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 NiCl 2 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 (CO 2) 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 NiCl 2 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.

Accumulation of Proline in Plants under Contaminated Soils—Are We on the Same Page?

“…In terms of photosynthesis, the application of proline has also been shown to attenuate the negative effects induced by metals [ 83 , 119 , 142 , 143 ]. Exogenously applied proline was reported to stabilize not only the electron transport chain between cell membranes and mitochondria but also the 3D structure of proteins, preserving the activity of important, photosynthesis-related enzymes such as ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO; EC 4.1.1.39) [ 119 ].…”

“…In eggplants ( S. melongena ) exposed to As, the exogenously applied proline seemed to act as an electron donor for PS II [ 143 ]. The CO 2 assimilation rate in metal-stressed plants was also restored upon the addition of exogenous proline by an increase in photosynthetic gas exchange attributes and by enhanced biosynthesis and/or the decreased degradation of chlorophylls and carotenoids [ 139 , 142 ].…”

“…Regarding the redox homeostasis, the application of proline, either by foliar spraying or through irrigation, usually leads to an enhanced antioxidant potential [ 120 , 130 , 135 , 139 , 142 , 144 , 145 , 146 ]. This happens not only due to the direct role of proline as an antioxidant per se but also because of its ability to trigger other defensive pathways, including antioxidants.…”

Non-Essential Elements and Their Role in Sustainable Agriculture

“…Olive trees (Olea europaea) under induced water stress and treated with a foliar spray solution containing sodium selenite showed increased photosynthetic ability and fruit yield, while keeping a considerable water level in leaves and showing improved WUE [120]. Selenium also proved to be of aid for species experiencing heat stress [121], promoting plant growth during periods with water shortage in rice and wheat [122,126].…”

“…As also demonstrated for water and salinity stress as well as pest and pathogen resistance, the stimulation of antioxidant enzyme activity is a key process in Si's protective role against toxic metals. When challenged with heavy metal toxicity, plants often display increased levels of oxidative stress as well as membrane permeability and degradation due to lipid peroxidation [121]. Under heavy metal stress, the application of Si was shown to benefit numerous crops, including soybean, barley, rice, cotton, banana, and peanut [207], by increasing the ascorbate-glutathione [184] and glyoxalase [208] systems and enhancing the activity of scavenging enzymes, such as SOD, POD, and CAT [186,206].…”