Effects of 5-aminolevulinic Acid on the Bioactive Compounds and Seedling Growth of Oilseed Rape (Brassica napus L.)

Application of 5-Aminolevulinic acid (ALA) to plants not only affects their growth, but also influences the nutritional values of plant organs. Oilseed rape (Brassica napus L.) is an important source of vegetable oil and various compounds benefiting human health. However, limited information is available regarding the effect of ALA on the growth of this important crop. Here, we investigated the consequence of ALA application on oilseed rape seedlings. We found that moderate ALA concentrations (0.5 or 1 mg/L) caused an increase in the dry weight of the seedling biomass and the contents of various bioactive compounds, i.e. soluble sugar, phenolic compounds, ascorbate, and glucosinolates etc, and the upregulated expressional levels of the genes encoding RuBisCO, namely, BnRBCL and BnRBCS, and other genes such as BnUGT79B1, BnMYB12 and MYB28 that regulate the synthesis of phenolic compounds and glucosinolates respectively. On the other hand, high ALA concentrations (5 and 10 mg/L) gave rise to oxidative stress that negatively affected oilseed rape growth, and caused deleterious effects by reducing various bioactive compounds, but increasing tocopherols that may serve as a stress mitigatory agent. With the high ALA concentrations, the ultrastructure of chloroplasts was notably damaged, featured with large starch grains and fewer plastoglobules.