Rui ZENG, Li MA, Jun-yan WU, Gang YANG, Na ZHANG, Jia XU, Ming-chuan ZHU, Min MA, Xiao-lei TAO, Xue-cai LI, Li-jun LIU, Wan-cang SUN
In order to study the relationship between the beginning of withered leaf stage and cold resistance of winter Brassica rapa under low temperature, two varieties of winter Brassica rapa cultivars Longyou 7 (strong cold-resistance) and Longyou 99 (weak cold-resistance) were investigated. Plant phenotype, cell activity, active oxygen metabolism and expression of related genes regulated by reactive oxygen species were comprehensively analyzed under low temperature stress (5 to 19℃ at 5-leaf stage, -8 to 0℃ at 7-leaf stage, -14 to -4℃ at 7-leaf stage). Results showed that after low temperature stress before winter, Longyou 7 entered the withered leaf stage earlier, while Longyou 99 entered the stage later. The number of cell death in leaves increased gradually during low temperature stress, and the number from Longyou 7 was significantly more than that from Longyou 99. Before stress, contents of H2O2 and in leaves of Longyou 7 were significantly lower than those of Longyou 99, while the activities of SOD, POD and CAT were significantly higher. As the leaves began to yellowing on Longyou 7, the leaf contents of H2O2 and increased rapidly, and became significantly higher than those of Longyou 99. Activities of SOD, POD and CAT became significantly lower. qRT-PCR results showed that earlier withered leaf stage resulted in lower expression of antioxidant enzyme gene and higher expression of NADPH oxidase gene. It was inferred that the early or late beginning of leaf withering stage for winter B. rapa, was related to content of reactive oxygen species (H2O2 and ), and also to antioxidant enzymes activity, e.g. expression of genes related to active oxygen metabolism. The above results were expected to provide theoretical support for regulation mechanism of leaves withering and the relationship between withered leaf and cold resistance of winter B. rapa under low temperature stress.