Membrane potential, adenylate levels and Mg2+ are interconnected via adenylate kinase equilibrium in plant cells

Abstract

Concentrations of adenylate species and free magnesium (Mg(2+)) within cells are mediated by the equilibrium governed by adenylate kinase (AK), the enzyme abundant in plants in chloroplast stroma and intermembrane spaces of chloroplasts and mitochondria. Ratios of free and Mg-bound adenylates (linked to the values of [Mg(2+)] established under AK equilibrium) can be rationalized in terms of the overall dependence of concentrations of Mg(2+) and free and Mg-bound adenylates, as well as electric potential values across the inner membranes of mitochondria and chloroplasts. The potential across the inner mitochondrial membrane, by driving adenylate translocators, equilibrates free adenylates across the inner membrane according to the Nernst equation and contributes to the ATP(total)/ADP(total) ratio in the cytosol. The ratio affects the exchange of free adenylates with chloroplasts and this, in turn, influences the value of potential across the inner chloroplast membrane. From measurements of subcellular ATP(total)/ADP(total) ratios, we suggest a method of estimating the values of potential across inner membranes of mitochondria and chloroplasts in vivo, which allows a comparison of the operation of these organelles under different physiological conditions. We discuss also how the equilibration of adenylates by AK drives adenylate transport across membranes, and establishes [Mg(2+)] in the cytosol and chloroplast stroma, maintaining the rates of photosynthesis and respiration. This provides a tool for metabolomic research, by which the determined concentrations of adenylate species could be used for computation of essential metabolic parameters in the cell and in subcellular compartments.

Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystems�I and II

“…At low [Mg 2+ ], the binding of Mg by ATP is more efficient than by ADP, and therefore an enrichment of Mg-complexed ATP compared to Mg-complexed ADP content occurs Kleczkowski 2001, 2003). As most metabolic enzymes utilizing Mg-ATP are inhibited by Mg-ADP in a competitive way, the rate of metabolic flux in roots may be even higher under Mg 2+ depletion because of a higher Mg-ATP/Mg-ADP ratio (Igamberdiev and Kleczkowski 2003). Likewise, it was previously reported in Pi-deficient bean plants that root growth was unaffected and the adenylate metabolism was altered (Rychter et al 1992).…”

Hypertonic Stress Increased Extracellular ATP Levels and the Expression of Stress-Responsive Genes inArabidopsis thalianaSeedlings

“…In the case of Mg 2þ , magnesium is important to maintain the homeostasis of the ATP level in cells. [21][22][23] Most ATP exists with magnesium when the magnesium concentration exceeds the ATP concentra- Stresses. Expression levels of stress-related genes (A, AtMAPK3; B, AtPAL1; C, AtACS6; D, AtERF4) were determined by qRT-PCR under 100 mM hypertonic stress treatments at 1, 3, and 6 h. The transcript levels were normalized using the mRNA level of Actin11 as an internal control.…”

Deficiency of a Plastidial Adenylate Kinase in Arabidopsis Results in Elevated Photosynthetic Amino Acid Biosynthesis and Enhanced Growth

“…plants (see Schlattner et al, 1993Schlattner et al, , 1994, one located in the stroma, the other tightly bound to the envelope of the intermembrane space (Murakami and Strotmann, 1978;Igamberdiev and Kleczkowski, 2003). That the loss of activity on treatment with detergent was similar in the mutant and its corresponding wild type suggests that the gene At2g37250 encodes the nonbound stromal isoform.…”