Partial root-zone drying enhances cottonseed kernel weight by increasing the proportion of oil accumulation as a countermeasure against drought stress

Partial root-zone drying (PRD) mitigates the adverse effects of drought on cotton yield; however, its impact on the accumulation of cottonseed oil and protein remains unclear. To investigate this, we tested three irrigation strategies in pond experiments: full irrigation (75/75, where both sides of the root-zones were at 75 ± 5 % soil water), PRD (75/45, with one side of the root-zones at 75 ± 5 % and the other at 45 ± 5 % soil water), and drought stress (45/45, where both sides of the root-zones were at 45 ± 5 % soil water). Results indicated that drought reduced cottonseed kernel yield and oil content but increased protein content. Conversely, PRD treatment maintained yield while enhancing oil accumulation and reducing protein content within cottonseed kernels. This shift in metabolic allocation was associated with elevated pyruvate and malonyl-CoA, as well as increased activities of key oil-synthesis enzymes, including acetyl-CoA carboxylase (ACCase), phosphatidic acid phosphatase (PAPase), and diacylglycerol acyltransferase (DGAT). Simultaneously, PRD suppressed protein biosynthesis by limiting α-ketoglutaric acid accumulation and downregulating the activities of glutamine synthetase (GS) and glutamate synthase (GOGAT). Correlation analysis confirmed that under PRD treatment, carbon flux in developing cottonseeds is preferentially directed toward oil synthesis rather than protein formation. These findings demonstrate that PRD not only mitigates the negative effects of drought stress but also optimizes the metabolic balance in favor of oil accumulation, ultimately enhancing cottonseed oil yield and quality. This study provides novel insights into the physiological mechanisms underlying drought adaptation in cotton and offers a practical strategy for improving cottonseed value under water-limited conditions.