Abstract
Soil salinity is one of the major abiotic stresses restricting plant growth and development. Application of plant growth regulators (PGRs) is a possible practical means for minimizing salinity-induced yield losses, and can be used in addition to or as an alternative to crop breeding for enhancing salinity tolerance. The PGRs auxin, cytokinin, nitric oxide, brassinosteroid, gibberellin, salicylic acid, abscisic acid, jasmonate, and ethylene have been advocated for practical use to improve crop performance and yield under saline conditions. This review summarizes the current knowledge of the effectiveness of various PGRs in ameliorating the detrimental effects of salinity on plant growth and development, and elucidates the physiological and genetic mechanisms underlying this process by linking PGRs with their downstream targets and signal transduction pathways. It is shown that, while each of these PGRs possesses an ability to alter plant ionic and redox homeostasis, the complexity of interactions between various PGRs and their involvement in numerous signaling pathways makes it difficult to establish an unequivocal causal link between PGRs and their downstream effectors mediating plants’ adaptation to salinity. The beneficial effects of PGRs are also strongly dependent on genotype, the timing of application, and the concentration used. The action spectrum of PGRs is also strongly dependent on salinity levels. Taken together, this results in a rather narrow “window” in which the beneficial effects of PGR are observed, hence limiting their practical application (especially under field conditions). It is concluded that, in the light of the above complexity, and also in the context of the cost–benefit analysis, crop breeding for salinity tolerance remains a more reliable avenue for minimizing the impact of salinity on plant growth and yield. Further progress in the field requires more studies on the underlying cell-based mechanisms of interaction between PGRs and membrane transporters mediating plant ion homeostasis.
Highlights
Salinity is one of the major abiotic stresses affecting crop plants and limiting production worldwide [1,2]
The main aim of this review was to summarize the bulk of the reported data on the use of plant growth regulators (PGRs) for improving performance of plants grown on salt-affected lands, revealing underlying cellular mechanisms and downstream targets, and critically assessing the applicability of PGR for sustainable crop production under conditions of soil salinity
The effectiveness of PGRs depends on the level of salt stress, genotype, timing, and methods of applications, as well as PGR concentrations
Summary
Salinity is one of the major abiotic stresses affecting crop plants and limiting production worldwide [1,2]. Transgenic technology is considered as a fast and effective method to obtain salt-tolerant varieties, the public acceptance of genetically modified (GM) crops remains a major stumbling block in most countries [38,39,40] In this context, PGPRs could potentially minimize the detrimental effects of salinity stress on plant growth and yield without triggering these public/governmental concerns. PGRs cross-talk with each other and may act synergistically or antagonistically to regulate plant growth, development, and defense responses, generally by inducing gene expression [45] This complexity may result in a certain level of unpredictability and negate expected beneficial effects. The main aim of this review was to summarize the bulk of the reported data on the use of PGRs for improving performance of plants grown on salt-affected lands, revealing underlying cellular mechanisms and downstream targets, and critically assessing the applicability of PGR for sustainable crop production under conditions of soil salinity
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