Chen Bing-Xian, Peng Yuan-Xuan, Gao Jia-Dong, Zhang Qi, Liu Qin-Jian, Fu Hua, Liu Jun
Argo-Biological Gene Research Center, Guangdong Academy of Agricultural Sciences, Guangzhou, China.
College of Agriculture and Biology, Zhongkai University of Agriculture and Engineering, Guangzhou, China.
Front Plant Sci. 2019 Jun 27;10:828. doi: 10.3389/fpls.2019.00828. eCollection 2019.
Abscisic acid (ABA) is a crucial phytohormone for the regulation of seed germination. The ABA content of seeds is regulated by synthesis and catabolic pathways. Coumarin, an important plant allelochemical, can inhibit seed germination effectively, although whether it is involved in the regulation of ABA content during seed germination has not been elucidated. For the study reported herein, we show that coumarin effectively inhibits rice seed germination and vivipary. We found that the ABA content gradually decreased in water-imbibed rice seeds and that the content and activity of the 9-cis epoxycarotenoid dioxygenases (OsNCEDs), which are ABA synthases, decreased during seed germination. At the transcription level, the expression of appeared to decrease, whereas the expression of the ABA 8'-hydroxylase 2 and 3 genes () first appeared to increase and then decrease. Samples of rice seeds were also imbibed in water containing coumarin, which increased their ABA content but did not significantly increase the activity or content of their OsNCEDs or transcription. Interestingly, coumarin imbibition remarkably reduced expression in rice embryos, which partially explained how coumarin increased the ABA content of germinating rice embryos. Coumarin also inhibited the accumulation of reactive oxygen species (ROS) in rice embryos and increased the activity of superoxide dismutase and catalase, which are indispensable for seed germination. These results indicate that coumarin delays seed germination by inhibiting ABA catabolism, particularly by decreasing the expression of rather than by increasing ABA synthesis. Moreover, coumarin increases the ABA content while decreasing the ROS content in rice embryos. Our results enhance our understanding of the regulation of ABA and ROS during seed germination and provide theoretical support for application of coumarin to prevent sprouting before crop harvesting.
脱落酸（ABA）是调控种子萌发的一种关键植物激素。种子中的ABA含量受合成和分解代谢途径调控。香豆素是一种重要的植物化感物质，能有效抑制种子萌发，不过其是否参与种子萌发过程中ABA含量的调控尚未阐明。在本文所报道的研究中，我们发现香豆素能有效抑制水稻种子萌发和胎萌。我们发现，吸胀水稻种子中的ABA含量逐渐降低，且作为ABA合成酶的9-顺式环氧类胡萝卜素双加氧酶（OsNCEDs）的含量和活性在种子萌发过程中下降。在转录水平上，[具体基因名称未给出]的表达似乎下降，而ABA 8'-羟化酶2和3基因（[具体基因名称未给出]）的表达起初似乎增加，随后下降。水稻种子样品还在含有香豆素的水中吸胀，这增加了它们的ABA含量，但未显著增加其OsNCEDs的活性或含量，也未显著增加[具体基因名称未给出]的转录。有趣的是，香豆素吸胀显著降低了水稻胚中[具体基因名称未给出]的表达，这部分解释了香豆素如何增加萌发水稻胚的ABA含量。香豆素还抑制了水稻胚中活性氧（ROS）的积累，并增加了超氧化物歧化酶和过氧化氢酶的活性，而这两种酶对种子萌发不可或缺。这些结果表明，香豆素通过抑制ABA分解代谢来延迟种子萌发，特别是通过降低[具体基因名称未给出]的表达，而非通过增加ABA合成。此外，香豆素增加了水稻胚中的ABA含量，同时降低了ROS含量。我们的结果增进了我们对种子萌发过程中ABA和ROS调控的理解，并为香豆素在作物收获前防止发芽的应用提供了理论支持。
