Foliar treatment with Lolium perenne (Poaceae) leaf extract alleviates salinity and nickel-induced growth inhibition in pea

Abstract

The plants of pea (Pisum sativum L.) were grown under NaCl and/or NiCl2 stress, to comparatively evaluate stress-mitigating effects of pure proline and naturally proline-enriched Lolium perenne (L.) aqueous leaf extract. Both stress factors (salinity and nickel) significantly reduced plant biomass, chlorophyll content, photosynthetic activity, stomatal conductance, intercellular carbon dioxide (CO2) level, number of stomata, stomatal size, water-use efficiency, relative water content (RWC), and the membrane stability index (MSI). However, the proline and glycinebetaine contents, lipid peroxidation, electrolyte leakage, and activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase) were significantly increased. Exogenously applied proline and Lolium perenne (LP) leaf extracts significantly overcame the nickel and/or salinity-induced toxic effects on growth, RWC, and various photosynthetic attributes. However, follow-up treatment with proline and LP-leaf-extract detoxified the stress caused by NiCl2 and/or NaCl, by suppressing lipid peroxidation and electrolyte leakage, accelerating the antioxidant enzyme activities, and improving the MSI, leaf/root proline, and glycinebetaine contents. LP-leaf-extract proved to be better than pure proline for improving growth, gas exchange parameters, osmolytes, RWC, and antioxidant enzyme activities. As LP-leaf-extract was enriched with a substantial amount of proline along with many other essential osmoprotectants, it was found to be as effective as pure proline in ameliorating growth, some major physiological attributes, and non-enzymatic and enzymatic antioxidant activities in the pea, under nickel and/or salinity stress. Thus, it could be used as an alternative inexpensive source of proline, to be used as a mitigating agent for protecting plants against the deleterious effects of nickel and/or salinity stress.