Table_1_Ethylene Enhances Seed Germination and Seedling Growth Under Salinity by Reducing Oxidative Stress and Promoting Chlorophyll Content via ETR2 Pathway.docx

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.

紫花苜蓿（Alfalfa，*Medicago sativa* L.）是一类重要的饲用牧草，盐胁迫是制约其产量的主要非生物胁迫因子。本研究结果表明，渗透胁迫会延缓紫花苜蓿幼苗的生长，而离子/氧化胁迫则会降低其种子萌发率。乙烯（Ethylene, ETH）处理可恢复盐胁迫下紫花苜蓿种子的萌发率，而乙烯抑制剂硫代硫酸银（silver thiosulfate, STS）则会加剧盐胁迫的负面影响。ETH可降低丙二醛（Malondialdehyde, MDA）与过氧化氢（Hydrogen Peroxide, H₂O₂）的积累量，并提升过氧化物酶（Peroxidase, POD）活性；在盐胁迫条件下，ETH与1-氨基环丙烷羧酸（1-aminocyclopropane-1-carboxylic acid, ACC）可通过提升脯氨酸含量，增强紫花苜蓿的耐盐性。与之相反，STS可通过降低POD活性抑制紫花苜蓿种子的萌发。NaCl处理会降低紫花苜蓿叶片中的叶绿素含量，而ETH与ACC则可提升叶绿素含量并促进幼苗生长。ETH可通过抑制MsACO与MsERF8基因的表达，促进盐胁迫下紫花苜蓿的生长；同时通过上调MsERF11基因的表达，提升其种子萌发率。沉默紫花苜蓿中推定的乙烯受体基因MsETR2后，乙烯介导的耐盐胁迫响应会被完全阻断。综上，本研究证实乙烯可通过依赖于MsETR2的途径提升紫花苜蓿的耐盐性，并解析了盐胁迫下乙烯在紫花苜蓿种子萌发过程中的调控机制。