Effect of Auxin and Abscisic Acid on RNA and Protein Synthesis prior to the First Cell Division in Jerusalem Artichoke Tuber Tissue Cultured in vitro

Abstract

Summary The present paper deals with the effects of auxin (NAA) and abscisic acid on the rates of RNA and protein synthesis at different times during the lag period prior to DNA synthesis in Jerusalem artichoke tuber explants. While an auxin is found to be essential for the induction of DNA synthesis, it is not required for the initiation of RNA or protein synthesis in this tissue. RNA synthesis, as studied by the incorporation of 3H-uridine into TCA insoluble material begins within 2 hrs of excision and incubation in the growth medium. In explants grown in hormonefree medium two peaks of RNA synthesis are seen. The presence of NAA (1 mg/1) causes slight inhibition of RNA synthesis during the first peak while the second peak is slightly delayed to coincide with the initiation of DNA synthesis in the cells. The presence of ABA in the medium further augments NAA effects. Protein synthesis, as studied by the incorporation of 3H-leucine into TCA insoluble material, starts at about 4-8 hrs of incubation. In the absence of hormones in the medium two peaks of increased rate of protein synthesis are observed. While the presence of NAA (1 mg/1) or NAA and ABA (1 and 2 mg/l, respectively) has no significant effect during the first peak of protein synthesis, the second peak is completely suppressed in their presence. Neither NAA nor ABA has any significant effect on the uptake of radioactive precursors (uridine or leucine) by the tissue. It is suggested that the auxin probably induces certain qualitative changes in the kinds of RNA and proteins being synthesized in response to wounding, without significantly altering the total rates of their synthesis during the early part of the lag period. Alternatively, it may alter the turnover rates of these macromolecules. Abscisic acid, on the other hand, does not cause any additional changes during this period over and above those of NAA. The presence of ABA does not seem to be crucial during this period. Its effect on the stimulation of auxin-induced cell division is largely confined to the time just before the onset of DNA replication.