Photosynthetic activity and metabolic profiling of bread wheat cultivars contrasting in drought tolerance

Abstract

The rapid increase in population growth under changing climatic conditions causes drought stress, threatening world food security. The identification of physiological and biochemical traits acting as yield-limiting factors in diverse germplasm is pre-requisite for genetic improvement under water-deficit conditions. The major aim of the present study was the identification of drought-tolerant wheat cultivars with a novel source of drought tolerance from local wheat germplasm. The study was conducted to screen 40 local wheat cultivars against drought stress at different growth stages. Barani-83, Blue Silver, Pak-81, and Pasban-90 containing shoot and root fresh weight >60% of control and shoot and root dry weight >80% and 70% of control, respectively, P (% of control >80 in shoot and >88 in root), K⁺ (>85% of control), and quantum yield of PSII > 90% of control under polyethylene glycol (PEG)-induced drought stress at seedling stage can be considered as tolerant, while more reduction in these parameters make FSD-08, Lasani-08, Punjab-96, and Sahar-06 as drought-sensitive cultivars. FSD-08 and Lasani-08 could not maintain growth and yield due to protoplasmic dehydration, decreased turgidity, cell enlargement, and cell division due to drought treatment at adult growth stage. Stability of leaf chlorophyll content (<20% decrease) reflects photosynthetic efficiency of tolerant cultivars, while ~30 µmol/g fwt concentration of proline, 100%-200% increase in free amino acids, and ~50% increase in accumulation of soluble sugars were associated with maintaining leaf water status by osmotic adjustment. Raw OJIP chlorophyll fluorescence curves revealed a decrease in fluorescence at O, J, I, and P steps in sensitive genotypes FSD-08 and Lasani-08, showing greater damage to photosynthetic machinery and greater decrease in JIP test parameters, performance index (PI_ABS), maximum quantum yield (Fv/Fm) associated with increase in Vj, absorption (ABS/RC), and dissipation per reaction center (DIo/RC) while a decrease in electron transport per reaction center (ETo/RC). During the present study, differential modifications in morpho-physiological, biochemical, and photosynthetic attributes that alleviate the damaging effects of drought stress in locally grown wheat cultivars were analyzed. Selected tolerant cultivars could be explored in various breeding programs to produce new wheat genotypes with adaptive traits to withstand water stress.

Keywords: Triticum aestivum; chlorophyll fluorescence; drought stress; mineral nutrients; osmotic adjustment; water relations.

Figure 1

Shoot and root fresh and dry weights (mg/plant) of wheat seedlings, when plants of 40 local wheat cultivars were grown under normal or PEG-induced drought stress for 2 weeks. Means (± SE; n=5) are presented on the primary vertical axis, while % of the control values are presented on the secondary vertical axis. (A) Shoot fwt, (B) shoot dwt, (C) root fwt, and (D) root dwt.

Figure 2

Shoot and root K⁺ and P accumulation in wheat seedlings when plants of 40 local wheat cultivars were grown under normal or PEG-induced drought stress for 2 weeks. Means (± SE; n=5) are presented on the primary vertical axis, while percent of the control values is presented on the secondary vertical axis. (A) Shoot K⁺, (B) root K⁺, (C) shoot P, and (D) root P.

Figure 3

Growth attributes of selected wheat cultivars subjected to control or drought stress at adult stage. Means (± SE; n=5) are presented on the primary vertical axis, while percent decrease value is presented on the secondary vertical axis. Different letters represent significant differences among cultivars at p < 0.05 according to LSD test. (A) Shoot fresh weight, (B) shoot dry weight, (C) root fresh weight, (D) root dry weight, (E) plant height, (F) flag leaf area, (G) total chlorophyll content (SPAD), and (H) quantum yield of PSII.

Figure 4

Water relations attributes of selected wheat cultivars subjected to control or drought stress at adult stage. Means (± SE; n=5) are presented on the primary vertical axis, while percent decrease value is presented on the secondary vertical axis. Different letters represent significant differences among cultivars at p < 0.05 according to LSD test. (A) Water potential, (B) osmotic potential, (C) turgor potential, and (D) % relative water content.

Figure 5

Accumulation of mineral nutrients and MDA in selected wheat cultivars subjected to control or drought stress at adult stage. Means (± SE; n=5) are presented on the primary vertical axis, while percent decrease value is presented on the secondary vertical axis. Different letters represent significant differences among cultivars at p < 0.05 according to LSD test. (A) Shoot N, (B) shoot P, (C) shoot K⁺, and (D) MDA.

Figure 6

Accumulation of organic osmolytes in selected wheat cultivars subjected to control or drought stress at adult stage. Means (± SE; n=5) are presented on the primary vertical axis, while percent increase/decrease value is presented on the secondary vertical axis. Different letters represent significant differences among cultivars at p < 0.05 according to LSD test. (A) Total soluble sugars, (B) proline, (C) total soluble proteins, and (D) free amino acids.

Figure 7

Yield attributes of selected wheat cultivars subjected to control or drought stress at adult stage. Means (± SE; n=5) are presented on the primary vertical axis, while percent decrease value is presented on secondary vertical axis. Different letters represent significant differences among cultivars at p < 0.05 according to LSD test. (A) Grain yield, (B) 100 grain weight, (C) number of grains/spike, (D) number of spikelets/spike, (E) spike length, and (F) number of tillers/plant.

Figure 8

Raw OJIP chlorophyll a fluorescence curves (Ft) of the four selected wheat cultivars when plants were subjected to control or drought stress at adult stage. (A) FSD-08, (B) Lasani-08, (C) Barani-83, and (D) Blue Silver.

Figure 9

Kinetic differences of four selected wheat cultivars subjected to control or drought stress at adult stage. (A) Double normalized between Fo and Fk (L-band). (B) Double normalized between Fo and Fj (K band).

Figure 10

Radar plot of selected JIP test parameters showing changes in chlorophyll a fluorescence transients (normalized to control as reference) of four selected wheat cultivars subjected to drought stress at adult growth stage.