Temporal sensitivity of maize starch to short-term low-light stress: Critical window during early grain filling

Low-light stress is increasingly recognized as a significant abiotic stress factor compromising global crop productivity and quality stability. To deeper understand the effects of short-term low-light stress on the starch accumulation and quality attributes in a tested maize ( Zea mays L.) hybrid, 10-day shading treatments (50% light reduction) were applied during six growth phases from anthesis to maturity, and starch accumulation and physical and chemical properties were analyzed. The results showed that low-light stress had a greater impact during early grain filling stages than later stages. Low-light stress significantly impeded the conversion of soluble sugars to starch, leading to a marked reduction in total starch content. Starch granule size distribution shifted towards larger granules, with the proportion of granules >20 μm increasing by up to 64%. Amylose content increased while relative crystallinity decreased. These structural alterations were accompanied by substantial functional declines, including lower gelatinization temperature and enthalpy, a 18.6% reduction in peak viscosity, and a dramatic 93.4% enhancement in retrogradation percentage. Principal component analysis confirmed that the primary variations induced by shading were decreases in viscosity and gelatinization parameters, alongside increases in retrogradation properties. Crucially, the S2 stage (11-20 days after anthesis) was identified as the most vulnerable period to low-light stress, providing a key target for future protective strategies. • 11-20 days after anthesis is the critical low-light sensitivity window for maize starch synthesis. • Low-light stress reduces the total starch content by 11.6% via impaired sugar conversion and increased sucrose. • Amylose content rises by 29.7%, relative crystallinity (RC) drops by 35.4%, large granules (>20μm) surge by 64%. • Pasting viscosity declines by 18.6%, thermal stability (ΔHgel) weakens by 28.8%, retrogradation accelerates.