The Fine Structure of Secretion by Plasmodium knowlesi Merozoites during Red Cell Invasion

The secretory organelles of Plasmodium knowlesi were studied ultrastructurally to examine their mode of action during invasion. The formation of lamellar structures in merozoite rhoptries within late stage schizonts is prevented by the protease inhibitors chymostatin and leupeptin. Under normal conditions vesicles lined by 6-nm membranes are formed in rhoptries during erythrocyte invasion. Stereoscopic viewing of tilted sections shows that where the merozoite apex contacts the parasitophorous vacuole (PV) membrane during invasion, a domed elevation of the PV surface lies within the mouth of the rhoptry duct in contact with the secretory matrix. The membrane of the early invasion pit is thinner (6 nm) than the red cell membrane elsewhere, and sheets of lamellar material are frequently present on the invasion pit surface. These findings support the proposal that the rhoptry-microneme complex is capable of generating membranous material and inserting it into the red cell surface in a controlled manner to create the parasitophorous vacuole. On the basis of this model, measurements from serial sections show that the rhoptries could provide enough material to create a membrane lining the parasitophorous vacuole, and, with the contribution of the microspheres, could double it to accommodate the early ring stage of the parasite.     

The control of incompatibility in distylous Pulmonaria affinis Jordan (Boraginaceae)

In P. affinis, pin pollen is shorter on average than thrum pollen. Pins have more coronal hooks on stigmatic papillae than thrums, but gaps between papillae are relatively smaller for thrums. Pin stigmas receive more pollen than thrum stigmas. Thrum stigmas receive more (dissortive) pin pollen, but pin stigmas are assortively pollinated. Pollen only germinates when trapped below papilla coronas. On thrum stigmas, most trapped pollen is pin. Pollen germination is better on thrum stigmas than pin stigmas, and thrum stigmas show a close relationship between numbers of legitimate pollen grains, numbers of germinating grains, and numbers of pollen tubes in the style. There is no inhibition of illegitimate pollen germination. Illegitimate pollen tubes are inhibited in the style. Incompatibility operates by a combination of dissortive pollination, dissortive pollen trapping, and stylar pollen tube inhibition. All heteromorphic features differing between pins and thrums are implicated in the inhibition of within-morph fertilization in thrums.     

Common Epitopes In the Circumsporozoite Proteins of Plasmodium Berghei and Plasmodium Gallinaceum Identified By Monoclonal Antibodies to the P. Gallinaceum Circumsporozoite Protein

ABSTRACT. Monoclonal antibodies that react with the circumsporozoite protein of the avian malaria Plasmodium gallinaceum sporozoites also reacted with circumsporozoite protein of the rodent malaria Plasmodium berghei. Two types of reactivity were identified: 1) two monoclonal antibodies reacted with P. berghei sporozoite protein by enzyme-linked immunosorbent assay, Western blot and indirect immunofluorescence antibody, 2) six other monoclonal antibodies reacted with P. berghei sporozoites by ELISA and Western blot only. We studied whether these differences could be explained by reactivity in enzyme-linked immunosorbent assay with different P. berghei circumsporozoite peptides. Although all P. gallinaceum monoclonal antibodies reacted with the P. berghei repeats, the first group reacted with a conserved peptide sequence, N1, whereas the second group did not. These results suggest that circumsporozoite proteins from P. gallinaceum and P. berghei share common epitopes. the biological significance of our finding is not yet clear. Indeed, the cross-reactive monoclonal antibodies giving a positive indirect immunofluorescence antibody with the P. berghei sporozoites only caused a borderline effect on the living P. berghei parasites in vitro as measured by inhibition of sporozoite infectivity.