[Enzyme activities and substrate levels of carbohydrate metabolism in proliferating and suberin synthesizing potato tuber cells].
Isolation of tissue fragments from the potato tuber can initiate either periderm formation including suberin synthesis or cell proliferation without cicatrization effects. TCA-cycle activity has been shown to develop only in causal correlation with suberin synthesis (Lange, 1970). Biochemical pathways of carbohydrate metabolism are analysed by investigating the changing levels of 10 intermediates and the activities of 12 corresponding enzymes. Differences between the metabolic kinetics of the two contrasting types of tissue are discussed as the biochemical background of different respiratory behaviour and different histogenetic development.Glucose and pyruvate as well as all triose- and hexosephosphates investigated except 6-phospho-gluconate generally show an intensive rise in concentration after derepression with subsequent degradation. In several cases not a concomitant rise but rather a contrary drift between the concentration of metabolites and the activity of corresponding enzymes is observed, e.g. phosphoglucomutase/glucose-6-phosphate, enolase/phosphoenolpyruvate. This phenomenon is connected with the occurrence of suberin synthesis and remains totally absent in proliferating tissue.After derepression the pentose phosphate shunt (6-phosphogluconate-dehydrogenase) is strongly activated independently of different histogenetic processes. On the other hand, the glycolytic pathway via fructose-6-phosphate becomes more effective in suberizing tissue, as is indicated by enhanced activity of phosphoglucoisomerase and accumulation of F-6-P.Little or no difference can be found with regard to hexokinase, triosephosphateisomerase, aldolase and pyruvate-kinase; on the other hand suberin formation strongly stimulates phosphoglyceromutase. From the high activity of the TCA-cycle in suberin synthesizing cells it must be concluded that acetyl-CoA is formed at a high rate by oxidative decarboxylation of pyruvate, which leads finally to citrate synthesis. Measurements of different steps of pyruvate metabolism and respiration suggest an inhibition of this pathway in proliferating tissue. Sim a taneously certain compensatory reactions are activated. The activity of glutamaulpyruvate-transaminase increases considerably, whereas it is almost entirely eliteinated in suberin synthesizing cells. Moreover, malic enzyme activity showsmgreater increase in proliferating tissue, and large pools of pyruvate, phospho(enol)-pyruvate, and 2-phospho-glycerate are accumulated. The difference in the glycolytic metabolism of the two tissues suggests a suppression of periderm formation and its substitution by cell proliferation as a result of insufficient production of precursors of suberin biosynthesis such as acetyl-CoA and fatty acids.
Botanisches Institut der Universität Frankfurt a.M., Frankfurt a.M., Deutschland.
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Lange
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Kahl
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Rosenstock