Effects of exogenous melatonin on the physiological growth of zucchini seedlings under drought stress

QIN Lanli; HUANG Jinqiu; LI Yanting; XIE Yanjun; SHI Chenyu; QIN Baoshan

doi:10.16861/j.cnki.zggc.2024.0384

Abstract：To investigate the effects of exogenous melatonin(MT)on the physiological growth of zucchini seedlings under drought stress,the zucchini variety Zaoqing F,was selected as the experimental material.A drought stress environment was simulated using polyethylene glycol(PEG-6000),and seven treatment groups were established:CK(normal watering),T0(PEG+distilled water),T1(PEG+50 μmol·L-1 MT),T2(PEG+100 μmol·L-1 MT),T3(PEG+150 μmol·L-1 MT),T4(PEG+200 μmol·L-1 MT),and T5(PEG+250 μmol·L-1 MT).Growth and physiological indexes of the seedlings were measured.The results showed that,compared to CK,drought stress(T0)significantly inhibited seedling growth,leading to a decrease in total chlorophyll content,an increase in the levels of osmotic regulators(soluble sugars,soluble proteins,and proline)and malondialdehyde(MDA)content,as well as elevated accumulation of superoxide anion radicals(O2-·)and enhanced activities of antioxidant enzymes(superoxide dismutase,SOD;peroxidase,POD;catalase,CAT).Com-pared to the drought stress alone,the application of an appropriate concentration of exogenous MT improved seedling growth parameters,total chlorophyll content,osmotic regulator levels,and antioxidant enzyme activity,while reducing MDA content and O2-·accumulation.Among the treatments,50 μmol·L-1 MT exhibited the most pronounced effects in in-creasing soluble sugar and related indices,while 100 μmol·L-1 MT yielded the best results in enhancing total chlorophyll and soluble protein content while reducing MDA levels.In conclusion,under drought stress,exogenous MT application promoted zucchini seedling growth by increasing plant height and root length(facilitating water absorption),elevating os-motic regulator levels(maintaining water balance),and strengthening antioxidant capacity(reducing oxidative inju-ry).There effects collectively alleviated drought-induced stress and improved drought resistance,with an optimal concen-traion range of 50-100 μmol·L-1 MT.