Chromium-induced depression of 15N content and nitrate reductase activity in rice seedlings

Abstract

Hydroponic experiments were conducted to investigate the influence of chromium (Cr) exposure on assimilation of 15N-labeled nitrate in rice (Oryza sativa L. cv. XZX 45) seedlings. Results showed that exposure of young seedlings to both Cr compounds led to a linear decrease in relative growth rate, nitrate reductase (NR) activity and tissue 15N accumulation though responses differed between the two Cr variants, in which potassium chromate [Cr(VI)] caused more severe effects than chromium chloride [Cr(III)]. Analysis of subcellular distribution of Cr showed that Cr deposition in cell wall was the highest in tissues of rice seedlings exposed to Cr(III), whereas the largest deposition of Cr in the roots was associated with cytosol in the Cr(VI) treatments. Analysis of a partial correlation between tissue fractions of Cr, NR activity and 15N content revealed that depression of NR activity in plant materials of rice seedlings exposed to Cr(III) was mainly associated with a decrease in 15N accumulation, whereas inhibition of NR activity from exposure of plants to Cr(VI) was most likely due to the presence of Cr in cytosol. Information collected here indicated that mechanisms of transport, subcellular distribution and phytotoxicity of the two Cr compounds were different in rice seedlings.