Partial root-zone drying restricts root ABA accumulation thereby restoring fiber strength via synergistic regulation of cellulose biosynthesis and crystallinity

Enhanced cotton fiber strength under partial root-zone drying (PRD) is fundamentally associated with alterations in root-source abscisic acid (ABA). However, the underlying mechanism remains unclear. To investigate this, we simulated PRD treatment using a split-root system in pots. Compared with drought-stressed plants in which the entire root zone was dried, PRD treatment significantly reduced the accumulation of root-source ABA, which notably restored fiber strength that was otherwise diminished by drought. To elucidate the potential mechanisms, an exogenous ABA biosynthesis inhibitor, fluridone (applied via root irrigation), as well as ABA itself (applied through foliar spraying) was introduced under PRD conditions. Decreased root-source ABA under PRD primarily enhanced fiber strength by influencing cellulose synthesis and crystallinity. Specifically, decreased root-source ABA stimulated cellulose biosynthesis by enhancing sucrose synthase activity and promoting the gene expression of cellulose synthase. Furthermore, reduced root-source ABA significantly increased fiber crystallinity, thereby altering the supramolecular structure of the fiber. These two processes functioned synergistically to substantially restore fiber strength under PRD. The realistic simulation of fixed partial root-zone irrigation treatments has also provided a comprehensive supplementary explanation for the aforementioned observations. Overall, we propose a regulatory model that underscores the significance of root-source ABA in regulating fiber strength under PRD conditions. This model provides a valuable reference for future studies in arid regions. • Partial root-zone drying (PRD) enhanced fiber strength. • Fiber strength enhancement under PRD related to lower root-source abscisic acid (ABA). • Reduced root-source ABA under PRD facilitated fiber cellulose biosynthesis. • Reduced root-source ABA under PRD increased fiber crystallinity to improve its strength.