No abstract

Changes in photosynthetic pigment ratios showed that the Chlorophyll d-dominated oxyphotobacterium Acaryochloris marina was able to photoacclimate to different light regimes. Chl d per cell were higher in cultures grown under low irradiance and red or green light compared to those found when grown under high white light, but phycocyanin/Chl d and carotenoid/Chl d indices under the corresponding conditions were lower. Chl a, considered an accessory pigment in this organism, decreased respective to Chl d in low irradiance and low intensity non-white light sources. Blue diode PAM (Pulse Amplitude Modulation) fluorometry was able to be used to measure photosynthesis in Acaryochloris. Light response curves for Acaryochloris were created using both PAM and O(2) electrode. A linear relationship was found between electron transport rate (ETR), measured using a PAM fluorometer, and oxygen evolution (net and gross photosynthesis). Gross photosynthesis and ETR were directly proportional to one another. The optimum light for white light (quartz halogen) was about 206+/-51 micromol m(-2) s(-1) (PAR) (Photosynthetically Active Radiation), whereas for red light (red diodes) the optimum light was lower (109+/-27 micromol m(-2) s(-1) (PAR)). The maximum mean gross photosynthetic rate of Acaryochloris was 73+/-7 micromol mg Chl d(-1) h(-1). The gross photosynthesis/respiration ratio (P(g)/R) of Acaryochloris under optimum conditions was about 4.02+/-1.69. The implications of our findings will be discussed in relation to how photosynthesis is regulated in Acaryochloris.

The major light-harvesting protein complex containing chlorophyll (Chl) d was isolated from Acaryochloris marina thylakoid membranes. Isolation was achieved by detergent solubilisation followed by separation on 6^40% sucrose gradients using ultracentrifugation. The best Chl d yield (70%) used 0.3% dodecyl maltoside, 0.15% octyl glucoside, 0.05% zwittergent 3-14 with the detergent:total Chl d ratio around 10:1 (w/w). Characterisation of the light-harvesting pigment protein complex (lhc) involved non-denaturing electrophoresis, SDS^PAGE, absorbance and fluorescence spectroscopy. The main polypeptide in the lhc was shown to be ca. 34 kDa and to contain Chl d and Chl a, indicating that the Acaryochloris lhc is similar to that of prochlorophytes. The Chl a level varied with the culture conditions, which is consistent with previous findings. ß

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~~~~~~~~~~~~~~~~~~~~~~ ~Soluble extracts of Bradyrhizobium japonicum bacteroids from soybean root nodules showed substantial rates of NAD+ and NADP+ reduction which were malate and MnC12 dependent. Pyruvate was formed stoichiometrically and the NAD-and NADP-dependent rates were additive, indicating the presence of two malic enzymes. The NADP-dependent malic enzyme had a high affinity for malate (apparent K , = 0.1 mM) and was stimulated by ammonium. The NAD-dependent malic enzyme had a lower affinity for malate (apparent K,,, = 1.9 mM) and was stimulated by potassium and ammonium salts. The maximum velocities of the two enzymes were similar and of comparable magnitude to the activities of tricarboxylic acid cycle enzymes in the extracts. Possible roles of the malic enzymes in the metabolism of malate and succinate in bacteroids are discussed.