Aqsa Tariq

By Aqsa Tariq and Ambreen Ahmed

Phytohormones play a fundamental role in the development of plants. Among various phytohormones produced by the plants, Auxins act as a master hormone that plays a major role during plant development and differentiation through cell division. Besides plants, many rhizospheric microorganisms are also capable of producing auxins specifically indole-3-acetic acid (IAA), that act as signaling molecules for the regulation of gene expressions in plants. However, bacterial IAA is majorly linked with the modulation of plant roots architecture and developing positive plant-microbe interactions. Bacterial auxin modifies root morphology by enhancing root length, forming adventitious root and root hair, thereby, increasing surface area for water and nutrient absorption affecting various aspects of plant biology in a number of ways. Bacteria mostly utilize tryptophan, present in plant root exudates, to synthesize IAA that eventually helps bacteria to colonize roots by establishing beneficial associations with plant roots. Auxins also stimulate the formation of exopolysaccharides and biofilms that help bacterial root colonization. Auxins have given the survival benefit to rhizobacteria that make them more competent to establish symbiotic interaction with plants. Synergistic and antagonistic interactions of auxins (both interkingdom and Intrakingdom) with other phytohormones play a key role in plant development and growth improvement.

Part of the book: Plant Hormones

By Aqsa Tariq and Ambreen Ahmed

Phosphorous limits agricultural productivity due to its limited plant availability. Use of synthetic phosphate fertilizers disturbs soil fertility and ecosystem ecology as it contaminates environment. Plants have developed certain mechanisms to respond to P-scarcity, which involve release of specific chemical messengers through root exudates that attract rhizospheric phosphorbacteria to colonize plant root vicinity. Thus, use of phosphate-solubilizing bacteria/rhizobacteria (PSB/PSR) as biofertilizers is a safer approach toward sustainable agrobiology. These PSR are capable of solubilizing soil phosphate from insoluble to plant available form. Due to instability and slow movement of available phosphates in soils, they readily get incorporated with soil particles or chelates as metal complexes. In this scenario, PSR provide continuous chain of soluble phosphate to plants. PSR direct plant root system architecture toward available phosphate zones in soils. Moreover, there is an increased number of roots, root hair and lateral root, increase root absorbing surface area by increasing contact to soil particles. Hence, PSR-based root system morphology is a significant trait in measuring their agronomic efficiency. Moreover, PSB also possess phytostimulatory properties that significantly contribute to agricultural efficiency. Hence, the use of phosphate-solubilizing bacteria can improve crop productivity by increasing soil P-mobility and soil fertility.

Part of the book: Sustainable Management of Natural Resources

By Aqsa Tariq and Ambreen Ahmed

Rhizosphere is the hub for microbial activities where microbes and plants interact with complex signaling mechanisms. Plants release various metabolites in response to environmental factors which are significant in shaping rhizospheric microbial communities. These microbes develop symbiotic relation with plants by quorum sensing signals and regulate various microbial activities including biofilm formation. Biofilms are important in inhabiting rhizosphere and provide platform for cell-to-cell microbial interactions. Biofilm- forming rhizobacteria can successfully colonize plant roots and establish symbiotic relations with host. During this association, rhizobacteria are flourished by using plant root exudates, while the bacteria benefit the plants by synthesizing phytohormones, locking soil minerals for plant, protecting them from pathogenic invasions and enhancing plant immunity by improving plant tolerance against various environmental conditions. Indole is an effector molecule in regulating bacterial gene expression related to biofilm production. These interactions are coordinated by bacterially released phytohormones mainly auxin which act as key factor in regulating plant-microbe symbiotic interactions. It is characterized as inter- kingdom signaling molecule that coordinates various plant and rhizobacterial activities. Thus, understanding the nature and interacting behaviors of these molecules would lead to the exploitation of plant growth-promoting rhizobacteria for better plant growth in agricultural fields.

Part of the book: Symbiosis in Nature