Glucose mitigates spatial heterogeneous cold damage in wheat via enhanced carbohydrate allocation to spike

Low temperature during the reproductive stage, particularly late-spring cold events, severely threatens wheat (Triticum aestivum L.) yield. This study explored how exogenous glucose promotes the source-flow-sink balance under low temperature by assessing its effects on sucrose metabolism, carbohydrate partitioning, vascular development, and yield components in wild-type (WT) and chlorophyll b-deficient mutant (ANK 32B) plants. Low temperature inhibited the activities of sucrose metabolism enzymes (soluble acid invertase, neutral invertase, sucrose phosphate synthase, and sucrose synthase) in spikes, while inducing abnormal activation in leaves and uppermost internodes. This disturbance caused carbohydrate retention in non-spike organs and severe depletion in spikes, markedly reducing starch, glucose, fructose, and sucrose in the basal and apical spikelets. Consequently, spike development was impaired, grain number and weight decreased, and main-stem yield declined by 60.66 %, 31.05 %, and 52.63 % in the basal, central, and apical spikelets. Micro-CT analysis revealed that cold stress also restricted rachis vascular bundle formation, particularly the bundles delivering assimilates to basal spikelets. The assimilate-limited ANK 32B mutant exhibited compounded sensitivity to low temperature. Exogenous glucose provided sufficient assimilates, stabilized the "source" by mitigating the sucrose metabolism enzyme disturbance, ensured the "flow" by maintaining vascular development, and strengthened the "sink" by increasing carbohydrate accumulation and dry matter in spikes. This coordinated regulation ultimately optimized source-flow-sink system, alleviating cold-induced yield loss by 4.54 %, 0.32 %, and 6.75 % in the basal, central, and apical spikelets, respectively.