Giddings TH, Staehelin LA. Changes in thylakoid structure associated with the differentiation of heterocysts in the cyanobacterium, Anabaena cylindrica.
BIOCHIMICA ET BIOPHYSICA ACTA 1979;
546:373-82. [PMID:
110342 DOI:
10.1016/0005-2728(79)90074-4]
[Citation(s) in RCA: 38] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The thylakoids of vegetative cells of the filamentous cyanobacterium, Anabaena cylindrica, are capable of oxygen-evolving photosynthesis and contain both Photosystems I and II (PSI and PSII). The heterocysts, cells specialized for nitrogen fixation, do not produce oxygen and lack Photosystem II activity, the major accessory pigments, and perhaps the chlorophyll a associated with PSII. Freeze-fracture replicas of vegetative cells and of heterocysts reveal differences in the structure of the thylakoids. A histogram of particle sizes on the exoplasmic fracture face (E-face, EF) of vegetative cell thylakoids has two major peaks, at 75 and 100 A. The corresponding histogram for heterocyst thylakoids lacks the 100 A size class, but has a very large peak at about 55 A with a shoulder at 75 A. Histograms of protoplasmic fracture face (P-face, PF) particle diameters show single broad peaks, the mean diameter being 71 A for vegetative cells and 64 A for heterocysts. The thylakoids of both cell types have about 5600 particles/micrometers2 on the P-face. On the E-face, the density drops from 939 particles/micrometers2 on vegetative cell thylakoids to 715 particles/micrometers2 on heterocyst thylakoids. The data suggest that the 100 A E-face particle of vegetative cell thylakoids is a PSII complex. The 55 A EF particle of heterocysts may be part of the nitrogenase complex or a remnant of the PSII complex. The role of the 75 A EF particle is unknown. Other functions localized on cyanobacterial thylakoids, such as respiration and hydrogenase activity, must be considered when interpreting the structure of these complex thylakoids.
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