Ribonucleic Acid Synthesis by Cucumber Chromatin: Developmental and Hormone-induced Changes

When intact etiolated 2-day cucumber (Cucumis sativus) embryos were treated with indoleacetic acid (IAA), gibberellin A(7) (GA(7)), or kinetin, chromatin derived from the embryonic axes exhibited an increased capacity to support RNA synthesis in either the presence or the absence of bacterial RNA polymerase. An IAA effect on cucumber RNA polymerase activity was evident after 4 hours of hormone treatment; the IAA effect on DNA template activity (bacterial RNA polymerase added) occurred after longer treatments (12 hours). GA(7) also promoted template activity, but again only after a prior stimulation of endogenous chromatin activity. After 12 hours of kinetin treatment, both endogenous chromatin and DNA template activities were substantially above control values, but longer kinetin treatments caused these activities to decline in magnitude. When chromatin was prepared from hypocotyl segments that were floated on a GA(7) solution, a GA-induced increase in endogenous chromatin activity occurred, but only if cotyledon tissue was left attached to the segments during the period of hormone treatment.Age of the seedling tissue had a profound influence on the chromatin characteristics. With progression of development from the 2-day to the 4-day stage, the endogenous chromatin activity declined while the DNA template activity increased.