Exogenous proline and proline-enriched Lolium perenne leaf extract protects against phytotoxic efects of nickel and salinity in Pisum sativum by altering polyamine metabolism in leaves

Abstract

Pea plants (Pisum sativum L.) were exposed to NaCl and/or NiCl2 stress to investigate whether pure proline and Lolium perenneL. (LP) leaf extract could efcaciously protect against the phytotoxicity generated by nickel and/or salinity stress in pea. Both stressfactors (salinity and nickel) signifcantly inhibited growth, total chlorophyll content, photosynthetic activity, stomatal conductance,intercellular CO 2 level, relative water content (RWC), and membrane stability index (MSI). However, superoxide, hydrogen peroxide,proline, glycine betaine, total free amino acids, total soluble sugars, total phenolic compounds, tocopherol contents, lipid peroxidation,and electrolyte leakage were signifcantly increased. Similarly, free, soluble-conjugated, and insoluble-bound polyamine contents[spermine (Spm), spermidine (Spd), and putrescine (Put)] and activities of polyamine-biosynthetic enzymes (arginine decarboxylase,ornithine decarboxylase, and S-adenosylmethionine decarboxylase) in leaves were also increased in response to nickel and/or salinitystress. Exogenously applied proline and LP leaf extracts signifcantly overcame the nickel- and/or salinity-induced toxic efects ongrowth, RWC, and various photosynthetic attributes. Te follow-up treatment with proline and LP leaf extract detoxifed the stresscaused by NiCl2 and/or NaCl by suppressing the lipid peroxidation and electrolyte leakage, accelerating the activities of polyamine-biosynthetic enzymes, and improving the MSI, leaf polyamines (Spm, Spd, and Put), and organic osmolytes (free proline, glycinebetaine, total free amino acids, total soluble sugars, total phenols, and tocopherol contents). Natural proline (LP leaf extract) provedbetter than pure proline in improving growth, photosynthetic activity, RWC, organic osmolytes, and polyamine metabolism. Since LPleaf extract is enriched with substantial amounts of proline along with many other essential nutrients, it was as efcacious as pure prolinein improving growth, some major physiological attributes, and polyamine metabolism in pea under nickel and/or salinity stress. Tus,it can be used as an alternative inexpensive source of proline for its utilization as a mitigating agent for protecting plants against thephytotoxic efects of nickel and/or salinity stress.