Endogenous cytokinins in oil palm (Elaeis guineensis L.) callus, embryoids and regenerant plants measured by radioimmunoassay

Abstract

The cytokinins present in callus cultures, embryoids, regenerant shoots and germinating zygotic embryos of oil palm have been characterized by radioimmunoassay (RIA). The levels found in callus were extremely low and accurate estimates were limited by the availability of material. The major compounds were the 9-glucosides of isopentenyladenine (IPA9G) and dihydrozeatin (DHZ9G), (0.5 and 0.4 pmolg-1), with lesser amounts of dihydrozeatin (DHZ) (0.16), dihydrozeatin riboside (0.13), and isopentenyladenosine (IPAdo) (0.15). Zeatin (Z), zeatin riboside (ZR), and isopentenyladenine (IPAde) were present at less than 0.1 pmol g-1 of tissue. There was no consistent change in concentration during a 6-week callus growth cycle but there was a significantly higher level of IPA9G at three weeks, and zeatin was not detectable on weeks 3 and 4. Attempts to measure O-glucosides indicated that there were no major pools of these derivative, although trace amounts may be present. In embryoids and regenerant shoots the predominant cytokinins were again the 9-glucosides of IPA and DHZ, with some Z9G. The pattern in germinating zygotic embryos was quite different with, generally, much higher levels of cytokinins present, predominantly DHZ9G. Embryos also contained significant amounts of the biologically active cytokinins ZR and IPAde.