Department of Biochemistry, Warsaw University of Life Sciences - SGGW, Nowoursynowska 159, 02-776 Warsaw, Poland.
Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5A, 02-106 Warsaw, Poland.
J Plant Physiol. 2018 Jul;226:48-55. doi: 10.1016/j.jplph.2018.03.021. Epub 2018 Apr 16.
Abscisic acid (ABA) is a phytohormone involved in the acquisition of primary dormancy during seeds maturation as well as dormancy maintenance in imbibed seeds. After imbibition, the ABA content decreased to a much lower level in embryos of freshly harvested triticale grains of the Leontino cultivar, which is more susceptible to pre-harvest sprouting (PHS) than embryos of the Fredro cultivar. Lower ABA content in the Leontino cultivar resulted from increased expression of TsABA8'OH1 and TsABA8'OH2, which encode ABA 8'-hydroxylase and are involved in ABA catabolism. Higher ABA content and maintenance of dormancy in Fredro grains were correlated with intensified ABA biosynthesis, which resulted from higher expression of TsNCED1, which encodes 9-cis-epoxycarotenoid dioxygenase. These results suggest that grains of triticale cultivars with different resistance to PHS vary in their ability to metabolize ABA after imbibition. After-ripening did not affect the ABA content in embryos of dry grains of either triticale cultivar. However, after-ripening caused dormancy release in Fredro grains and significantly affected the ABA content and the rate of its metabolism after imbibition. A more rapid decline in ABA content in imbibed Fredro grains was accompanied by decreased transcript levels of TsNCED1 as well as increased expression of TsABA8'OH1 and TsABA8'OH2. Thus, after-ripening may affect dormancy of grains through reduction of the ABA biosynthesis rate and intensified ABA catabolism. Overexpression of TsNCED1 in tobacco increases ABA content and delays germination, while overexpression of TsABA8'OH2 decreases ABA content, accelerates germination, and reduces the sensitivity to ABA of transgenic seeds compared to seeds of wild-type plants. Therefore, these genes might play an important role in the regulation of triticale grain dormancy, thus affecting susceptibility to PHS.
脱落酸（ABA）是一种参与种子成熟过程中获得初生休眠以及吸胀种子休眠维持的植物激素。吸胀后，Leontino 品种的新鲜收获黑小麦种子胚中的 ABA 含量下降到一个低得多的水平，而该品种比 Fredro 品种更容易发生收获前发芽（PHS）。Leontino 品种中 ABA 含量较低是由于 TsABA8'OH1 和 TsABA8'OH2 的表达增加，这两个基因编码 ABA 8'-羟化酶，参与 ABA 分解代谢。Fredro 品种中较高的 ABA 含量和休眠维持与 ABA 生物合成的增强有关，这是由于 TsNCED1 的表达增强所致，该基因编码 9-顺式-环氧类胡萝卜素双加氧酶。这些结果表明，不同 PHS 抗性的黑小麦品种在吸胀后 ABA 代谢能力上存在差异。后熟处理对两种黑小麦品种干种子胚中的 ABA 含量没有影响。然而，后熟处理会导致 Fredro 种子休眠释放，并显著影响吸胀后 ABA 含量和代谢速率。在吸胀的 Fredro 种子中，ABA 含量的快速下降伴随着 TsNCED1 转录水平的降低以及 TsABA8'OH1 和 TsABA8'OH2 表达的增加。因此，后熟处理可能通过降低 ABA 生物合成速率和增强 ABA 分解代谢来影响种子休眠。烟草中 TsNCED1 的过表达增加了 ABA 含量并延迟了发芽，而 TsABA8'OH2 的过表达降低了 ABA 含量，加速了发芽，并降低了与野生型植物种子相比的转基因种子对 ABA 的敏感性。因此，这些基因可能在调控黑小麦种子休眠中发挥重要作用，从而影响对 PHS 的敏感性。
