Physiological and Biochemical Mechanisms and Cytology of Cold Tolerance inBrassica napus

Cold damage has negatively impacted the yield, growth and quality of the edible cooking oil in Northern China andBrassica napusL.(rapeseed) planting areas decreased because of cold damage. In the present study we analyzed twoBrassica napuscultivars of 16NTS309 (highly resistant to cold damage) and Tianyou2238 (cold sensitive) from Gansu Province, China using physiological, biochemical and cytological methods to investigate the plant's response to cold stress. The results showed that cold stress caused seedling dehydration, and the contents of malondialdehyde (MDA), relative electrolyte leakage and O(2)(-)and H(2)O(2)were increased in Tianyou2238 than 16NTS309 under cold stress at 4 degrees C for 48 h, as well as the proline, soluble protein and soluble sugars markedly accumulated, and antioxidant enzymes of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) were higher in 16NTS309 compared with in Tianyou2238, which play key roles in prevention of cell damage. After exposure to cold stress, the accumulation of the blue formazan precipitate and reddish brown precipitate indicated that O(2)(-)and H2O2, respectively, were produced in the root, stem, and leaf were higher than under non-cold conditions. Contents of O(2)(-)and H(2)O(2)in cultivar Tianyou2238 were higher than 16NTS309, this is consistent with the phenotypic result. To understand the specific distribution of O(2)(-)in the sub-cellular, we found that in both cultivars O(2)(-)signals were distributed mainly in cambium tissue, meristematic cells, mesophyll cytoplasm, and surrounding the cell walls of root, stem, leaves, and leaf vein by morphoanatomical analysis, but the quantities varied. Cold stress also triggered obvious ultrastructural alterations in leaf mesophyll of Tianyou2238 including the damage of membrane system, destruction of chloroplast and swelling of mitochondria. This study are useful to provide new insights about the physiological and biochemical mechanisms and cytology associated with the response ofB. napusto cold stress for use in breeding cold-resistant varieties.