In potato leaf discs incubation in the dark for 40-48 h induced a marked drop of chlorophyll, a decrease of proteins and a strong increase of free aminoacids, a decrease of the capacity of isolated chloroplasts to carry on the Hill reaction, a fall of the activity of citochrome oxidase, malate dehydrogenase, glucose-6-P dehydrogenase, NADH2 oxidase. All of these manifestations of senescence appeared strongly counteracted by the presence of sucrose, glucose, fructose, galactose, and glycerol (which was efficiently converted into sugar within the tissue). A protective effect fairly similar to that of the sugars was obtained by illuminating the leaf discs during incubation. This effect of light was almost completely suppressed by the presence of the photosynthetic CO2 fixation inhibitor DCMU, thus suggesting that protection by light is largely due to the production of photosyntates. These results are interpreted as indicating a regulatory function of the level of sugars on the enzyme and protein pattern of the leaf cell.
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Con il contributo del Ministero per i Beni e le Attività Culturali