Li Qiuxia, Zhang Yiqiu, Liu Yu, Li Tianyue, Xu Hua, Wei Qinwen, Zeng Huiliang, Ni Huiyi, Li Shuzhen
Ganzhou Key Laboratory of Greenhouse Vegetable, College of Life Science, Gannan Normal University, Ganzhou, 341000, China.
BMC Plant Biol. 2025 Mar 19;25(1):359. doi: 10.1186/s12870-025-06359-3.
Exogenous melatonin plays a crucial role in various plant developmental processes and stress responses and has considerable potential for future agricultural applications. However, its effects on early cucumber seedling growth and resistance to alkaline stress have not been adequately explored. This study investigated the role of exogenous melatonin during the early growth stages of cucumber, specifically focusing on seed germination, post-germination seedling growth, and 1-leaf stage seedling growth, with particular emphasis on its influence on alkali stress resistance. These findings are intended to enhance the application of melatonin in cucumber seedling cultivation and provide a theoretical basis for promoting growth and improving stress tolerance in agricultural production.
Exogenous melatonin enhanced cucumber seed germination and early seedling growth with promoting and inhibitory effects at low and high concentrations, respectively. However, the effects of exogenous melatonin on cucumber growth varied at different developmental stages. Additionally, alkali stress significantly hampered the growth of cucumber seedlings; however, the external application of melatonin mitigated the damage caused by this stress. This protective effect was evidenced by a marked increase in the survival rate, stem diameter, and biomass of cucumber seedlings, along with a significant reduction in malondialdehyde content and electrolyte leakage rate. Further investigation revealed that exogenous melatonin promotes the accumulation of osmoregulatory substances, specifically soluble sugars, and proline, under alkaline stress. It also enhances the activities of antioxidant enzymes, including peroxidase, superoxide dismutase, catalase, and dehydroascorbate reductase, while significantly decreasing the accumulation of reactive oxygen species such as HO and O⋅-. Furthermore, exogenous melatonin increased the activities of PM-H-ATPase and V-H-ATPase and stimulated the expression of stress-related genes, thereby regulating Na and K homeostasis under alkali stress. Additionally, exogenous melatonin promoted the synthesis of endogenous melatonin in cucumbers subjected to alkaline stress by inducing the expression of melatonin synthase genes, namely, CsASMT, CsCOMT, CsTDC, and CsSNAT.
Exogenous melatonin promoted cucumber seed germination and seedling establishment and enhanced cucumber alkali stress tolerance by mediating osmotic adjustment, reactive oxygen species scavenging, ion homeostasis maintenance, endogenous melatonin synthesis, and expression of stress-related genes.
外源褪黑素在植物的各种发育过程和应激反应中发挥着关键作用，在未来农业应用中具有巨大潜力。然而，其对黄瓜幼苗早期生长及碱性胁迫抗性的影响尚未得到充分研究。本研究调查了外源褪黑素在黄瓜早期生长阶段的作用，特别关注种子萌发、萌发后幼苗生长和一叶期幼苗生长，尤其强调其对碱胁迫抗性的影响。这些发现旨在加强褪黑素在黄瓜幼苗栽培中的应用，并为促进农业生产中的生长和提高胁迫耐受性提供理论依据。
外源褪黑素分别在低浓度和高浓度时对黄瓜种子萌发和幼苗早期生长具有促进和抑制作用。然而，外源褪黑素对黄瓜生长的影响在不同发育阶段有所不同。此外，碱胁迫显著阻碍了黄瓜幼苗的生长；然而，外源褪黑素的施用减轻了这种胁迫造成的损害。黄瓜幼苗的存活率、茎直径和生物量显著增加，丙二醛含量和电解质渗漏率显著降低，证明了这种保护作用。进一步研究表明，外源褪黑素在碱性胁迫下促进渗透调节物质（特别是可溶性糖和脯氨酸）的积累。它还增强了抗氧化酶（包括过氧化物酶、超氧化物歧化酶、过氧化氢酶和脱氢抗坏血酸还原酶）的活性，同时显著减少了如HO和O⋅-等活性氧物质的积累。此外，外源褪黑素增加了质膜H⁺-ATP酶和液泡膜H⁺-ATP酶的活性，并刺激了胁迫相关基因的表达，从而在碱胁迫下调节Na⁺和K⁺稳态。此外，外源褪黑素通过诱导褪黑素合成酶基因（即CsASMT、CsCOMT、CsTDC和CsSNAT）的表达，促进了碱性胁迫下黄瓜内源褪黑素的合成。
外源褪黑素通过介导渗透调节、活性氧清除、离子稳态维持、内源褪黑素合成和胁迫相关基因的表达，促进了黄瓜种子萌发和幼苗建立，并增强了黄瓜对碱胁迫的耐受性。
