The Language of Reactive Oxygen Species Signaling in Plants

Figure 4

Thiol-disulphide, plastoquinone-plastoquinol interactions in chloroplast leading to activation of enzymes and redox signaling. In chloroplasts, reduced ferridoxin (Fd_red) reduces the regulatory protein thioredoxin (T_rx) via enzyme ferridoxin-thioredoxin reductase (FTR). This, in turn, activates chloroplastic enzymes. Molecular oxygen is a natural oxidant that reverses this activation via formation of superoxide (O_2•−) and H₂O₂·H₂O₂ is diffusive and moderately stable oxidant and inactivates these enzymes. H₂O₂ production particularly from the electron flow of Z-scheme of photosynthesis is exacerbated during stress. Ascorbate-glutathione cycle, on the other hand, destroys H₂O₂. Turning over of GSH pool is central to the processes. The accumulation of H₂O₂ together with changes in thiodisulfide, plastoquinone-plastoquinol ratio of cell, provides the redox signals leading to changes in gene expression.