Abscisic acid increases leaf starch content of polyethylene glycol-treated wheat seedlings by temporally increasing transcripts of genes encoding starch synthesis enzymes

The molecular mechanism of starch synthesis regulated by abscisic acid (ABA) under water deficiency in plants was explored in this study. Starch content in leaves of wheat seedlings hydroponically grown in full-strength Hoagland solution increased quickly, however, 15 % polyethylene glycol (PEG)-induced water deficiency significantly inhibited starch content. ABA treatment markedly alleviated starch content inhibition in the leaf organ of wheat seedlings suffering from PEG-induced water deficiency. The expression levels of the starch biosynthesis enzyme genes were measured using quantitative real-time polymerase chain reaction analysis. Under PEG-induced water deficiency conditions, exogenous ABA significantly enhanced transcript levels of many starch biosynthesis enzyme genes at different time points, including TaAGPS2 at 1, 2, 3, and 4 days; TaAGPL2 at 1, 4, and 5 days; TaGBSSII at 2, 3, and 4 days; TaSSI at 1, 3, and 4 days; TaSSIIIb at 1 and 5 days; TaSSIV at 1, 2, and 3 days; TaBEIIa at 1 and 5 days; TaPHOL at 1, 3, and 4 days; and TaDPE2 at 3, 4, and 5 days. Our results indicate that exogenous ABA application increased starch content in the leaf organ of wheat seedlings under PEG-induced water deficiency, possibly by temporally regulating the expression levels of the starch synthesis enzyme genes.