Hulless barley (Hordeum vulgare L. var. nudum) on the Qinghai–Tibet Plateau is consistently exposed to intense solar irradiance, yet whether and how reproductive spikes and flag leaves partition photoprotection remains unclear. Here, we compared a pigmented black landrace (Cai Peng Zi, CPZ) with a white cultivar (Zang Qing 3000, ZQ3000) across early, middle, and late spike coloration stages under field conditions. By integrating measurements of anthocyanin and chlorophyll contents, chlorophyll fluorescence parameters, and rapid light-response curves, we dissected organ-specific strategies in photochemistry and energy dissipation in spikes and flag leaves. The results showed that anthocyanin accumulation in CPZ spikes increased significantly during spike coloration, while chlorophyll a and the chlorophyll a/b ratio declined, indicating a shift from light harvesting to photoprotection in reproductive tissues. This pigment transition coincided with reduced PSII performance (declines in QYmax, qP, and qL) but stable non-photochemical quenching (NPQ and qN), pointing to reduced photochemical capacity with relatively stable energy dissipation in the spike. In contrast, CPZ leaves maintained higher QYmax than ZQ3000 but exhibited a pronounced decline in NPQ and qN at late stages, reflecting CPZ’s attenuated regulated energy dissipation capacity. Rapid light-response analysis further supported differences between organs and cultivars. Under high PAR, ZQ3000 spikes exhibited steeper declines in Y(II) and stronger downregulation of ETR(II), whereas CPZ spikes showed more moderate decreases; in leaves, ZQ3000 maintained consistently lower Y(NO) and higher Y(NPQ), indicating greater reliance on regulated energy dissipation. Collectively, our results reveal how pigment-mediated screening in reproductive structures and dynamic regulation of energy dissipation in leaves are coordinated to optimize light-use efficiency in high-altitude environments, providing physiological insights for breeding resilient hulless barley varieties.
Qin et al. (2026) studied this question.