Journal of Hunan Ecological Science

【Objective】The effects of exogenous melatonin on the growth and physiological character- istics of pepper (Capsicum annuum L. ) seedlings under drought stress were studied to provide a theoreti- cal basis for the application of exogenous melatonin in pepper production and cultivation. 【Method】Pep- per seedling ‘CT29’ was identified as experimental materials, and was treated with different concentra- tions (0, 50, 100, 150, 200 and 250 μmol/ L) of melatonin for 7 days. The changes of seedling growth, pigment content, osmoregulation substance content and antioxidant enzyme activity under drought stress were analyzed. 【Result】The results showed that long-term drought stress ( drought for 6 days) could significantly inhibit the growth of pepper seedlings. However, different concentrations of melatonin treatments reduced the content of malondialdehyde, and the content of carotenoid, relative water content, soluble protein, soluble sugar and proline were increased by 11. 62% ~ 59. 11% , 2. 44% ~ 6. 28% , 5. 34% ~ 21. 75% , 7. 61% ~ 46. 44% and 42. 88% ~ 62. 26% , respectively, compared with the control group. In addition, 100 ~ 250 μmol/ L melatonin enhanced the activities of catalase and peroxidase in pepper leaves under drought stress, with an increase of 7. 08% ~ 26. 81% and 23. 65% ~ 39. 23% , re- spectively. The results of membership function analysis of physiological indexes showed that the total membership function values of pepper seedlings treated with 150 μmol/ L and 200 μmol/ L melatonin were larger, and the seedlings had better growth potential. 150 μmol/ L and 200 μmol/ L could be determined as the optimal melatonin concentration to alleviate drought stress. Further dynamic analysis showed that 150 μmol/ L and 200 μmol/ L melatonin had little effect on the growth of pepper seedlings at the early stage of drought stress. After 4 days of drought, exogenous melatonin could significantly reduce the con- tent of malondialdehyde in leaves, increase the activity of two antioxidant enzymes (catalase and peroxi- dase) and the content of three osmotic regulators (soluble protein, soluble sugar and proline). 【Conclu- sion】Exogenous melatonin can induce the increase of antioxidant enzyme activity and the accumulation of osmoregulation substances in plants, and effectively remove malondialdehyde, thereby alleviating the growth inhibition of drought on pepper seedlings and enhancing their drought resistance. These are not only beneficial to analyze the physiological mechanism of melatonin in alleviating drought stress in pepper, but also provide a theoretical basis for the application of exogenous melatonin in pepper produc- tion and cultivation.

pepper ( Capsicum annuum L. ); drought stress; melatonin; growth characteristics; physiological characteristics