Abstract
As two coexisting abiotic stresses, salt stress and alkali stress have severely restricted the development of global agriculture. Clarifying the plant resistance mechanism and determining how to improve plant tolerance to salt stress and alkali stress have been popular research topics. At present, most related studies have focused mainly on salt stress, and salt-alkali mixed stress studies are relatively scarce. However, in nature, high concentrations of salt and high pH often occur simultaneously, and their synergistic effects can be more harmful to plant growth and development than the effects of either stress alone. Therefore, it is of great practical importance for the sustainable development of agriculture to study plant resistance mechanisms under saline-alkali mixed stress, screen new saline-alkali stress tolerance genes, and explore new plant salt-alkali tolerance strategies. Herein, we summarized how plants actively respond to saline-alkali stress through morphological adaptation, physiological adaptation and molecular regulation.
Highlights
With the increase in population and the deterioration of natural environments, soil salinealkalization has become an increasingly serious global problem (Shabala, 2013)
Exogenous application of salicylic acid and nitric oxide has been reported to increase plant salt tolerance by enhancing the synthesis of proline, glycine betaine, and sugars that contribute to the maintenance of the tissue water content in Vigna angularis (Ahanger et al, 2019). These results show that different plant species and different varieties of the same species can respond to salt-alkali stress through changes in different osmotic adjustment substances
The expression levels of SbNCED3, SbPP2C09, SbPP2C23, SbPP2C52, SbPP2C54, SbPP2C58, SbSAPK1, SbSAPK5, and SbSAPK9 were significantly upregulated under saline-alkali stress, indicating that these genes may play an important role in abscisic acid (ABA) signaling under salt-alkali stress (Ma et al, 2019)
Summary
With the increase in population and the deterioration of natural environments, soil salinealkalization has become an increasingly serious global problem (Shabala, 2013). Studies have shown that in the ABA signaling pathway, the expression of five genes (SaPYL4−1, SaPYL4−2, SaPYL4−3, SaPYL4−4, and SaPYL5−1) related to ABA receptors in Sophora alopecuroides is downregulated under salt and alkali treatment These genes regulate stomatal closure by promoting the accumulation of ABA, thereby reducing the inhibitory effect of saline-alkali stress on photosynthesis and allowing plants to better adapt to the stress environment (Guo et al, 2015; Yan et al, 2020). The expression levels of SbNCED3, SbPP2C09, SbPP2C23, SbPP2C52, SbPP2C54, SbPP2C58, SbSAPK1, SbSAPK5, and SbSAPK9 were significantly upregulated under saline-alkali stress, indicating that these genes may play an important role in ABA signaling under salt-alkali stress (Ma et al, 2019) These results indicate that an increase in hormone content enhances the salt-alkali resistance of plants. The application of exogenous hormones such as ABA, SA, and JA alleviated harmful effects of salt and alkali stresses on various plants, which further verified the role of hormones in enhancing plant resistance (Ahanger et al, 2019; Ali et al, 2020; Li X. et al, 2020)
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