Silicon-seed priming promotes seed germination under CA-induced autotoxicity by improving sucrose and respiratory metabolism in cucumber (Cucumis sativus L.)

Seed germination is one of the critical and sensitive stages of early plant growth, and its process is prevented by cinnamic acid (CA). Silicon (Si) plays a critical role in mitigating abiotic stresses and seed germination in plants, but little is known about its role in seed germination and physiology in CA-stressed cucumber. Here, we conducted experiments in the State Key Laboratory of Aridland Crop Science, Gansu Agricultural University from March to June 2021 to investigate the effects of Si-seed priming on growth, antioxidant capacity, sucrose mobilization and respiratory metabolism during germination under CA stress. Our results showed that seed soaking with Si (9 mmol/L) significantly reduced membrane lipid peroxidation and promoted post-germination growth of cucumber seeds under CA (2.0 mmol/L) stress. Si increased key enzyme activities in sucrose metabolism in CA-stressed seeds after germination, accelerating sucrose degradation and fructose synthesis. Si also enhanced the activities of key enzymes in the glycolytic pathway and pentose phosphate pathway in seeds, as well as in the post-germination tricarboxylic acid cycle, promoting glucose decomposition and ATP synthesis. Principal component analysis significantly separated the CK, Si, and CA + Si treatments from the CA treatment in the first principal component after 48 h of treatment. In addition, qRT-PCR analysis showed that Si induced overexpression of genes related to sucrose and respiratory metabolism in seeds treated with CA for 48 h. In conclusion, our findings provide evidence that Si priming may be an effective method to reverse CA inhibition of cucumber seeds, which effectively improve germination under CA stress by attenuating membrane lipid peroxidation and enhancing sucrose mobilization and respiratory metabolism in cucumber.