Interactive effect of potassium and spermidine protects growth, photosynthesis and chlorophyll biosynthesis in Vigna angularis from salinity induced damage by up-regulating the tolerance mechanisms

Pot experiments were conducted to evaluate the role of potassium (100 mg KCl / kg soil) and the spermidine (100 μM Spd) in regulation of growth, chlorophyll synthesis and photosynthesis in Vigna angularis under salinity stress (100 mM NaCl). Salinity declined chlorophyll synthesis by causing a significant decline in the synthesis of B-amino levulinic acid (ALA), prototoporphyrin IX (Proto IX) and Mg-prototoporphyrin IX (Mg-Proto IX), however application of K and Spd alone as well as combinedly alleviated the decline to considerable extent. Further, K and Spd treated plants exhibited a significant decline in reactive oxygen species and the lipid peroxidation and such effects were also obvious under salinity stress. Photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, Fv/Fm and photochemical quenching increased significantly due to K and Spd application, and salinity induced alleviation of the decline was maximal due to combined K and Spd treatment. Up-regulation of antioxidant enzymes activity, increased content of ascorbic acid and glutathione (GSH), and the accumulation of compatible osmolytes due to K and Spd application strengthened the tolerance against the salinity stress thereby lessening the oxidative effects considerably. Accumulation of phenols and flavonoids increased significantly due to application of K and Spd. Salinity caused significant increase in Na however K and Spd application induced a significant decline concomitant with increase in K content reflecting in decreased Na/K. Results suggest that K and Spd application protect the growth and photosynthesis from salinity induced oxidative damage by up-regulating the ion homeostasis, antioxidant system, osmolyte accumulation and secondary metabolite synthesis.