Cox, GC, Hiller, RG & Larkum, AWD 1985, 'An unusual cyanophyte, containing phycourobilin and symbiotic with ascidians and sponges', Marine Biology, vol. 89, no. 2, pp. 149-163.
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A study was made of the pigment composition and ultrastructure of a unicellular cyanophyte living in symbiosis with colonial didemnid ascidians and encrusting sponges collected from the southern end of the Great Barrier Reef, Australia, in 1981-1984. The ascidians were Trididemnum tegulum Kott and T. clinides. Kott; the sponges were Prianos aff. melanos de Laubenfels, Spirastrella aff. decumbens Ridley and an unidentified brown fleshy sponge (BFS). This cyanophyte seems to be identical with Synechocystis trididemni Lafargue et Duclaux. A phycoerythrin containing both phycourobilin and phycoerythrobilin chromophores was shown to be present; the urobilin was carried on α and β subunits, no γ subunit was found. A second phycoerythrin possessing only erythrobilin chromophores was also present. In thin-sections the cells showed no central DNA-containing nucleoid, and an unusual thylakoid arrangement with some thylakoids having greatly expanded lumens forming pseudo-vacuoles in the centre of the cell. Freeze-fracture showed 11 to 12 nm particles on both PF (protoplasmic face) and EF (exoplasmic face) faces of thylakoids. In many ways, the ultrastructure resembled that of the chlorophyll-b containing prokaryote Prochloron spp. © 1985 Springer-Verlag.
Hiller, RG & Larkum, AWD 1985, 'The chlorophyll-protein complexes of Prochloron sp. (Prochlorophyta)', BBA - Bioenergetics, vol. 806, no. 1, pp. 107-115.
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Chlorophyll-protein complexes have been isolated from Prochloron sp. by SDS-polyacrylamide gel electrophoresis and SDS-sucrose-gradient centrifugation. Complexes associated with Photosystem I have significant amounts of chlorophyll b and a principle polypeptide of 70 kDa. The largest Photosystem I complex had an Mr of more than 300 000 kDa, a chlorophyll a b ratio of 3.8 and a chlorophyll/P-700 ratio of approx. 100. Complexes enriched in chlorophyll b showed reduced electrophoretic mobility compared to spinach LHCP3, a higher Chl a b ratio (approx. 2.4) and had a principle polypeptide of 34 kDa. Neither the 34 kDa or any other polypeptide showed cross-reactivity with antibodies to spinach light-harvesting chlorophyll a b protein in a Western blot test. © 1985.
Ritchie, RJ & Larkum, AWD 1985, 'Potassium transport in Enteromorpha intestinalis (L.) link: II. Effects of medium composition and metabolic inhibitors', Journal of Experimental Botany, vol. 36, no. 3, pp. 394-412.
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In springwater (25.5 mol m-3 Cl-, 20.4 mol m-3 Na+, 0.14 mol m-3 K+) Enteromorpha intestinalis could not survive for more than a few weeks unless provided with 0.5 mol m-3 K+ in the medium or alternatively exposed to seawater for 1 day per week. Maintenance of a cytoplasmic K+ level of about 200 mol m-3 is critical for the maintenance of normal metabolic activity. Net gains of intracellular K+ occurred when the plants were transferred from low-salinity to seawater; conversely large net losses occurred when plants were transferred from seawater to springwater. These two processes were not simply the reverse of one another; net gain of K+ involved a large increase in the tracer flux both into and out of the cell but net loss of K+ virtually halted the tracer flux into the cell. Any injury incurred by rapid salinity changes was short-lived; plants were rapidly able to adjust intracellular [K1.K+). K+(or to some extent Rb+) was found to be necessary in the efflux medium for 42K+ exchange to occur. The osmotic concentration of the medium was also important but extracellular Na+ and Cl-concentrations were not critical. K+ influx and efflux in both springwater and seawater were largely independent of light and were sensitive in varying degrees to a range of common metabolic inhibitors and uncouplers. The results are best explained by the presence of an active K+ influx, generated by an ATP-dependent K+ pump at the plasmalemma. © 1985 Oxford University Press.
Ritchie, RJ & Larkum, AWD 1985, 'Potassium transport in Enteromorpha intestinalis (L.) link: Measurement OF intracellular k+, EXCHANGE fluxes AND thermodynamic analysis', Journal of Experimental Botany, vol. 36, no. 1, pp. 63-78.
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Potassium transport has been studied in the marine euryhaline alga, Enteromorpha intestimlis cultured in seawater and in low-salinity medium (Artificial Cape Banks Spring Water, ACBSW; 25·5 mol m-3 Cl-, 20·4 mol m-3 Na+, 0·5 mol m-3 K+). K+ fluxes were measured using 42K+ and 86Rb+ although 86Rb+ does not act as an efficient K+ analogue in this plant. 42K+ experiments on seawater plants typically exhibited a single protoplasmic exchange phase whereas 86Rb+ exhibited two exchange phases. Compartmental analysis of 86Rb+ efflux experiments on seawater-grown Enteromorpha plants were used to deduce the intracellular partition of K+ between the cytoplasm (279±38 mMolal) and vacuole (405±68 mMolal). The plasmalemma K+ flux in plants in seawater was greater in the light than in the dark (563±108 nmol m-2 s-1 versus 389±66·7 nmol m-2 s-1). In low-salinity plants, separate cytoplasmic and vacuolar exchange phases were apparent. Analysis of 42K+ efflux experiments on low-salinity plants yielded a cytoplasmic K+ of 222±38 mMolal and a vacuolar K+ of 82±11 mMolal. The plasmalemma and tonoplast flux was 23±4·5 nmol m-2 s-1.The Nernst equation showed that, although K+ was close to electrochemical equilibrium, active accumulation of K+ across the plasmalemma occurred in plants in seawater and ACBSW both in the light and dark. K+ was also actively transported inwards across the tonoplast in low-salinity plants. The electrochemical potential for K+ across the plasmalemma ranged from 2·41±0·60 kJ mol-1 in plants grown in seawater in the light to 5·79±0·87 kJ mol-1 for plants in ACBSW in the light. Although K+ is close to electrochemical equilibrium, the flux of K+ in plants in both seawater and ACBSW media is high, hence the power consumption of K+ transport is high. The permeability of K+ (PK+) was significantly higher in the light than in the dark in plants in seawater (about 7·0 versus 2·5 nm s-1) but in plants in low-salinity (ACBSW) medium the permeability was independent of l...