Sammendrag
We are using microarray technology and glycine betaine (GB) gene activation to discover new stress determinants in plants. Several of the genes discovered so far are involved in three distinct processes; i.e. 1) Reactive oxygen species (ROS) metabolism, 2) Cell wall synthesis or 3) Regulatory signal transduction pathways. Based on these studies and studies on knockout mutants for specific candidate genes as well as YFP and GUS transgenics, we have developed a new model for photoprotection in Arabidopsis as follows: under conditions when an imbalance in light harvesting and carbon assimilation occurs, light energy is converted in the chloroplast to strong reductant which is used to reduce oxygen to superoxide and for further ROS production. According to our results, it appears that substantial amounts of ROS are detoxified in the cell wall by extracellular peroxidases made on the ER, then transported through the Golgi system to the cell wall via vesicle trafficking to the plasma membrane. We have identified transcription factors involved in this process as well as membrane trafficking components such as AtRabA4b, AtRabA4c and PRA-1. In addition, we have identified specific peroxidases activated by GB and membrane bound NADPH oxidases that we propose are acting to shuttle electrons from the cytosol to the cell wall where they are used in ROS metabolism. The most sensitive tissues in Arabidopsis leaves with regard to photodamage are cells associated with vascular bundles. Consistent with this, the highest expression of both AtRabA4 genes and NADPH oxidases in leaves is associated with these tissues.
Vis fullstendig beskrivelse
