Asparagine and nitric oxide jointly enhance antioxidant capacity and nitrogen metabolism to improve drought resistance in cotton: Evidence from long-term field trials

Asparagine (Asn) and nitric oxide (NO) can enhance plant tolerance to abiotic stress, but their interaction is not well understood. Cotton is a vital resource for the textile industry, but its yield is reduced by drought stress, which could threaten its global supply in a warming and stressful world. Improving cotton's drought tolerance is crucial for supporting the textile industry. Two simultaneous field experiments were conducted to study the effect of Asn and sodium nitroprusside (SNP), a NO donor, on cotton's drought tolerance. Two irrigation treatments were applied: control (C: 100% A pan) and drought stress (50% A pan). The plants were also sprayed with two plant stimulants before imposing drought stress: Mock control, 20 mM Asn, and 0.2 mM SNP, either alone or together. Drought stress impaired plant growth, photosynthesis, yield, nitrogen metabolism, and antioxidant defense, while increasing oxidative stress and free amino acid levels. However, Asn and SNP treatments alleviated these negative effects and improved antioxidant enzyme activity, plant growth, yield, and nitrogen content. The Asn + SNP treatment also increased irrigation water productivity under water-limited conditions, suggesting its potential for enhancing water use efficiency in cotton production. The combined treatment was more effective than the single treatments, indicating a synergistic effect of Asn and SNP in enhancing drought tolerance in cotton. These results imply that Asn and SNP could be useful tools for sustaining cotton production under drought conditions by boosting nitrogen metabolism and antioxidant defense, thereby contributing to the global supply of cotton and supporting the textile industry.