P 014 - Rapid ascorbate response to bacterial elicitor treatment in Arabidopsis thaliana cells

Abstract

An early event of the incompatible plant-pathogen interactions is an oxidative burst. The major water soluble, low molecular weight antioxidant, ascorbic acid plays a crucial role in Reactive Oxygen Species (ROS) balancing (scavenging). The regulation of ascorbate level therefore can be an important point of the fine tuning of ROS level during the early phase of plant-pathogen interaction. To evaluate how this interaction affects the biosynthesis, the recycling and the level of ascorbate, we challenged Arabidopsis thaliana cells with 2 different harpin proteins (HrpZpto and HrpWpto). HrpZpto and HrpWpto treatments caused a well-defined ROS peak. The expression of the alternative oxidase (AOX1a) and vtc5, one of the paralog genes that encode the rate limiting enzyme of ascorbate biosynthesis followed the elevation of ROS. Similarly the activity of ascorbate-peroxidase and galactono-1,4-lactone dehydrogenase (GLDH), the enzyme catalyzing the ultimate, mitochondria coupled step of ascorbate biosynthesis and the level of ascorbate and glutathione also followed the elevation of ROS due to harpin treatment. The enhanced expression of AOX1a, the elevated activity of GLDH and the increased level of ascorbate and glutathione all can contribute to the mitigation or absence of programmed cell death. Finally a new function, the fine tuning of redox balance during plant-pathogen interaction can be proposed to vtc5.