Interactive Effect of Melatonin and Sodium Nitroprusside on Seed Germination and Seedling Growth of Catharanthus roseus under Cadmium Stress

In this study, impact of seed presoaking with melatonin and sodium nitroprusside (SNP) (as a NO donor) was evaluated on seed germination and seedling growth of Catharanthus roseus (L.) G. Don under both normal and Cd stress conditions. Results showed that 200 mu M Cd reduced the relative seed germination, root elongation tolerance and seed germination tolerance index. The melatonin and SNP improved the seed germination, germination rate, seedling length, and vigor index under Cd stress in a dose-dependent manner and the maximum biological responses obtained by 100 M melatonin and 200 M SNP. However, 200-400 M melatonin and 400 M SNP negatively influenced the seed germination indices and seedling establishment. The cadmium suppressed the amylase activity and contents of soluble and reducing sugars in germinating seeds; thereby it reduced seed germination. Cd stress also decreased subsequent growth of seedlings and increased electrolyte leakage in them. These Cd-induced inhibitory effects were ameliorated by applying both melatonin and SNP. Importantly, melatonin as well as SNP was able to markedly boost the NO content in seeds. The addition of the specific scavenger of NO (cPTIO) reversed the protective effects conferred by melatonin, but inhibition of melatonin biosynthesis by p-CPA could not alleviate effects elicited by SNP completely, suggesting that NO plays role a downstream signal in melatonin-mediated germination responses especially under cadmium stress.