Developmeental and compartmenitation studies were used to evaluate the relative roles of the oxidative pentose phosphate cycle, the Calvin cycle, and the glycoly-sis in cotvledons of radish (Raphanus sativus L.).Glucose-6-P dehydrogenase, 6-P-gluconate dehydrogenase, glucose-6-P isomerase, and the NAD-dependent glyceraldehyde-3-P dehydrogenase were present in high activity in ungerminated seeds, increased about 2-fold during germination in the dark, and were slightly enhanced by light. In contrast, NADP-dependent glyceraldehvde-3-P dehydrogenase was developed to only a small degree in the dark, but increased severalfold in continuous white or far red light. The activity of phosphofructokinase was low throughout germinationi.The separation of cell conmpartment-specific isoenzymes showed that, except in ungerminated seeds, the plastid enzyme accouinted for 40 to 45% of the total activity of 6-Pgluconate dehydrogenase and for 13 to 20% of glucose-6-P isomerase. The remaining activity was due to the cytosolic isoenzymes. The presence of gltucose-6-P dehydrogenase and 6-P-gluconate dehydrogeniase in plastids was also established by their presence in the isolated organelle. The NAD -dependenit glyceraldehyde-3 -P dehydrogeniase was mostly due to the cytosolic isoenzyme, whereas the NADdependent activity associated with the NADP-dependent glyceraldehyde-3-P dehydrogenase was very small.The data indicate that the en-zynmes of the oxidative penitose phosphate cycle are present in the cytosol throughotut germiniation. IIn the plastids these enzy-iies already becanie fully developed duiring early germninationi in the dark, whereas entzymes of the Calvin cycle increased onlly in the light. Glycolvsis seemned to be of m-linor importanice.Enzymes involved in the sugar phosphate metabolism of plants have been found in two subcellular compartments, the chloroplasts and the cytosol (15, 25). Only enzymes specific for the Calvin cycle were restricted to the chloroplasts (12,16,27). When enzyme activities are present in both cell compartments, they are due to isoenzymes, one located in the chloroplasts and the other in the cytosol (1, 2, 4). This distribution also applies to the two key enzymes of the oxidative pentose phosphate cycle, glucose-6-P dehydrogenase and 6-P-gluconate dehydrogenase (11,25,26).At present only little evidence is available about the intra-'This investigation was supported by the Deutsche Forschungsgemeinschaft. cellular distribution of enzymes in etiolated plant tissues, since most work has been performed using green leaves. In general, one can assume the same intracellular distribution of enzymes in etiolated tissues as in green leaves. In addition to changing levels of total enzyme activities in etiolated tissues (10, 28) it is possible that the quantitative distribution may be different in the two cellular compartments. Previous studies have measured only total enzyme activities from crude extracts, so that the extent of compartmentation of enzyme activities in the plastids and in the cytosol wa...

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