Growth characteristics of hormone and vitamin independent photoautotrophic cell suspension cultures fromChenopodium rubrum

Abstract

This communication reports the photoautotrophic growth of hormone and vitamin independent cell suspension cultures ofChenopodium rubrum. The transfer of cells from stationary growth into fresh culture medium results in a high protein formation, followed by an exponential phase of cell division, whereas the onset of rapid chlorophyll formation is delayed for 4 days. At the stage of most rapid cell division there is no net synthesis of starch and sugar. When the cells enter stationary growth, there is a progressive accumulation of chlorophyll, sugar, and starch. Photoautotrophic cell cultures assimilate about 80–90 μmol CO2/mg chlorophyll X hour. Dark CO2 fixation is about 3.7% to 2.2% of the light values during exponential and stationary growth, respectively. As shown by short-term14CO2 fixation, CO2 is predominantly assimilated through ribulosebisphosphate carboxylase via the Calvin pathway. There is a significant increase in the14C label of C4 carboxylic acids in exponentially dividing cells as compared to cells from stationary growth. Thein vitro activity of phosphoenolpyruvate carboxylase and ribulosebisphosphate carboxylase is almost equal during exponential cell division. A decrease in cell division activity is accompanied by a significant change in the specific activities of both carboxylation enzymes. In non dividing cells from stationary growth the activity of ribulosebisphosphate carboxylase is greately enhanced and that of phosphoenolpyruvate carboxylase is reduced, documenting the development of carboxylation capacities typical for C3-plants. The experimental results provide evidence that phosphoenolpyruvate carboxylase activity might be regulated by ammonia and could be involved in anaplerotic CO2 fixation which supplies carbon skeletons of the citric acid cycle.