The present study showed that exogenous abscisic acid (ABA) pre-treatment remarkably increases the freeze tolerance of common wheat (Triticum aestivum L.) seedlings at the anther connective tissue formation phase (ACFP) and tetrad developmental phase. After 3-day freeze stress, ABA pre-treatment significantly increases the content of soluble sugar, soluble protein, and proline, activities of superoxide dismutase (SOD) and peroxidase (POD) and decreases hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels. Under freeze stress conditions, ABA treatment at the ACFP and tetrad developmental phase resulted in a marked increase in leaf ascorbic acid (ASA) and glutathione (GSH) levels. Temporal and spatial expression patterns of eight genes encoding ASA–GSH synthesis-related enzymes and eight stress-responsive genes were measured using quantitative real-time PCR (qRT-PCR). The results showed that ABA temporally regulated the transcript levels of these genes. Moreover, these genes were differentially expressed in ABA-treated wheat seedlings between the ACFP and tetrad developmental phase during freeze stress. These results implied that exogenous ABA increases the levels of GSH and ASA in freeze stressed wheat seedlings in time- and developmental phase-specific manners. Furthermore, we found that the ABA-independent and ABA-dependent pathways were not completely independent in this study and that ABA-independent stress-responsive genes were also induced by exogenous ABA in at least one stress exposure time point. Comparison of our results with the findings of previous studies showed that plant hormones induce an increase in GSH and ASA levels, possibly by differentially regulating the expression levels of genes encoding ASA–GSH synthesis enzymes. Our results provide the first insights on the molecular mechanism of ABA-induced spring freeze tolerance in wheat.

本研究表明，外源脱落酸（ABA）预处理显着提高了普通小麦（Triticum aestivum L.）幼苗在花药结缔组织形成阶段（ACFP）和四倍体发育阶段的耐冻性。经过3天的冷冻胁迫后，ABA预处理显着增加了可溶性糖，可溶性蛋白和脯氨酸的含量，超氧化物歧化酶（SOD）和过氧化物酶（POD）的活性并降低了过氧化氢（H ₂ O _2））和丙二醛（MDA）含量。在冰冻胁迫条件下，在ACFP和四倍体发育阶段进行ABA处理导致叶片抗坏血酸（ASA）和谷胱甘肽（GSH）含量显着增加。使用定量实时PCR（qRT-PCR）测量了八个编码ASA–GSH合成相关酶的基因和八个应激反应基因的时空表达模式。结果表明，ABA在时间上调节了这些基因的转录水平。而且，这些基因在冷冻胁迫期间在ACFP和四倍体发育期之间在ABA处理的小麦幼苗中差异表达。这些结果表明，外源ABA以时间和发育阶段特异性方式增加了冷冻胁迫小麦幼苗中GSH和ASA的水平。此外，我们发现，这项研究中ABA依赖性和ABA依赖性途径并不完全独立，并且外源ABA在至少一个应激暴露时间点也诱导了ABA依赖性应激反应基因。我们的结果与先前研究结果的比较表明，植物激素可能通过差异调节编码ASA–GSH合成酶的基因的表达水平来诱导GSH和ASA水平升高。我们的结果为ABA诱导的小麦春季抗冻性的分子机制提供了第一见解。我们的结果与先前研究结果的比较表明，植物激素可能通过差异调节编码ASA–GSH合成酶的基因的表达水平来诱导GSH和ASA水平升高。我们的结果为ABA诱导的小麦春季抗冻性的分子机制提供了第一见解。我们的结果与先前研究结果的比较表明，植物激素可能通过差异调节编码ASA–GSH合成酶的基因的表达水平来诱导GSH和ASA水平升高。我们的结果为ABA诱导的小麦春季抗冻性的分子机制提供了第一见解。