Abstract

This work investigated the effects of endogenous abscisic acid (ABA) and physiologic parameters related to yield in two wheat cultivars (Triticum aestivum L.), Marvdasht and Zagros (sensitive and tolerant to terminal season drought, respectively) grown in pots under well watered and water-stressed starting from anthesis until maturity. All physiological parameters were affected by drought stress. Results show that water deficits enhanced the senescence by accelerating loss of leaf chlorophyll and soluble proteins and the loss was more in Marvdasht than Zagros. The net CO₂ assimilation rate (PN) in flag leaves during water deficit displayed a strict correlation with the drought sensitivity of the genotypes and showed an early reduction in Marvdasht. Water stress resulted in a marked increase just in the ABA content of the drought-sensitive that led to reduced transport of sucrose into the grains and lowered the starch synthesis ability of grains, whereas, sucrose uptake and conversion by grains was stimulated by low ABA concentrations in Zagros. The effect of drought on grain yield was primarily due to the significant reduction in grain weight, particularly in drought-sensitive. The results indicate that grain filling processes under water restriction are limited by low substrate availability and reduced synthesis capacity of the sink. These results raised the possibility that water stress-induced elevated levels of endogenous ABA contribute to reduced grain growth.

Key words: Abscisic acid, chlorophyll, flag leaves, grain yield, soluble proteins, soluble sugar, starch, wheat (Triticum aestivum L.).

Abbreviation

ABA, Abscisic acid; DAA, days after-anthesis; HI, harvest index;WW, well-watered; g_s, stomatal conductance.