Photosystem I (PSI) is a multi-subunit integral pigment-protein complex that performs light-driven electron transfer from plastocyanin to ferredoxin in the thylakoid membrane of oxygenic photoautotrophs. In order to achieve the optimal photosynthetic performance under ambient irradiance, the absorption cross section of PSI is extended by means of peripheral antenna complexes. In eukaryotes, this role is played mostly by the pigment-protein complexes of the LHC family. The structure of the PSI-antenna supercomplexes has been relatively well understood in organisms harboring the primary plastid: red algae, green algae and plants. The secondary endosymbiotic algae, despite their major ecological importance, have so far received less attention. Here we report a detailed structural analysis of the antenna-PSI association in the stramenopile alga Nannochloropsis oceanica (Eustigmatophyceae). Several types of PSI-antenna assemblies are identified allowing for identification of antenna docking sites on the PSI core. Instances of departure of the stramenopile system from the red algal model of PSI-Lhcr structure are recorded, and evolutionary implications of these observations are discussed.

• Keywords
• Electron microscopy, Light-harvesting complex, Nannochloropsis, Photosystem I, Stramenopila,
• MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Plastids metabolism   MeSH
• Rhodophyta metabolism   MeSH
• Spectrophotometry, Ultraviolet MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Photosystem I Protein Complex 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