Impact of Elevated Temperature Stress on Aroma and Its Gene Expression in Different Developmental Stages of Photoinsensitive Basmati Rice

Abstract

Aroma is an important grain quality trait of aromatic rice, controlled by a recessive gene which increases the accumulation of numerous volatile compounds to produce it. The aroma quality of rice grain also depends on the cultivation practice, genetic condition, environmental components and their interaction. Among the environmental components, the temperature is the vital component that can affect the aroma quality and chemical composition of aromatic rice. This study assessed the effects of different temperatures (early, normal and late sown condition) for relative expression of badh2 and p5cs gene, 2AP (2- acetyl -1- pyrroline) concentration, proline and amylose content as well as morpho-agronomic performance of photoinsensitive basmati rice variety PB1121. The results indicated that higher temperature does not favour rapid the grain filling; favours early maturity; favours 1000 grain weight, reduced the kernel length, amylose content as well as the grain yield per plant significantly. The relative expression of the badh2 gene had an inverse relation with the 2AP production so more the down regulation of the badh2 gene higher was the production of the 2AP in all the developmental stages in PB 1121. In contrast the p5cs gene expression shared a direct relation with the proline production, more the up regulation of the p5cs gene more was the production of the proline content in all the developmental stages. It can also be concluded that the temperature had a tremendous affect on the gene expression of the badh2 and the p5cs genes. The expression of badh2 gene (-1.66 log10fc) was masked more in the lower temperatures while the p5cs gene (2.42 log10fc) expression increased when the average temperature was high. Consequently, the 2AP concentration (68.38 ppb) increased in the late sown condition than the early sown condition while the proline content (9.69 µmoles/g FW) increased in the early sown condition. This investigation also revealed that when the proline content was low the 2AP concentration increased in all the developmental stages in the early as well as in the late sown condition. While in the normal sown condition the 2AP concentration remained constant in all the three developmental stages irrespective of the increase or decrease in the proline content. Temperature affects the agronomic performance, expression of aroma gene, the proline and amylose content, as well as the production of 2AP. Therefore, when the photo insensitive basmati rice variety PB 1121 was sown earlier than the normal sown condition then the aroma content decreased as the average temperatures was higher in the early sown condition during all the developmental stages. This decrease in the aroma content can be attributed to lesser down regulation of the expression of badh2 gene at higher temperature and higher expression of p5cs gene as a consequence the 2AP production was reduced while the proline content increased in the early sown condition. In the late sown condition although the aroma content increased but the grain yield, grain weight and the kernel length was compromised. The obtained information will be helpful for exploring possible reasons for variation in the biochemical composition as well as aroma quality of a genotype which might be used to further improve grain quality of aromatic rice