Exogenous proline application ameliorates toxic effects of arsenate in Solanum melongena L. seedlings

• AsV exerts toxic effects on Sonalum melongena L. seedlings.
• This occurred due to enhanced uptake of AsV ultimately leading to oxidative stress.
• Exogenous Pro protects S. melongena against AsV toxicity.
• Pro-mediated amelioration of As toxicity is due to decline in AsV uptake, and up-regulation of defense system of S. melongena.
• Pro metabolism could play a role in AsV tolerance.

Hydroponic experiments were conducted to investigate an effect of exogenous application of proline (Pro; 25 µM) in alleviating arsenate (AsV; 5 and 25 µM) toxicity in Solanum melongena L. (eggplant) seedlings. Exposure of AsV declined growth of eggplant, which was coincided with an enhanced accumulation of As. However, exogenous Pro application alleviated AsV toxicity in eggplant seedlings by reducing the accumulation of As. The fluorescence characteristics (JIP-test): φP0, Ψ0, φE0, PIABS, ABS/RC, TR0/RC, ET0/RC, DI0/RC, NPQ and qP were also affected by AsV. However, the effects of AsV were more prominent on PIABS DI0/RC and NPQ. In Pro treated seedlings, following parameters viz. φP0, Ψ0, φE0 and PIABS were stimulated, while, energy flux parameters (ABS/RC, TR0/RC, ET0/RC and DI0/RC) were inhibited. Toxic effects of AsV on photochemistry of photosystem II (PS II) were ameliorated by an exogenous application of Pro. Oxidative stress markers: superoxide radical, hydrogen peroxide and malondialdehyde (lipid peroxidation) were enhanced by AsV exposure, however, their levels were significantly diminished by an exogenous application of Pro. Treatment of AsV stimulated the activities of superoxide dismutase, peroxidase and catalase except that of glutathione-S-transferase. Exogenous Pro application improved the activities of enzymatic antioxidants. The level of endogenous Pro was higher in AsV treated as well as in Pro fed seedlings. The activity of a key enzyme of Pro biosynthesis: Δ1-pyrroline-5-carboxylate synthetase was higher in Pro fed seedlings. The activity of Pro dehydrogenase was inhibited under AsV stress, and its activity was minimum in case of Pro+AsV combination. These results indicate that Pro metabolism could play a key role in regulating the accumulation of As and levels of antioxidants, which concomitantly result into a better growth of eggplant seedlings when compared to the AsV treatments alone.

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