Silicon alleviates autotoxicity by regulating membrane lipid peroxidation and improving photosynthetic efficiency in cucumber seedlings (Cucumis sativus L.)

Autotoxicity is one of the main causes of cucumber continuous cropping obstacles. Cinnamic acid (CA), a phenolic acid derivative, acts as an autotoxin found in cucumber root exudates. The autotoxicity mimicked by CA significantly increases membrane lipid peroxidation in root and leaf cells, resulting in damage to the structure and function of root tip cells and leaf cells. It also injures the activity of photosystem PSII, reducing the photosynthetic rate and inhibiting the growth of cucumber plants. Supplementing Si alleviates CA-mimicked autotoxicity by increasing the thickness and smoothness of root tip cell walls, inhibiting the absorption and accumulation of CA, as well as relieving osmotic stress and membrane lipid peroxidation caused by CA in cucumber roots and leaves. Additionally, Si promotes grana lamella (GL) stacking and increases thylakoid numbers in chloroplasts. It also enhances the chlorophyll content in cucumber leaves and improves the energy conversion efficiency of photosystem PSII. These effects lead to an improvement in both photosynthetic efficiency and dry matter accumulation, as well as increased the resistance to CA-induced autotoxicity in cucumber plants. The same concentration of Si had no significant effect on the growth of cucumber seedlings, indicating that Si plays an important role in improving the tolerance to autotoxicity in cucumbers. These findings provide an effective theoretical basis and methods for research regarding the alleviation of continuous cropping obstacles.