Kinetin mitigates Cd-induced damagesto growth, photosynthesis and PS II photochemistry of Trigonella seedlings by up-regulating ascorbate-glutathione cycle.

Cytokinins (CKs) plays a key role in plant adaptation over a range of different stress conditions. Here, we analyze the effects of a cytokinin (i.e., kinetin, KN) on the growth, photosynthesis (rate of O2 evolution), PS II photochemistry and AsA-GSH cycle in Trigonella seedlings grown under cadmium (Cd) stress. Trigonella seeds were sown in soil amended with 0, 3 and 9 mg Cd kg-1 soil, and after 15 days resultant seedlings were sprayed with three doses of KN, i.e.,10 µM (low, KNL), 50 µM (medium, KNM) and 100 µM (high, KNH); subsequent experiments were performed after 15 days of KN application, i.e., 30 days after sowing. Cadmium toxicity induced oxidative damage as shown by decreased seedling growth and photosynthetic pigment production (Chl a, Chl b and Car), rates of O2-evolution, and photochemistry of PS II of Trigonella seedlings, all accompanied by an increase in H2O2 accumulation. Supplementation with doses of KN at KNL and KNM significantly improved the growth and photosynthetic activity by reducing H2O2 accumulation through the up-regulation AsA-GSH cycle. Notably, KNL and KNM doses stimulated the rate of enzyme activities of APX, GR and DHAR, involved in the AsA-GSH cycle thereby efficiently regulates the level of AsA and GSH in Trigonella grown under Cd stress. The study concludes that KN can mitigate the damaging effects of Cd stress on plant growth by maintaining the redox status (>ratios: AsA/DHA and GSH/GSSG) of cells through the regulation of AsA-GSH cycle at 10 and 50 µM KN under Cd stress conditions. At 100 µM KN, the down-regulation of AsA-GSH cycle did not support the growth and PS II activity of the test seedlings.

Physiological and biochemical characterization of two Amaranthus species under Cr(VI) stress differing in Cr(VI) tolerance.

The present study was undertaken to evaluate Cr(VI) toxicity tolerance in two Amaranthus species viz. Amaranthus viridis and Amaranthus cruentus exposed to hexavalent chromium [Cr(VI)] stress. To ascertain this, both Amaranthus species were grown under various concentrations (0, 10 and 50 µM) of Cr(VI) in the hydroponic system. After 7 days of Cr(VI) treatment, various traits such as growth, Cr accumulation, photochemistry of photosystem II (PS II) (JIP-test), oxidative stress and antioxidant defense system were analyzed. Cr(VI) treatments caused inhibition in growth and PS II photochemistry, which was accompanied with increased accumulation of Cr that results into enhanced generation of reactive oxygen species (ROS): O2- and H2O2, which subsequently induced the peroxidation of lipids and leakage of electrolyte in both the Amaranthus species. Cr(VI) accumulation, lipid peroxidation and electrolyte leakage were more pronounced in A. viridis than in A. cruentus. On the other hand, A. cruentus seedlings showed higher activities of enzymatic antioxidants: SOD, POD, CAT and GST, and non-enzymatic antioxidants: cysteine and non-protein thiols (NP-SH) levels than A. viridis. The overall results suggest that A. cruentus is more tolerant than A. viridis due to its higher antioxidant defense system that protected seedlings under Cr(VI) stress.

Exogenous IAA differentially affects growth, oxidative stress and antioxidants system in Cd stressed Trigonella foenum-graecum L. seedlings: Toxicity alleviation by up-regulation of ascorbate-glutathione cycle.

In the present study, effect of exogenous indole-3-acetic acid at their different levels (i.e. low; IAAL, 10µM and high; IAAH, 100µM) were studied on growth, oxidative stress biomarkers and antioxidant enzymes (SOD, POD, CAT and GST), and metabolites (AsA and GSH) as well as enzymes (APX, GR and DHAR) of ascorbate-glutathione cycle in Trigonella foenum-graecum L. seedlings grown under cadmium (Cd1, 3mgCd kg(-1) soil and Cd2, 9mgCd kg(-1) soil) stress. Cadmium (Cd) at both doses caused reduction in growth which was correlated with enhanced lipid peroxidation and damage to membrane as a result of excess accumulation of O2(•-) and H2O2. Cd also enhanced the oxidation of AsA and GSH to DHA and GSSG, respectively which give a clear sign of oxidative stress, despite of accelerated activity of enzymatic antioxidants: SOD, CAT, POD, GST as well as APX, DHAR (except in Cd2 stress) and GR. Exogenous application of IAAL resulted further rise in the activities of these enzymes, and maintained the redox status (> ratios: AsA/DHA and GSH/GSSG) of cells. The maintained redox status of cells under IAAL treatment declined the level of ROS in Cd1 and Cd2 treated seedlings thereby alleviated the Cd toxicity and this effect was more pronounced under Cd1 stress. Contrary to this, exogenous IAAH suppressed the activity of DHAR and GR and disturbed the redox status (< ratios: AsA/DHA and GSH/GSSG) of cells, hence excess accumulation of ROS further aggravated the Cd induced damage. Thus, overall results suggest that IAA at low (IAAL) and high (IAAH) doses affected the Cd toxicity differently by regulating the ascorbate-glutathione cycle as well as activity of other antioxidants in Trigonella seedlings.