Abstract
Soybean is an important and staple oilseed crop worldwide. Salinity stress has adverse effects on soybean development periods, especially on seed germination and post-germinative growth. Improving seed germination and emergence will have positive effects under salt stress conditions on agricultural production. Here we report that NaCl delays soybean seed germination by negatively regulating gibberellin (GA) while positively mediating abscisic acid (ABA) biogenesis, which leads to a decrease in the GA/ABA ratio. This study suggests that fluridone (FLUN), an ABA biogenesis inhibitor, might be a potential plant growth regulator that can promote soybean seed germination under saline stress. Different soybean cultivars, which possessed distinct genetic backgrounds, showed a similar repressed phenotype during seed germination under exogenous NaCl application. Biochemical analysis revealed that NaCl treatment led to high MDA (malondialdehyde) level during germination and the post-germinative growth stages. Furthermore, catalase, superoxide dismutase, and peroxidase activities also changed after NaCl treatment. Subsequent quantitative Real-Time Polymerase Chain Reaction analysis showed that the transcription levels of ABA and GA biogenesis and signaling genes were altered after NaCl treatment. In line with this, phytohormone measurement also revealed that NaCl considerably down-regulated active GA1, GA3, and GA4 levels, whereas the ABA content was up-regulated; and therefore ratios, such as GA1/ABA, GA3/ABA, and GA4/ABA, are decreased. Consistent with the hormonal quantification, FLUN partially rescued the delayed-germination phenotype caused by NaCl-treatment. Altogether, these results demonstrate that NaCl stress inhibits soybean seed germination by decreasing the GA/ABA ratio, and that FLUN might be a potential plant growth regulator that could promote soybean seed germination under salinity stress.
Highlights
Salinity is one of the most important abiotic stresses in the world
This study shows that exogenous NaCl treatment inhibits soybean seed germination by mediating the abscisic acid (ABA) and GA biogenesis pathways, and importantly, our evidences demonstrate that an ABA biogenesis inhibitor, fluridone (FLUN), might be a potential plant growth regulator that could be used to enhance soybean seed germination under salinity stress conditions
The results revealed that NaCl treatment inhibited HD-19 seed germination processes (Figures 1C,D), and the post-germinative growth analysis showed that postgerminative growth was reduced by NaCl (Figures 1G,H)
Summary
Salinity is one of the most important abiotic stresses in the world It has adverse effects on almost all development stages during the plant life-cycle, including seed germination, seedling establishment and development, vegetative and reproductive growth, and crop survival and yield (Zhu, 2016). The physiological and molecular mechanisms through which plants adapt to salt stress need further investigating and the results could lead to improvements in agricultural production worldwide, especially on saline land. Salinity stress has significantly decreased soybean yield by inhibiting seed germination and post-germinative growth. High and uniform germination and emergence in the field are the key determinants of soybean yield, especially under salt stress conditions. Potential plant growth regulators need to be developed to promote soybean seed germination and emergence under salinity stress conditions
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