Studies on messenger and ribosomal RNA synthesis in plant tissue cultures induced to undergo synchronus cell division.

Messenger and ribosomal RNA metabolism was tudied in a plant tissue culture system: cells from the quiescent tubers of Helianthus tuberosus (Jerusalem artichoke) were induced to divide synchronously and dedeifferentiate by excision and culture of explants in nutrient medium. Large accumulations of ribosomal RNA and protein started early in the 20-h lag-period preceding the first division. In pulse-labelling experiments, two types of polydisperse messenger-like RNAs were detected one with and one without a poly(adenylic acid) sequence. In the first 2 h of culture the two polydisperse RNA fractions were the predominant types of RNA synthesised. Ribosomal RNA synthesis was very low during the first 2 h, but acclerated later. Low concentrations of actinomycin-D strongly inhibited ribosomal RNA synthesis, but had little effect on the synthesis of transfer RNA or either type of polydisperse messenger-like RNA. In explants cultured with low concentrations of actinomycin-D ribosomal RNA accumulation was completely inhibited, but cell division and protein accumulation occurred, though at a reduced rate. It is concluded that the synthesis and accumulation of new ribosomal RNA which normally occur during culture are not required for the induction of cell division or for protein accumulation, i.e. the ribosomal RNA existing in the quiescent tuver cells can support protein accumulation and cell division induced by excision and culture. The quiescent tuber tissue is also shown to contain significant amounts of messenger-like RNA.