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Physiological and biochemical responses of cotton seedlings to NaCl stress and analysis of salt tolerance thresholds

Lupeng Sun, xin Cai, Dianjun Chen, Yang Cai, fenghua Zhang

Abstract

Soil salinisation is increasing in extent and area, which seriously limits the growth of crops. Clarifying the salt tolerance mechanism and salt tolerance threshold of cotton seedlings is of great significance for the timely taking reasonable measures in the later stage to ensure the normal growth and high and stable yield of cotton. In this pot experiment, We investigated the differences in physiological responses and salt tolerance thresholds between salt-tolerant variety “Xinluzao 53” and salt-sensitive variety “Xinluzao 60” under NaCl stress (control, 2, 4, 6, 8 and 10 g/kg). The peroxidase (POD) activities of “Xinluzao 53” was the highest at 6 g/kg salt treatment, which was increased by 29.37% compared with the control; The POD enzyme activities of “Xinluzao 60” was highest at 4 g/kg salt treatment and increased by 59.35% compared to control. The catalase (CAT) activity of “Xinluzao 53” and “Xinluzao 60” was the highest at 2 g/kg salt treatment, which was 101.00% and 61.59% higher than that of the control, respectively. The overall increase of malondialdehyde (MDA) content in the leaves of “Xinluzao 53” was smaller than that of “Xinluzao 60”, in which the MDA content of “Xinluzao 53” was 32.59% and 35.27% lower than that of “Xinluzao 60” under the salt treatments of 8 g/kg and 10 g/kg, respectively. The net photosynthetic rate (Pn) of “Xinluzao 60” was reduced by 13.31%, 22.83%, and 21.52% compared to “Xinluzao 53” at salt concentrations of 2, 8, and 10 g/kg, respectively. “Xinluzao 53” protected the cell membrane structure by maintaining higher antioxidant enzyme activities, lower MDA content and electrolyte leakage under salt stress; higher SPAD values, chlorophyll fluorescence parameters and photosynthetic rates were further maintained to safeguard normal physiological metabolism and photosynthetic system, higher salt tolerance than “Xinluzao 60”. In this study, correlation analysis and quadratic regression equation were used to establish an integrated, comprehensive and reasonable screening method for cotton seedling salt tolerance threshold in combination with the actual growth of seedlings. The salt tolerance threshold of salt-tolerant “Xinluzao 53” seedlings was 10.1 g/kg, and the salt tolerance threshold of sensitive “Xinluzao 60” seedlings was 8.5 g/kg.

FP24204  Accepted 19 April 2025

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