RESUMO
Cellulose biosynthesis in plant secondary cell walls forms the basis of vascular development in land plants, with xylem tissues constituting the vast majority of terrestrial biomass. We used plant lines that contained an inducible master transcription factor controlling xylem cell fate to quantitatively image fluorescently tagged cellulose synthase enzymes during cellulose deposition in living protoxylem cells. The formation of secondary cell wall thickenings was associated with a redistribution and enrichment of CESA7-containing cellulose synthase complexes (CSCs) into narrow membrane domains. The velocities of secondary cell wall-specific CSCs were faster than those of primary cell wall CSCs during abundant cellulose production. Dynamic intracellular of endomembranes, in combination with increased velocity and high density of CSCs, enables cellulose to be synthesized rapidly in secondary cell walls.
Assuntos
Proteínas de Arabidopsis/análise , Arabidopsis/enzimologia , Parede Celular/enzimologia , Glucosiltransferases/análise , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/metabolismo , Proteínas de Bactérias/análise , Parede Celular/ultraestrutura , Celulose/biossíntese , Celulose/metabolismo , Fluorescência , Glucosiltransferases/química , Glucosiltransferases/metabolismo , Complexo de Golgi/enzimologia , Proteínas Luminescentes/análise , Microtúbulos/enzimologia , Transporte Proteico , Xilema/enzimologia , Xilema/crescimento & desenvolvimentoRESUMO
Four examples of infiltrating gastric tumours which had light microscopic features suggestive of carcinoid or oat-cell carcinoma are documented. Histological and ultrastructural findings indicated that these tumours were atypical carcinoids. A spectrum of endocrine cell neoplasia in the stomach analogous to that observed in the bronchus is postulated. It is felt that increased recognition of poorly differentiated endocrine tumours of the stomach might be of prognostic and therapeutic importance.