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Developmental Changes in Multiple Forms of Deoxyribonucleic Acid-dependent Ribonucleic Acid Polymerase in Soybean Hypocotyl ¹

^a Department of Horticulture, Purdue University, West Lafayette, Indiana 47907

The relative levels of multiple RNA polymerases were determined in soybean (Glycine max L. var. Wayne) hypocotyl during various stages of development. The meristematic region of the hypocotyl contains more total polymerase activity per gram fresh weight and a greater proportion of polymerase I relative to II than the differentiated regions. The fully elongated tissue comprising the lower half of the hypocotyl contains mainly RNA polymerase II. The hook region contains a polymerase activity peak which is completely sensitive to -amanitin and partially sensitive to rifamycin SV. This peak is not detectable in other regions of the hypocotyl. Polymerase I is reproducibly separated into a major and a minor component, both being resistant to -amanitin. The two components elute at salt concentrations of 0.2 M and 0.23 M KCl, respectively, while the -amanitin-sensitive polymerase (II) elutes at 0.3 M KCl. The polymerase activity peak which is detectable only in the hook region elutes at approximately 0.5 M KCl. Polymerase levels were also determined in water-stressed tissue and in tissue which was harvested after three days of growth instead of the usual four days.