| Copper (Cu) is one of essential micronutrients for plants growth and plays a crucial role in both photosynthetic and respiratory electron transport, and functions as a cofactor for a variety of enzymes such as superoxide dismutase, cytochrome c, and plastocyanin. However, excessive copper is harmful to plants. Ascorbic acid (AsA) is a kind of essential elements within animals and plants for life maintenance. AsA involves in the processes of abiotic stress response and defense, e.g. active oxygen, ultraviolet rays, high temperature and strong light. AsA plays important role in plant resistance. MicroRNAs (miRNAs) are approximately21-nucleotide (nt) non-coding RNAs that play critical roles in plant resistance. In this research, alleviatory effect of ascorbic acid and the different expression of miRNAs under copper stress in non-heading Chinese cabbage were studied.1. The changes in mineral elements content, chlorophyll, malondialdehyde (MDA), ascorbic acid (AsA) and DNA methylation level were studied in leaves of three cultivars of non-heading Chinese cabbage under copper stress, and the role of exogenouse AsA were also investigated. Under copper stress, the copper content in the leaves increased significantly, while the copper content is lowest in’Wutacai’, which showed the highest copper tolerance in the three cultivars of non-heading Chinese cabbage. Other mineral elements such as iron (Fe), manganese (Mn), magnesium (Mg), sodium (Na) and potassium (K) reduced remarkably, the content of chlorophyll decreased, while the MDA content and DNA methylation level increased significantly. Compared with that under copper treatment, exogenous AsA decreased the contents of copper and MDA, and DNA methylation level, while increased the content of chlorophyll and other mineral contents, which implied that ascorbic acid alleviated copper stress in non-heading Chinese cabbage.2. The different expression of miRNAs and their target genes in different concentration of copper treatments were studied in different tissues and cultivars in non-heading Chinese cabbage. Number and type of cis-acting elements in the5’-flanking region were also investigated. Under copper stress, the expression of the ten miRNAs including bra-miR1530a, bra-miR1533ah, bra-miR1533aj, bra-miR1533d, bra-miR1533m, bra-miR1533t, bra-miR1533v, bra-miR172f, bra-miR414a and bra-miR398b were significantly dose-related decreased. The expression of their target genes were negatively correlated with miRNAs and increased significantly under copper stress. The ten miRNA showed different expression patterns in different tissues. The expressions of bra-miR1530a and bra-miR1533v were highest in petiole and lowest in root. Bra-miR1533ah, bra-miR1533m, bra-miR1533t, bra-miR414a and bra-miR398b had highest expression level in leaf and lowest in root. The expression of bra-miR172f was highest in root and lowest in leaf. Bra-miR1533aj and bra-miR1533d had similar expression level in petiole and leaf. In addition to the bra-miRl530a, the expression of other miRNAs showed a decreased trend over time. The expressions of miRNAs in different cultivars were different. Under copper stress, the expressions of bra-miR1533d, bra-miRl533m, bra-miR1533t and bra-miR172f were no significant change in’Suzhouqing’but significantly decreased in’Wutacai’. Moreover, the expressions of other miRNAs were decreased in two cultivars, but’Wutacai’had bigger magnitude of the decline. The ten miRNAs had more than one of stress-responsive cis-acting elements such as MBS, ARE and ABRE in promoter regions, suggesting that these miRNA involved in response to various biotic and abiotic stress. |
PDF Full Text Request