Coumarin-Induced Delay of Rice Seed Germination Is Mediated by Suppression of Abscisic Acid Catabolism and Reactive Oxygen Species Production

Abstract

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 Oryza sativa 9-cis epoxycarotenoid dioxygenases (OsNCEDs), which are ABA synthases, decreased during seed germination. At the transcription level, the expression of OsNCED1–3 appeared to decrease, whereas the expression of the ABA 8′-hydroxylase 2 and 3 genes ( OsABA8’ox2/3 ) 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 OsNCED1–3 transcription. Interestingly, coumarin imbibition remarkably reduced OsABA8’ox2/3 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 OsABA8’ox2/3 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.

Momilactone B inhibits Arabidopsis growth and development via disruption of ABA and auxin signaling

“…Recently coumarin, which has been reported to play a role in allelopathic interactions, was also shown to inhibit rice seed germination by suppressing ABA catabolism and promoting ROS accumulation (Chen et al, 2019). Additionally, seed storage protein mobilization, a process regulated by ABA, has been shown to be impaired in response to MB treatment in germinating seeds , suggesting that ABA may be involved in the MB-mediated inhibition of seed germination.…”

Coumarin Interferes with Polar Auxin Transport Altering Microtubule Cortical Array Organization in Arabidopsis thaliana (L.) Heynh. Root Apical Meristem

“…Coumarin’s phytotoxicity and its ability to alter both root anatomy and morphology have been primarily documented [ 12 , 50 ]. Previous studies have demonstrated that this molecule is a potent inhibitor of germination and seedling growth and development [ 51 , 52 ]. On the contrary, at relatively low concentrations (100 µM), it significantly stimulates lateral root and root hair production, whereas the total root length is significantly reduced [ 22 ].…”

Delayed germination of Brassica parachinensis seeds by coumarin involves decreased GA4 production and a consequent reduction of ROS accumulation

“…Furthermore, as ROS production is prevented by inhibitors such as diphenylene iodonium chloride, adenine, SDIC among others, seed germination is also delayed (Müller et al, 2009; Zhang et al, 2014a). Previously, we found that coumarin inhibits rice germination by suppressing ABA catabolism (Chen et al, 2019).…”