Effect of exogenous l-aspartate nano‑calcium on root growth, calcium forms and cell wall metabolism of Brassica napus L

Currently, l-aspartate nano‑calcium (Ca(L-asp)-NPs) has been sued as a calcium supplement for humans, but its effects on plants are not well elucidated. This study aimed to investigate the effect of exogenous Ca(L-asp)-NPs on the growth of rapeseed (Brassica napus L.) for the first time. Different concentrations (0, 50, 100, 150, and 200 mg L^-1) of Ca(L-asp)-NPs and 1.18 g L^-1 Ca(NO₃)₂ were used in the nutrient solution. The results indicated that Ca²⁺ released from Ca(L-asp)-NPs were absorbed by the roots, and had a significant effect on plant height, root length, biomass accumulation, and root structure formation, especially on the growth and development of coarse roots at 100 mg L^-1 Ca(L-asp)-NPs. Calcium (Ca) accumulation, Ca-pectinate, Ca-phosphate and Ca‑carbonate, and Ca-oxalate in plant roots and leaves were positively linked with Ca(L-asp)-NPs concentration. For cell wall, Ca(L-asp)-NPs treatment increased the content of pectin, and the activity of cell wall degrading enzymes in roots, such as pectin methyl-esterase (PME), cellulose enzyme (CE), polygalacturonase (PG), and β-galactosidase (β-Gal). For cell membrane osmotic regulation, Ca(L-asp)-NPs promoted the accumulation of soluble sugar and soluble protein. This finding suggests that 100 mg L^-1 Ca(L-asp)-NPs had the best growth-promoting effect on rapeseed. This study provides a valuable reference for exogenous Ca(L-asp)-NPs as new nano Ca supplements for plant growth.