The properties of chlorophyll (Chl) a and pheophytin (Pheo) a embedded in the rigid anhydrous polymer fihns, polyvinyl alcohol (PVA) and nitrocellulose (NC) are reviewed. The aggregation capability of these pigments in two matrices is characterized by absorption, fluorescence, excitation spectra combined with fluorescence lifetime and time-resolved anisotropy. The dimer creation ability for Chl a and Pheo a is strongly affected by the polymer systém ušed for investigation. The Chl a and Pheo a ability to aggregate in polymer matrices is compared. We háve been looking for a good systém suitable for the study of properties of monomeric forms when embedded in the rigid matrix on the one hand, and for the study of energy transfer between different forms of Chl molecules on the other one. Chl a, when embedded in an anhydrous PVA matrix, is in a very stable monomeric form while Pheo a molecules in this film tend to aggregate and in the NC film they exist in the monomeric form. Thus the PVA systém can be ušed as a model systém for investigation of the properties of and processes between both dimeric and monomeric structures. The NC film, however, can be ušed as a rigid matrix when only the existence of monomeric forms of the pigments is required.
Spermatozoa of the monogenean Heterocotyle capricornensis Chisholm et Whittington, 1996 are long and filiform, comprising an elongate nucelus, probably a single elongate mitochondrion and two incorporated axonemes, one of which is shifted with respect to the other. The shift results in a region at each end of the sperm where only one axoncmc is present, accompanied by the nucleus and mitochondrion at one end and the nucleus and/or mitochondrion at the other. By taking note of the direction of dyncin arms on the axonemal doublet microtubules, each axoneme is identified and followed from beginning to end. No basal bodies remain in mature sperm but the main nuclear end is interpreted as proximal/anterior based on the final stages of spermiogenesis. A group of four or five cortical microtubules from the spermatid zone of differentiation persists in mature sperm, but is not closely associated with a region of extracellular matrix, as it is in other monocotylids. The sperm structure is compared with that of other monocotylids and the phylogenetic implications are discussed. Aberrant sperms in one individual were folded and fused along much of their length.
Spermiogenesis and the spermatozoon were studied in the digenean Mesocoelium monas Rudolphi, 1819 (from the toad Bufo sp. in Gabon). An ultrastructural study revealed that spermiogenesis follows the usual pattern found in digeneans, i.e. proximo-distal fusion of axonemes with a median cytoplasmic process followed by elongation. The spermatozoon has two fully incorporated axonemes with the 9 +“1” trepaxonematan pattem. Indirect immunofluorescence localization of tubulin and fluorescent labelling of the nucleus were used to obtain additional information on the structure of the spermatozoon. It was thus shown that one of the axonemes is slightly shorter than the other (190 versus 220 pm) and that the filiform nucleus (65 pm in length) is located at the distal extremity of the spermatozoon (220 pm in length). Various monoclonal and polyclonal antibodies, specific to alpha, beta, acetylated-alpha, or general tubulin, were used and produced similar labelling.
Sphingolipids are a diverse and ubiquitous group of lipids. They are widely distributed in parasites and a number of novel forms have been described. Sphingolipid synthesis has been investigated in the malarial parasite, cestodes, digencans and nematodes. Although there are differences in detail, the synthetic pathways involved are similar to those found in mammals.
Spirocamallanus rebecae sp. n. is described from freshwater cichlids in some lakes of Southeast Mexico. It has 14 spiral bands in the buccal capsule, similar unequal spicules 503-544 and 281-297 long, 3 precloacal and 6 postcloacal pairs of papillae, vulva situated in the middle part of the body. An updated list of the species of the genus is presented.