polypeptides and Translatable mRNAs in Roots of a Salt-Tolerant and a Salt-Sensitive Cultivar of Barley

The effect of salt stress on polypeptide and mRNA levels in roots of two barley (Hordeum vulgare L.) cultivars differing in salt tolerance (cv CM 72, tolerant; cv Prato, sensitive) was analyzed using two-dimensional polyacrylamide gel electrophoresis. Preliminary experiments indicated that germination of Prato was inhibited significantly in the presence of NaCl, but growth of the surviving Prato seedlings was not substantially different from that of CM 72. Fluorographs of two-dimensional gels containing in vivo labeled polypeptides or in vitro translation products were computer analyzed to identify and quantitate changes that resulted when plants were grown in the presence of 200 millimolar NaCl for 6 days. The patterns of in vivo labeled polypeptides and in vitro products of CM 72 and Prato were qualitatively the same. Salt caused quantitative changes in numerous polypeptides and translatable mRNAs, but, overall, the changes were relatively small. Salt did not induce the synthesis of unique polypeptides or translatable mRNAs and did not cause any to disappear. Because of the similarities of the two cultivars with respect to growth and polypeptide patterns and the slight changes in polypeptide and translation product levels caused by salt, specific polypeptides or translatable mRNAs that are related to salt tolerance in barley could not be identified.     

Accumulation of Microsomal Polypeptides in Barley Roots during Aluminium Stress

Accumulation of two peripheral membrane polypeptides (20 and 28 kDa) in roots of Al-sensitive (cv. Alfor) and Al-resistant (cv. Bavaria) barley cultivars were analysed during Al stress. Both cultivars were subjected to Al concentration ranging from 0 to 150 µM for 24, 48, 72 and 96 h. Accumulation of both polypeptides was determined 24 h after exposure of plants to Al and content of both polypeptides showed only small depedence upon Al concentration and duration of Al treatment. Although, based on root growth test, Bavaria showed significantly greater resistance to Al than Alfor, analysis of 20 and 28 kDa polypeptide pattern has not revealed significant difference between the two cultivars. However, accumulation of 20 and 28 kDa polypeptides in Alfor was selectively induced by Al treatment because different pH of the root media (pH 3.5 to 6.5) or application of other metals (Cu, Co, or Cd) failed to induce these two bands. On the other hand, accumulation of these polypeptides in Bavaria was induced not only by Al, but also by Cd and in a lesser extent by Co treatment.     

Proteomics to identify pathogenesis-related proteins in rice roots under water deficit

Upland and lowland rice (Oryza sativa L.) showed different mechanisms of water stress resistance. Hydroponically grown 3-week-old seedlings of a lowland variety IR64 and an upland variety were exposed to 15% polyethylene glycol (PEG-6000). After 7 d of treatment, IR64 maintained high relative water content and developed a well-branched root. Therefore, IR64 had better water-deficit tolerance than Azucena under PEG treatment. To identify water-deficit-responsive proteins associated with the tolerance differences between two ecotypes, a comparative proteomic analysis of roots was conducted. Out of 700 proteins reproducibly detected on two-dimensional electrophoresis gels, 65 proteins exhibited significant changes in at least one ecotype at 48 h of water deficit. Only 15 proteins showed different responses to water deficit between the two ecotypes. Twelve proteins were identified by matrix-assisted laser desorption/ionization-time of flight/time of flight-mass spectrometry, which involved in energy and metabolism, protein processing and degradation, detoxification and pathogenrelated (PR) proteins, i.e. PR-1a, RSOsPR10 and JIOsPR10. All three PR proteins were induced more strongly in IR64 than in Azucena by water deficit at both protein and mRNA level. The results suggested that PR-1a, RSOsPR10 and JIOsPR10 may play important roles in protecting root cells against water deficit in rice.     

Water availability effects on antioxidant enzyme activities, lipid peroxidation, and reducing sugar contents of alfalfa (Medicago sativa L.)

To understand alfalfa (Medicago sativa L.) reactions to osmotic stress, solutions with −0.5, −1 and −1.5 MPa osmotic potentials using PEG (Poly ethyleneglycol) and distilled water as control were prepared. In a germination test, eleven alfalfa cultivar seeds were allowed to germinate in these solutions. M. sativa cv. Yazdi and M. sativa cv. Gharayonje, selected as tolerant and sensitive cultivars, respectively, and were used for further studies. In all PEG solutions, root and shoot dry weights decreased in both cultivars. Under different levels of osmotic stress, root to shoot ratio increased significantly in Yazdi, whereas this parameter showed no significant differences in Gharayonje. Yazdi cultivar also showed higher activities of SOD (Superoxide dismutase), APX (Ascorbate peroxidase), CAT (Catalase), POD (Peroxidase), and higher reducing sugar contents of leaves in comparison with Gharayonje. These higher antioxidant activities help the tolerant cultivar to decrease oxidative damages of osmotic stress to membrane lipids as compared with its sensitive counterpart. As a result, electrolyte leakage and the amounts of MDA (Malondialdehyde), were higher in Gharayonje. This study highlights the importance of enzymatic and non-enzymatic antioxidant systems in scavenging reactive oxygen species which is caused by osmotic stress. It is seems that antioxidant systems are more active in tolerant cultivars than those of sensitive ones.     

Drought-induced root aerenchyma formation restricts water uptake in rice seedlings supplied with nitrate

Previous studies demonstrated that ammonium nutrition results in higher water uptake rate than does nitrate nutrition under water stress, and thus enhances the tolerance of rice plants to water stress. However, the process by which water uptake is related to nitrogen form under water stress remains unknown. A hydroponic experiment with simulated water stress induced by polyethylene glycol (PEG6000) was conducted in a greenhouse to study the relationship between root aerenchyma formation and water uptake rate, such as xylem sap flow rate and hydraulic conductance, in two different rice cultivars (cv. 'Shanyou 63' hybrid indica and cv. 'Yangdao 6' indica, China). The results showed that root aerenchyma tissue increased in water-stressed plants of both cultivars fed by nitrate. No significant difference was found in root hydraulic conductivity and/or xylem sap flow rate between the two rice cultivars fed by ammonium regardless of water status, whereas these parameters decreased significantly in water-stressed plants fed by nitrate. It was concluded that aerenchyma that formed in the root cortex impeded the radial transport of water in the root cylinder and decreased water uptake in water-stressed rice plants fed by nitrate. Water transport occurred mainly through Hg-sensitive water channels in rice roots supplied with ammonium.     

Modeling seed germination of unprimed and primed seeds of sweet sorghum under PEG-induced water stress through the hydrotime analysis

The effects of reduced water potential (ψ) on seed germination at 25 and 15 °C in unprimed (UP) and primed (P) seeds of two cultivars of sweet sorghum (cv. Keller and cv. Makueni local), were analyzed through the hydrotime model. Six ψ (from 0 to ?1.0 MPa) in polyethylene glycol 6000 (PEG) solutions were used for the tests. Seeds were primed in 250 g/L PEG solution at 15 °C for 48 h. Decreasing ψ of imbibition solution reduced and delayed germination. At 15 °C seeds germinated less and slower than at 25 °C at any ψ. Seeds of cv. Makueni local exhibited a greater sensitivity to water stress in terms of germination percentage, than seeds of cv. Keller, but they were faster in germination. Osmopriming was beneficial for seed germination, both in terms of final percentage and rate, at any temperature and ψ. The hydrotime analysis revealed that predicted θ _H constant was increased when temperature was reduced to 15 °C and at this temperature median base water potential [ψ _b(50)] for germination was higher (less negative) than at 25 °C. Seed priming shifted ψ _b(50) towards more negative values and reduced θ _H requirements for germination. At 25 °C the two cultivars behaved similarly while at 15 °C cv. Keller exhibited a ψ _b more negative but required a greater θ _H to germinate, indicating a greater water-stress tolerance but a slower germination, than cv. Makueni local. The application of the model allows to identify water stress tolerant cultivars during germination, to include into breeding programs for the selection of well-performing cultivars under stress conditions.     

Optimized potassium nutrition improves plant-water-relations of barley under PEG-induced osmotic stress

Aims

Water use efficiency (WUE) of crop plants is an important plant trait for maintaining high yield in water limited areas. By influencing osmoregulation of plants, potassium (K) plays a critical role in stress avoidance and adaptation. However, whole plant physiological mechanisms modulated by K supply in respect of plant drought tolerance and water use efficiency are not well understood. In the present study, growth, development and transpiration dynamics of two barley cultivars were evaluated with and without PEG-induced osmotic stress using an automated balance system and image based leaf area determination.

Methods

Experiments were conducted to study the effects of varied K supply under different osmotic stress treatments on a wide range of morphological, biochemical and physiological characteristics of barley plants such as leaf area development, daily whole plant transpiration rate (DTR), stomatal conductance (g_s), assimilation rate (A_N), biomass and leaf water use efficiency (WUE) as well as foliar abscisic acid (ABA) concentrations. Two barley cultivars (cv. Sahin-91 and cv. Milford) were treated with two K supply levels (0.04 and 0.8 mM K) and osmotic stress induced by polyethylene glycol 6000 (PEG) for a period of 9 days (in total 48 days experiment) in the hydroponic plant culture (non-PEG and + 20% PEG ).

Results

Without PEG, low-K supply depressed dry matter (DM) by almost 60% averaged across both cultivars. Under osmotic stress (+PEG), total leaf area was reduced by almost 70% in low-K compared to adequate-K plants. Low K concentration under PEG stress was correlated with higher ABA concentration and was correlated with lower leaf- and whole plant transpiration rate. Biomass-WUE under low K supply decreased significantly in both barley cultivars, to a greater extent in cv. Milford under osmotic stress. However, leaf-WUE was not affected by K supply in the absence of osmotic stress.

Conclusions

It was suggested that reduced biomass-WUE in low-K treated barley plants was not related to inefficient stomatal control under K deficiency, but instead due to reduced assimilation rate. It was further hypothesized that under low K supply, a number of energy consuming activities reduce biomass-WUE, which are not distinguished by measuring leaf-WUE. This study showed that low K supply under osmotic stress increases foliar ABA concentration thereby decreasing plant transpiration.

     

Growth of Arabidopsis thaliana seedlings under water deficit studied by control of water potential in nutrient-agar media

We have characterized the growth responses of Arabidopsis thaliana seedlings to water deficit. To manipulate the water potential, we developed a method whereby the nutrient-agar medium could be supplemented with polyethylene glycol (PEG 8000); PEG was introduced into gelled media by diffusion, which produced media with water potential as low as -1.6 MPa. For dark-grown plants, hypocotyl growth had a hyperbolic dependence on water potential, and was virtually stopped by -1 MPa. In contrast, primary root elongation was stimulated by moderate deficit and even at -1.6 MPa was not significantly less than the control. That these results did not depend on a direct effect of PEG was attested by obtaining indistinguishable results when a dialysis membrane impermeable to PEG was placed between the medium and the seedlings. For light-grown seedlings, moderate deficit also stimulated primary root elongation and severe deficit reduced elongation only partially. These changes in elongation were paralleled by changes in root system dry weight. At moderate deficit, lateral root elongation and initiation were unaffected and at higher stress levels both were inhibited. Primary root diameter increased steadily with time in well-watered controls and under water deficit increased transiently before stabilizing at a diameter that was inversely proportional to the deficit. Along with stimulated primary root elongation, moderate water deficit also stimulated the rate of cell production. Thus, A. thaliana responds to water deficit vigorously, which enhances its use as a model to uncover mechanisms underlying plant responses to water deficit.     

Regulation by ABA of osmotic-stress-induced changes in protein synthesis in tomato roots

Polypeptide synthesis and accumulation were examined in the roots of tomato seedlings exposed to a polyethylene glycol‐imposed water deficit stress. In these roots, the synthesis of a number of polypeptides was induced, while that of several others was enhanced or repressed. To examine the role played by abscisic acid (ABA) in co‐ordinating the accumulation of these proteins, water‐deficit‐stress‐responsive polypeptide synthesis was investigated in the roots of the ABA‐deficient mutant flacca. In the roots of this mutant, the ability to accumulate a complete set of water‐deficit‐stress‐responsive polypeptides was impaired, indicating that ABA is required for their synthesis. The role of ABA was further examined by exposing the roots of both genotypes to exogenous ABA, which, with one exception, elicited the accumulation of all water‐deficit‐stress‐responsive proteins. Polyethylene glycol‐induced polypeptide accumulation was accompanied by a 1·6‐fold increase in the level of endogenous ABA in the roots of wild‐type plants and a 5‐fold increase in the roots of flc. Thus, although the absolute level was lower than that of the wild‐type, flc has the capacity to accumulate ABA in its roots. When fluridone was used to prevent the biosynthesis of ABA, the accumulation of several water‐deficit‐stress‐responsive polypeptides was reduced further. The synthesis of polypeptides was also examined in the roots of salt‐treated seedlings. Salt altered the accumulation of several polypeptides, all of which were previously observed in water‐deficit‐stressed roots, indicating that their synthesis was the result of the osmotic component of the salt stress. However, the accumulation of these polypeptides was not impaired in flc roots, indicating that the role played by ABA in regulating their accumulation in salt‐and polyethylene glycol‐treated roots differs. As such, salt‐ and water‐deficit‐stress‐induced changes in gene expression may be effected by different mechanisms, at least at the level of polypeptide accumulation.     

Upland rice and lowland rice exhibited different PIP expression under water deficit and ABA treatment

Aquaporins play a significant role in plant water relations. To further understand the aquaporin function in plants under water stress, the expression of a subgroup of aquaporins, plasma membrane intrinsic proteins （PIPs）, was studied at both the protein and mRNA level in upland rice （Oryza sativa L. cv. Zhonghan 3） and lowland rice （Oryza sativa L. cv. Xiushui 63） when they were water stressed by treatment with 20% polyethylene glycol （PEG）. Plants responded differently to 20% PEG treatment. Leaf water content of upland rice leaves was reduced rapidly. PIP protein level increased markedly in roots of both types, but only in leaves of upland rice after 10 h of PEG treatment. At the mRNA level, OsPIP1,2, OsPIP1,3, OsPIP2;1 and OsPIP2;5 in roots as well as OsPIP1,2 and OsPIP1;3 in leaves were significantly up-regulated in upland rice, whereas the corresponding genes remained unchanged or down-regulated in lowland rice. Meanwhile, we observed a significant increase in the endogenous abscisic acid （ABA） level in upland rice but not in lowland rice under water deficit. Treatment with 60 μM ABA enhanced the expression of OsPIP1;2, OsPIP2;5 and OsPIP2;6 in roots and OsPIP1;2, OsPIP2;4 and OsPIP2;6 in leaves of upland rice. The responsiveness of PIP genes to water stress and ABA were different, implying that the regulation of PIP genes involves both ABA-dependent and ABA-independent signaling oathways during water deficit.     

Response of alfalfa to putrescine treatment under drought stress

Alfalfa (Medicago sativa L. cv. Siwa 1) seeds were germinated in polyethylene glycol (PEG 4000) of different concentrations and with or without putrescine. The decrease in water potential of the PEG solution reduced germination rate, germination percentage, and growth criteria (e.g., hypocotyl length, fresh and dry masses of shoot and root), while the root length was increased. The decrease in water potential also reduced the contents of total soluble and reducing sugars, and proteins, and activities of α-and β-amylases and invertase, while increased protease activity. Putrescine treatment improved germination and all growth criteria and increased the activity of the hydrolytic enzymes except protease. In a pot experiment, drought stress was imposed by decreasing the soil moisture. Growth criteria, contents of proteins, chlorophyll a, b and carotenoids, as well as Hill reaction activity decreased while the hydrolytic enzyme activity and total soluble and reducing sugar contents increased under drought stress. Putrescine treatment decreased the activity of the hydrolytic enzymes and increased the polysaccharide, protein and photosynthetic pigment contents, and Hill reaction activity.     

Water-deficit tolerance induction during germination of Jalo Precoce bean (Phaseolus vulgaris L.) cultivar

Bean (Phaseolus vulgaris L.) cultivars are susceptible to water stress, especially during germination. Salicylic acid and thermal shock improve tolerance level in this plant to different kinds of stresses. However, in the present work, effects of cold shock and salicylic acid alone or combined on germinating beans under imposed water deficit were evaluated. Bean seeds from the Jalo Precoce cultivar were imbibed either in water or in salicylic acid for 24 h. After treatment, lots were divided and exposed to cold shock (7 °C) for another 24 h. The seeds were then placed on paper rolls imbibed with different concentrations of mannitol to impose a water deficit on them. They were evaluated for germination; seedling vigour; dry and total weights and length of shoot root; superoxide dismutase activity and proline content. Proline accumulates as a response to water-deficit stress, and SA alone or combined with cold shock improves this response. The use of SA increases many of the physiological variables than cold shock and decreases the antioxidant activity of SOD.     

The role of aquaporin RWC3 in drought avoidance in rice

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and drought resistance still remains elusive. From an agronomic viewpoint, upland rice is traditionally considered as showing drought avoidance. In the investigation of different morphological and physiological responses of upland rice (Oryza sativa L. spp indica cv. Zhonghan 3) and lowland rice (O. sativa L. spp japonica cv. Xiushui 63) to water deficit, we observed young leaf rolling and the remarkable decline of cumulative transpiration in the upland rice. The expression of water channel protein RWC3 mRNA was increased in upland rice at the early response (up to 4 h) to the 20% polyethylene glycol (PEG) 6000 treatment, whereas there was no significant expression changes in lowland rice. Protein levels were increased in upland rice and decreased in lowland rice at 10 h after the water deficit. The up-regulation of RWC3 in upland rice fits well with the knowledge that upland rice adopts the mechanism of drought avoidance. The physiological significance of this RWC3 up-regulation was then explored with the over-expression of RWC3 in transgenic lowland rice (O. sativa L. spp japonica cv. Zhonghua 11) controlled by a stress-inducible SWPA2 promoter. Compared to the wild-type plant, the transgenic lowland rice exhibited higher root osmotic hydraulic conductivity (Lp), leaf water potential and relative cumulative transpiration at the end of 10 h PEG treatment. These results indicated that RWC3 probably played a role in drought avoidance in rice.     

Responses of growth and antioxidant systems in <Emphasis Type="Italic">Carthamus</Emphasis><Emphasis Type="Italic">tinctorius</Emphasis> L. under water deficit stress

An investigation was carried out to find out the extent of changes occurred in two safflower (Carthamus tinctorius L.) cultivars in response to water deficit stress. Two safflower cultivars namely IL.111 and Isfahan were used for the study. Thirty days after sowing, plants were grown under soil moisture corresponding to 100, 85, 70 and 55% field capacity for next 30 days. Water deficit treatments significantly decreased the shoot length, shoot dry matter, root dry matter, relative growth rate, leaf relative water content (LRWC) and leaf water potential (Ψ_W), whereas root length, root-to-shoot ratio, lipid peroxidation and antioxidant compounds such as ascorbic acid (AA), α-tocopherol (α-Toc) and reduced glutathione (GSH) and superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), and peroxidase (POX, EC 1.11.1.7) activities were increased. Water deficit stressed plants maintained higher levels of compounds and scavenging enzymes. Significant differences were observed between cultivars and irrigation levels treatments. The cv. IL.111 could be considered more tolerant to water stress than cv. Isfahan, registering greater biomass, LRWC and leaf water potential (Ψ_W), associated with high antioxidant activity.     

Response of antioxidant and osmoprotective systems of wheat seedlings to drought and rehydration

Complex study of the effect of soil drought (72 h) and subsequent rehydration for 24 and 48 h on the activities of antioxidant and osmoprotective systems in the leaves of young plants of winter wheat (Triticum aestivum L.) cvs. Ballada (high productivity) and Beltskaya (low productivity) was carried out. Under drought conditions, the content of water in the leaves of cv. Ballada reduced to a lesser degree than in the leaves of cv. Beltskaya. Drought did not affect the rate of leaf growth in cv. Ballada but retarded leaf growth in cv. Beltskaya. Under drought conditions, the content of ascorbate reduced in cv. Beltskaya but was not changed in cv. Ballada; the content of glutathione increased by 19% in cv. Ballada and by 30% in cv. Beltskaya. Under drought conditions, ascorbate peroxidase activity was not changed in cv. Ballada whereas in cv. Beltskaya there was a tendency to its decrease. Glutathione reductase activity in the leaves of cv. Beltskaya increased stronger than in cv. Ballada. Substantial differences between cultivars in the accumulation of reducing sugars and sucrose under water deficit were observed. In both cultivars, drought induced an active proline accumulation. Observed differences in the cultivar responses to water stress evidently indicate differences in the strategy of their adaptation to drought. Drought did not affect the contents of chlorophyll and MDA in both cultivars. The data obtained allow a suggestion that, under conditions of moderate soil drought, the coordinated system of antioxidant defense and osmotic control functioned sufficiently effective; as a result, oxidative stress was not developed in both cultivars. Young plants of both cultivars differing in their responses to water deficit retained the ability to recover after rehydration.     

Low irradiance stress tolerance in rice (Oryza sativa L.)

The effect of low irradiance on three rice cultivars (shade tolerant cvs. Swarnaprabha and CO 43 and shade susceptible cv. IR 20) was studied. The large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase with molecular mass of 55 kDa was reduced in cv. IR 20 grown under low irradiance (LI). Native protein profile studied showed, under LI, reduction in the contents of proteins with RF values 0.03, 0.11 and 0.37. Analysis of chloroplast polypeptides revealed an induction of light-harvesting chlorphyll-protein 2 (LHCP2) under shade. The induction was more expressed in cv. CO 43 than in cv. IR 20. Under LI, in vivo labelled protein bands in the molecular range of 26 - 27 kDa were induced. These proteins were highly turned over in the LI-grown plants of cv. CO 43 than in cv. IR 20. A signal for rbcL gene sequences in EcoRI digested lanes was also found. Isozyme analysis of peroxidase showed an induction of a new band with RF 0.43 in cv. IR 20 subjected to LI. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physiological responses of two Jerusalem artichoke cultivars to drought stress induced by polyethylene glycol

Physiological responses of two Jerusalem artichoke (Helianthus tuberosus L.) cultivars with different drought sensitivity to drought stress induced by polyethylene glycol (PEG) 6000 were investigated by characterizing water status, membrane lipid peroxidation, key antioxidant enzymes activity, and proline accumulation. It was observed that the drought-tolerant Jerusalem artichoke cv. Xiuyan maintained a relatively higher water status than the drought-sensitive cv. Yulin upon drought treatments. Meanwhile, lower levels of malondialdehyde (MDA) as well as higher levels of free proline occurred in cv. Xiuyan after 36 h drought treatments. Moreover, the activities of catalase (CAT) and superoxide dismutase (SOD) in cv. Xiuyan were higher than cv. Yulin after drought stress. These results indicated that drought sensitivities actually differ between Jerusalem artichoke cv. Xiuyan and cv. Yulin, and the cv. Xiuyan was more tolerant to drought stress caused by polyethylene glycol.