Reactive oxygen species, abscisic acid and ethylene interact to regulate sunflower seed germination

Sunflower (Helianthus annuusL.) seed dormancy is regulated by reactive oxygen species (ROS) and can be alleviated by incubating dormant embryos in the presence of methylviologen (MV), a ROS-generating compound. Ethylene alleviates sunflower seed dormancy whereas abscisic acid (ABA) represses germination. The purposes of this study were to identify the molecular basis of ROS effect on seed germination and to investigate their possible relationship with hormone signalling pathways. Ethylene treatment provoked ROS generation in embryonic axis whereas ABA had no effect on their production. The beneficial effect of ethylene on germination was lowered in the presence of antioxidant compounds, and MV suppressed the inhibitory effect of ABA. MV treatment did not alter significantly ethylene nor ABA production during seed imbibition. Microarray analysis showed that MV treatment triggered differential expression of 120 probe sets (59 more abundant and 61 less abundant genes), and most of the identified transcripts were related to cell signalling components. Many transcripts less represented in MV-treated seeds were involved in ABA signalling, thus suggesting an interaction between ROS and ABA signalling pathways at the transcriptional level. Altogether, these results shed new light on the crosstalk between ROS and plant hormones in seed germination. This work investigates the relationship between reactive oxygen species (ROS), abscisic acid (ABA) and ethylene in the regulation of sunflower seed germination and it deciphers the molecular basis of the effects of ROS on seed germination. We show that ROS, provided by methylviologen to the dormant sunflower seeds, and ethylene act synergistically to promote germination whereas ROS and ABA have antagonistic effects. Microarrays analyses allowed identifying molecular players of ROS signaling and they show that ROS transcriptionally repress ABA signaling pathways but that they stimulate the expression of genes related to redox and calcium signaling for stimulating germination. Our work allows proposing ROS as a central hub in the regulation of seed germination.