Toshio Yamaki

Relationship between cell division and endogenous auxin in synchronously-cultured tobacco cells

In the cultured tobacco cell, we succeeded in obtaining a partial synchronization of cell division by a combination of pre-starvation, rhythmic light-dark pre-treatment and air tight pre-conditioning. The mitotic index increased during the light period according to the time interval after the end of pre-treatment, and reached its maximum (max=12%) at about 2.5 hr of irradiation, and about 80% of cells completed division 1.5 hr thereafter.During this period, IAA was biosynthesized in the cells, though these cells had been cultured in Murashige and Skoogs medium with 1 mg/l of 2,4-D as a growth substance. IAA was identified by paper chromatography, followed byAvena curvature test and combined gas chromatography-mass spectrometry. The time course of the increase and decrease in the amount of free IAA was parallel to that of the mitotic index. On the other hand, bound IAA increased later and decreased gradually after the end of cell division. Free IAA may have an important role in mitosis.

Electron microscopy of isolated tobacco mesophyll protoplasts cultured in vitro

Summary Some ultrastructural changes of tobacco mesophyll protoplasts cultured in vitro were examined under the electron microscope. An early stage of wall regeneration was recognizable after 2 days of culture when randomly oriented fibrils composed of cellulose appeared at the surface of protoplasts. The regenerated walls grew gradually in thickness and the fibrils became oriented parallel to the plasmalemma. During the process of colony formation differentiated mesophyll cells reverted to meristematic ones, accompanying the degeneration of chloroplasts. The significance of these phenomena is discussed.

EFFECT OF LIGHT ON AUXIN TRANSPORT AND ELONGATION OF AVENA MESOCOTYL

The present work was undertaken to find if there are relations between light and auxin action on elongation of coleoptilar node and mesocotyl with Avena seedlings. Red light inhibited the elongation of mesocotyl and simultaneously decreased the rate of transport of diffusible auxin through the node. Red light also inhibited the transport of exogenously given IAA through the nodal region. The light inhibition of IAA transport was closely related to the increase of IAA immobilization.

Increase in activity of IAA-synthesizing enzymes prior to cell division

During the course of cell division in synchronously dividing cultured tobacco cells, the activity of IAA-synthesizing enzymes increased first, then the amount of endogenous IAA, and finally, the number of dividing cells. Based on the results obtained, we discussed the role of endogenous IAA in cell division.

INDOLE‐3‐ACETIC ACID IN CHICK EMBRYOS

The occurrence of IAA, a plant‐growth‐regulating substance of the auxin group, was investigated in developing chick embryos. Paperchromatography followed by the Avena curvature test revealed the presence of a substance with auxin activity and the same Rf as IAA. This substance was identified as IAA by combined gas chromato‐graphy‐mass spectrometry. The amount of IAA in a unit weight of embryo was almost identical during embryo development, the total amount of IAA in an embryo increasing as it developed. The amount of IAA in the whole egg was also examined and it was found that an egg incubated for 9 days at 37°C contained a larger amount of IAA than one not incubated.

Auxin in SRNA Fraction of Mung Bean Hypocotyl

Auxin regulates many aspects of the growth of plants. At the cellular level, it regulates cell expansion and cell division, at the subcellular level, the synthesis of many kinds of enzymes, e.g. acid phosphatase (Palmer, 1967), cellulase (MacLachlan, et al, 1967), hemicellulase, β-1,3-glucanase (Masuda, 1967), peroxidase (Glasziou et al, 1967, Galston et al, 1967). This indicates the multiplicity of auxin action even in enzyme synthesis. This multiplicity will be observed in nucleic acid synthesis, when we consider the correspondence of an enzyme to a messenger RNA. Actually, auxin promotes the synthesis of mRNA (Key and Ingle, 1967), and there must be many kinds of mRNAs whose synthesis are regulated by auxin. What is the main point of action of auxin? O’Brien et al. (1967) and others tried to find a repressor protein(s) for a gene which is derepressed by auxin. This is a possible way to elucidate the multiple action of auxin monistically.