Abstract
Boron (B) is an essential trace element required for the physiological functioning of higher plants. B deficiency is considered as a nutritional disorder that adversely affects the metabolism and growth of plants. B is involved in the structural and functional integrity of the cell wall and membranes, ion fluxes (H+, K+, PO43−, Rb+, Ca2+) across the membranes, cell division and elongation, nitrogen and carbohydrate metabolism, sugar transport, cytoskeletal proteins, and plasmalemma-bound enzymes, nucleic acid, indoleacetic acid, polyamines, ascorbic acid, and phenol metabolism and transport. This review critically examines the functions of B in plants, deficiency symptoms, and the mechanism of B uptake and transport under limited B conditions. B deficiency can be mitigated by inorganic fertilizer supplementation, but the deleterious impact of frequent fertilizer application disrupts soil fertility and creates environmental pollution. Considering this, we have summarized the available information regarding alternative approaches, such as root structural modification, grafting, application of biostimulators (mycorrhizal fungi (MF) and rhizobacteria), and nanotechnology, that can be effectively utilized for B acquisition, leading to resource conservation. Additionally, we have discussed several new aspects, such as the combination of grafting or MF with nanotechnology, combined inoculation of arbuscular MF and rhizobacteria, melatonin application, and the use of natural and synthetic chelators, that possibly play a role in B uptake and translocation under B stress conditions.
Highlights
B is cross-linked with pectin assembly, glycosylinositol phosphorylceramides (GIPCs), and rhamnoglacturonan-II (RG-II) [3,4] that control the tensile strength and porosity of the cell wall [5,6]
B is found in the form of boric acid or borate; among all the essential elements, the percolation of B is in the form of uncharged molecules instead of ions [32]
Three pathways or mechanisms are recognized for the uptake and transport of B in plants: passive diffusion through plasma membrane; facilitated transport via channel proteins, such as the nodulin 26-like intrinsic proteins (NIPs); and high-affinity active transport reconciled by borate transporters (BOR) persuaded under low B availability [1,32,35]
Summary
B is one of the essential nutrients for the optimum growth, development, yield, and quality of crops [1] It performs many important functions in plants and is mainly involved in cell wall synthesis and structural integration. B limitation negatively alters the reproductive performance of plants by causing abrupt changes in flowering and fruiting modes This often results in empty and shriveled anthers, pollen tubes bursting, pollen viability loss, abscission of flower buds, failure of fruit setting, and premature fruit drop because of failure of photosynthate transport resulting in yield loss [12,14]. These findings suggest that B predominantly affects reproductive growth compared with vegetative growth in plants
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