1 Acta Physiologiae Plantarum 2012 Vol: 35(2):451-461. DOI: 10.1007/s11738-012-1088-6

Impact of osmotic stress on physiological and biochemical characteristics in drought-susceptible and drought-resistant wheat genotypes

In this study, the seedlings of two wheat cultivars were used: drought-resistant Chinese Spring (CS) and drought-susceptible (SQ1). Seedlings were subjected to osmotic stress in order to assess the differences in response to drought stress between resistant and susceptible genotype. The aim of the experiment was to evaluate the changes in physiological and biochemical characteristics and to establish the optimum osmotic stress level in which differences in drought resistance between the genotypes could be revealed. Plants were subjected to osmotic stress by supplementing the root medium with three concentrations of PEG 6000. Seedlings were grown for 21 days in control conditions and then the plants were subjected to osmotic stress for 7 days by supplementing the root medium with three concentrations of PEG 6000 (D1, D2, D3) applied in two steps: during the first 3 days of treatment −0.50, −0.75 and −1.00 and next −0.75, −1.25 and −1.5 MPa, respectively. Measurements of gas exchange parameters, chlorophyll content, height of seedlings, length of root, leaf and root water content, leaf osmotic potential, lipid peroxidation, and contents of soluble carbohydrates and proline were taken. The results highlighted statistically significant differences in most traits for treatment D2 and emphasized that these conditions were optimum for expressing differences in the responses to osmotic stress between SQ1 and CS wheat genotypes. The level of osmotic stress defined in this study as most suitable for differentiating drought resistance of wheat genotypes will be used in further research for genetic characterization of this trait in wheat through QTL analysis of mapping population of doubled haploid lines derived from CS and SQ1.

Mentions
Figures
Figure 1: Changes in photosynthesis (Pn) in CS and SQ1 wheat seedlings after 1, 3, 4 and 7 days of growth in three levels of osmotic stress (D1, D2 and D3). Data are presented as percentage of control (C). Error bars indicate SE (n = 16) Figure 2: Changes in transpiration rate (E) in CS and SQ1 wheat seedlings after 1, 3, 4 and 7 days of growth in three levels of osmotic stress (D1, D2 and D3). Data are presented as percentage of control (C). Error bars indicate SE (n = 16) Figure 3: Changes in stomatal conductance (g s) in CS and SQ1 wheat seedlings after 1, 3, 4 and 7 days of growth in three levels of osmotic stress (D1, D2 and D3). Data are presented as percentage of control (C). Error bars indicate SE (n = 16) Figure 4: Changes in water use efficiency (WUE) in CS and SQ1 wheat seedlings after 1, 3, 4 and 7 days of growth in three levels of osmotic stress (D1, D2 and D3). Data are presented as percentage of control (C). Error bars indicate SE (n = 16) Figure 5: Changes in chlorophyll content (SPAD) in CS and SQ1 wheat seedlings after 1, 3, 4 and 7 days of growth in three levels of osmotic stress (D1, D2 and D3). Data are presented as percentage of control (C). Error bars indicate SE (n = 16) Figure 6: Plant height (a) and root length (b) of CS and SQ1 wheat seedlings after 7 days of growth in three levels of osmotic stress (D1, D2 and D3). Values are mean ± SE (n = 3). Mean values followed by the same letter are not significantly different (p = 0.05) Figure 7: Leaves (a) and roots (b) relative water content (RWC) of CS and SQ1 wheat seedlings after 7 days of growth in three level of osmotic stress (D1, D2 and D3). Values are mean ± SE (n = 3). Mean values followed by the same letter are not significantly different (p = 0.05) Figure 8: Leaf osmotic potential (a) and content of malondialdehyde (MDA) (b) of CS and SQ1 wheat seedlings after 7 days of growth in three levels of osmotic stress (D1, D2 and D3). Values are mean ± SE (n = 3). Mean values followed by the same letter are not significantly different (p = 0.05) Figure 9: Content of proline (a) and carbohydrates (b) in leaves of CS and SQ1 wheat seedlings after 7 days growth in three levels of osmotic stress (D1, D2 and D3). Values are mean ± SE (n = 3). Mean values followed by the same letter are not significantly different (p = 05)
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    • . . . On the last day of osmotic stress, plant height, length of roots, fresh weight (FW), fresh weight at full turgor (TW) and dry weight (DW) of stem and roots were measured in order to determine relative water content {RWC = (FW − DW/TW − DW) × 100} according to Slatyer (1967) . . .
  61. Smirnoff N; Cumbes QJ Hydroxyl radical scavenging activity of compatible solute. Phytochemistry 28, 1057-1060 (1989) .
    • . . . The accumulation of proline serves as a depot for energy to regulate redox potentials (Hong-Boa et al. 2006; Saradhi and Saradhi 1991), and functions as a hydroxyl radical scavenger (Smirnoff and Cumbes 1989) . . .
  62. Sumera I; Asghari B Effect of drought and abscisic acid application on the osmotic adjustment of four wheat cultivars. J Chem Soc Pakistan 32(1), 13-19 (2010) .
    • . . . Proline and carbohydrates are the two most important organic solutes that are accumulated in higher plants under drought conditions (Changhai et al. 2010; P’erez-Alfocea and Larcher 1995; Sumera and Asghari 2010) . . .
  63. Tan Y; Liang Z; Shao H et al Effect of water deficits on the activity of anti-oxidative enzymes and osmoregulation among three different genotypes of Radix Astragali at seeding stage. Colloid Surf B Biointer 49, 60-65 (2006) .
    • . . . Plants usually experience a fluctuating water supply during their life cycle due to continuously changing climatic factors (Blum 1998; Bohnert et al. 1995; Chaves et al. 2002; Passioura et al. 1993; Tan et al. 2006) . . .
  64. Ting SV; Rouseff RL Proline content in Florida frozen concentrated orange juice and canned grapefruit juice. Proc Fla State Hortic Soc 92, 143-145 (1979) .
    • . . . The level of carbohydrates was expressed in μg g−1 DW (dry weight of leaves). Proline Proline content was measured spectrophotometrically according to Ting and Rouseff (1979) with modifications . . .
  65. Winter SR; Musick JT; Porter KB Evaluation of screening techniques for breeding drought resistant winter wheat. Crop Sci 28, 512-516 (1988) .
    • . . . Differences in resistance to drought stress are known to exist amongst genotypes of plant species, e.g. in maize (Martiniello and Lorenzoni 1985; Lorens et al. 1987), wheat (Winter et al. 1988), and triticale (Grzesiak et al. 2003) . . .
  66. Yagmur M; Kaydan D Alleviation of osmotic stress of water and salt in germination and seedling growth of triticale with seed priming treatments. Afr J Biotechnol 7:2156-2162 , (2008) .
    • . . . These results are in agreement with Yagmur and Kaydan (2008) who also observed a decrease of RWC in hexaploid triticale when drought has been induced by PEG 6000 . . .
  67. Yong T; Zongsuo L; Hongboc S; Feng D Effect of water deficits on the activity of anti-oxidative enzymes and osmoregulation among three different genotypes of Radix Astragali at seeding stage. Colloids Surf B 49, 60-65 (2006) .
    • . . . Plants usually experience a fluctuating water supply during their life cycle due to continuously changing climatic factors (Blum 1998; Bohnert et al. 1995; Chaves et al. 2002; Passioura et al. 1993; Tan et al. 2006) . . .
  68. Zhang J; Dell B; Conocono E; Waters I; Setter T; Appels R Water deficits in wheat: fructan exohydrolase (1-FEH) mRNA expression and relationship to soluble carbohydrate concentrations in two varieties. New Phytol 81(4), 843-850 (2009) .
    • . . . The accumulation of soluble carbohydrates in plants has been widely reported as a response to salinity (Ashraf and Harris 2004) and drought (Zhang et al. 2009) in addition to a significant decrease in the net CO2 assimilation rate . . .
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