Neutral invertase, hexokinase and mitochondrial ROS homeostasis

Abstract

Alkaline/neutral invertases (A/N- Invs) are unique to plants and photosynthetic bacteria. Although con- siderable advances have been made in our understanding of sucrose metabolic enzymes in plants, the function of A/N- Invs remained puzzling. In a recent study, we have analyzed the subcellullar localization of a cytosolic (At-A/N- InvG, At1g35580) and a mitochondrial (At-A/N-InvA, At1g56560) Arabidopsis A/N-Inv. Unexpectedly, At-A/N-InvA knockout plants showed a more severe growth defect than At-A/N-InvG knock- out plants and a link between the two A/N-Invs and oxidative stress defense was found. Overexpression of At-A/N- InvA and At-A/N-InvG in leaf mesophyll protoplasts reduced the activity of the ascorbate peroxidase 2 (APX2) promoter, that was stimulated by hydrogen perox- ide and abscisic acid. It is discussed here how sugars and ascorbate might con- tribute to mitochondrial reactive oxygen species homeostasis. We hypothesize that both mitochondrial and cytosolic A/N- Invs and mitochondria-associated hexo- kinases are key mediators, integrating metabolic and sugar signaling processes.