Autoradiographic and Cytofluorimetric Analysis of DNA Synthesis in Endosperm and Cotyledons of Germinating Castor Bean

Abstract

Galli, M. G., Balzaretti, R. and Sgorbati, S 1986. Autoradiographic and cytofluorimetric analysis of DNA synthesis in endosperm and cotyledons of germinating castor bean.—J. exp. Bot 37: 1716–1724. DNA synthesis occurs both in cotyledons and in endosperm of germinating castor bean and is completely independent of the presence of the embryo axis. Cytofluorimetric analysis has shown that, in cotyledon cells, it probably represents normal replication processes preceding mitosis; in contrast, in the endosperm, which is mixoploid in the quiescent condition, DNA synthesis leads to a further increase in the DNA content of the nuclei which cannot be grouped into defined classes, revealing rather a continuous distribution over a wide range of fluorescence values. This finding, together with the labelling pattern of some nuclei in the autoradiographic samples, suggests the possibility of endoreduplication cycles, sometimes involving only part of the genome. Possible meanings of the DNA increase in this tissue, which has a very short life span and never becomes green, are discussed.