Sorghum faces significant production challenges due to drought stress. Melatonin has been demonstrated to play a crucial role in coping with stresses in plants. This study investigated the effect of exogenous melatonin on the sorghum seedling growth, photosynthetic capacity, and antioxidant system under drought stress. The results indicated that drought stress inhibited the growth of sorghum seedlings by a marked reduction in leaf relative water content, along with a significant increase in both malondialdehyde and hydrogen peroxide content. The drought stress also led to a significant diminution in chlorophyll contents, thereby curtailing the capacity for light energy capture. Furthermore, the efficiency of the photosynthetic electron transport chain was adversely impacted. However, the application of exogenous melatonin notably mitigated the adverse effects on sorghum seedlings under the drought stress. Additionally, it stimulated an elevation in the photosynthetic rate and a decrease in non-photochemical quenching. The exogenous melatonin also facilitated the preservation of the chloroplast ultra-structure and boosted the activity of antioxidant enzymes and the content of non-enzymatic antioxidants. Cluster heat maps and principal component analysis further revealed significant correlations among various parameters under different treatment conditions. These results highlight melatonin’s role in improving sorghum’s drought tolerance, which is beneficial for agricultural management.

Seed aging has adverse effects on agricultural production, mainly because seed vigor is inhibited. Spermidine can improve seed vitality and germination ability to a certain extent and is essential for plant growth and plant response to stress. This study explored how spermidine counteracted aging effects on sorghum seed germination through antioxidant metabolism regulation. Aged seeds showed decreased vigor due to heightened reactive oxygen species (ROS) and diminished antioxidants. Applying spermidine notably enhanced aged seeds’ germination and vigor by boosting antioxidant enzyme activity and curbing ROS. Integrated transcriptomic, proteomic, and metabolomic analyses demonstrated that the majority of differentially expressed genes following exogenous spermidine treatment in aged sorghum seeds were significantly enriched in pathways related to glutathione metabolism, phenylpropanoid, and flavonoid biosynthesis, resulting in increased expression of genes encoding peroxidase, chalcone synthase, and glutathione s-transferase. Exogenous spermidine facilitated the synthesis of peroxidases and glutathione transferases. Analysis of flavonoid pathway intermediates showed a notable increase in antioxidant metabolites like isoquercitrin, underscoring their role in oxidative stress resistance. This multi-omics strategy underscores Spd’s role in boosting aged seeds’ antioxidants, highlighting the molecular basis of seed aging and Spd’s rejuvenating impact.

Salt stress notably inhibits the germination of sorghum seeds. CaCl₂ priming effectively promotes seed germination under salt stress, but the underlying mechanisms remain unclear. This study explored the CaCl₂ -primed regulation of sorghum seed germination under salt stress. Hydro-primed seeds (HPS) and CaCl₂-primed seeds (CaPS) were cultured under NaCl stress. The unprimed seeds were cultured in distilled water (NPN) or 150 mM NaCl stress (NPS). Primed and unprimed seeds were evaluated for amylase activity, starch content, sugar metabolism, and mitochondrial repair. We found that salt stress significantly inhibited sorghum seed germination and reduced the germination rate. It also decreased amylase activity, starch decomposition, and sugar accumulation during germination, indicating inhibition of sugar metabolism. However, CaCl₂ priming reversed the adverse effects of salt stress, increasing amylase activity, starch decomposition, and sugar content. It also up-regulated the expression of genes for phosphofructokinase and other enzymes involved in the glycolytic, tricarboxylic acid cycle (TCA), and pentose phosphate pathways. CaCl₂ priming also resulted in the repair and maintenance of mitochondrial structural integrity, contributing to activation of the TCA cycle. In short, CaCl₂ priming promotes sorghum seed germination by activating sugar metabolism under salt stress and provides a strategy for improving seed germination during agricultural production.