Photosynthetic utilization of bicarbonate in Zostera marina is reduced by inhibitors of mitochondrial ATPase and electron transport.

When Zostera marina was irradiated after a period of darkness, initiation of photosynthetic O2 evolution occurred in two phases. During a lag phase, lasting 4 to 5 min, photosynthesis was supported by a diffusive entry of CO2. Photosynthesis then rapidly increased to its full rate. Tris buffer, at a concentration of 50 mm, completely inhibited this increase without affecting CO2-supported photosynthesis during the lag phase. These results verify that the increase in photosynthesis after the lag phase depended on an activation of bicarbonate (HCO3-) utilization through acid zones generated by proton pumps located to the outer cell membrane. In similar experiments, 6.25 microm of the mitochondrial ATPase blocker oligomycin inhibited photosynthetic HCO3(-) utilization by more than 60%. Antimycin A, a selective blocker of mitochondrial electron transport, caused a similar inhibition of HCO3(-) utilization. Measurements at elevated CO2 concentrations verified that neither oligomycin nor antimycin interfered with linear photosynthetic electron transport or with CO2 fixation. Thus, a major part of the ATP used for the generation of acid zones involved in HCO3(-) utilization in Z. marina was derived from mitochondrial respiration.

Parallel changes in non-photochemical quenching properties, photosynthesis and D1 levels at sudden, prolonged irradiance exposures in Ulva fasciata Delile.

The photosynthetic response to a sudden and prolonged high irradiance exposure and following recovery at low irradiance were studied with the aim of investigating the ability to withstand and adapt to high irradiance without prior high light adaptation. When thalli of Ulva fasciata, accustomed to a low irradiance (80 micromol photons m(-2) s(-1)), were exposed to a high irradiance (1500 micromol photons m(-2) s(-1)), the D1 protein was rapidly degraded, reaching a steady-state level after 110 min. This was followed by a fast recovery when thalli were transferred to dim light. The overall ability of non-photochemical quenching of chlorophyll fluorescence decreased and levelled off at a sudden and prolonged exposure to high irradiance and followed the same trend as the D1 level with a fast recovery in dim light. Ulva had intrinsic means to acclimate rapidly to high irradiance, when non-photochemical quenching did not operate properly, by maintaining a smaller fraction of high light tolerant PSII assemblages and by maintaining a high non-photochemical quenching capacity of chlorophyll fluorescence in relation to the variable fluorescence. The overall absorption of light (400-700 nm) remained high during the period of high irradiance exposure. When Ulva were deprived of nutrients in the form of PES media the ability of non-photochemical quenching decreased at photoinhibitory conditions. The possible causes for the responses at prolonged irradiance and the mechanisms for the decrease of non-photochemical quenching are discussed, with implications for field measurements.

A screening procedure for the solubilization of chloroplast membrane proteins from the marine green macroalga Ulva lactuca using RP-HPLC-MALDI-MS.

A protocol for purification and analysis of chloroplast membrane proteins in the green macroalga Ulva lactuca has been developed, including reversed phase high performance liquid chromatography (RP-HPLC) and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Five different solvents were evaluated for extraction of membrane proteins by three methods. The highest protein yield was achieved when proteins were extracted directly from the chloroplasts using the solvent hexafluoroisopropanol. A range of proteins of increasing hydrophobicity was separated by HPLC. Analysis of both HPLC fractions and non-separated samples by MALDI-TOF-MS revealed proteins with molecular weights spanning between 1 and 376 kDa.