Physiological and biochemical responses of Carthamus tinctorius L. to zinc at vegetative stage.

Background: Environment contamination with heavy metals is a major problem both to the environment and human health. Aims: The aim of this work is to evaluate the physiological, nutritional, and biochemical responses of safflower plants (Carthamus tinctorius L.) grown under different zinc concentrations at vegetative stage. Methods: The effect of zinc on safflower plants was studied through the evaluation of growth parameters, colorimetric assay of phenolic compounds, and antioxidant enzymes activities. Results: Zinc inhibited shoot and root growth and resulted in leaf chlorosis at 75, 225, and 1000 µM zinc concentrations. At higher concentrations, Zn also reduced photosynthetic parameters except the internal CO2 concentration that was higher at these levels. Zinc reduced potassium content of the shoots at 75 µM of zinc. The presence of Zn at 1000 µM concentration reduced the iron content and led to the accumulation of the copper content in the shoots. In roots, iron and copper contents were reduced from 15 µM Zn. In the case of copper, this content was canceled out at 225 and 1000 µM of zinc. Lipid peroxidation (evaluated as thiobarbituric acid reactive substances content) increased with zinc treatment. Safflower plants generally responded to this oxidative stress by enhancing the antioxidant enzymes activities, namely, catalase, ascorbate peroxidase, and guaiacol peroxidase. There was no increase in superoxide dismutase activity in shoots and roots, except at the highest zinc concentration in the roots. Total soluble sugars (TSS) and starch contents increased, whereas proline content decreased in shoots. In roots, TSS was not altered, whereas starch was decreased, and proline content was increased. There were no changes in the protein content in both organs under different Zn treatments. There was a gradual increase in the total polyphenols in shoots with increasing zinc concentration; however, no changes were observed in the roots. Flavonoids decreased in roots at 225 and 1000 µM Zn. Total antioxidant activity increased in shoots but it decreased in roots with increasing zinc concentration. The inverse trend was observed for the DPPH and ABTS tests. Conclusions: Our results suggest that the decline in safflower plant growth under high zinc concentrations is related to altered photosynthetic activity and antioxidant response to oxidative stress. [ABSTRACT FROM AUTHOR]