Spermidine alleviates drought-induced wheat floret degeneration by mitigating oxidative damage and maintaining energy homeostasis

Drought stress at the booting stage causes severe floret degeneration and a decrease in grain number. Polyamines are involved in wheat floret development under drought stress, but the underlying physiological mechanisms are unclear. This study showed that drought-induced accumulation of reactive oxygen species led to wheat spikelet cell apoptosis and floret degeneration. Drought induced stomatal closure to reduce photosynthesis, then inhibited the activities of sucrose phosphate synthase, sucrose synthetase (cleavage direction) and ADP-glucose pyrophosphorylase in spikes and leaves, and soluble vacuolar invertase and cell wall invertase in spikes, thus providing a poor nutrient base for floret development. Exogenous spermidine application increased antioxidant enzyme activities and polyamine metabolism, promoted starch and sucrose metabolism, amino acid utilization and increased the levels of glycolytic and tricarboxylic acid cycle intermediates to mitigate oxidative damage and maintain energy homeostasis in the spike, thereby reducing floret degeneration and increasing grain number.