The nature of Thelohania solenopsae (Microsporidia) cysts in abdomens of red imported fire ants, Solenopsis invicta.

Sixty four percent of Solenopsis invicta workers infected with Thelohania solenopsis contained 1-6 "cysts" ranging from 70 to 260 microm in diameter. Light and electron microscope analyses showed that cysts are hypertrophied adipocytes transformed by the parasites, each cyst presumably forming from a single cell. In the first step of the pathogenesis, Nosema-like spores functioning in autoinfection are produced; a diplokaryotic sequence leading to their formation causes fat body hypertrophy. When meiosis occurs, it switches parasite development to production of octospores and/or megaspores. Adipocytes become 2-4xlarger than normal in conjunction with intensive parasite multiplication and octospore maturation. Infected cells eventually lose their cellular organization and are converted into reservoirs for spores. There were no manifestations of cellular immunity, such as encapsulation or nodule formation. Similarly, there were no signs of specialized host-parasite interaction that might be interpreted as xenoma-like complexes. The role of the cysts in the parasite's life cycle is unclear. They may represent a defensive reaction of the host sacrificing the infected cells to segregate the infection. Alternatively, the cyst may help protect spores from environmental hazards and provide a concentrated infectious dose to aid horizontal transmission of the microsporidium. We propose to refer to hypertrophied adipocytes filled with T. solenospsae spores as "sporocytosacs", not "cysts."

Phragmoplast-mediated cytokinesis in Trentepohlia: results of TEM and immunofluorescence cytochemistry.

This paper reports transmission electron microscopy (TEM) and immunofluorescence evidence for phragmoplast-mediated cytokinesis in the green alga, Trentepohlia (Ulvophyceae, Chlorophyta). This type of cytokinesis is normally found only in land plants and some charophycean green algae. Earlier TEM work documented a phragmoplast in another trentepohlialean alga, Cephaleuros. Numerous molecular studies have shown that both Trentepohlia and Cephaleuros are clearly not in the charophycean (streptophyte) lineage of green algae. Also, details of vegetative cytokinesis in Trentepohlia and Cephaleuros indicate differences from the processes and structures observed in the streptophytes. Parallel evolution could be the explanation for a phragmoplast-mediated cytokinesis in both the chlorophycean Trentepohliales and the streptophyte lineage of charophycean green algae and land plants.

Targeting and release of phytohemagglutinin from the roots of bean seedlings.

Phytohemagglutinin (PHA), an abundant vacuolar seed protein of the common bean (Phaseolus vulgaris), is a tetramer of two homologous polypeptides, PHA-E and PHA-L. The roots of bean seedlings release into the culture medium a cross-reacting lectin that is most closely related to PHA-E. Reverse-transcriptase polymerase chain reaction with root mRNA as template was used to identify PHA transcripts in the roots of bean seedlings. Roots were found to contain mRNA for PHA-E but not for PHA-L. Indirect immunocytochemical detection with colloidal gold and antibodies to deglycosylated PHA showed that in the meristem of the primary root, PHA accumulates in vacuoles. However, in elongated root cells PHA was found only in the cell walls, indicating targeting to an alternate location. These results are discussed in relation to the various mechanisms that may account for the release of a normally vacuolar protein by roots.

Plant nuclear pore complex proteins are modified by novel oligosaccharides with terminal N-acetylglucosamine.

Only a few nuclear pore complex (NPC) proteins, mainly in vertebrates and yeast but none in plants, have been well characterized. As an initial step to identify plant NPC proteins, we examined whether NPC proteins from tobacco are modified by N-acetylglucosamine (GlcNAc). Using wheat germ agglutinin, a lectin that binds specifically to GlcNAc in plants, specific labeling was often found associated with or adjacent to NPCs. Nuclear proteins containing GlcNAc can be partially extracted by 0.5 M salt, as shown by a wheat germ agglutinin blot assay, and at least eight extracted proteins were modified by terminal GlcNAc, as determined by in vitro galactosyltransferase assays. Sugar analysis indicated that the plant glycans with terminal GlcNAc differ from the single O-linked GlcNAc of vertebrate NPC proteins in that they consist of oligosaccharides that are larger in size than five GlcNAc residues. Most of these appear to be bound to proteins via a hydroxyl group. This novel oligosaccharide modification may convey properties to the plant NPC that are different from those of vertebrate NPCs.

Assessment of the autonomy of replicative and structural functions encoded by the luteo-phase of pea enation mosaic virus.

The genome of pea enation mosaic virus (PEMV) is composed of two taxonomically unrelated RNAs, interacting to create what has traditionally been considered a bipartite virus. The cohesiveness of this interaction was assessed by examining the autonomy of each RNA in viral replication, coat protein expression and systemic invasion. Using a pea protoplast system, in vitro transcripts of RNA1 were found to be capable of initiating RNA2-independent replication, including the formation of the distinctive nuclear membrane-based replication complex associated with wild-type PEMV infection. Western blotting and electron microscopic analysis demonstrated that the synthesis of the RNA1-encoded coat protein, as well as virion assembly, was also independent of RNA2-directed functions. Mechanical inoculations with transcripts of RNA1 failed to establish a systemic RNA1 infection, whereas inoculations with RNA2 were able to establish a largely asymptomatic systemic infection. Combined inoculum containing RNA1 and RNA2 transcripts were able to recreate wild-type PEMV symptomatology, demonstrating the dependence of RNA1 on RNA2 for mechanical passage. With the notable exception of the adaptation of PEMV to establish a true systemic invasion, these data further strengthen the analogy between PEMV and the helper-dependent complexes associated with members of the luteovirus group.

Colocalization of barley lectin and sporamin in vacuoles of transgenic tobacco plants.

Various targeting motifs have been identified for plant proteins delivered to the vacuole. For barley (Hordeum vulgare) lectin, a typical Gramineae lectin and defense-related protein, the vacuolar information is contained in a carboxyl-terminal propeptide. In contrast, the vacuolar targeting information of sporamin, a storage protein from the tuberous roots of the sweet potato (Ipomoea batatas), is encoded in an amino-terminal propeptide. Both proteins were expressed simultaneously in transgenic tobacco plants to enable analysis of their posttranslational processing and subcellular localization by pulse-chase labeling and electron-microscopic immunocytochemical methods. The pulse-chase experiments demonstrated that processing and delivery to the vacuole are not impaired by the simultaneous expression of barley lectin and sporamin. Both proteins were targeted quantitatively to the vacuole, indicating that the carboxyl-terminal and amino-terminal propeptides are equally recognized by the vacuolar protein-sorting machinery. Double-labeling experiments showed that barley lectin and sporamin accumulate in the same vacuole of transgenic tobacco (Nicotiana tabacum) leaf and root cells.