Abstract: Effects of nitrogen rates on activities of key regulatory enzymes for grain starch and protein accumulation in two wheat varieties (Triticum aestivum L.) under drought and waterlogging from anthesis to maturity were studied in a cement pool culture experiment. Total three water treatments were established from anthesis to maturity, i.e. waterlogging, drought and moderate water supply (CK). Under each water treatment, two nitrogen levels of 120 and 240 kg·ha-1 were implemented. Both drought and waterlogging significantly reduced glutamine synthetase (GS) and glutamate pyruvic aminotransferase (GPT) activities in flag leaf, compared with CK. Nitrogen increased sucrose phosphate synthase (SPS), GS and GPT activities in flag leaf under drought and waterlogging. Sucrose synthase (SS), soluble starch synthase (SSS), granule-bounded starch synthase (GBSS), GS and GPT activities in grains decreased with the progress of grain filling. Drought and waterlogging reduced SS and GS activities while drought increased GPT activity in grain, and waterlogging reduced GPT activity. Nitrogen increased SS activity in grain under CK and drought, while reduced it under waterlogging. Nitrogen increased SSS, GBSS, GS and GPT activities under both drought and waterlogging. Drought increased amylose accumulating rate and protein content while waterlogging reduced them. Under drought and waterlogging nitrogen reduced amylose and amylopectin accumulating rate, while increased protein content in grain. Nitrogen increased protein accumulation under CK and drought while reduced protein accumulation under waterlogging.

Key words: Common wheat(Triticum aestivum L.), Drought, Waterlogging, Grain starch Grain protein, Synthesis enzymes