Combating Salinity Through Natural Plant Extracts Based Biostimulants: A Review

Abstract

Enhanced crop growth and yield are the recurring concerns in agricultural field, considering the soaring world population and climate change. Abiotic stresses are one of the major limiting factors for constraining crop production, for several economically important horticultural crops, and contribute to almost 70% of yield gap. Salt stress is one of these unsought abiotic stresses that has become a consistent problem in agriculture over the past few years. Salinity further induces ionic, osmotic, and oxidative stress that result in various metabolic perturbations (including the generation of reactive oxygen, carbonyl, and nitrogen species), reduction in water potential (ψw), distorted membrane potential, membrane injury, altered rates of photosynthesis, leaf senescence, and reduced nitrogen assimilation, among others); thereby provoking a drastic reduction in crop growth and yield. One of the strategies to mitigate salt stress is the use of natural plant extracts (PEs) instead of chemical fertilizers, thus limiting water, soil, and environmental pollution. PEs mainly consist of seeds, roots, shoots, fruits, flowers, and leaves concentrates employed either individually or in mixtures. Since PEs are usually rich in bioactive compounds (e.g., carotenoids, flavonoids, phenolics, etc.), therefore they are effective in regulating redox metabolism, thereby promoting plant growth and yield. However, various factors like plant growth stage, doses applied, application method, soil, and environmental conditions may greatly influence their impact on plants. PEs have been reported to enhance salt tolerance in plants primarily through modulation of signaling signatures and pathways (e.g., Na+, ANNA4, GIPC, SOS3, and SCaBP8 Ca2+ sensors, etc.), and regulation of redox machinery [e.g., superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), non-specific peroxidase (POX), glutathione peroxidase (GPX), peroxiredoxin (Prx), ascorbic acid (AsA), glutathione (GSH), α-tocopherol, etc.]. The current study highlights the role of PEs in terms of their sources, methods of preparation, and mode of action with subsequent physiological changes induced in plants against salinity. However, an explicit mode of action of PEs remains nebulous, which might be explicated utilizing transcriptomics, proteomics, metabolomics, and bioinformatics approaches. Being ecological and economical, PEs might pave the way for ensuring the food security in this challenging era of climate change.

Changes in Carotenoid Concentration and Expression of Carotenoid Biosynthesis Genes in Daucus carota Taproots in Response to Increased Salinity

“…Salt stress can exert numerous negative impacts on plants and provoke a serious reduction in crop growth and yield. If plants suffer from inordinate amounts of salt, this will lead to various metabolic perturbations, cutback in water potential (ψw), disordered membrane potential, weaken photosynthesis and diminish nitrogen assimilation [26][27][28]. However, plants have evolved many adaptative mechanisms in response to the condition of high salinity, which involves interacting physiological traits, biochemical or metabolic pathways, and molecular mechanisms [29].…”

Salt-tolerant endophytic bacterium Enterobacter ludwigii B30 enhance bermudagrass growth under salt stress by modulating plant physiology and changing rhizosphere and root bacterial community

“…resistance (Ahmad et al, 2022). Our results show CAT and SOD activities markedly decreased within E. ludwigii B30 inoculated bermudagrass compared with non-inoculated bermudagrass under SS (Figure 3).…”

“…SOD has been recognized as the first line of defense to resist ROS by enhancing ROS scavenging through the catalysis of O 2 – dismutation into O 2 and H 2 O 2 ( Wei et al, 2022b ). Likewise, CAT can eliminate excess plant superoxide radicals, thereby protecting against OS, promoting the accumulation of dry matter, and improving plant resistance ( Ahmad et al, 2022 ). Our results show CAT and SOD activities markedly decreased within E. ludwigii B30 inoculated bermudagrass compared with non-inoculated bermudagrass under SS ( Figure 3 ).…”

Physiological Response of Miscanthus sinensis (Anderss.) to Biostimulants

“…According to Ahmad et al [26], one of the strategies for alleviating salt stress is to apply natural extracts of plants in place of artificial fertilizers, thus reducing water, soil, and environmental pollution. Plant biostimulants are substances that have positive effects on plant growth and nutrition and enhance tolerance to both biotic and abiotic stresses.…”