Abstract
Growth regulator herbicides are widely used in paddy fields to control weeds, however their role in conferring environmental stress tolerance in the crop plants are still elusive. In this study, the effects of recommended dose of 2,4-dichlorophenoxyacetic acid (2,4-D) on growth, oxidative damage, antioxidant defense, regulation of cation transporter genes and anatomical changes in the roots of rice cultivars XS 134 (salt resistant) and ZJ 88 (salt sensitive) were investigated under different levels of saline stress. Individual treatments of saline stress and 2,4-D application induced oxidative damage as evidenced by decreased root growth, enhanced ROS production, more membrane damage and Na+ accumulation in sensitive cultivar compared to the tolerant cultivar. Conversely, combined treatments of 2,4-D and saline stress significantly alleviated the growth inhibition and oxidative stress in roots of rice cultivars by modulating lignin and callose deposition, redox states of AsA, GSH, and related enzyme activities involved in the antioxidant defense system. The expression analysis of nine cation transporter genes showed altered and differential gene expression in salt-stressed roots of sensitive and resistant cultivars. Together, these results suggest that 2,4-D differentially regulates the Na+ and K+ levels, ROS production, antioxidant defense, anatomical changes and cation transporters/genes in roots of rice cultivars.
Highlights
Crop plants growing under field conditions frequently face a variety of stresses that can cause severe yield losses
Exposure of rice cultivars to saline stress treatments effects plant growth, which causes a significant decrease in dry (DW) and fresh weights (FW) in a dose dependent manner
When plants were exposed to a combined stress of herbicide + mild salt treatment (T5), considerable increase in root biomass was noted compared to mild salt treatment (T3) in both rice cultivars
Summary
Crop plants growing under field conditions frequently face a variety of stresses that can cause severe yield losses. Plants must activate different adaptive features at both the physiological and molecular levels because they show altered anatomical and physiological mechanisms, enabling the stressed plants to grow well and maintain their reproductive capacity[6,7,8,9,10] These mechanisms include the regulation of hormones, the adjustment of photosynthesis and respiratory metabolism, the modulation of antioxidant defenses and the efflux of toxic ions. It would be interesting to determine how 2,4-D regulates root growth in contrasting rice cultivars at different levels of salinity The resolution of these questions will provide information about whether and how the application of growth regulator herbicide (2,4-D) significantly confers salt tolerance to rice plants. To investigate the changes at the molecular level, we have evaluated the gene expression profiling of antioxidant enzymes and cation transporters in the roots of rice cultivars under controlled and stress conditions
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