Abstract
BACKGROUND AND AIMS: Despite their toxicity, reactive oxygen species (ROS) play important roles in plant cell signalling pathways, such as mediating responses to stress or infection and in programmed cell death, at lower levels. Although studies have indicated that hydrogen peroxide (H(2)O(2)) promotes seed germination of several plants such as Arabidopsis, barley, wheat, rice and sunflower, the role of H(2)O(2) in soybean seed germination is not well known. The aim of this study therefore was to investigate the relationships between ROS, plant hormones and soybean seed germination. METHODS: An examination was made of soybean seed germination, the expression of genes related to ethylene biosynthesis, endogenous ethylene contents, and the number and area of cells in the root tip, using N-acetylcysteine, an antioxidant, to counteract the effect of ROS. KEY RESULTS: H(2)O(2) promoted germination, which N-acetylcysteine suppressed, suggesting that ROS are involved in the regulation of soybean germination. H(2)O(2) was produced in the embryonic axis after imbibition. N-Acetylcysteine suppressed the expression of genes related to ethylene biosynthesis and the production of endogenous ethylene. Interestingly, ethephon, which is converted to ethylene, and H(2)O(2) reversed the suppression of seed germination by N-acetylcysteine. Furthermore, morphological analysis revealed that N-acetylcysteine suppressed cell elongation at the root tip, and this suppression was also reversed by ethephon or H(2)O(2) treatments, as was the case in germination. CONCLUSIONS: In soybean seeds, ROS produced in the embryonic axis after imbibition induce the production of endogenous ethylene, which promotes cell elongation in the root tip. This appears to be how ROS regulate soybean seed germination.