Cadmium toxicity and its amelioration by kinetin in tomato seedlings vis-à-vis ascorbate-glutathione cycle

The supplementation of plant hormones may enhance the tolerance capacity of plants against certain environmental stresses by increasing their physiological functioning and detoxification capacity. To answer the question that whether a phytohormone 'kinetin' (KN, 6-furfuylaminopurine), one of the artificial cytokinins could ameliorate the cadmium induced toxicity in tomato seedlings, the effect of KN was assessed in differentially cadmium (Cd₁: 3mgkg^-1 sand and Cd₂: 9mgkg^-1 sand) intoxicated tomato seedlings by estimating the changes in reactive oxygen species (ROS, viz. superoxide radical and H₂O₂ generation) and probable alteration in photosystem II photochemistry, ascorbate-glutathione cycle enzymes and their metabolites. Accumulation of Cd in tomato seedlings increased the production of ROS by negatively impacting PS II photochemistry (decrease in F_v/F_m (ϕP₀), Ψ₀, ϕE₀ and PI_ABS and increase in energy fluxes per reaction centre: ABS/RC, ET₀/RC, TR₀/RC and DI₀/RC) manifested by lowered fresh mass despite the accelerated activity of AsA-GSH cycle enzymes (viz. ascorbate peroxidase, APX; glutathione reductase, GR; dehydroascorbate reductase, DHAR and monodehydroascorbate reductase; MDHAR). Simultaneous application of kinetin (10μM) alleviated the negative effects on the fresh mass and lowered the ROS level by positively affecting PS II photochemistry and further rise in AsA-GSH cycle enzymes and their metabolites.