Glyoxylate cycle and reactive oxygen species metabolism are involved in the improvement of seed vigor in watermelon by exogenous GA3

Exogenous application of gibberellins (GA) is a simple and effective way to improve seed vigor, which is probably achieved through its stimulation on the glyoxylate cycle activity and reactive oxygen species (ROS) metabolism in germinating seeds. However, the physiological mechanism of the stimulation still remains unclear. Here, we show that pre-soaking with GA(3) enhanced seed vigor and seedling growth of watermelon. GA(3) initiated the seed metabolic processes earlier, increased the respiration rate, and thus enhanced the respiration activity. Meanwhile, exogenous GA(3) increased the activity of isocitrate lyase (ICL), one of the key enzymes in the glyoxylate cycle, and activities of malate dehydrogenase (MDH), succinate dehydrogenas (SDH) and isocitrate dehydrogenase (IDH) as well. Also, exogenous GA(3) led to an enhancement in gene expression of ICL, MDH and IDH. Accompanied by the enhancement of glyoxylate cycle and tricarboxylic acid cycle, the production of O-2 center dot(-) and H2O2 was promoted by GA(3). In addition, GA(3) induced the activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPOD), promoted the expression of CSD and POD, so as to scavenge the excess ROS. Our results suggest that seed vigor of watermelon increased by exogenous GA(3) may be related to GA function in activation of the glyoxylate cycle and the regulation of ROS metabolism during seed germination.