Effects Of Exogenous Regulators On Cotton Seedling Growth Under Low Temperature And Salt Stress

Xinjiang is an important high-quality cotton production base in China,and its unique climate is highly favorable for cotton growth and high yields.However,the high salt content in the cultivated land makes cotton susceptible to salt damage.Additionally,low-temperature cold stress during the germination and seedling stages can result in poor seed germination,seedling decay,root decay,and seedling death.In order to address the issues of low-temperature and salt stress during cotton seed germination and early seedling stages,chemical regulation experiments were conducted from April to November 2022 in the artificial climate chamber at Tarim University.The study investigated the regulatory effects of exogenous agents,salicylic acid（SA）,and rhamnolipids（RLS）on cotton seed germination and seedling growth under low-temperature and salt stress conditions.The study identified suitable exogenous agents and their concentrations that promote the growth of cotton seedlings under low-temperature and salt stress.The main research conclusions are as follows:（1）Effects of different exogenous applications on root characteristics of cotton seedlings during the germination stage.Under low salt stress,0.05 mmol·L^-1 SA and 300 mg·L^-1 RLS effectively increased the activities of superoxide dismutase（SOD）,peroxidase（POD）,and catalase（CAT）in cotton seedling roots,as well as the accumulation of proline（PRO）and soluble sugars（SS）,while reducing the malondialdehyde（MDA）content.These effects promoted the growth of root parameters such as primary root length,total root length,root surface area,and root volume.Under high salt stress,0.01 mmol·L^-1 SA and 200 mg·L^-1RLS helped reduce the damage caused by salt stress to cotton seedlings and promoted the growth of their root systems.Low-temperature stress severely inhibited the growth of primary roots in cotton seedlings,but the application of SA(0.10 mmol·L^-1)and RLS(300 mg·L^-1)effectively alleviated the inhibitory effects of low-temperature stress on the root system of cotton seedlings and increased primary root length.（2）Effects of different exogenous regulators on the physiological and growth characteristics of cotton seedlings.Under low salt stress,the application of SA and RLS increased the activities of antioxidant enzymes and the accumulation of osmolytes in cotton seedling leaves,while reducing MDA content.Moreover,0.05 mmol·L^-1 SA and 300 mg·L^-1 RLS significantly promoted the absorption of K⁺,Ca²⁺,and Mg²⁺ions in cotton seedling leaves,while inhibiting Na⁺uptake.They also increased the content of photosynthetic pigments such as chlorophyll a and chlorophyll b,and significantly improved photosynthetic rate,stomatal conductance,and transpiration rate.High salt stress further exacerbated the inhibition of cotton seedling growth,but the application of SA and RLS maintained ion homeostasis in cotton seedling leaves and promoted the improvement of growth physiological characteristics.In particular,the application of 0.05 mmol·L^-1 SA or 200 mg·L^-1 RLS had a significant promoting effect on the physiological and growth characteristics of cotton seedlings.Low temperature significantly reduced various growth physiological indices in cotton seedling stages,while increasing MDA content and intercellular CO₂concentration.SA(0.05 mmol·L^-1)and RLS(300 mg·L^-1)promoted plant height,stem thickness,leaf area,and biomass accumulation in cotton seedlings,mitigating the inhibitory effects of low-temperature stress on their growth.（3）Comprehensive evaluation of the optimal exogenous agents and their concentrations under low-temperature/salt stress.The comprehensive evaluation indicates that the number of root tips and SOD activity in the root system during cotton seed germination can be considered as the main influencing factors for the physiological and growth regulation effects of SA and RLS under salt stress.Specifically,0.05mmol·L^-1 SA effectively alleviates the adverse effects of salt stress on cotton seed germination.In the seedling stage of cotton,net photosynthetic rate,Na⁺content,and POD activity in the leaves serve as the main influencing factors for the physiological and growth regulation effects of SA and RLS under low-temperature and salt stress.Moreover,300 mg·L^-1 RLS effectively mitigates the inhibitory effect of low-temperature stress on cotton seedling growth,while 0.05 mmol·L^-1 SA significantly alleviates the damage caused by salt stress to cotton seedlings.