Cell-density-dependent Changes in the Metabolism of Chloronema Cell Cultures

Abstract

In the growing chloronema cell suspension cultures of the moss F. hygrometrica Hedw., activities of several enzymes were cell-density-dependent. Cyclic nucleotide phosphodiesterase (cNPDE), nitrate reductase (NR) and protein kinase showed highest activity at a low cell density (1-2 mg/ml) while IAA oxidase and peroxidase were highest at a high cell density (> 10 mg/ml). 3''-Nucleotidase and the glycolytic enzymes (aldolase, hexokinase, phosphofructokinase, phosphoglucoisomerase, pyruvate kinase and triose phosphate isomerase) showed no significant dependence on the cell density. Alternatively, if the NR and peroxidase activities were determined as a function of time in batch cultures, their levels were maximal 60-70 and 320 h after subculture, respectively, the corresponding cell densities being 1-2 and 23 mg/ml. The relationship between cell density and NR and peroxidase activies was the same, whether these enzymes were measured in batch cultures during a growth cycle or in the cells cultured at different initial inoculum densities for a constant time. Conventionally, enzymic changes have been correlated with growth phases, but the pattern of enzymic activities can also be interpreted as cell-density-dependent. In moss protonema, the dependence of cNPDE, IAA oxidase and peroxidase on cell density may play an important role in modulating the endogenous levels of IAA and c[cyclic]AMP, both of which regulate the differentiation of specific cell types.