Changes in 5′-nucleotidase and glucose-6-phosphatase of Phaseolus vulgaris cotyledon tissue during germination

Abstract

Experiments with cotyledon tissue from Phaseolus vulgaris have shown that 5′-nucleotidase (5′-ribonucleotide phosphohydrolase, E.C. 3.1.3.5) and glucose-6-phosphatase ( d-glucose-6-phosphate phosphohydrolase, E.C. 3.1.3.9) activities increase during germination to reach a peak at 5 days of age and thereafter decline as the cotyledons become senescent. Cell fractionation studies of 4-day-old tissue showed that the enzymes are distributed in parallel among sedimentable subcellular fractions, 50–60% of the particulate activities being present in the microsomal fraction. This has been interpreted as indicating that both enzymes are associated with endoplasmic reticulum in the intact cell and thus the increased activities of the enzymes in the early stages of germination may well reflect in part a proliferation of endoplasmic reticulum at this time. The much reduced activities in senescent tissue are consistent with the digestion of cell cytoplasm that occurs in the late stages of germination. Both enzymes are also present in isolated soluble fractions in proportions which increase with advancing senescence. In 7- and 9-day-old tissue about 90% of the activity of each enzyme is soluble. This observation is discussed in terms of a possible inactivation or solubilization of the bound forms of the enzymes during the late stages of germination.