Abstract Seed germination is the most critical phase in the life cycle of plants and salt tolerance during seed imbibition is essential for germination and subsequent plant growth in saline soil. In this study, we found for the first time that overexpression of tobacco cyanoalanine synthase 1 (CAS1), i.e. an enzyme for cyanide detoxification, improved the germination rate of tobacco seeds under salt stress conditions. Measurement of cyanide content showed that there was a quick cyanide production during seed imbibition and germination, but less cyanide accumulated in CAS1 overexpressing seeds than in WT seeds, especially under salt stress conditions. CAS1 activity increased during seed imbibition and germination, reaching levels two- or three-times higher under stress conditions of 50 mM and 100 mM NaCl than under normal conditions. Moreover, salt stress inhibited the respiration of seeds, whereas CAS1 overexpressing seeds maintained higher levels of total respiration and alternative oxidase (AOX) pathway respiration than WT seeds. Notably, inhibiting the AOX pathway with 2 mM salicylhydroxamic acid (SHAM) significantly repressed the germination of WT seeds, and also impaired the CAS1 overexpressing-mediated seed germinability under both normal and salt stress conditions. These findings indicate that overexpression of CAS1 helps to improve tobacco seed germination under salt stress conditions, but requires the assistance of AOX.

中文翻译：

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氰基丙氨酸合酶 1 的过度表达提高了盐胁迫条件下烟草种子的发芽率

摘要 种子萌发是植物生命周期中最关键的阶段，种子吸收过程中的耐盐性对于盐渍土中的萌发和随后的植物生长至关重要。在这项研究中，我们首次发现烟草氰基丙氨酸合酶1 (CAS1)，即一种氰化物解毒酶，过表达提高了盐胁迫条件下烟草种子的发芽率。氰化物含量的测量表明，在种子吸胀和萌发过程中氰化物产生很快，但与野生型种子相比，CAS1 过表达种子中积累的氰化物较少，尤其是在盐胁迫条件下。CAS1 活性在种子吸收和萌发过程中增加，在 50 mM 和 100 mM NaCl 胁迫条件下达到比正常条件下高 2 或 3 倍的水平。而且，盐胁迫抑制种子的呼吸，而 CAS1 过表达的种子比 WT 种子保持更高水平的总呼吸和替代氧化酶 (AOX) 途径呼吸。值得注意的是，在正常和盐胁迫条件下，用 2 mM 水杨基异羟肟酸 (SHAM) 抑制 AOX 通路显着抑制了 WT 种子的萌发，并且还损害了 CAS1 过表达介导的种子发芽能力。这些发现表明CAS1的过表达有助于提高盐胁迫条件下烟草种子的萌发，但需要AOX的帮助。用 2 mM 水杨基异羟肟酸 (SHAM) 抑制 AOX 途径显着抑制了 WT 种子的萌发，并且还在正常和盐胁迫条件下损害了 CAS1 过表达介导的种子发芽能力。这些发现表明CAS1的过表达有助于提高盐胁迫条件下烟草种子的萌发，但需要AOX的帮助。用 2 mM 水杨基异羟肟酸 (SHAM) 抑制 AOX 途径显着抑制了 WT 种子的萌发，并且还在正常和盐胁迫条件下损害了 CAS1 过表达介导的种子发芽能力。这些发现表明CAS1的过表达有助于提高盐胁迫条件下烟草种子的萌发，但需要AOX的帮助。