Coordination of Abscisic Acid and Ultraviolet-B Radiations Dissociates Yield and Seed Quality Trade-Offs in Highland Barley under Water Deficit Stress

Current cereals face unassailable yield trade-offs under combined water deficit (D) and ultraviolet-B (UV–B) stress. Using integrated omics in qingke barley subjected to D, UV–B (low: LUVB; high: HUVB), and abscisic acid (ABA), we show that ternary DUVB-ABA cotreatment elevates ABA and GA, enabling concurrent stress resilience and growth recovery. This treatment activated NCED3 genes for ABA biosynthesis and KAO for GA biosynthesis. ABA with UV–B preserved membrane fluidity by upregulating fatty acid desaturases ( FADs ) and suppressing lipoxygenases ( LOX ); LUVB-ABA reduced oxidative damage by 81.8%. Crucially, conventional trade-offs were eliminated: D-LUVB-ABA improved 1000-seed weight by 10.3% above controls, while D-HUVB-ABA elevated grain sugar and protein content significantly. Potassium accumulation in the stem (>51%) and spectral priming (LUVB for stress memory; HUVB for growth reactivation) supported these effects. Findings show ABA-UVB interaction reprograms stress cues into productivity triggers, identifying spectral hormone discrimination and stem nutrient buffering as key adaptations for climate-resilient cereals.