Effect of low temperature on antioxidant mechenisims in sensitive and tolerance (Oryza sativa L.) genotypes in seedling stage

In order to study of oxidative stress caused by low temperature stress on three rice (Oryza sativa L.) genotypes, 2-week-old rice seedlings were subjected to 13/15oC and 22/29oC as control (night/day, respectively) in phytotrone for 14 days. This experiment was conducted as factorial using completely randomized design with four replications. Low temperature stress caused significant increases in ascorbate (total, oxide and reduce) and α-tocopherol levels in both roots and leaves. Both roots and leaves of cold tolerant genotype IRCTN33, ascorbate oxide was significantly higher than other genotypes. Leaf hydrogen peroxide in sensitive genotype Hoveizeh had significant increase, which had negative correlation with amount of chlorophylls content. Significant increase in MDA (malondialdehyde) in Hoveizeh leaves showed sever membrane phospholipids per-oxidation. In leaves the lowest amount of H2O2 was detected in cold tolerant genotype IRCTN34. Root ascorbate oxide form in IRCTN34 was significantly less than other genotypes. However, Hoveizeh had weak antioxidant mechanisem among studied genotypes, while it was highly efficient in low temperature tolerant genotypes (IRCTN33 and IRCTN34). Therefore, it is possible to suggest them as low temperature tolerant parents to be used in rice breeding programs.