Hatcher, AI & Larkum, AWD 1982, 'The effects of short term exposure to bass strait crude oil and corexit 8667 on benthic community metabolism in Posidonia australis Hook.f. dominated microcosms', Aquatic Botany, vol. 12, no. C, pp. 219-227.
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Microcosms consisting of a sublittoral seagrass meadow from Botany Bay, N.S.W. were maintained in aquaria in a controlled environment room from March to August 1979. Oxygen production and consumption in the microcosms and leaf turnover of the seagrass, Posidonia australis Hook.f. were measured before, during and after a 7-day treatment in June with Bass Strait crude oil and the dispersant Corexit 8667. Four microcosms received oil and two of these received dispersant. The leaf turnover of P. australis was not significantly affected by the addition of oil and dispersant. Photosynthetic oxygen production decreased and respiration incresed in the microcosms during treatment. In August, 40 days after treatment, oxygen production rates and P/R ratios in the oil-treated microcosms were higher thatn rates measured before treatment. The oil-and-dispersant-treated microcosms did not show this trend. The results of this study indicate that a more severe stress is placed on the P. australis dominated benthic community by oil and dispersant than by oil alone. © 1982.
Larkum, AWD & Anderson, JM 1982, 'The reconstitution of a Photosystem II protein complex, P-700-chlorophyll a-protein complex and light-harvesting chlorophyll ab-protein', Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 679, no. 3, pp. 410-421.
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A Photosystem II reaction centre protein complex was extracted from spinach chloroplasts using digitonin. This complex showed (i) high rates of dichloroindophenol and ferricyanide reduction in the presence of suitable donors, (ii) low-temperature fluorescence at 685 nm with a variable shoulder at 695 nm which increased as the complex aggregated due to depletion of digitonin and (iii) four major polypeptides of 47, 39, 31 and 6 kDa on dissociating polyacrylamide gels. The Photosystem II protein complex, together woth the P-700-chlorophylla protein complex and light-harvesting chlorophyll a b-protein complex (LHCP) also isolated using digitonin, were reconstituted with lipids from spinach chloroplasts to form proteoliposomes. The low-temperature (77 K) fluorescence properties of the various proteoliposomes were analysed. The F685 F695 ratios of the Photosystem II reaction centre protein complex-liposomes decreased as the lipid to protein ratios were increased. The F681 F697 ratios of LHCP-liposomes were found to behave similarly. Light excitation of chlorophyll b at 475 nm stimulated emission from both the Photosystem II protein complex (F685 and F695) and the P-700-chlorophyll a-protein complex (F735) when LHCP was reconstituted with either of these complexes, demonstrating energy transfer between LHCP and PS I or II complexes in liposomes. No evidence was found for energy transfer from the PS II complex to the P-700-chlorophyll a-protein complex reconstituted in the same proteoliposome preparation. Proteoliposome preparations containing all three chlorophyll-protein complexes showed fluorescence emission at 685, 700 and 735 nm. © 1982.
RITCHIE, RJ & LARKUM, AWD 1982, 'Cation Exchange Properties of the Cell Walls ofEnteromorpha intestinalis(L.) Link. (Ulvales, Chlorophyta', Journal of Experimental Botany, vol. 33, no. 1, pp. 125-139.
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The cell wall of Enteromorpha intestinalis (a marine alga) has been found to behave as a weakly cross-linked cation exchanger in NaCl solutions from 0.1-1020 mMolal (0.1-1000 mMolar). Anion adsorption could be described by Freundlich isotherms over this concentration range. The large anion, inulin carboxylate, was found to be a tracer of the anion free space of plant tissues only in salt solutions above 10 mMolal. The cell wall of Enteromorpha has a cation exchange capacity of about 2500 μ mol g-1 dry wt. (Na+ form). The cell wallvolume is a complex function of pH and the NaCl concentration. As a result, the cation exchange capacity is only predictable on a dry weight basis. The fixed negative charges of the cell wall have a pKa of2 in situ and 1.75 in vitro, and seem to be a mixture of sulphate and carboxyl sugar esters.The applicability of the Donnan equation to plant cell walls is discussed. Interpretation of the cell wall as a single thermodynamic phase is shown to be inappropriate. A large proportion of the cell wall solution is unaffected by the fixed anions. © 1982 Oxford University Press.
RITCHIE, RJ & LARKUM, AWD 1982, 'Ion Exchange Fluxes of the Cell Walls ofEnteromorpha intestinalis(L. ) Link (Ulvales, Chlorophyta)', Journal of Experimental Botany, vol. 33, no. 1, pp. 140-153.
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The 22Na+ and 36CI- exchange properties of the cell walls of Enteromorpha intestinalis (L. ) Link in simple monovalent salt systems have been shown to be similar to a 'leaky' cation exchange membrane rather than a homogeneous membrane. The ion exchange properties of the cation and anion cell wall contents are what would be expected of a cation exchange membrane i. e. anion exchange is strongly dependent on the bathing electrolyte concentration and becomes very slow in dilute salt. This would lead to the cell wall becoming a barrier to anions in dilute salt. However, measurements of the anion flux across cell walls in living and dead tissues show that anion exchange across cell walls is facilitated by pores. The exchange kinetics of the bulk of the cell wall anions does not limit the anion flux across cell walls of this plant. It is concluded that the cell wall is not a critical limitation to plasmalemma fluxes of the living plant and that unstirred layers are more important than cell walls in the measurement of anion flux rates. © 1982 Oxford University Press.
