Cycloheximide (CH) prevented tracheary element (TE) differentiation and cell division in a culture of single cells isolated from the mesophyll of Zinnia elegans at the concentrations which inhibited incorporation of [14C]-leucine into protein. When the cells were pulse-treated with this inhibitor for 12 h at various times of culture, TE formation was inhibited most strongly by the treatments made between 24 and 60 h of culture. Incorporation of [14C]-leucine into protein showed a high level during this period. The inhibitory effect of actinomycin D (Act-D) on TE differentiation was also marked when it was administered from 24 to 60 h of culture when incorporation of [14C]-uridine into nucleic acid was at a high level. These results indicate that RNA and protein syntheses are prerequisites for cytodifferentiation to TE and that the syntheses between 24 and 60 h of culture are closely associated with cytodifferentiation. Studies of qualitative changes in proteins using two-dimensional electrophoresis revealed that approximately 400 polypeptides extracted from [35S]-methionine-labeled cells could be reproducibly resolved and that most of them were synthesized in both differentiating and non-differentiating cells. During TE differentiation, however, the synthesis of two polypeptides was shut off and two other polypeptides were newly synthesized between 48 and 60 h of culture, preceding the morphological changes. The relationship between TE differentiation and the synthesis of RNA and protein is discussed.
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Fukuda et al. (1983) studied this question.