Belmonte Mark F, Macey Julie, Yeung Edward C, Stasolla Claudio
Department of Plant Science, University of Manitoba, Winnipeg, Man., Canada R3R-5Z9.
Plant Physiol Biochem. 2005 Apr;43(4):337-46. doi: 10.1016/j.plaphy.2005.01.022. Epub 2005 Mar 18.
Water stress is an important factor which regulates organized development of both zygotic and somatic embryos. Somatic embryos of white spruce were cultured in the presence of polyethylene glycol (PEG), a non-plasmolyzing agent which increases embryo quality and number, and mannitol, a plasmolyzing agent. The effects of these two compounds on both ascorbate and glutathione metabolism were investigated at different stages of embryo development. Compared to control and mannitol-treated embryos, embryos treated with PEG accumulated higher levels of endogenous ascorbate (ASC) in its reduced form, especially during the first half of the maturation period. This increase, also observed in immature seeds, was mainly the result of two different processes: activation of the de novo ASC machinery, and recycling of ASC from ascorbate free radicals (AFR) which was modulated by the activity of ascorbate free radical reductase (AFRR, EC. 1.6.5.4). The activity of this enzyme increased during the early phases of development in both PEG-treated somatic embryos and seeds. Compared to control somatic embryos, mannitol and PEG were shown to change the levels of reduced (GSH) and oxidized glutathione (GSSG). In particular, a constant decline in the GSH/GSSG ratio was observed in the presence of PEG. This pattern was also observed in maturing white spruce seeds. Overall, these data indicate that applications of non-plasmolyzing agents in the culture medium of spruce somatic embryos result in seed-like fluctuations of the ascorbate-glutathione metabolism, which may have a positive effect on embryo yield.
水分胁迫是调节合子胚和体细胞胚有序发育的重要因素。白云杉体细胞胚在聚乙二醇（PEG，一种可提高胚质量和数量的非质壁分离剂）和甘露醇（一种质壁分离剂）存在的情况下进行培养。在胚发育的不同阶段研究了这两种化合物对抗坏血酸和谷胱甘肽代谢的影响。与对照胚和甘露醇处理的胚相比，用PEG处理的胚积累了更高水平的还原型内源性抗坏血酸（ASC），尤其是在成熟期的前半段。在未成熟种子中也观察到这种增加，这主要是两个不同过程的结果：从头合成ASC机制的激活，以及由抗坏血酸自由基还原酶（AFRR，EC. 1.6.5.4）的活性调节的从抗坏血酸自由基（AFR）回收ASC。在PEG处理的体细胞胚和种子发育的早期阶段，这种酶的活性都有所增加。与对照体细胞胚相比，甘露醇和PEG显示出会改变还原型（GSH）和氧化型谷胱甘肽（GSSG）的水平。特别是，在PEG存在的情况下，观察到GSH/GSSG比值持续下降。在成熟的白云杉种子中也观察到这种模式。总体而言，这些数据表明在云杉体细胞胚培养基中应用非质壁分离剂会导致抗坏血酸 - 谷胱甘肽代谢出现类似种子的波动，这可能对胚产量有积极影响。
