Integrated physiological, hormonal, and metabolic mechanisms regulating wheat yield quality under combined drought and heat stress

• Combined drought-heat stress severely reduces wheat yield and quality. • Sucrose enzymes surge under combined stress, elevating leaf sucrose. • ABA and GA peaks drive nutrient reallocation to grains under stress. • Stress boosts albumin/gliadin but slashes wet gluten in wheat. • Mutant ANK32B shows heightened sensitivity to drought-heat stress. Heat and drought stress during the grain-filling stage are critical abiotic factors restricting wheat yield and quality. However, the genotype-dependent differences in physiological and biochemical responses under combined stress remain poorly understood. Hence, this study utilized a wheat chlorophyll b-deficient mutant (ANK32B) and its wild type (WT) to investigate the effects of post-anthesis drought stress (DT), heat stress (HT), and combined drought–heat stress (DHT) on yield and grain end-use quality. Compared with ANK32B, WT exhibited greater resilience across all stress treatments, maintaining higher photosynthetic capacity, spikelet fertility, and thousand-grain weight, particularly under DHT, where yield losses were 24.65% in WT versus 14.36% in ANK32B. Under combined stress, the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) in WT leaves increased significantly more than in ANK32B, leading to enhanced sucrose accumulation and more efficient carbohydrate translocation to spikes. WT also showed a stronger hormonal response, with abscisic acid (ABA) and gibberellin (GA) concentrations rising by 20.83% and 63.63%, respectively, under DHT, whereas ANK32B displayed overall hormone suppression. These differences suggest that WT mitigates stress-induced assimilate limitations through coordinated hormonal regulation and enzymatic adjustments, promoting nutrient remobilization to developing grains. In contrast, ANK32B’s chlorophyll deficiency and reduced hormonal signaling limited sucrose metabolism and sink strength, resulting in lower grain-filling efficiency. Protein composition analyses revealed that WT accumulated more albumin and gliadin under stress (DHT > HT > DT > control), whereas ANK32B showed significant reductions in these fractions under DHT. Stress treatments reduced wet gluten content and flour quality index (FQN) in both genotypes, but declines were more pronounced in WT due to higher protein turnover under combined stress. Overall, WT’s superior coordination of carbohydrate metabolism and hormonal regulation allowed partial preservation of grain quality despite yield penalties, while ANK32B’s impaired photosynthetic and metabolic responses amplified stress sensitivity. These genotype-specific mechanisms offer key insights for developing wheat cultivars with enhanced tolerance to concurrent heat and drought stress.