Spatial segregation of photosystems in the thylakoid membrane (lateral heterogeneity) observed in plants and in the green algae is usually considered to be absent in photoautotrophs possessing secondary plastids, such as diatoms. Contrary to this assumption, here we show that thylakoid membranes in the chloroplast of a marine diatom, Phaeodactylum tricornutum, contain large areas occupied exclusively by a supercomplex of photosystem I (PSI) and its associated Lhcr antenna. These membrane areas, hundreds of nanometers in size, comprise hundreds of tightly packed PSI-antenna complexes while lacking other components of the photosynthetic electron transport chain. Analyses of the spatial distribution of the PSI-Lhcr complexes have indicated elliptical particles, each 14 × 17 nm in diameter. On larger scales, the red-enhanced illumination exerts a significant effect on the ultrastructure of chloroplasts, creating superstacks of tens of thylakoid membranes.

• MeSH
• Chloroplasts metabolism   radiation effects   ultrastructure   MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Multiprotein Complexes metabolism   ultrastructure   MeSH
• Diatoms metabolism   radiation effects   ultrastructure   MeSH
• Light MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Microscopy, Electron, Transmission MeSH
• Thylakoids metabolism   radiation effects   ultrastructure   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH
• Multiprotein Complexes MeSH
• Light-Harvesting Protein Complexes MeSH

Red algae represent an evolutionarily important group that gave rise to the whole red clade of photosynthetic organisms. They contain a unique combination of light-harvesting systems represented by a membrane-bound antenna and by phycobilisomes situated on thylakoid membrane surfaces. So far, very little has been revealed about the mobility of their phycobilisomes and the regulation of their light-harvesting system in general. Therefore, we carried out a detailed analysis of phycobilisome dynamics in several red alga strains and compared these results with the presence (or absence) of photoprotective mechanisms. Our data conclusively prove phycobilisome mobility in two model mesophilic red alga strains, Porphyridium cruentum and Rhodella violacea. In contrast, there was almost no phycobilisome mobility in the thermophilic red alga Cyanidium caldarium that was not caused by a decrease in lipid desaturation in this extremophile. Experimental data attributed this immobility to the strong phycobilisome-photosystem interaction that highly restricted phycobilisome movement. Variations in phycobilisome mobility reflect the different ways in which light-harvesting antennae can be regulated in mesophilic and thermophilic red algae. Fluorescence changes attributed in cyanobacteria to state transitions were observed only in mesophilic P. cruentum with mobile phycobilisomes, and they were absent in the extremophilic C. caldarium with immobile phycobilisomes. We suggest that state transitions have an important regulatory function in mesophilic red algae; however, in thermophilic red algae, this process is replaced by nonphotochemical quenching.

• Publication type
• Journal Article MeSH

Photosynthetic carbon fixation by Chromophytes is one of the significant components of a carbon cycle on the Earth. Their photosynthetic apparatus is different in pigment composition from that of green plants and algae. In this work we report structural maps of photosystem I, photosystem II and light harvesting antenna complexes isolated from a soil chromophytic alga Xanthonema debile (class Xanthophyceae). Electron microscopy of negatively stained preparations followed by single particle analysis revealed that the overall structure of Xanthophytes' PSI and PSII complexes is similar to that known from higher plants or algae. Averaged top-view projections of Xanthophytes' light harvesting antenna complexes (XLH) showed two groups of particles. Smaller ones that correspond to a trimeric form of XLH, bigger particles resemble higher oligomeric form of XLH.

• MeSH
• Chlorophyll analysis   metabolism   MeSH
• Microscopy, Electron MeSH
• Spectrometry, Fluorescence MeSH
• Photosynthesis MeSH
• Photosystem I Protein Complex chemistry   ultrastructure   MeSH
• Photosystem II Protein Complex chemistry   ultrastructure   MeSH
• Stramenopiles chemistry   ultrastructure   MeSH
• Protein Multimerization MeSH
• Soil MeSH
• Soil Microbiology MeSH
• Light-Harvesting Protein Complexes chemistry   ultrastructure   MeSH
• Thylakoids chemistry   MeSH
• Chromatography, High Pressure Liquid MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chlorophyll MeSH
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH
• fucoxanthin-, chlorophyll a-c-containing protein MeSH Browser
• Soil MeSH
• Light-Harvesting Protein Complexes MeSH