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 O(2) 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, KN(L)), 50 μM (medium, KN(M)) and 100 μM (high, KN(H)); 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 O(2-)evolution, and photochemistry of PS II of Trigonella seedlings, all accompanied by an increase in H(2)O(2) accumulation. Supplementation with doses of KN at KN(L) and KN(M) significantly improved the growth and photosynthetic activity by reducing H(2)O(2) accumulation through the up-regulation AsA–GSH cycle. Notably, KN(L) and KN(M) 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.