Exogenous Uniconazole Application Positively Regulates Carbon Metabolism under Drought Stress in Wheat Seedlings

Drought is one of the most detrimental environmental factors restricting the growth of wheat (<i>Triticum aestivum</i> L.). The investigation of the impact of uniconazole on carbon metabolism in wheat seedlings under drought stress could provide new insights into wheat stress physiology and tolerance. The effects of uniconazole (30 mg L⁻¹) on wheat drought tolerance were investigated via a physiological analysis of the wheat genotypes ‘Wansu 1510’ (WS1510) and ‘Huacheng wheat 1688’ (HC1688) under a 15% polyethylene glycol (PEG) and 30% PEG treatment and a transcriptome analysis of ‘Wansu 1510’ (WS1510) under a 30% PEG treatment. The results revealed that uniconazole significantly increased the leaf relative water content (RWC), reduced plant height, and counteracted the reduction in fresh weight and root length under drought stress. It inhibited the excessive accumulation of reactive oxygen species (ROS) and protected against membrane lipid peroxidation caused by drought stress by regulating superoxide dismutase (<i>SOD</i>) gene expression, enhancing antioxidant enzymes activities, and adjusting the content of osmoregulatory compounds in drought-stressed plants. Furthermore, uniconazole treatment increased chlorophyll (Chl) and carotenoid (Car) contents, inhibited the increase in sucrose concentration, and alleviated the reduction in starch content due to increased sucrose synthase (SS) activity under drought stress. Transcriptome sequencing revealed that uniconazole regulated the expression of genes associated with starch and sucrose metabolism, porphyrin and chlorophyll metabolism, the photosynthetic antenna proteins, carotenoid biosynthesis, and carbon fixation in photosynthetic organisms, which are involved in carbon metabolism processes and photosynthetic pigment production and which regulate the conversion of sucrose and starch under drought stress. Our findings emphasize the importance of exogenous uniconazole in regulating carbon metabolism in wheat.