Chromium speciation and biochemical changes vary in relation to plant ploidy

Uptake of trivalent chromium (Cr(III)-chloride), Cr speciation and consequences for the metabolism in chamomile plants with two ploidy levels have been studied. Depletion of fresh biomass, tissue water content and soluble proteins in response to high (120 μM) Cr(III) was ploidy-independent. Cr mainly accumulated in the roots (only negligibly in the shoots) and total root Cr amount was higher in tetraploid ones including the proof with specific fluorescent indicator (naphthalimide-rhodamine) of Cr(III). Quantification of Cr(VI) detected its higher content in tetraploid roots (up to 4.2% from total Cr), indicating partial oxidation of applied Cr(III). Higher H2O2 presence but lower activities of peroxidases were observed in tetraploid roots while nitric oxide, superoxide dismutase and glutathione reductase activities did not differ extensively. Soluble phenols, lignin, non-protein thiols, individual thiols (glutathione and phytochelatin 2) and ascorbic acid responded to high Cr(III) similarly in both cultivars while decrease of minerals was more pronounced in tetraploid ones. It seems that Cr(III)-induced oxidative stress arises from high root Cr uptake and Cr(VI) presence and is related to depletion of thiols. Assay of Krebs cycle acids confirmed rather depletion under 120 μM Cr(III) in both cultivars but increase in citric acid may indicate its involvement in root Cr chelation. Subsequent comparison of Cr(III)-chloride and Cr(III)-nitrate showed similar influence on Cr accumulation and majority of biochemical responses while different impact on phytochelatin 2 amount was the most distinct feature.