Exogenous melatonin enhanced cadmium stress tolerance of cucumber seedlings (Cucumis sativus L.)

Abstract

Abstract Melatonin (MT) is a phytohormone that can improve plant stress resistance by regulating physiological processes and gene expression. The present study investigated the role of exogenous MT in alleviating cadmium (Cd) stress in cucumber seedlings. The results showed that Cd stress inhibited the growth of cucumber seedlings and exogenous MT reversed adverse effects of Cd stress. Compared with Cd treatment, MT + Cd treatment enhanced antioxidant enzyme activities, suppressed ROS production and improved photosynthesis in cucumber seedlings. Further research showed that hydrogen peroxide (H2O2) and nitric oxide (NO) played important roles in MT enhanced Cd stress tolerance in cucumber seedlings. RNA-seq results indicated that MT was not only related to photosynthetic and antioxidant systems in alleviating Cd injury in cucumber seedlings, but also various phytohormones, heavy metal transporter proteins and transcription factors were also involved. In addition, we selected six differentially expressed genes for qRT-PCR validation, the verification results were consistent with the RNA-seq results. In summary, exogenous MT pretreatment can alleviate Cd toxicity by enhancing antioxidant defense capacity and photosynthetic efficiency of cucumber seedlings, both H2O2 and NO play important roles. In addition, various phytohormones, transcription factors and heavy metal transport proteins are also involved in this regulation of MT.