The subcellular localization and function of APX3 in Arabidopsis

The physiological condition associated with increased levels of reactive oxygen species (ROS, e.g., .O2-, H2O2, .OH and 1O2) is called oxidative stress. Enzymatic actions of superoxide dismutase, catalase and ascorbate peroxidase (APX) remove ROS in plants. APX is a H2O2-scavenging enzyme that protects plant cells from detrimental effects of H2O2. Although H2O2 is toxic to cells, it also plays important roles in plants. For example, it is required for cell wall cross-linking and it serves as a secondary messenger during plant defense. Therefore, it is not entirely beneficial for plants to remove H2O2 as soon as it is produced, but rather to regulate its amounts within the cell. APX is one such enzyme that may help regulate the amounts of H2O2 in plant cells.

It was previously found that a 14-3-3-protein-interacting ascrobate peroxidase, APX3, was likely to be peroxisomal membrane bound. To test this hypothesis GFP-APX3 overexpressing plants were created. Fluorescence microscopy analyses from various tissues of GFP-APX3 plants indicated that APX3 is likely to be peroxisomal in its localization. To investigate the in vivo function of APX3, anti-APX3 antisense and APX3-overexpressing transgenic plants were created. Furthermore APX3-knockout plants from ABRC were also obtained. Data from analyzing APX3-knocout mutants show that loss of APX3 leads to modified electron transport during heat stress. Results from physiology experiments indicate that APX3 may play a role in thermal tolerance. This research indicates that a decrease in APX3 leads to an increase in other antioxidation enzymes. Therefore, it appears that the plant antioxidation system is redundant and highly interconnected.