Occurrence of the 32-kDa QB-binding protein of photosystem II in vegetative cells, heterocysts and akinetes ofAzolla carotiniana cyanobionts

Abstract

Transmission electron microscopy and immunocytological labeling were used to localize the 32-kilodalton (kDa) protein (DI polypeptide) of photosystem II in different cell types of the cyanobionts within leaf cavities ofAzolla caroliniana Willd. The 32-kDa protein binds the secondary electron acceptor QB, and is highly conserved between plants and cyanobacteria. Three antisera, specific for different epitopes of the 32-kDa protein, were used as primary antibodies. Immunologically recognizable 32-kDa protein was localized on membranes ofAzolla chloroplasts, vegetative cyanobacterial cells, akinetes, and heterocysts that were at all stages of the differentiation process. The 32-kDa protein was not detected in nonphotosynthetic endosymbiotic bacteria found within leaf cavities. The amount of the 32-kDa protein observed in different cyanobacterial cell types was dependent upon the primary antiserum used and membrane orientation within a cell with respect to the plane of sectioning. Therefore, although 32-kDa protein was present in all three cyanobacterial cell types and clear trends in labeling patterns could be elucidated, it was not possible to quantitate the amounts of protein with respect to either cell type or leaf-cavity age.

PHOTOSYNTHETIC CHARACTERIZATION OF DEVELOPING AND MATURE AKINETES OF APHANIZOMENON OVALISPORUM (CYANOPROKARYOTA)1

“…The location of the 32 kDa PsbA protein (D1 polypeptide) of PSII in akinetes (and other cell types) of cyanobionts within leaf cavities of Az. caroliniana was demonstrated by immunocytological labeling; however, due to technical constraints, the quantitative analysis of the cellular abundance of the protein was unreliable (Braun‐Howland and Nierzwicki‐Bauer 1990). Preliminary immunoblotting experiments with universal antibodies against the LSU of RUBISCO indicate the presence of LSU in Aph.…”

“…1983). Using TEM and immunocytological labeling, the 32 kDa PsbA protein (D1 polypeptide) of PSII was detected in akinetes (and other cell types) of the cyanobionts within leaf cavities of Azolla caroliniana Willd (Braun‐Howland and Nierzwicki‐Bauer 1990). These conflicting reports may stem from the fact that PC and chl and other components of the photosynthetic apparatus are progressively degraded as akinetes age (Herdman 1987).…”

An assessment of photosynthetic downregulation in cyanobacteria from the Gunnera–Nostoc symbiosis

“…The evidence presented by Silvester (1976) could, however, be consistent with the presence of a modified form of PSII that is unable to carry out light‐dependent electron transport. A similar possibility could also explain the absence of photosynthetic oxygen evolution in heterocysts from free‐living cyanobacterial cells, rather than invoking a total loss of PSII (Braun‐Howland & Nierzwicki‐Bauer, 1990; Wolk et al ., 1994). Earlier work had attributed the loss of photosynthetic activity in heterocysts to lower concentrations of photosynthetic pigments and a disruption of the manganese (Mn)‐tyrosine residue associated with the core D1 protein of PSII, rather than the absence of the PSII complex (Tel‐Or & Stewart, 1977).…”

NblA is essential for phycobilisome degradation in Anabaena sp. strain PCC 7120 but not for development of functional heterocysts

“…Thus, nblA is certainly not involved in heterocyst differentiation. It is known that heterocysts of Anabaena azollae and of Nostoc species retain (or regain) phycobiliproteins when these cyanobacteria live in symbiosis with their plant partners (Braun-Howland & Nierzwicki-Bauer, 1990;Kaplan et al, 1986). Since, for example, the heterocyst frequency of Anabaena azollae as a cyanobiont is about threefold higher than in the free-living state, the symbiosis is certainly a special situation (see Meeks & Elhai, 2002, for detailed information).…”

“…Since, for example, the heterocyst frequency of Anabaena azollae as a cyanobiont is about threefold higher than in the free-living state, the symbiosis is certainly a special situation (see Meeks & Elhai, 2002, for detailed information). Also detectable in the heterocysts of symbiotic Anabaena azollae was the photosystem II core subunit D1 (Braun-Howland & Nierzwicki-Bauer, 1990) which is essential for activity of the photosystem. Of the four photosystem II proteins we have analysed (Fig.…”