Abstract
Accumulation of protein and starch in grain is a key process determining grain yield and quality in wheat. Under drought endogenous plant hormone levels will change and may have an impact on the yield and quality of wheat. In a greenhouse experiment, two winter wheat (Triticum aestivum L.) varieties differing in post anthesis drought resistance, tolerant (cv. Zagros) and sensitive (cv. Marvdasht), were subjected to either well-watered (WW) or water-stressed (WS) from anthesis to maturity. On the 7, 15 (grain enlargement stage) and 31 (grain filling stage) days after anthesis (DAA), endogenous abscisic acid (ABA) and indole-3-acetic acid (IAA) were determined in grain of wheat plants by enzyme linked immunosorbent assay (ELISA). The patterns of hormonal changes were similar in two varieties. The ABA levels were much higher under water deficit than well water treatment. In comparison grain ABA levels in all sampling stages was more in Marvdasht than Zagros. The endogenous grains IAA content display a marked reduction by the time and the water stress aggravated this reduction in both cultivars, however, the depresstion was more in drought-sensitive than drought-tolerant. The relationship between yields and contents of starch and protein in grains and levels of two hormones in sink organ indicated that the changes in yield and content of grain starch and protein under water withholding were associated with the reduced IAA and elevated ABA level in grains. It was proposed that the changed levels of endogenous hormones under drought post-anthesis might indirectly affect protein and starch accumulation in grains by influencing the regulatory enzymes and processes.
Highlights
Plant growth and development can be inhibited by water stress at any time in crop life cycles, but the sensitivity to water stress is acute during the reproductive development, because reproduction involves several processes that are extremely vulnerable to a change in plant water status
Water stress rose substantially the abscisic acid (ABA) level during the 7 days from anthesis; during the subsequent periods (7 to 15 days after anthesis (DAA)); the differences between ABA content treatments was barely detectable in both cultivars (Figure 1), but after 31 days from anthesis, ABA concentration in water stressed increased markedly, as the values achieved to 101% and 72% in Marvdasht and Zagros respectively, contrast to their respective controls (Figure 1)
The amounts of grains indole-3-acetic acid (IAA) content reduced sharply with time in both treatments during 7 to 15 DAA (Figure 2), considerable differences were detected between treatments, as substantial reduction occurred in both cultivars under water stress compared with the control treatment
Summary
Plant growth and development can be inhibited by water stress at any time in crop life cycles, but the sensitivity to water stress is acute during the reproductive development, because reproduction involves several processes that are extremely vulnerable to a change in plant water status. With deficit soil water endogenous hormones act as responding signals (Bano et al, 1993; Davies et al, 1986; Jackson et al, 1988) and may play important roles in the growth and development processes, including synthesis and accumulation of starch and protein in grains. Understanding this issue may guide regulation of grain quality formation in wheat by exogenous application of growth substances
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