The study aims to investigate the physiological mechanisms associated with salt tolerance of different rice genotypes; with emphasis on carbohydrate metabolism and chlorophyll concentration. Studies were conducted in a greenhouse and fields at the International Rice Research Institute (IRRI) during the dry season (November 2008 to March 2009) and the wet season (April 2009 to October 2010). Salt stress increased chlorophyll concentration in leaves of a tolerant (IR651) and a moderately tolerant (IR64) rice genotypes, but significantly decreased chlorophyll a/b ratio. Chlorophyll a concentration and chlorophyll a/bratio were higher in the leaves of IR651 than in the leaves of IR64 under salt stress, and this is probably one of the reasons for the higher tolerance of IR651 compared with IR64. Differences between genotypes in dry weight and leaf area were not significant under control condition; however, higher soluble sugars and starch concentrations in plant tissues were observed under control conditions than under salt stress. Conversion of soluble sugars into starch seems to be partially inhibited by salt stress as suggested by the higher concentrations of soluble sugars compared with starch under salt stress. Apparently, the salt tolerant genotype maintained higher soluble sugars, higher chlorophyll a and chlorophyll a/b ratio under salt stress, and these traits could have partially contributed to its salt tolerance.
Key words: Carbohydrate metabolism, chlorophyll concentration, rice, salt stress, salt tolerance.
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