Effects Of Copper Sulphate Stress During Germination On The Growth Of Mung Bean And The Intracellular Density Change Response

Objective: Our previous studies have found that DANCE (Density Alteration in Non-physiological Cells) was a common cellular response. It occurred not only in animal cells, cultured human cell lines, but also in microorganisms such as Escherichia coli and Candida albicans, etc. However, it is not clear whether DANCE occurs in plant cells. The purpose of this study is to explore the effects of copper sulphate stress during germination on the growth of mung beans in soil and the intracellular density change, and the underline mechanisms by which the pathological changes and DANCE response caused by the heavy metal salt.Methods: Mung beans cultured in water for germination were stressed with copper sulphate at low, medium and high concentrations for differents days, and then transplanted to soil for normal growth. Growth statuses of the sprouts in water and seedlings in soil were observed, and growth rates of the seedlings were calculated. Mung bean sprouts and seedlings were determined for DANCE response by discontinuous sucrose gradient centrifugation (DSGC), and the sprouts were determined for the levels of superoxide dismutase (SOD) activity by NBT method, and malondialdehyde (MDA)contents by ELISA. The plant tissues were homogentaed and the cells were separated by DSGC. The plant cells in each DSGC band were examined for morphological changes under microscoge. Real - time PCR was used to determine the mRNA levels of SOD in the sprouts.Results: Mung beans cultured in water under copper sulphate stress showed significant retardation in the sprout growth, with a good dose dependence. However,growth of the seedlings transplanted to soil showed faster growth rates in the stressed groups. It was found that copper sulphate stress inhibited mung bean germination,signicantly in day 3 and 4, with DANCE response in the cells. After transplantation to soil, all seedlings of the stressed groups showed compensatory growth, and the growth rates increased with the concentration of copper sulphate. In day 3 after transplantation to soil, the seedlings of all stressed groups apparently recovered normal growth. Seedlings of all stressed groups showed DANCE response in roots, stems and leaves in day 1 after transplantation, which lasted for 1 day in roots, 3 days in stems, and 5 days in leaves.However, in day 6 all seedlings showed no DANCE response. SOD activity and MDA content significantly increased in the sprouts after copper sulphate stress, with elevated levels of SOD mRNAs, indicating increased production of free radicals.Conclusion: The present study suggests that DANCE response in the mung beans might be a result of delayed germination in water and compensatory growth after transplantation to soil; appropriate stress during germination might promote the growth of plantseedlings.