Involvement of abscisic acid in fructan hydrolysis and starch biosynthesis in wheat under soil drying

This study investigated the possibility that abscisic acid (ABA) may mediate the effect of post-anthesis soil drying on carbon remobilization from the stem and grain filling through regulating fructan hydrolysis and starch biosynthesis in wheat (Triticum aestivum L.). Two wheat cultivars showing difference in plant height were pot-grown. Three treatments, well watered (WW), moderate soil drying (MD) and severe soil drying (SD, were imposed from 9 days post-anthesis until maturity. The results showed that ABA contents in stems and grains, the remobilization of carbon reserves from the stem and its contribution to grain yield, and activities and gene expression levels of the enzymes involved in fructan hydrolysis in stems were increased with the increase in soil drying. When compared with the WW, the MD substantially increased, but the SD markedly decreased, grain filling rate, grain weight, and starch biosynthetic ability, in terms of activities and gene expression levels of ADP glucose pyrophosphorylase, soluble starch synthase, and starch branching enzyme in grains. The two cultivars showed the same tendency. ABA content was positively correlated with the remobilization of carbon reserves, and positively correlated with grain filling rate and starch biosynthetic ability under both WW and MD treatments. Exogenous application of a low concentration ABA to WW plants imitated the results under the MD, and applying with a high concentration ABA showed the effect of the SD. In summary, ABA enhances fructan hydrolysis in wheat stems and regulates starch biosynthesis in the grain.