Abstract
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.
Highlights
Contamination of air, soil and water due to various kinds of pollutants which are byproduct of industrial activity has created a worldwide problem [1,2,3]
Dehydroascorbic acid (DHA) is reduced by the enzyme dehydro ascorbate reductase (DHAR) by consuming the electrons provided by reduced glutathione (GSH) which oxidize into glutathione disulfide (GSSG)
Supplementation of KN at low (KNL) (10 μM KN) significantly improved the repressing effects of Cd on growth, the effect being more pronounced under Cd kg-1 soil (Cd1) stress
Summary
Contamination of air, soil and water due to various kinds of pollutants which are byproduct of industrial activity has created a worldwide problem [1,2,3]. A major mechanism of Cd- induced damage in plant is an increase in the generation of reactive oxygen species (ROS) due to disturbance of mitochondrion and chloroplast electron transport chain via the displacement of essential cations like Ca2+ and Zn2+ [5]. Increased generation of ROS, such as O2 , H2O2, and HO leads to oxidative stress by damaging the cell membranes through lipid peroxidation and proteins degradation, which results in disturbed cellular homeostasis [6, 7]. Plants protect themselves from ROS impairment through the mutual action of enzymatic and non-enzymatic antioxidants and the main pathway for scavenging of H2O2 is ascorbate (AsA)-glutathione (GSH) cycle [8, 9]. The reduction of H2O2 into water is catalyzed by the enzyme ascorbate peroxidase (APX) with the help of AsA, which serve as an electronic donor. The AsA–GSH cycle is crucial for maintaining the reductive environment in plant cells via the up-regulation of its enzymes under a variety of stress conditions [5, 9]
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