An acid pH in the lumen of chloroplast thylakoids is necessary in order to derive the required amount of CO2 to account for the observed rates of carbon fixation. We point out that the endosymbiotic derivation of the chloroplast from a cyanobacterium would have resulted in the lumen of the thylakoid having an acid pH. The thylakoids of cyanobacteria are continuous with the plasma membrane, resulting in the lumen of the thylakoid being open to the outside of the cell. Endosymbiosis resulted in the cyanobacterium being taken up into a food vacuole of a protozoan. The vacuole would have had an acid pH, probably around pH 5, so the endosymbiotic bacterium would have been surrounded by an environment with an acidic pH. The lumen of the thylakoids would have been at an acid pH since they were open to the exterior of the cell, and to the contents of the vacuole. and R. E. Lee, P. Kugrens.
In chloroplasts of Spinacea oleracea L., Hg2+ ions interact with some sites in the photosynthetic electron transport chain: (l) with the intermediates Z+/D+ situated in the D1 and D2 proteins and with the manganese cluster in the oxygen evolving complex which are located on the donor side of photosystem (PS) 2, (2) with the chlorophyll a dimer in the core of PS1 (P700). P700 is oxidized in the dark by HgCl2. The Hg2+ ions form organometallic complexes with amino acids contained in chloroplast proteins. and F. Šeršeň, K. Král'ová, A. Bumbálová.
From mature needles of white spruce, Picea glauca (Moench) Voss we isolated thylakoids capable of high rates of oxygen evolution. Oxygen-evolving activity of spruce thylakoids was labile in the absence of osmoticum and declined by 40 % during 1 h on ice, compared to a 9 % dechne observed in spinách thylakoids. We compared the relative activity in spruce and spinách of the oxygen evolving complex (OEC) and the reaction centre in Triton X-100 fractionated membranes prepared and stored for 20 or 240 h at 0 or -80 °C in media with different combinations of sucrose (0.3, 0.5 and 1.0 M) and two pH values (6.0 and 7.6). In membranes detergent- fractionated and stored at pH 7.6, photosystem 2 (PS2) activity (H2O -> DCIP) was sensitive to sucrose concentration of the medium. Spruce and spinách membranes prepared and stored in 0.3 M sucrose and pH 7.6, showed 22 and 48 % activity of their respective control membranes, freshly prepared in 1 M sucrose at pH 6.0. In contrast, in membranes prepared and stored at pH 6.0, PS2 activity was less sensitive to sucrose concentration: spruce and spinách membranes in 0.3 M sucrose showed 73 and 88 % (respectively) of the activity of membranes freshly prepared in 1 M sucrose. In both species, the degree of stimulation of DCIP photoreduction by diphenylcarbazide suggested minimal damage to the reaction centre (RC) except during preparation in 0.3 M sucrose, pH 7.6. Since the spruce RCs were not more labile than those of spinách, the extra sensitivity of spruce thylakoids in media of low sucrose concentration was likely due to extra lability of the OEC.
The effect of 30 % defoliation of shaded leaves in lower layers of plant was studied on activities of carbonic anhydrase (CA) and ribulose-1,5-bisphosphate carboxylase (RuBPC), leaf dry mass per unit leaf area, and plant dry mass of mustard (Brassica juncea). Removal of 30 % of leaves resulted in increased CA and RuBPC activities of leaves, and leaf and plant dry masses.