Studies on the Growth in Culture of Plant Cells

Abstract

Aspects of the carbohydrate and nitrogen metabolism of Acer pseudcplatanus, L cell suspension cultures grown on a synthetic medium containing 2 per cent glucose and 1.0 mg/l 2,4-dichlorophenoxyacetic acid and kinetin either at 0.25 mg/l (low kinetin) or at 2.5 mg/l (high kinetin) are described. High kinetin inhibits growth as measured by increase in cell number, packed-cell volume, and cell dry weight. Although not inhibitory to glucose utdization, high kinetin inhibits the O2 uptake of the cells. Such cells contain only a trace amount of fructose and their rate of O2 uptake can be raised to that of the low kinetin cells by a period of fructose feeding. The O2 uptake of both kinds of cell is sensitive to malonate but the stimulation of O2 uptake induced by bis(hexafiuoroacetonyl)-acetone (‘1799’) at 0.2 mM is much less with the high-kinetin than the low-kinetin cells. The enzymes phosphoglucoseiseomerase and glucose-6-phosphate dehydrogenase are much less active in the high-kinetin cells. Mitochondria isolated from both kinds of cells show good respiratory control although slightly lower values for QO2(N), ADP/O ratio and control ratio are recorded with mitochondria from the high kinetin cells. Kinetin at 2.5 mg/l slightly reduces the ADP/O ratio of isolated mitochondria but at 4.0 mg/l their response to ADP is completely suppressed. Extracellular hemicellulose formed in presence of high kinetin has a reduced content of galactose and xylose and an increased content of glucose. These observations indicate that the inhibition of respiration by high kinetin is mainly due to suppression of glucose conversion to other sugars rather than to inhibition of glycolysis or terminal respiration. High kinetin decreases the rate of protein but not of amino-acid synthesis. Suppression of the synthesis of particular proteins may be an important factor responsible for the reduced cell yield of the cultures in presence of high kinetin. The significance of these observations to our understanding of the critical metabolic effects of cytokinina is discussed. Acer pseudoplatanus cells release amino acids into their culture medium early in the period of batch culture and largely reabsorb them as incubation proceeds.