Nitrogen modulates strontium uptake and toxicity in Hypericum perforatum plants

Strontium is an unavoidable element occurring in plants due to its abundance in the soil and similarity with calcium. To mimic natural conditions, impacts of additional inorganic (nitrate) or organic (urea and allantoin) nitrogen sources (1 mM of each N form in addition to 3.53 mM N in the basic cultivation solution) or N deficit on strontium-induced changes (100 µM Sr) in the widely used medicinal plant Hypericum perforatum L. were studied. Though various effects of Sr on primary (stimulation of amino acids but depression of most Krebs acids, ascorbic acid and thiols) and secondary metabolites (stimulation of phenols but no change of pseudo/hypericin) or mineral elements were observed (reduction of Ca amount in both shoots and roots), organic N forms often mitigated negative action of Sr or even combined stimulatory impact was observed. Organic N forms also elevated shoot accumulation of Sr while N deficit reduced it. Additional N forms, rather than Sr itself, modulated reactive oxygen species and nitric oxide formation in the root tissue. Germination experiment showed no toxicity of Sr to H. perforatum up to 1 mM Sr and even stimulated accumulation of amino acids and phenols, indicating similar ontogenetic-related responses.