Dose-Response Analysis of Factors Involved in Germination and Secondary Dormancy of Seeds of Sisymbrium officinale: I. Phytochrome.

The germination of seeds of Sisymbrium officinale is light- and nitrate dependent. A close interaction between the effects of light and nitrate on germination has been reported previously (HWM Hilhorst, CM Karssen [1988] Plant Physiol 86: 591-597). In this study, a detailed dose-response analysis of the light-induced germination during induction of secondary dormancy is presented. Germination in water dropped from 90 to 0% after a dark incubation of 15 degrees C of approximately 160 hours. In the presence of 25 millimolar KNO(3), the decrease in germination level was delayed. At 24-hour intervals fluence-response curves were obtained in the presence of 25 millimolar KNO(3). With increasing length of the preincubation period, fluence-response curves shifted along the abscissa to the right. After 120 hours the maximal germination level started to decline. The fluence-response curves were simulated by using formulations from receptor occupancy theory for a simple bimolecular reaction in which the reaction partners were Pfr and its tentative receptor X. A good simulation was obtained when cooperativity of the binding of Pfr to X was assumed. The experimental curve parameters could then be interpreted as binding parameters.