High Levels of Malic Enzyme Activities in Vicia faba L. Epidermal Tissue

Abstract

ABSTRACT

Rethinking Guard Cell Metabolism

“…When stomatal closure was accelerated by ABA in isolated C. communis epidermis, the guard cells lost most of the labeled malate to the medium (Dittrich and Raschke, 1977a), suggesting that gluconeogenesis may not be fast enough to remove all malate when the loss of turgor occurs quickly. By contrast, Schnabl (1981) and Outlaw et al (1981a) failed to detect PEPCK activity in guard cells, questioning the decarboxylation of malate via this carboxykinase. The authors instead found high levels of NAD-ME and NADP-ME activity, suggesting that malate is metabolized directly to pyruvate by this enzyme and subsequently to PEP, potentially by pyruvate, orthophosphate dikinase (Outlaw et al, 1981a;Schnabl, 1981).…”

“…By contrast, Schnabl (1981) and Outlaw et al (1981a) failed to detect PEPCK activity in guard cells, questioning the decarboxylation of malate via this carboxykinase. The authors instead found high levels of NAD-ME and NADP-ME activity, suggesting that malate is metabolized directly to pyruvate by this enzyme and subsequently to PEP, potentially by pyruvate, orthophosphate dikinase (Outlaw et al, 1981a;Schnabl, 1981). NADP-ME also is expressed in Arabidopsis guard cells (Wheeler et al, 2005) and was implicated in the mechanism of stomatal closure when NADP-ME was overexpressed in tobacco (Nicotiana tabacum) plants (Laporte et al, 2002).…”

Roles of Ion Channels in Initiation of Signal Transduction in Higher Plants.

“…Analysis of the effects of the ABll phosphatase on these individual components may reveal the physiological function and the location within the signaling cascade of ABI1 and should allow refinements in our understanding of direct regulation of ion channels during stomatal closure. Analysis of the intermediate signaling events should give us insights into the unidentified links between plasma membrane and vacuolar membrane signaling discussed here and links to the important metabolic conversion of malate to starch during stomatal closing (Outlaw et al, 1981).…”

Strong regulation of slow anion channels and abscisic acid signaling in guard cells by phosphorylation and dephosphorylation events.

“…Guard cells, which pairwise surround stomatal pores, are the active elements controlling the stomatal pore aperture. Stomatal closing is mediated by potassium and anion efflux from guard cells and parallel malate metabolism (2,3). The plant hormone abscisic acid (ABA) is synthesized in response to drought and triggers the signaling cascade in guard cells leading to stomatal closure (4,5).…”