Neuraminidase stimulates Division and Sugar Uptake in Density-inhibited Cell Cultures

THE proliferation of normal cells stops when the cultures have formed confluent monolayers; this process is termed density-dependent inhibition of growth (DDI). The cells can be released from DDI by proteolytic enzymes and other substances acting on the cell surface¹, indicating that the cell surface may be important in regulating cell proliferation. Sialic acid residues also may be important in this regulation. Growing and virus-transformed cells contain less sialic acid in glycolipids² and possibly also in glycoproteins³ than normal resting cells. We report direct evidence that the control of cell growth is related to sialic acid residues on the cell surface. Small concentrations of neuraminidase initiate proliferation in stationary cell cultures and cause an early increase in sugar uptake.     

Ultrastructural Changes and Electrolyte Leakage from Ozone Fumigated Epiphytic Lichens

The ultrastructure of lichens and leakage of electrolytes fromthem were studied to assess the effects of ozone on four epiphytes.Bryoriacapillaris(Ach.) Brodo & Hawksw.,Bryoria fuscescens(Gyelnik)Brodo & Hawksw.,Hypogymnia physodes(L.) Nyl. andUsnea hirta(L.)Wigg. were fumigated with control (<10), 40, 150 and 300ppb ozone in controlled growth chambers for 2 and 4 week periods.The ultrastructural results suggest a direct effect of O₃oncarbon assimilation and storage in these lichens. Both the highconcentrations of ozone (150 ppb and 300 ppb) and longer exposuretime significantly increased starch volume and electron opacityof the pyrenoid matrix in chloroplasts ofU. hirtaandB. capillaris.Furthermore, inU. hirta, cytoplasmic lipid droplets and thenumber of pyrenoglobuli in pyrenoids were significantly increasedat higher ozone concentrations.B. fuscescensshowed little responseto ozone at the ultrastructural level. In bothBryoriaspeciesthe potassium leakage, and inB. fuscescensthe conductivity ofleachate, decreased during 4 weeks fumigation with high concentrations(150 and 300 ppb) of ozone. In most lichens, the total concentrationof K⁺was either unchanged or increased at 150 ppb O₃, suggestingthat no leaching due to membrane damage occurred, but K⁺uptakeby the lichens tended to increase at the concentrations of O₃used.Copyright1997 Annals of Botany Company Epiphytic lichens; Bryoria capillaris; Bryoria fuscescens; Hypogymnia physodes; Usnea hirta; electrolyte leakage; conductivity; potassium; ozone; ultrastructure