The activity of some synthetic cytokinins in breaking thermodormancy of lettuce (Lactuca sativa L.)

The following synthetic cytokinins: 6-furfurylaminopurine (kinetin), 6-(3-methyl-2-butenylamino)purine (isopentenyladenine) and their l-deaza-,8-aza-l-deaza-, 3-deaza-, and 8-aza-3-deaza-analogs were investigated for biological activity in breaking thermodormancy in lettuce seed (Lactuca sativa L. cv. meikoningin, Asteraceae). In dose-response experiments 6- (3-methyl-2-butenylamino)-l-deazapurine appeared to be the most active substance tested. This chemical stimulated germination at lower concentrations and to a greater extent than the others. All the isopentenyl derivates were more active than the corresponding furfuryl analogs. In general, the results are similar to those obtained with a callus growth test, which supports the view that the results definitely indicate cytokinin activity.