Brassica juncea and the Se-hyperaccumulator Stanleya pinnata exhibit a different pattern of chromium and selenium accumulation and distribution while activating distinct oxidative stress-response signatures

Soils high in chromium and selenium exist in some countries, like China, India and the US. In the forms of chromate and selenate, these elements can compete during uptake by plants and lead to secondary effects on the absorption of the essential nutrient sulfur. In this study, we evaluated the potential of Brassica juncea and the Se-hyperaccumulator Stanleya pinnata to take-up and store chromium and selenium when applied individually or jointly, the effect on sulfur content, and the plant antioxidant responses. The aim is to advise the best use of these species in phytotechnologies. Plants were grown hydroponically with 50 μM chromate, 50 μM selenate and equimolar concentrations of both elements (50 μM chromate + 50 μM selenate). Our results suggest that B. juncea and S. pinnata possess transport systems with different affinity for chromate and selenate. The joint application of chromate and selenate restricted the accumulation of both elements, but the reduction of selenate uptake by chromate was more evident in B. juncea. On the other hand, selenate decreased chromium accumulation in B. juncea, whereas in S. pinnata such effect was evident only in roots. B. juncea plants stored more chromium and selenium than S. pinnata due to the higher biomass produced, but less selenium when treated with both elements. Chromate and selenate decreased sulfur accumulation in both species, but B. juncea was more sensitive to their toxicity when applied individually, as revealed by increased lipid peroxidation, hydrogen peroxide content in roots and antioxidant enzyme activity. This species can still be efficient for chromium and selenium phytoextraction as these elements in soil are less available than in hydroponics. In soils high in both elements, or low in selenium, S. pinnata is preferred for selenium phytoextraction and the biomass could be used for crop biofortification due its negligible chromium content.