FIG. 4.

The photosynthesis - respiration - TCA-cycle - ascorbate network. The electron flux through the photosynthetic ETC enhances the mitochondrial cytochrome c, AOX pathways, and the biosynthesis of ascorbate. Furthermore, the activity of AOX itself enhances the biosynthetic rate of ascorbate. Since ascorbate is synthesized tightly coupled to the mitochondrial ETC, the oxidation of L-galactono-1,4-lactone to ascorbate provides electrons to complex IV in the case of the inhibition of TCA cycle. The reductant overload of the respiration can be reduced by light inhibition of TCA cycle and TCA cycle-linked respiration during light conditions. The inhibition of TCA cycle (by genetic approaches) accompanies by the dramatic increase in ascorbate levels. Ascorbate can elevate the intensity of photosynthesis by its multiple roles in photoprotection. Any changes in either of these elements of this network influence the others. AOX, alternative oxidase. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars