High-temperature stress alters grain quality, starch granule structure, and gene expression in basmati rice cultivars

High-temperature stress is a serious issue for rice production, yet the molecular and biochemical foundation of heat-induced deterioration of grain quality is remains poorly understood, especially in the case of aromatic rice. In the current study, 15 rice cultivars including Basmati rice, Non-Basmati aromatic rice and non-aromatic heat-tolerant cultivar Nagina 22 as a check were evaluated for high temperature stress. Physiological, biochemical, and molecular characteristics related to grain quality characteristics including starch parameters, amino acid composition, starch granule structure, and gene expression of starch synthesis related genes viz. GBSSI, Wx and Pro were studied. High-temperature stress during flowering and grain filling stage significantly lowered photosynthetic rate, stomatal conductance, transpiration rate, amylose content and essential amino acids such as lysine, methionine, and glutamine. Scanning electron microscopy indicated abnormal and deformed starch granules in Basmati genotypes, while Nagina 22 was affected the least. Gene expression analysis indicated down-regulation of GBSSI Wx and Pro 7 genes leads to inhibition of starch synthesis and accelerating grain deterioration. Collectively, these results prove that rice that is inherently aromatic is especially sensitive to heat-induced deterioration of grain quality and reveal new knowledge of the physiological, biochemical, and molecular basis of heat-induced sensitivity of rice. The results also indicate possible molecular targets for developing thermotolerant Basmati and Non-Basmati aromatic rice.