How cadmium affects the fitness and the glucosinolate content of oilseed rape plantlets

Secondary metabolites such as glucosinolates (GSLs) are involved in plant response to biotic stress but can be significantly influenced by abiotic factors as well. Oilseed rape (Brassica napus L.) produces large quantities of several GSLs both in seeds and at the vegetative stage. These sulfur-containing compounds are known to play an important role in cadmium stress tolerance within the Brassicaceae family probably due to specific cross-talk between the S primary and secondary metabolism. Sulfur assimilation is in the middle of multiple metabolic pathways including Cd stress responses at physiological level. Our research focused on the assessment of GSL profiles and content in the roots and shoots of 28-day-old winter oilseed rape plantlets. The study was conducted under in vitro sterile conditions using concentration gradients of 0, 5, 15 and 45 μM of cadmium. A phenotypic analysis was carried out at the end of this experiment in order to evaluate the plantlets' fitness. Our results described hormetic growth curves for root elongation, root biomass and shoot biomass at Cd concentrations of 5 μM and 15 μM respectively. Our experiment shows that a concentration of 5 μM can be considered as non-toxic, while one of 45 μM represents a lethal dose. Strong relationships were found between Cd accumulated in roots or translocated to shoots and the total sulfur accumulation in the plantlets' different organs. A decrease of both indole and aliphatic GSL content associated with an increase of Cd accumulation and an increase of total sulfur accumulation was observed in the roots and shoots of the plantlets. It was also further demonstrated that Cd stress has a highly significant effect on roots' and shoots' GSL content bringing new insights into GSL's possible role in the priming of Cd stress.