pH Changes in the Cytoplasm of the Blue-Green Alga Anacystis nidulans Caused by Light-dependent Proton Flux into the Thylakoid Space

Abstract

The pH in the cytoplasmic and thylakoid spaces of the blue-green alga, Anacystis nidulans, has been determined in the light and in the dark by uptake of 5,5-dimethyloxazolidine-2,4-dione and methylamine into the sucrose-impermeable 3H-H20 space, as measured by silicon layer filtering centrifugation.Illumination causes an linization in the cytoplasm which is accompanied by an The principle of the method of pH measurement, utilizing the distribution of DMO and methylamine inside and outside the cell, has been described elsewhere (3). The intracellular space was defined as the sucrose-impermeable 3H-H20 space (2). The thylakoid space was assumed to be 7% of the intracellular space; this value is based on a planimetric estimation by Allen (1). There are two factors that complicate the pH measurement with Anacystis. First, it is possible that methylamine could undergo metabolic changes. For this reason, the substance was not incubated for longer than 2 min. During this period of time, any errors due to metabolic conversion were within the standard deviation of the method. Any change of the pH or redistribution of methylamine between inside and outside the cell caused by light-dark alterations occurs within 40 sec. Secondly, the accuracy of the absolute pH values may be affected to a certain extent by the influence of the several layers of the cell wall on the sucrose space.A linear relationship between the 5,5-dimethyloxazolidine-2,4-dione anion concentration in the medium and in the large sucrose-impermeable 3H-H20 space was noted over a large concentration range (0.1-6.0 mm 5,5-dimethyloxazolidine-2,4-dione); that is, the results of the pH measurement in the cytoplasm are independent of the DMO concentration. With methylamine, such a linearity exists only when the methylamine concentration is below 70 AM, almost certainly as a result of the uncoupling effect of methylamine at higher concentrations. The concentration of methylamine employed for pH measurement in the thylakoid space was, therefore, 70 A.M. RESULTS AND DISCUSSIONValues for the pH in the cytoplasmic and in the thylakoid space in the light and in the dark are given in Table I

pH determines the energetic efficiency of the cyanobacterial CO 2 concentrating mechanism

“…S8). This is expected because the photosynthetic light reactions pump H + from the cytosol into the thylakoid lumen (44) and the pH values are consistent with previous measurements of cytosolic pH in cyanobacteria (45)(46)(47)(48). The pH in the light coincides well with our prediction of an optimal cytosolic pH range for carbon-fixing cyanobacteria.…”

“…As such, it is unclear whether the prevailing pH is an adaptation to the CCM or the CCM adapted to the pH. Indeed, active photosynthesis requires pumping of protons into the thylakoid and so it is sensible that the pH should increase in the stroma/ cytoplasm (45,58). We simply note that these explanations are not mutually exclusive (i.e., that it is possible that a pH ≈8 results from photosynthetic proton pumping and also optimizes CCM efficiency).…”

Inorganic Carbon Accumulation and Photosynthesis in a Blue-green Alga as a Function of External pH

“…5) that Coccochloris is able to regulate the internal pH adequately in the light over the external pH range of 7.0 to 10.0, which corresponds to the optimal pH range for photosynthesis. The estimates of internal pH over this external pH range, both in the light and the dark, are similar to those determined for another unicellular blue-green alga Anacystis nidulans (12). At pH values below 7.0 and above 9.5, however, the intracellular pH of Coccochloris in the light is significantly influenced by the external pH and it is over these external pH ranges that the rate ofphotosynthesis is substantially reduced, particularly below pH 7.0.…”

The Minimal CO2-Concentrating Mechanism of Prochlorococcus spp. MED4 Is Effective and Efficient

“…3C). The CO 2 concentration in the carboxysome was calculated from the intracellular C i concentration by assuming that the cytoplasmic pH was 7.35 (Falkner et al, 1976;Kallas and Dahlquist, 1981;Belkin et al, 1987), that the carboxysome pH is the same as that of the cytoplasm (Menon et al, 2010), and that CO 2 and HCO 3 2 are in equilibrium in the carboxysome. At seawater C i (2 mM), the internal C i pool was approximately 15 mM and the estimated CO 2 concentration in the carboxysome was approximately 500 mM.…”