Seed glucosinolates in rapeseed (Brassica napus) provide sulfur nutrition required for early seedling growth under sulfur limitation

Brassica crops accumulate specific sulfur (S)-containing compounds, glucosinolates (GSL), in their seeds. GSL function in plant defense, but a few exert toxic effects on animals. Rapeseed (Brassica napus) cultivars accumulating low levels of GSL have been bred to avoid the toxic effects of GSL. GSL store S to support early seedling growth in Arabidopsis under S deficiency. In this study, we tested the effects of different S conditions on growth and S metabolism in B. napus cultivars containing high and low GSL concentrations in the seeds (hereafter referred to as high- and low-seed GSL cultivars, respectively) to determine the appropriate fertilizer design for B. napus. Seed S content was lower in the low-seed GSL cultivars than that in the high ones, indicating that seed GSL content can contribute S accumulation in B. napus seeds. Under S-sufficient (+S) and -deficient (–S) conditions, both shoots and roots fresh weights were similar among the cultivars, but the leaves turned yellowish in the low-seed GSL cultivars. The sulfate and cysteine levels in the seedlings were similar among the cultivars, but glutathione content was lower in the low-seed GSL cultivars than that in the high-seed GSL cultivars, especially in the shoots grown under–S conditions. The S levels in the protein fraction were lower in the shoots of the low-seed GSL cultivars than in those of the high-seed GSL cultivars. These results indicated that seed GSL help support early seedling growth in B. napus under–S conditions. S deficiency and lack of GSL affected shoot growth rather than root growth. Thus, we recommend applying S fertilizers to low-seed GSL cultivars and minimizing the use of S fertilizers for high-seed GSL cultivars. This study provides novel insights for designing and applying fertilizers according to the B. napus cultivar and the soil environment.