BackgroundIn response to various environmental stresses, many plant species synthesize L-proline in the cytosol and accumulates in the chloroplasts. L-Proline accumulation in plants is a well-recognized physiological reaction to osmotic stress prompted by salinity, drought and other abiotic stresses. L-Proline plays several protective functions such as osmoprotectant, stabilizing cellular structures, enzymes, and scavenging reactive oxygen species (ROS), and keeps up redox balance in adverse situations. In addition, ample-studied osmoprotective capacity, L-proline has been also ensnared in the regulation of plant improvement, including flowering, pollen, embryo, and leaf enlargement.Scope and conclusionsAlbeit, ample is now well-known about L-proline metabolism, but certain characteristics of its biological roles are still indistinct. In the present review, we discuss the L-proline accumulation, metabolism, signaling, transport and regulation in the plants. We also discuss the effects of exogenous L-proline during different environmental conditions. L-Proline biosynthesis and catabolism are controlled by several cellular mechanisms, of which we identify only very fewer mechanisms. So, in the future, there is a requirement to identify such types of cellular mechanisms.
Plant growth‐promoting rhizobacteria (PGPR) are diverse groups of plant‐associated microorganisms, which can reduce the severity or incidence of disease during antagonism among bacteria and soil‐borne pathogens, as well as by influencing a systemic resistance to elicit defense response in host plants. An amalgamation of various strains of PGPR has improved the efficacy by enhancing the systemic resistance opposed to various pathogens affecting the crop. Many PGPR used with seed treatment causes structural improvement of the cell wall and physiological/biochemical changes leading to the synthesis of proteins, peptides, and chemicals occupied in plant defense mechanisms. The major determinants of PGPR‐mediated induced systemic resistance (ISR) are lipopolysaccharides, lipopeptides, siderophores, pyocyanin, antibiotics 2,4‐diacetylphoroglucinol, the volatile 2,3‐butanediol, N‐alkylated benzylamine, and iron‐regulated compounds. Many PGPR inoculants have been commercialized and these inoculants consequently aid in the improvement of crop growth yield and provide effective reinforcement to the crop from disease, whereas other inoculants are used as biofertilizers for native as well as crops growing at diverse extreme habitat and exhibit multifunctional plant growth‐promoting attributes. A number of applications of PGPR formulation are needed to maintain the resistance levels in crop plants. Several microarray‐based studies have been done to identify the genes, which are associated with PGPR‐induced systemic resistance. Identification of these genes associated with ISR‐mediating disease suppression and biochemical changes in the crop plant is one of the essential steps in understanding the disease resistance mechanisms in crops. Therefore, in this review, we discuss the PGPR‐mediated innovative methods, focusing on the mode of action of compounds authorized that may be significant in the development contributing to enhance plant growth, disease resistance, and serve as an efficient bioinoculants for sustainable agriculture. The review also highlights current research progress in this field with a special emphasis on challenges, limitations, and their environmental and economic advantages.
Plant growth promoting rhizobacteria (PGPR) are a group of useful bacteria that colonize the plant roots and significantly enhances the plant growth promotion. Keeping this in mind, an investigation was performed for the screening of potent PGPR strains for enhancing seed germination and vigour index of Hordeum vulgare (commonly called barley). Rhizobacterial strains were isolated and screened for various plant growth promoting traits, their effect on seed germination and vigour index of barley plant through pot trial, and resistant ability under various temperature and pH range. Based upon 16S rRNA sequencing data, Pseudomonas punonensis LMT03 (R1), Pseudomonas plecoglossicida R4, Pseudomonas aeruginosa DSM50071 (R2) and Alcaligenes faecalis (DBHU5) isolates were selected and showed positive result for IAA production, Phosphate solubilization, ammonia production, catalase activity, siderophore production and MR-VP test. Barley plants treated with P. punonensis and P. plecoglossicida both showed 94.44% of highest seed germination %, while P. aeruginosa and A. faecalis showed 83.11% and 77.33% respectively in comparison to the control plant shows which 49.99% seed germination only. These respective isolates also showed 2.57, 2.37, 2.0 and 1.69 fold of increase in vigour index as compare to the control plants. The above increase in fold in vigour index and seed germination is much higher as compared to earlier reports. Collectively, the data of current study underpin that addition of these PGPRs to barley rhizosphere appears a promising strategy to enhance root and shoot biomass of this important agriculture crop. To the best of our knowledge this is the first report demonstrating the effect of P. punonensis and P. plecoglossicda on barley crop.
The study was conducted to examine the effect of plant growth promoting rhizobacteria; Pseudomonas punonensis LMT03 (R1), Pseudomonas plecoglossicida (R4), Pseudomonas aeruginosa DSM 50071 (R2), Alcaligenes faecalis (DBHU5) and their consortium on yield and lignin deposition of the barley crop. Consortium treated plants had the highest plant height, leaf surface area, number of fertile tillers, spike length, grains per spike, 1000 grain weight, grain yield, straw yield, total biomass, and harvest index percent and the lowest values were found in control plots. The consortium treated plant produced the highest grain yield 7976 kg/ha, while control plants produced 3200 kg/ha. In comparison to the control plant, the PGPR-treated barley plant showed dense lignin deposition in the vascular bundles of the stem section.This is the first report on the effect of P.punonensis and P. plecoglossicida on barley crop yield parameters under field conditions, also the first report on lignin deposition in barley plant treated with P. punonensis and P. plecoglossicida strains.
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