Abstract
Due to the frequent occurrence of continuous high temperatures and heavy rain in summer, extremely high-temperature and high-humidity environments occur, which seriously harms crop growth. High temperature and humidity (HTH) stress have become the main environmental factors of combined stress in summer. The responses of morphological indexes, physiological and biochemical indexes, gas exchange parameters, and chlorophyll fluorescence parameters were measured and combined with chloroplast ultrastructure and transcriptome sequencing to analyze the reasons for the difference in tolerance to HTH stress in HTH-sensitive ‘JIN TAI LANG’ and HTH-tolerant ‘JIN DI’ varieties. The results showed that with the extension of stress time, the superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) activities of the two melon varieties increased rapidly, the leaf water content increased, and the tolerant varieties showed stronger antioxidant capacity. Among the sensitive cultivars, Pn, Fv/Fm, photosystem II, and photosystem I chlorophyll fluorescence parameters were severely inhibited and decreased rapidly with the extension of stress time, while the HTH-tolerant cultivars slightly decreased. The cell membrane and chloroplast damage in sensitive cultivars were more severe, and Lhca1, Lhca3, and Lhca4 proteins in photosystem II and Lhcb1-Lhcb6 proteins in photosystem I were inhibited compared with those in the tolerant cultivar. These conclusions may be the main reason for the different tolerances of the two cultivars. These findings will provide new insights into the response of other crops to HTH stress and also provide a basis for future research on the mechanism of HTH resistance in melon.
Highlights
In recent years, with the increase in the global greenhouse effect and climate change, the global temperature fluctuations have intensified, and the frequency of extremely high temperatures and heavy rain has increased significantly in summer [1,2]
Under High temperature and humidity (HTH) stress, superoxide dismutase (SOD), POD, and ascorbate peroxidase (APX) activities of two different genotypes of melon seedlings increased rapidly to remove excess reactive oxygen species (ROS) to cope with the damage caused by HTH stress, and the HTH-tolerant ‘JIN DI’ variety had a stronger antioxidant capacity
With the extension of stress time, chlorophyll content and soluble protein in leaves of the HTH-sensitive ‘JIN TAI LANG’ variety decreased rapidly, the cell membrane permeability increased, and the H2 O2 and OFR content increased compared with the HTH-tolerant
Summary
With the increase in the global greenhouse effect and climate change, the global temperature fluctuations have intensified, and the frequency of extremely high temperatures and heavy rain has increased significantly in summer [1,2]. Coupled with extremely high-temperature weather, the environment of high temperature and high humidity has a serious impact on the growth and quality of plants [3]. Different crop varieties have different stress resistances, which provides relevant evidence for genetic resources [4]. It is of great significance to study the physiological changes and molecular mechanisms of vegetable crops in the resistance to extremely high-temperature and high-humidity environments to improve the tolerance of vegetables and breed new varieties
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