Melatonin improves the multiple stress tolerance in pepper (Capsicum annuum)

Plants are often simultaneously exposed to various abiotic stress factors such as herbicide and drought at agricultural areas. The aim of this study is to investigate the effects of pendimethaline (Pend) on pepper, which is a culture plant, to determine interaction of multiple stresses when Pend and drought stresses are applied simultaneously on pepper and also to establish how exogenous melatonin (MEL) application affects multiple stress interaction and antioxidant responses in pepper. The results of the study show that for peppers exposed to 10% polyethylene glycol (PEG) and Pend at different concentrations (8, 16 and 32 mM) both separately and simultaneously, total chlorophyll content and relative water content decreased while carotenoid, proline, glutathione, endogenous MEL and malondialdehyde contents, ascorbate peroxidase, glutathine S-transferase and glutathine reductase activities as well as mRNA levels increased. These changes were found to be more significant statistically for (Pend + PEG) groups treated with stress simtdtaneously. While malondialdehyde content decreased, compared to untreated plants, for plants pre-treated with 50 mu M MEL; relative water content, chlorophyll, carotenoid, proline, glutathione and endogenous MEL contents as well as niRNA levels and activities of anticacidant enzymes (ascorbate peroxidase, glutathine S-transferase and glutathine reductase) increased. Our findings show that both Pend and PEG created some phytotoxic responses on pepper plant and multiple stress treatment induced these responses. However, exogenous MEL application alleviated negative effects of herbicide and drought stresses by inducing antiwddant defense responses of pepper.