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Plant Growth–Promoting Rhizobacteria (PGPR) and Bioremediation of Industrial Waste
Published in Ram Chandra, R.C. Sobti, Microbes for Sustainable Development and Bioremediation, 2019
Sangeeta Yadav, Kshitij Singh, Ram Chandra
However, relatively few studies determine the role of exogenous ABA in plant-microbe interactions and whether bacterial ABA influences ABA status of plants under salt stress. However, PGPR modulate ABA biosynthesis and ABA-mediated signaling pathways that may contribute to the enhanced growth of salt-stressed plants. The transport of abscisic acid can occur in both xylem and phloem tissues and can also be translocated through parenchyma cells. The movement of abscisic acid in plants does not exhibit polarity like auxins. Abscisic acid was reported to stimulate the stomatal closure, inhibit shoot growth while not affecting or even promoting root growth, induce seeds to store proteins and in dormancy, induce gene transcription for proteinase inhibitors, and thereby provide pathogen defense and counteract with gibberellins.
Plant Responses and Tolerance to Drought
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Sumit Jangra, Aakash Mishra, Priti, Kamboj Disha, Neelam R. Yadav, Ram C. Yadav
A series of physiological, biochemical and molecular changes are triggered by drought stress, which has a negative effect on plant growth and development. Physiological and biochemical responses include stomatal closure, reduction in cell growth and photosynthetic efficiency and respiration activation. Plants also respond to drought stress both at the cellular and molecular level by accumulating osmolytes and proteins involved in mitigating drought stress (Shinozaki and Yamaguchi-Shinozaki, 2006). A wide range of genes with diverse functions are upregulated or downregulated by drought stress (Shinozaki et al., 2003; Bartels and Sunkar, 2005; Yamaguchi-Shinozaki and Shinozaki, 2005). Production of a phytohormone, abscisic acid (ABA), is triggered by drought, which leads to closure of stomata and switches on several stress-related genes. However, evidence for both ABA-induced and ABA-independent, regulation of drought-inducible gene expression is available (Yamaguchi-Shinozaki and Shinozaki, 2005).
Bioprospecting of Microbial Diversity for Sustainable Agriculture and Environment
Published in Vineet Kumar, Vinod Kumar Garg, Sunil Kumar, Jayanta Kumar Biswas, Omics for Environmental Engineering and Microbiology Systems, 2023
Hiren K. Patel, Nensi K. Thumar, Priyank D. Patel, Azaruddin V. Gohil
Abscisic acid is a natural phytohormone that affects the dormancy of seed, adaptation towards stress, and abscission of leaf. It contains sesquiterpenoids and is synthesized via a direct or indirect pathway. In the direct pathway, isopentenyl pyrophosphate was synthesized through mevalonate pathway and it is mostly operated in plant disease-causing fungi. In indirect pathway, isopentenyl pyrophosphate is synthesized from precursor compound methylerythritol. Azospirillum brasilense and Bradyrhizobium japonicum were reported for the production of abscisic acid in soil (Maheshwari et al. 2015). Drought resistance was adapted in Saccharum officinarum with inoculation of Gluconacetobacter diazotrophicus through activation of abscisic acid-dependent signalling genes. The study also indicates that in in vitro conditions, Bacillus pumilus can synthesize five times higher abscisic acid than Pseudomonas sp. Stomatal closing process is enhanced by abscisic acid to prevent water loss by transpiration. Thus, in drought conditions, abscisic acid prevents extra water loss from agricultural crops. Dried soil conditions can induce abscisic acid synthesis. By metabolizing abscisic acid, bacteria can decrease its concentration. As abscisic acid and ethylene have antagonistic relation, decreased concentration can lead to induction of ethylene, which diminishes microbial ethylene production need (Kudoyarova et al. 2019). Variovorax paradoxus, which is Proteobacteria 5C-2, can in vitro decrease abscisic acid 40%–60% in pea plant (Jiang et al. 2012).
Diffusional and Thermal Resistances of Substomatal Cavity and Its Application on Wick
Published in Heat Transfer Engineering, 2022
Transpiration is the most important physiological activity of plant and the stoma plays an essential role as the terminal in this activity. Some interesting phenomena, such as the phase change and heat and mass transfer, keep happening within the stoma and substomatal cavity, just like that happens within the wick. It was found that the abscisic acid triggered a signal in the guard cells that led to stomatal closure for reducing the water loss in response to the drought [14]. The guard cell controls the stomatal aperture through its expansion and contraction by the osmotic potential [15]. To indicate the extent of stomatal opening, a parameter named stomatal conductance was used, which relates to the net photosynthetic rate and CO2 concentration [16, 17]. There were some classical theoretical models of the stomatal conductance, such as the Jarvis model [18], Ball-Berry model [19] and Leuning model [20].
Growth of zinnia, Italian ryegrass, and alfalfa and their remediation effects in diesel oil-contaminated soils
Published in International Journal of Phytoremediation, 2019
Hiromi Ikeura, Suzuka Ozawa, Masahiko Tamaki
In contrast, the levels of growth inhibition of zinnia in oil-contaminated soils were similar to those of Italian ryegrass. Zinnia is originally from Mexico and has a higher tolerance to drought stress than many other species (Carter and Grieve 2010). Abscisic acid (ABA), a plant hormone which is involved in responses to environmental stresses such as drought, low temperature, and high salinity, is required for stress tolerance and is known to control various resistance genes (Iuchi et al. 2001). ABA is synthesized when plants are exposed to dryness or when seeds mature, leading to increased levels of ABA. Increased ABA activates the Defense mechanism against drying and thus enables drought tolerance (Umezawa et al. 2006). This may explain why zinnia was abler than alfalfa to endure oil contamination in the soil.
Roles of phytohormones in mitigating abiotic stress in plants induced by metal(loid)s As, Cd, Cr, Hg, and Pb
Published in Critical Reviews in Environmental Science and Technology, 2023
Zhi-Hua Dai, Dong-Xing Guan, Jochen Bundschuh, Lena Q. Ma
Other phytohormones also play a role in plant photosynthesis. For example, abscisic acid is a well-known regulator of stomatal closure, which decreases photosynthesis by limiting CO2 diffusion (Pinheiro & Chaves, 2011), while cytokinins, auxin, and ethylene induce stomatal opening (Zlobin et al., 2020). In addition, gibberellin plays a positive role in enhancing photosynthesis activity and promotes chloroplast biogenesis (X. J. Li et al., 2016).