Effect of extreme temperatures at different stages during grain filling on rice seed weight and germination and its regulations

A series of studies were carried out in chamber room to investigate the injury mechanism under extreme temperature and at different grain filling stages with foliar application of plant growth regulators (Abscisic acid-ABA and salicylic acid-SA) on the rice cultivar Huanghuazhan. Grain filling rate and grain weight were measured as yield components, while seed germination rate, germination index and seed vigour index were measured as seed quality indices. Chlorophyll fluorescence parameters and active oxygen resistance activity were also analyzed. The results showed that the rate of grain filling and grain weight were significantly reduced under the extreme temperature conditions and at higher concentrations of the plant growth regulators. Superoxide dismutase (SOD) activity increased and decreased among treatments, while malondialdehyde (MDA) content was significantly high. Maximal photochemical efficiency of PS II (Fv/Fm) and the potential photochemical efficiency of PS II (Fv/Fo) also decreased under high temperature stress, whilst it increased and decreased under low temperature stress among treatments.