Expression levels of some starch metabolism related genes in flag leaf of two contrasting rice genotypes exposed to salt stress.

An objective of this investigation was to compare the transcriptional expression of starch metabolism involving genes, soluble sugar, physiological changes and yield components in flag leaf of two contrasting indica rice genotypes, Homjan (HJ; salt-tolerant) and Pathumthani 1 (PT1; salt-sensitive), in response to 150 mM NaCl salt stress. AGPL1, SBEIIb and GWD starch involved genes were up-regulated in salt stressed PT1, leading to accumulation of soluble starch, glucose fructose and total soluble sugars. In HJ, expression levels of AGPL1 AGPS2b, SBEIIb genes in salt stressed plants were higher than in control plants while the soluble sugar level in flag leaf was unchanged. Also, an expression level of some starch related genes i.e. AGPL1, SSI, SBEIIb, ISA2a, and GWD in HJ salt stressed plants was lower than that in PT1. Water use efficiency in salt stressed PT1 was significantly dropped for 35.42% whereas that in HJ was unchanged. Chlorophyll b (Chlb) and total chlorophyll (TC) contents in salt stressed PT1 were significantly degraded for 61.76% and 44.93%, respectively, leading to reduce net photosynthetic rate (Pn). The starch metabolism and sugar accumulation in PT1 were clearly unrelated with salt tolerant ability. In contrast, the starch degradation, photosynthetic abilities and sugar accumulation in salt stressed HJ may play a key role as osmoregulation salt defense mechanism, leading to maintain productivity when subjected to salt stress.