Chitin synthesis in apical hyphal growth

Chitin synthesis in apical hyphal growth

Colloque franco-belge de M.E.. mai 1988 CHITIN SYNTHESIS IN APICAL HYPHAL GROWTH. Robert DARGENT, 3ane-Marie TOUZE-SOULET and C. SAIDALI-SAVY. Labora...

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Colloque franco-belge de M.E.. mai 1988

CHITIN SYNTHESIS IN APICAL HYPHAL GROWTH. Robert DARGENT, 3ane-Marie TOUZE-SOULET and C. SAIDALI-SAVY. Laboratoire de Cryptogamie U.P.S., 118 route de Narbonne, 31062 T O U L O U S E CEDEX. Vegetative hyphae grow by deposition of new material in the apical region. Electron microscopy of hyphal apices of Mucor mucedo and Hypomyces chlorinus shows the characteristic aggregation of vesicles which must have major roles in the apical biosynthesis of the hyphal wall, but the details of these role remains elusive. Furthermore the mechanism responsible for cell wall plasticity at the hyphal apex is not well understood. In the investigation of these problems we used three complementary methods ; cytochemical detection of polysaccharides ; specific labeling of chitin with n-acetyl [I-3H] glucosamine by light and electron microscopy ; distribution of chitin in cell walls using a WGA-colloidal gold complex as specific marker. The combinaison of these methods allows certain conclusions about the distribution of chitin in the filamentous cell wall. The results indicate that there are differences in wall composition and structure between the growing apex and the subapical part of hyphae. The apical tips do not appear to contain sufficient N-acetyl glucosamin groups (chitin) to bind WGA. In order to account for this unexpected result, we surmise that the neosynthesized chitin chains undergo deacetylation at the apical extremities. This would not, however, exclude the detection of chitin by autoradiography using a tritium label on the secondary alcohol group in position 1 on acetyl-glucosamine. In conclusion, a deacetylase may thus regulate the synthesis of chitin at the apex.

COURT-CIRCUIT DE LA VOIE GOLGIENNE DANS LES CELLULES-HOTES DES MYCORHIZES A VESICULES ET ARBUSCULES. Jean DEXHEIMER. Lgbo~c~o~J~g de 8iolog~g de6 Lig~eux, ].E. CNRS 034613, U ~ u g ~ s ~

de Ng~ag I, B.P. 239, 54506 VANPOEUVRE CEDEX. L'invasion d'une cellule-hSte par l'endophyte des mycorhizes VA induit de profondes perturbations qui se traduisent par des transformations remarquables de son organisation et de son fonctionnement. Nous mentionnerons, en particulier, l'augmentation considerable du volume du cytoplasme, de la surface plasmalemmique, la redistribution de certaines activit4s enzymatiques, l'apparitlon de chromoplastes tubulor4ticulaires & la place d'amyloplastes dans certaines esp&ces. Le fonctionnement des syst~mes cellulaires impliqu4s dans la production des polysaccharides est aussl modifi4. Diverses 4tudes ont montr~ que l'interface des mycorhizes est le si~ge d'une production importante de polysaccharides utilis~s pour ~difier la couche d'isolement. Pourtant, les dlctyosomes sont peu abondants. En falt, la vole golglenne de synth~se des polysaccharides est court-circuitde. Ii y a un transfert direct des pr4curseurs polysaccharidiques de la lumi~re des trav4es du r4tlculum endoplasmique au plasmalemme de l'interface, comme le montrent les tr~s nombreux contacts entre les trav4es r4ticulaires et le plasmalemme.

S.E.M STUDYOF HUMANCEHENTOGENESIS : Gwenaelle GERARD , Mich~le DECOMBAS,Aurore BLANC, Arabelle GOUVERNAIRE : Laboratoire d' Anatomie Pathologique, Facult~ de Chirurgie Dentaire, I, Rue Maurlce Arnoux 92120 MONTROUGE.FRANCE. Cementum is a mineralized connective tissue, covering the whole dental roots from cemento-enamel Junction to the apex. Two types of cementum have been generally described : acellularand cellular. The distribution and thickness of each of them vary according to the considered areas. SEM has been wldely used to study cementum surface and numerous authors have already observed i t in sound and patho logical conditions ( BERCYand FRANK, 1980. BOYDEand JONES 1968,1970,1972; SELVIG 1969,1977). The aim of this work is to observe in SEM, human apical root formation of premolars aged 10 to 15, extracted for orthodontics reasons. Roots have been separated from their crowns and after careful rinses, fixed in Karnovsky's solution, treated by sodium hypochlorite to destroy all organic component dehydrated, meta111zed with platlne and observed in a Stereoscan S 600 Cambridge. Results at low magnifications show diffePent steps of cementogenesis and incremental lines of root elaboration. Occasionally, mineralization defects giving birth to openings of different sizes were seen occurring preferentially in the middle of the root. When the apical third of the root is achieved, numerous foramina of extremely various diameters and arranged in a random manner, form the apical delta. At a high magnification, cementoblasts lacunae with their dendritic channels appear scattered among the superposed layers of formating cementum. Relationships between predentin calcospherites and cementum domes are also clearly visible on the edge of the root aperture. Sn conclusion, SEM allows the identification of the successive steps of root elaboration and the immediate visualization of structure anomalies which are involved in the growth of pulpo-parodontal pathological lesions.

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