Abscisic acid involved in trehalose improved melon photosynthesis via regulating oxidative stress tolerance and cell morphology structure under cold stress
2022
Liu, Tao | Han, Yuqing | Shi, Jiali | Liang, Adan | Xu, Dongdong | Ye, Xueling | Qi, Hongyan
Melon is a thermophilic vegetable crop with high economic benefits. Cold stress is often encountered in the growth period of melon seedlings in early spring and limits the normal growth and development of seedlings. Exogenous trehalose (Tre) is a green and healthy sugar, known as the ‘sugar of life’, and has a significant role in regulating crop cold tolerance. In this study, we explored whether exogenous Tre induced abscisic acid (ABA) signal involved in regulating melon photosynthesis under cold tolerance and clarified the associated regulatory mechanism. Melon seedlings were pre-treated with nordihydroguaiaretic acid (NDGA), a synthetic inhibitor of the key enzyme 9-cis-epoxycarotenoid dioxygenase for ABA synthesis, followed by spraying with exogenous Tre and then treated with normal temperature or cold stress. Results showed that exogenous Tre induced the up-regulation of CmNCED3 gene expression and increase in ABA level under normal temperature conditions. Cold stress treatment significantly caused leaf membrane lipid peroxidation damage; reduced relative water content, net photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency and the spongy ratio of leaves; caused chloroplast structure damage. The use of NDGA in inhibiting the synthesis of endogenous ABA further aggravated the damages compared with cold treatment alone. Exogenous Tre treatment alleviated the inhibitory effects of cold stress and NDGA and maintained relatively normal cell morphology structure and photosynthesis. Therefore, we speculate that exogenous Tre pretreatment increases the level of endogenous ABA by up-regulating the expression of the CmNCED3 gene and triggers the defence system of melon plants. Under cold stress, cell membrane lipid peroxidation damage in the melon seedlings was significantly reduced by Tre treatment. Meanwhile, the absorption and utilisation of water maintained the relative integrity of the structure and function of mesophyll cells and chloroplasts, thereby reducing the inhibitory effect of cold stress on plant photosynthesis. In conclusion, ABA participates in exogenous Tre-enhanced melon oxidative stress tolerance and alleviation of cell morphology structure damage, which combined to improve melon cold tolerance and photosynthesis.
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