Abstract
The results are reported of autoradiographic analyses accomplished on roots ofCalystegia soldanella fed with a 2,5 mCi/l solution of3H-thymidine and a 10mCi/l solution of3H-uridine. Two regions of the meristem were investigated: cap-initial (CI) and quiescent center (QC). It is shown, in agreement with the literature data, that cap initials and quiescent center cells display a different pattern of labelling. Within the quiescent center the presence of 4 groups of cells is suggested, each group being characterized by some morphological differentiation and/or by a typical pattern of3H-thymidine and3H-uridine incorporation. Based on the labelling pattern the suggestion is advanced that some cells of QC undergo selective replication of particular DNA sequences which are active in transcription. The present observations demonstrating the heterogeneity of quiescent center are discussed in relation toTorrey's (1972) view that the quiescent center might be a site of a specialized biosynthesis of a hormone essential to cell division.
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