Physiological responses of two rice (Oryza sativa L.) genotypes to chilling stress at seedling stage

In this study, quantitative changes of dry matter, proline and total soluble protein in shoot and root, stomatal conductance (gs), total chlorophyll, chlorophyll stability index (CSI) and soil and plant analyzer development (SPAD) number of latest fully-expanded leaves were determined in an Iranian coldsensitive rice genotype (Hoveizeh) in comparison to an international check genotype (IRCTN34, coldtolerant). The hydroponic experiment was arranged in a completely randomized design with three replications under the growth chamber condition under a controlled environment of 29/22°C (day/night) and 12 h light photoperiod. Then, the treatment plants were exposed to 15/10°C (day/night) cold stress for two weeks and control plants were kept at 29/22°C (day/night). Dry matter accumulation decreased with chilling stress in the two genotypes, with decreases been more pronounced in Hoveizeh genotype. Our results showed that cold treatment increased accumulation of total soluble protein (only in coldtolerant genotype) and proline in rice seedlings, while it decreased the content of chlorophyll, stomatal conductance, total soluble protein (only in cold-sensitive genotype) and dry matter. The results indicated that higher contents of protein and chlorophyll under stress were associated with tolerance to chilling.Key words: Abiotic stress, cold, total soluble protein, proline, total chlorophyll, stomatal conductance