Physiological, Photochemical and Antioxidant Responses of Wild and Cultivated Carthamus Species Exposed to Nickel Toxicity and Evaluation of Their Usage Potential in Phytoremediation

Abstract

The responses of growth, photochemical and antioxidant defence of safflower species (Carthamus oxyacantha M. Bieb. and Carthamus tinctorius L. exposed to nickel (Ni) toxicity were investigated in the study. Fourteen-day-old seedlings were treated with excessive Ni levels [control, 0.50, 0.75 and 1.00 mM] for 7 days. The results of chlorophyll a fluorescence indicated that toxic nickel exposure led to changes in specific, phenomenological energy fluxes and quantum yields in thylakoid membranes, and activities of donor and acceptor sides of photosystems. These changes resulted in a significant decrease in the photosynthetic performance of the species, but these negative effects of Ni were not in a level to destroy the functionality of the photosystems. At the same time, toxic Ni affected membrane integrity and the amount of photosynthetic pigments in the antenna and active reaction centers. Additionally, the accumulation of Ni was higher in roots than in stem and leaves for both species. Depending on Ni accumulation, a significant reduction in dry biomass of root and shoot was observed in both species. Two species could probably withstand deleterious Ni toxicity with better upregulating own protective defence systems such as antioxidant enzymes. Among of them, SOD and POD activities were increased with increasing Ni concentrations. The POD activities of both species were most prominent and consistently increased in toxic Ni levels and may be protected them from damaging effect of H2O2. When all results are evaluated as a whole, Carthamus species produced similar responses to toxicity and also both species have Bioconcentration (BCF) and Bioaccumulation factors (BF) > 1 and Translocation factor (TF) < 1 under Ni toxicity may be regarded a good indication of Ni tolerance. Consequently, it is possible to use the Carthamus species in the remediation (phytostabilization) of soils contaminated with nickel, because of their roots accumulating more nickel.