Abstract
Alfalfa (Medicago sativa L.) is an important forage, and salinity is a major stress factor on its yield. In this study, we show that osmotic stress retards alfalfa seedling growth, while ionic/oxidative stress reduces its seed germination. Ethylene treatment can recover the germination rate of alfalfa seeds under salt stress, while ethylene inhibitor silver thiosulfate exacerbates salt effects. ETH reduces the accumulation of MDA and H2O2 and increases POD activity. ETH and ACC improve the salt tolerance of alfalfa by increasing proline content under salt stress. In contrast, STS inhibits alfalfa seed germination by reducing POD activity. NaCl treatment reduces chlorophyll content in alfalfa leaves, while ETH and ACC can increase the chlorophyll content and promote seedling growth. ETH promotes the growth of alfalfa in saline condition by reducing the expression of MsACO and MsERF8 genes, while increases its germination rate by upregulating MsERF11 gene. Silencing of MsETR2, a putative ethylene receptor gene in alfalfa, abolishes ethylene triggered tolerance to salt stress. In summary, we show that ethylene improves salt tolerance in alfalfa via MsETR2 dependent manner, and we also analyze the regulatory mechanism of ethylene during germination of alfalfa seeds under salt stress.
Highlights
Soil salinity is one of the most common stresses that affect plant growth and development
The results demonstrated that relieving effects of ethylene on salt stressed alfalfa plants were dependent on MsETR2. qPCR results indicated that the level of MsACO, MsERF8 and MtERF11 were all down-regulated in MsETR2 RNAi plants after ETH treatment in NaCl solution, which was in accordance with the above observation and MsETR2 might have feedback regulatory role on MsACO expression (Supplementary Figures 15A–D)
Both NaCl and mannitol treatments inhibited the growth of alfalfa seedlings, but the water content under NaCl stress was significantly higher than that under isotonic mannitol treatment
Summary
Soil salinity is one of the most common stresses that affect plant growth and development. Most plants cannot grow normally in saline and alkaline soil environment, and medium salt concentration (100 mM NaCl) is sufficient to cause a sharp decline in most crop yields (Cheeseman, 2015). When the salt content in soil exceeds the Ethylene Inhibits Salt Stress on Alfalfa threshold, it will cause higher water potential in the seed than that in the soil, inhibiting the water absorption of the seed from the external environment. Without sufficient water content in the seed, its germination and growth will be inhibited. Saline soil contains high concentration of metal ions, the toxic effect of metal ions on seeds is another reason for inhibiting seed germination (Zhang et al, 2011)
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