The rice crop is cold sensitive plant that under cold stress is more decreasing yield. Therefore, knowing defense mechanism of rice crop and low temperature is necessary. In order to, the effects of cold on some morphological and physiological characters of two rice (Oryza sativa L.) varieties (Onda and Domsiah) were studied under control treatment (day/night 28o/25o) and were treated after two weeks with cold stress (day/night 15o/13o). The results showed that dry weight, length of shoot and root decreased in both varieties significantly, but the Domsiah variety was more decreased. The amount of chlorophyll a, b and starch content was decreased under stress in two varieties. However, the amount of decreasing was about 48, 54 and 38 percentages related to control treatment in leaves of the Domsiah variety, respectively. The content of proline, MDA, soluble sugars were increased in the Domsiah variety in which the amount of increasing of proline and MDA were 62 and 70 percentages respectively Fructose content in Onda variety was observed about 74% as to control. Results showed that Onda variety was tolerant than Domsiah variety and as a results was more tolerance to cold stress.

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