The effect of nickel phytotoxicity on photosystem II activity and antioxidant enzymes in barley

In this study, the effect of mild (100 µM), moderate (300 µM) and severe (500 µM) nickel (NiSO4.7H2O) toxicity on the photosynthetic activity, photosynthetic pigment content and some antioxidant enzymes in the leaves of a barley cultivars (Hordeum vulgare L. cv. Tarm-92) was investigated. Moderate and severe nickel toxicity decreased root length while shoot length was not affected by nickel stress, probably due to over accumulation of nickel in roots. Similarly, biomass accumulation was declined by moderate and severe nickel toxicity as reflected by the lowered fresh and dry weight. Chlorophyll a, chlorophyll b and consequently total chlorophyll content decreased by all nickel applications, presumably because the reduced level of carotenoids. Chlorophyll a fluorescence measurements showed that nickel toxicity blocked electron movement in some specific points of the photosynthetic electron transport system. The constant Fo value indicated that PSII reaction centers was not damaged in the leaves of barley under nickel toxicity while the reduced Fm value showed that acceptor side of PSII was more sensitive to nickel toxicity as compared to donor side. Changes in JIP test parameters in the leaves of barley showed that primary photochemical reactions are reduced, and thermal dissipation of excess energy is increased. SOD and CAT activity is elevated in the leaves of barley under moderate and severe nickel toxicity which demonstrate an efficient superoxide dismutation. Severe nickel toxicity, however, did not affect SOD and CAT activity. The ascorbate-glutathione cycle was activated in the leaves of barley plants under nickel toxicity, probably indicating an efficient H2O2 detoxification. However, considerable H2O2 and MDA accumulation was observed in the leaves of barley under nickel stress. As a result, it may be concluded that the barley genotype Tarm-92 is moderately tolerant to nickel toxicity.

Role of Jasmonic and Salicylic Acid on Enzymatic Changes in the Root of Two Alyssum Inflatum Náyr. Populations Exposed to Nickel Toxicity

Salicylic acid (SA) and jasmonic acid (JA) as plant growth regulators (PGRs) have the potential to ameliorate plant development and tolerance to deleterious effects of toxic metals like nickel (Ni). Therefore, the current study was carried out to evaluate SA and JA's interactive effect on the root antioxidative response of two Alyssum inflatum Nyár. populations against Ni-toxicity. Two A. inflatum species under Ni-stress conditions (0, 100, 200, and 400 µM) were exposed to alone or combined levels of SA (0, 50, and 200 µM) and JA (0, 5, and 10 µM) treatments. Results showed that high Ni doses reduced the roots fresh weight (FW) in two populations than control; however, the use of external PGRs had ameliorated roots biomass by mitigated Ni-toxicity. Under Ni toxicity, SA and JA, especially their combination, induced high Ni accumulation in plants' roots. Moreover, the application of SA and JA alone, as well as combined SA + JA, was found to be effective in the scavenging of hydrogen peroxide (H2O2) by improving the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in both populations under Ni-toxicity. Overall, our results manifest that SA and JA's external use, especially combined SA + JA treatments, ameliorate root biomass and plant tolerance by restricting translocation Ni to the shoot, accumulating in roots, and also enhancing antioxidant defense systems.

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

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.

Role of Jasmonic and Salicylic Acid on Enzymatic Changes in The Root of Two Alyssum Inflatum Náyr. Populations Exposed to Nickel Toxicity

Salicylic acid (SA) and jasmonic acid (JA) as plant growth regulators (PGRs) have the potential to ameliorate plant development and tolerance to deleterious effects of toxic metals like nickel (Ni). Therefore, the current study was carried out to evaluate SA and JA's interactive effect on the root antioxidative response of two Alyssum inflatum Nyár. populations against Ni-toxicity. Two A. inflatum species under Ni-stress conditions (0, 100, 200, and 400 µM) were exposed to alone or combined levels of SA (0, 50, and 200 µM) and JA (0, 5, and 10 µM) treatments. Results showed that high Ni doses reduced the roots fresh weight (FW) in two populations than control; however, the use of external PGRs had ameliorated roots biomass by mitigated Ni-toxicity. Under Ni toxicity, SA and JA, especially their combination, induced high Ni accumulation in plants' roots. Moreover, the application of SA and JA alone, as well as combined SA + JA, was found to be effective in the scavenging of hydrogen peroxide (H2O2) by improving the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in both populations under Ni-toxicity. Overall, our results manifest that SA and JA's external use, especially combined SA + JA treatments, ameliorate root biomass and plant tolerance by restricting translocation Ni to the shoot, accumulating in roots, and also enhancing antioxidant defense systems.