Physiological Basis of High Nighttime Temperature-Induced Chalkiness Formation during Early Grain-Filling Stage in Rice (Oryza sativa L.)

Heat stress during the grain-filling stage seriously affects grain quality in rice. However, very limited information is available regarding effects of short-term high nighttime temperature (HNT) on chalkiness formation In this paper, HNT at early (7 days after ear emergence) rice and potential causes were investigated by using two varieties that differed susceptibility to temperature. Although treatment night dramatically increased Jiuxiangzhan (JXZ) Huanghuazhan (HHZ), increase was greater JXZ compared HHZ. The net photosynthetic rate SPAD value significantly reduced flag leaves JXZ, while no significant differences observed Furthermore, antioxidant enzyme activity opposite HHZ, exhibiting activity. Moreover, altered endogenous hormone levels, enhanced enzymatic activities related starch biosynthesis, accelerated filling grains when Scanning electron microscopy (SEM) observation exhibited granules endosperm loosely packed together more with small pits produced treatment. Based these data, we inferred but shortened duration changing levels enhancing responsible for resulting changes morphological structure arrangement eventually causing occurrence chalkiness.