Larkum, AWD 1972, 'Frond Structure and Growth in Laminaria Hyperborea', Journal of the Marine Biological Association of the United Kingdom, vol. 52, no. 2, pp. 405-418.
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On rocky shores of the British Isles and neighbouring regions of the North Atlantic coastline, the sporophyte of Laminaria hyperborea (Gunn) Foslie is the dominant member of most sublittoral algal communities. The bathymetric distribution, like the geographical distribution, is extensive; L. hyperborea is often dominant from extreme low water level of spring tides (E.L.W.S.) to depths of up to 32 m. The great changes in environment encountered by this species over this wide range of distribution would suggest a highly adaptable organism. Changes in size, rate of growth and growth pattern have indeed been recorded between plants at different latitudes and different depths. Plants from northerly waters generally are much larger with longer stipes and have a greater frond area (Kain, 1962; Bellamy & Whittick, 1968; Greenhager, 1958), although Kain (1963, 1967) points out that this is often due to greater longevity of individuals rather than greater growth rates. Increasing depth affects the density of distribution; the typical L. hyperborea forest becomes more sparse until an open community, called 'the park' when first recorded by Kitching in 1941, replaces the forest at about 15 m. The plants in the open community are smaller than those in the forest and have shorter stipes (Kain, 1962, 1966, and observations described in this communication). However, despite these changes in growth,, almost no morphological variation had been recorded prior to the present investigation. More recently there has been a report of a form L. hyperborea f. cucullata (Svendsen & Kain) from deep water and waters not subject to water movement with thin enlarged fronds and short stipes (Svendsen & Kain, 1971; Kain, 1971).
Larkum, AWD & Bonner, WD 1972, 'Light-induced absorbance changes of cytochromes and other pigments in pea chloroplasts and chloroplast fragments', Archives of Biochemistry and Biophysics, vol. 153, no. 1, pp. 249-257.
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In high-salt intact chloroplasts the reversible cytochrome f photo-oxidation is relatively insensitive to 3,4(dichlorophenyl) 1,1′-dimethylurea (DCMU) and is accompanied by changes in the region 560 to 572 nm which are inhibited by n-heptyl-4-hydroxyquinoline-N-oxide and antimycin A. These results indicate a cyclic electron-transport system around photosystem I which may involve chtochrome b6. In intact chloroplasts (low-salt) treated with medium concentrations (1 μm) of carbonylcyanide p-trifluoromethoxy phenylhydrazone (FCCP), cytochrome b-559 is photo-oxidized in far-red light. This also occurs to a small extent with high concentrations of antimycin A and in aged chloroplast fragments. It is not found in chloroplasts uncoupled by valinomycin plus nigericin (or plus NH4Cl). These results are taken to mean that FCCP induces a secondary effect as well as its primary uncoupling action, causing structural changes which result in an unnatural connection of cytochrome b-559 to photosystem I. Other effects of FCCP are also discussed. Valinomycin alone, caused marked changes in the light-induced responses of cytochrome f and in the region of the b cytochromes but these were substantially different from the effect in combination with nigericin (or NH4Cl). The results are discussed in terms of a possible effect of an electrical potential difference across the functional photosynthetic membrane. © 1972.
Larkum, AWD & Bonner, WD 1972, 'Light-induced absorbance changes of cytochromes and other pigments in pea chloroplasts and chloroplast fragments', Archives of Biochemistry and Biophysics, vol. 153, no. 1, pp. 241-248.
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Light-induced spectral changes in the region 540 to 580 nm were studied by means of dual-wavelength differential spectrophotometry and by a Q-switched ruby laser flash technique in intact chloroplasts, swollen chloroplasts, and chloroplast fragments. In intact chloroplasts the major spectral components are attributed to cytochrome f (photo-oxidized), an unknown pigment with a broad band (decrease in absorbance) centered around 572 nm, and possibly a b-type cytochrome (photo-oxidized). In swollen chloroplasts and chloroplast fragments the photo-oxidation of cytochrome f is modified, cytochrome b6 is photoreduced, and the P-572 response is diminished. The changeover from the intact to the swollen response is brought about by the addition to the suspension medium of certain cations of which sodium, with an effect beginning at about 10 mm, is the most potent. Laser flashes onto dense suspensions of high-salt chloroplasts produced fast (t 1 2, 300 μsec) oxidation of cytochrome f, even in the absence of ascorbate and slower (t 1 2, 5 msec) reduction of a b-type cytochrome. However, it is suspected that cations leaking from the chloroplasts in these dense suspensions modified the cytochrome responses. © 1972.
Larkum, AWD & Bonner, WD 1972, 'Light-induced absorbance changes of P518 in intact chloroplasts', Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 256, no. 2, pp. 396-408.
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The light-induced absorbance change centred at 518 nm (P518 response) is 20-30-fold greater in intact chloroplasts than in swollen chloroplasts. The various characteristics of this large P518 response, including induction effects and chromatic transients, were studied. 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU) (2 μM) strongly inhibited the response and the uncoupler, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, abolished it. Other uncouplers such as NH4Cl, methylamine, atebrin and nigericin were without effect. Valinomycin inhibited the response and valinomycin in combination with NH4Cl or nigericin abolished it. In the presence of DCMU the P518 response could be restored with 2,6-dichlorophenolindophenol (+ ascorbate) but not with N,N,N′,N′-tetramethyl-p-phenylenediamine (+ ascorbate). The results support a correlation between the P518 response and a membrane potential across the functional photosynthetic membrane, which may be produced by two mechanisms, one fast and one slow. It is suggested that an oxidation-reduction loop between the two photosystems, forms a significant component of the slower mechanism. © 1972.
Larkum, AWD & Bonner, WD 1972, 'Light-induced oxidation of cytochrome f in isolated chloroplasts of Pisum sativum', Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 256, no. 2, pp. 385-395.
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Photooxidation of cytochrome f has been studied in a number of types of chloroplast preparations from pea leaves. On the basis of the dark reversibility after far-red illumination, the effect of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea and other criteria, it is possible to distinguish three basic types of response according to the type of preparation: (a) high-salt chloroplasts; (b) intact chloroplasts and unswollen chloroplast fragments, and (c) swollen chloroplasts and swollen chloroplast fragments. Types a and b were further characterised by relatively high oxidation of cytochrome f in red light. It is suggested that in type b preparations photooxidation of cytochrome f can be explained by (i) a large component of electron flow through an intermediate pathway between the two photosystems in which a large redox pool is linked through a coupling site to cytochrome f, and (ii) a small component of endogenous cyclic electron flow involving cytochrome f. In high-salt chloroplasts there may be in addition a pool of low molecular weight substance capable of reducing cytochrome f in the dark. © 1972.
Larkum, AWD & Bonner, WD 1972, 'The effect of artificial electron donor and acceptor systems on light-induced absorbance responses of cytochromes f and other pigments in intact chloroplasts', Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 267, no. 1, pp. 149-159.
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An investigation has been made into the effect of low concentrations of 2,6-dichlorophenolindophenol (DCIP) and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), in the presence of ascorbate, on light-induced absorbance changes in the α-band region of cytochrome f and b-type cytochromes. Strong photo-oxidation of cytochrome f occurred with DCIP, in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) (2 μM), but not with TMPD. However, with TMPD a large light-induced absorbance increase occurred due to a broad band centred at 566 nm. With DCIP, the uncoupler, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP), in conjunction with the electron acceptor 1,1′-ethylene-2,2′-bipyridylium dibromide (diquat), inhibited the cytochrome f response and an absorbance increase in the 560-575 nm region occurred similar to that with TMPD. Neither FCCP nor diquat had any great effect on the TMPD system. The results support a pathway of electron transport between the two photosystems in which (a) DCIP-ascorbate interacts with an intermediate on the Photosystem II side of a coupling site; (b) TMPD-ascorbate interacts after this site, and (c) cytochrome f is located on the Photosystem I side of the site. © 1972.
