Comparative Analyses Of The Physiological Responses Of Different Rice Cultivars To Cold Stress

Rice is one of the most important food crops in the world, and its growth and geographical distribution are affected by low temperature. Although it is well known that Indica and Japonica rice culrivars differ in cold tolerance, how such a general difference is reflected in individual cultivars is still unclear. As an effort to improve this situation, we carried out a analysis on cold tolerance in a selected set of cultivars. First, we used four indicators, including plant height, chlorophyll content, praline content and soluable protein content, to compare cold tolerance of 9 different cultivars and found that low temperature caused similar trends of changes in all the cultivars analysed with respect to each of the indicators, i.e. reduced plant height and chlorophyll content and increased praline and soluable protein contents. However, the degree of changes varied among the cultivars, with indica rice Nipponbare showing the biggest degree of changes and the japonica cultivar Xie B the smallest degree of changes with every indicator. We then selected Nipponbare and Xie B for further analyses using more cold tolerance indicators(including leaf water content, root length, conductivity, soluable sugar content, malonic aldehyde content, SOD, POD) and more time points for the cold treatment. At 28℃, Nipponbare and Xie B showed very little difference in each of the indicators. However, at 4℃, clear difference was observed between the two cultivars with all the indicators. Furthermore, the differences in the physiological and morphological indicators correlate well with their difereence in cold tolerance. Our results not only shows clear differences in cold tolerance among rice cultivars, but also confirm that there is a close correlation between many of the used cold tolerance indicators and cold tolerance phenotype in rice seedlings and thereby demonstrate the usfulness of these indicators in assessing cold tolerance in rice seeslings. As Nipponbare and Xie B are widely used in rice studies, our results can also serve as an importance reference for future studies on cold tolerance in rice.