The rate of nuclear gene transcription in barley endosperm syncytia increases sixfold before cell-wall formation.

The rate of gene transcription in endosperm nuclei up to the formation of the first cell layers was investigated by pulse-labelling young fertilized barley (Hordeum vulgare L.) ovules with [(3)H]uridine. Quantitative autoradiographic studies of silver grains accumulating over the nuclei of wild-type endosperm demonstrated that the rate of transcription increased sixfold in the period from 3 to 7 d after pollination (DAP). Based on this observation, and the fact that cell-wall formation is initiated at 6 DAP, it is concluded that at least a proportion of the transcripts encode proteins involved in cell-wall formation. A similar study was also undertaken with the two barley sex mutants B7 and B15, in which developmental arrest at the syncytical stage leads to a complete lack of endosperm cell walls. This study showed that [(3)H]uridine is incorporated into the nuclei of the mutant syncytia, although at a rate different from that in the wild-type. Thus, the lack of cell-wall formation is not caused by a total block of gene transcription in these mutants, but rather by the lack of a gene product essential for cell-wall formation in the endosperm.