RNA Synthesis during Synchronous Cell Division in Cultured Explants of Jerusalem Artichoke Tuber

Abstract

Explants of Jerusalem artichoke tuber tissue were cultured in nutrient medium with the hormone, 2,4-dichlorophenoxyacetic acid. After a lag period, 90 per cent of the cells divided synchronously. During the first two cell cycles, the rate of ribosomal RNA synthesis increased sharply in two steps ; before the onset of DNA synthesis for the first division, and early in interphase before the second division. Rates of RNA and protein accumulation, and phosphate uptake also increased sharply at these times. From experiments with expiants in which DNA synthesis and cell division had been inhibited, it was concluded that the stepwise pattern of ribosomal RNA synthesis was not caused by the replication of ribosomal RNA genes, as can happen in mammalian cells. Instead, the periodicity of metabolism was found tobe independent of the DNA synthesis-cell division cycle. A cause of the stepwise nature of ribosomal RNA synthesis is suggested. It is considered that despite the high synchrony of division, the system is not completely suited for the study of events associated with the cell cycle in higher plants. However, the synchrony of much of early metabolism suits it to the study of induction of cell division in previously non-dividing cells, and the consequent process of de-differentiation.