Different Responses to Water Deficit of Two Common Winter Wheat Varieties: Physiological and Biochemical Characteristics

Abstract

Since water scarcity is one of the main risks for the future of agriculture, studying the ability of different wheat genotypes to tolerate a water deficit is fundamental. This study examined the responses of two hybrid wheat varieties (Gizda and Fermer) with different drought resistance to moderate (3 days) and severe (7 days) drought stress, as well as their post-stress recovery to understand their underlying defense strategies and adaptive mechanisms in more detail. To this end, the dehydration-induced alterations in the electrolyte leakage, photosynthetic pigment content, membrane fluidity, energy interaction between pigment-protein complexes, primary photosynthetic reactions, photosynthetic and stress-induced proteins, and antioxidant responses were analyzed in order to unravel the different physiological and biochemical strategies of both wheat varieties. The results demonstrated that Gizda plants are more tolerant to severe dehydration compared to Fermer, as evidenced by the lower decrease in leaf water and pigment content, lower inhibition of photosystem II (PSII) photochemistry and dissipation of thermal energy, as well as lower dehydrins' content. Some of defense mechanisms by which Gizda variety can tolerate drought stress involve the maintenance of decreased chlorophyll content in leaves, increased fluidity of the thylakoid membranes causing structural alterations in the photosynthetic apparatus, as well as dehydration-induced accumulation of early light-induced proteins (ELIPs), an increased capacity for PSI cyclic electron transport and enhanced antioxidant enzyme activity (SOD and APX), thus alleviating oxidative damage. Furthermore, the leaf content of total phenols, flavonoids, and lipid-soluble antioxidant metabolites was higher in Gizda than in Fermer.

Keywords: antioxidant activity; chlorophyll fluorescence; dehydration; photosynthetic pigments and proteins; primary photosynthetic reactions; rehydration; thermoluminescence.

Figure 8

Changes in the content of the main thylakoid-related proteins D1 (a), PsaB (b) and cyt b₆ (c) of Gizda and Fermer varieties in control (C), dehydrated for 3 days (D 3d) or 7 days (D 7d), and rehydrated (R) plants. The abundances of proteins are presented in percentage of the control values (C). Values are given as mean ± SE. The same letters within a graph indicate no significant differences assessed by Fisher’s LSD test (p ≤ 0.05) after performing ANOVA.

Figure 1

RWC (a) and EL (b) of leaves of control, well-hydrated plants (C), and after 3 days (D 3d) and 7 days (D 7d) of dehydration and 3 days of rehydration (R) of wheat plants (Gizda and Fermer). Values are presented as mean ± SE (n = 4). Significant differences between values are indicated by different letters according to Fisher’s LSD test (p ≤ 0.05) of multifactor ANOVA analysis.

Figure 2

Effect of water deprivation for 3 (D 3d) and 7 (D 7d) days, and after 3 days of rehydration (R) of two wheat varieties (Gizda and Fermer) on photosynthetic pigment content. Results are presented as a percentage from the respective control. Mean values ± SE (n = 4) were calculated from four parallel samples at each time point. (a) Chl a; (b) Chl b; (c) Carotenoids (Car). Different letters indicate significant differences between values at p < 0.05 as estimated by Fisher’s LSD test of multifactor ANOVA analysis.

Figure 3

Changes in the quantum yield of PSII electron transport during illumination, Y(II), the quantum yield of light-induced non-photochemical fluorescence quenching, (Y)NPQ, and the quantum yield of non-regulated heat dissipation and fluorescence emission, Y(NO), in control (C), dehydrated for 3 days (D 3d) or 7 days (D 7d) and rehydrated (R) wheat plants (Gizda and Fermer). Values are presented as mean ± SE (n = 4). Significant differences between values are indicated by different letters according to Fisher’s LSD test (p ≤ 0.05) of multifactor ANOVA analysis.

Figure 4

Changes in the levels of FR light-induced P700 photooxidation (P₇₀₀⁺) measured by ΔA_820–860 and half-times of P₇₀₀⁺ re-reduction (t_1/2) after turning off the FR light illumination in control (C), dehydrated for 3 days (D 3d) or 7 days (D 7d), and rehydrated (R) wheat plants (Gizda and Fermer). Values are presented as mean ± SE (n = 4). Significant differences between values are indicated by different letters according to Fisher’s LSD test (p ≤ 0.05) of multifactor ANOVA analysis.

Figure 5

Thermoluminescence curves of leaves from two wheat varieties: Gizda (a) and Fermer (b), from Control (C), dehydrated for 3 days (D 3d) or 7 days (D 7D), and rehydrated (R) plants. Curves were recorded after excitation by two flashes after at least 3 h of dark adaptation. Values of T_max (c) and integrated intensity of B band (d) obtained after curves decomposition. Means ± SE (n = 3). Significant differences between values are indicated by different letters according to Fisher’s LSD test (p ≤ 0.05) of multifactor ANOVA analysis.

Figure 6

Fluidity of the lipid phase, estimated by the degree of fluorescence polarization of DPH (P) in thylakoid membranes isolated from Gizda and Fermer leaves, affected by dehydration for 3 (D 3d) and 7 days (D 7d) and after rewatering (R) in comparison with control (well-watered) plants (C). Values are presented as mean ± SE (n = 4). Significant differences between values are indicated by different letters according to Fisher’s LSD test (p ≤ 0.05) of multifactor ANOVA analysis.

Figure 7

Fluorescence ratios F685/F695 (a) and F735/F685 (b) in isolated thylakoid membranes from control (well-watered) plants (C), dehydrated for 3 days (D 3d) or 7 days (D 7d) and rewatered (R) wheat plants (Gizda and Fermer). Fluorescence ratios were calculated from 77 K fluorescence emission spectra at excitation with 436 nm after baseline correction. Mean values ± SE (n = 4) were calculated from four parallel samples for each time point. Significant differences between values are indicated by different letters according to Fisher’s LSD test (p ≤ 0.05) of multifactor ANOVA analysis.

Figure 9

Representative Western blots of dehydrins and ELIPs of Gizda and Fermer varieties in control, normally watered (C), dehydrated for 3 days (D 3d) or 7 days (D 7d), and rehydrated (R) plants. Thylakoid samples corresponding to 1.5 μg Chl were applied per lane. St: ROTI^®Mark TRICOLOR (Carl Roth GmbH + Co. KG, Karlsruhe, Germany).

Figure 10

The activity of antioxidant enzymes (a) superoxide dismutase (SOD), (b) catalase (CAT), (c) ascorbate peroxidase (APX), and (d) guaiacol peroxidase (GPX) in the leaves of two wheat varieties (Gizda and Fermer): normally watered (C), dehydrated for 3 days (D 3d) or 7 days (D 7d), and rehydrated (R) plants. Values are given as mean ± SE (n = 4); different letters indicate significant differences assessed by Fisher LSD test (p ≤ 0.05) after performing multifactor ANOVA analysis.

Figure 11

Content of metabolites with antioxidant power and total antioxidant potential in Gizda and Fermer plants: normally watered (C), dehydrated for 3 days (D 3d) or 7 days (D 7d), and rehydrated (R) plants. (a) total phenols; (b) total flavonoids; (c) water-soluble antioxidant metabolites, expressed as ascorbate equivalents—WS-AOM; (d) lipid-soluble antioxidant metabolites expressed as α-tocopherols equivalents—LS-AOM; (e) DPPH radical scavenging activity; (f) ferric reducing antioxidant power—FRAP. Values are given as mean ± SE (n = 4); different letters indicate significant differences assessed by the Fisher LSD test (p ≤ 0.05) after performing multifactor ANOVA analysis.