Determination of nickel tolerances of domestic (Carthamus tinctorius L.) and wild (Carthamus oxyacantha M.Bieb.) genotypes of safflower and evaluation of their usage potential in phytoremediation

Nickel (Ni+2) is a micronutrient that is essential for plant growth and development, and its high concentrations have highly toxic effects. In this study, the effects of nickel on the growth and photochemical activities of domestic (Carthamus tinctorius L., Olas) and wild (Carthamus oxyacantha M. Bieb) safflower genotypes and the potential of accumulation with the nickel tolerance of the genotypes were aimed. 14 day-old seedlings grown in climate cabinet with controlled conditions (16/8 hour photoperiod, 180-200 µmol. m-2s-1 light intensity, 23-25 ± 1 °C day/night temperature, 50 ± 5% humidity) were exposed to different nickel concentrations [control, 0.5mM, 0.75mM and 1.0mM (NiCl2.6H2O)] for 7 days. In both domestic and wild genotypes, the biomass of root and shoot decreased depending on nickel accumulation, and this decrease was found to be higher in the roots. Furthermore, both genotypes translocated the nickel which uptaken by their roots to the leaves by approx. 8-18%. Although a small amount of nickel was transferred to the leaves, photosynthetic apparatus were adversely affected. Toxic nickel levels caused the changes in the specific (ABS/RC, TRO/RC, ETO/RC, REO/RC and DIO/RC) and phenomenological energy fluxes (ABS/CS, TRO/CSO, ETO/CSO and DIO/CSO), quantum yields (Po and DIo), the efficiencies of PSII's donor (VK/VJ) and PSI's acceptor (ΔVIP) sides in the thylakoid membranes. These changes led to a significant decrease in the photosynthetic performance (PIABS ve PITOP) of the genotypes. However these negative effects of nickel were not at a level to destroy the functionality of the photosystems, even though it affected membrane integrity and the amount of pigments in the antenna and active reaction centers. While superoxide (O2- ) and hydrogen peroxide (H2O2) which are oxidative damage products caused by toxic nickel levels were detoxified by high activity of superoxide dismutase (SOD) and guaiacol peroxidase (POD) enzymes in the roots of genotypes. In addition to these enzymes, ascorbate peroxidase (APX) and glutathion reductase (GR) activities and the increase in the amount of anthocyanins and flavonoids being accessory pigments were determined to have impact on the defence system in the leaves. Wild and domestic genotypes showed similar tolerance behavior against to nickel toxicity. It may be possible to take advantage of the potential usage of the safflower plants for remediation (phytostabilization) in soils contaminated with nickel due to accumulation in large amount of nickel in the roots of genotypes.