study of some cryoprotectives role to induce low temperature tolerance in rice (oryza sativa l.) seedlings

to study of some cryoprotectives in cold tolerant rice genotypes (irctn33 and irctn34) and cold-sensitive rice genotype (hoveize) were selected in previous experiment, fourteen-day rice seedlings exposed fourteen days in 13/15oc (respectively night-day) temperatures as the stress treatment and 22/28oc (night-day) temperature as control treatment in phytotrone. this experiment was conducted in factorial design with four replications. results showed that the highest amount of stomatal conductance in stress treatment was in variety irctn33 and the lowest amount was in hoveizeh (sensitive variety). total soluble sugars (tss) of leaves in stress condition was significantly more than control. the highest leaf tss was measured in hoveizeh variety, but tss accumulation could not induce tolerance to low temperature at this sensitive variety. while, tss of roots in control condition was significantly more than stress treatment and the lowest amount was in irctn33. starch of leaves in control condition was significantly more than stress condition. highest level of leaves starch was in hoveizeh. sucrose and fructose amount in stress condition were significantly more than control condition. inorganic phosphate of roots in control was significantly more than stress. osmotic potential of leaves in control was significantly more than stress. lowest level of osmotic potential in stress condition was in hoveizeh variety. stomatal conductance had a high correlation with water potential and osmotic potential. increase of sucrose and fructose in leaves, result in significant decrease of stomatal conductance. while, increase of tss of roots, caused increasing of stomatal conductance. in addition, low temperature stress caused decrease of photosynthetic capacity and some disorders in source-sink relations. tss accumulation in sensitive variety hoveizeh could not induce low temperature tolerance.