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Evidence of a low stromal magnesium concentration in intact chloroplasts in the dark studies with the ionophore a 23187

, : Evidence of a low stromal magnesium concentration in intact chloroplasts in the dark studies with the ionophore a 23187. Plant Physiology (Rockville) 67(5): 985-989

The loss of Mg2+ upon the addition of the ionophore A23187 in the dark was prevented by less than 0.1 mM MgCl2 with intact chloroplasts [from spinach, Spinacia oleracea] suspended in a sorbitol medium but required 1-3 mM MgCl2 if the chloroplasts were in a K+-gluconate medium. Measurements of stromal pH in the dark indicated that, in the K+-gluconate medium, the stromal pH is nearly the same as that of the medium; in the sorbitol medium it is much more acidic as reported previously. The free Mg2+ concentration in the stroma in the dark is between 1 and 3 mM. Other experiments on the inhibition by A23187 of CO2 fixation in the light and in a system capable of catalyzing CO2 fixation in the dark and on the Mg2+ binding properties of thylakoid membranes, are consistent with this conclusion. Light-induced Mg2+ concentration changes may occur in the stroma that are important in the light-dark regulation of CO2 fixation.

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Related references

Portis, A.R., 1981: Evidence of a Low Stromal Mg Concentration in Intact Chloroplasts in the Dark: I. STUDIES WITH THE IONOPHORE A23187. The loss of Mg(2+) upon the addition of the ionophore A23187 in the dark was prevented by less than 0.1 millimolar MgCl(2) with intact chloroplasts suspended in a sorbitol medium, but required 1 to 3 millimolar MgCl(2) if the chloroplasts were in...

Portis, A.Jr, 1981: Evidence of a low stromal Mg2+ concentration in intact chloroplasts in the dark. I. Studies with the ionophore A23187. Plant physiology 67(5): 985-989

Portis A.R., 1980: Evidence that the stromal magnesium ii concentration of intact chloroplasts is low in the dark. Plant Physiology (Rockville) 65(6 SUPPL): 69

Miginiac-Maslow, M.; Hoarau, A., 1977: The effect of the ionophore a 23187 on magnesium ion and calcium ion movements and internal ph of isolated intact chloroplasts. The kinetics of the Mg and Ca efflux from intact spinach [Spinacia oleracea] chloroplasts were measured in the presence of the ionophore A23187 [2-[3.beta.,9.alpha.,11.beta.-trimethyl)-8-(2-pyrrolecarboxymethyl)-1,7-dioxaspiro [6.6]undecyl-2.beta....

Flatman P.; Lew U.L., 1977: Use of ionophore a 23187 to measure and to control free and bound cytoplasmic magnesium in intact red cells. Nature (London) 267(5609): 360-362

Ben-Hayyim, G., 1978: Magnesium ion translocation across the thylakoid membrane studies using the ionophore a 23187. The degree of the light-dependent Mg2+ efflux across the thylakoid membrane [lettuce] is a function of pH. There is a considerable efflux at pH 7.2 which decreases to a negligible amount at pH 8.6. This conclusion is derived from studies using the...

Portis, A.R.Jr ; Heldt, H.W., 1976: Light dependent changes of the magnesium concentration in the stroma in relation to the magnesium dependency of carbon di oxide fixation in intact chloroplasts. Light-dependent changes of the Mg2+ content of thylakoid membranes [Spinacia oleracea] were measured at pH 8.0 and compared with earlier measurements at pH 6.6. In a NaCl and KCl medium, the light-dependent decrease in the Mg2+ content of the thyl...

Pfeiffer, D.R.; Lardy, H.A., 1976: Ionophore a 23187 the effect of proton concentration on complex formation with divalent and monovalent cations and the demonstration of potassium ion transport in mitochondria mediated by a 23187. The 2 phase extraction technique was used to study the equilibrium between A23187 (C29H37N3O6), metal cations and H+. Under these conditions the ionophore forms charge neutral isostoichiometric complexes with divalent cations in which both carboxy...

Boag S.; Agostino A.; Furbank R.T.; Hatch M.D., 1989: Effects of external magnesium and ph on the photosynthetic activities and stromal ph of intact chloroplasts isolated fron c 4 plants. Exogenous Mg2+ inhibited PGA- and OAA-dependent photosynthetic O2 evolution by isolated mesophyll chloroplasts from Zea mays and also HCO3--dependent O2 evolution by chloroplasts from Panicum miliaceum bundle sheath cells. Inhibition of 50-75% was...

Sokolove P.M.; Marsho T.V., 1979: Effect of stromal potassium ion concentration on electron transport in intact chloroplasts. Plant Physiology (Rockville) 63(5 SUPPL): 28