INTERACTION OF ROOT-APPLIED 2,4-D AND COLCHICINE ON MORPHOGENESIS

18 RESEARCH REPORTS

PNL Volume 13

1981

Ingensiep, H. W.

Institute of Genetics, University of Bonn, Federal Republic of Germany

Microtubules (MT) have been shown to play an important role in cell

division and cell shape (1). It has long been known that endogenously applied

colchicine affects plant morphogenesis in a manner similar to that of some

phytohormones (2), but the extent to which phytohormones and colchicine

interact to influence MT-disorganization is not yet clear (1, 2, 3). This

prompted me to perform some experiments using the 2,4-D culture system for

etiolated pea seedlings (4).

It is well known that colchicine in low concentrations acts on the

microtubule system, in particular on the MT of the mitotic spindle (10^-6 M).

In higher concentrations colchicine is known to induce peculiar swellings

in root tips named "C-tumors" (2), giving rise to the idea that because of

these morphogenetic effects it acts like a phytohormone. Less known are

the macroscopic effects on shoot development as we found in our culture

system.

One-week-old etiolated pea seedlings

were used for studying auxin-colchicine

interactions. The seedlings were

treated with colchicine (5 x 10^-3M

and colchicine/2,4-D (5 x lO^-3 M/10^-4M;

24 h root-applied) and further cultivated

on moist vermiculite for one week

(light/dark: 16/8 h; 2500 lux). Under

these conditions colchicine induced

C-tumors in root tissue of the seedlings

(Fig. 1). In the shoots, basal and

apical parts were strongly swollen

and their length reduced; the develop-

ment of the green leaves was inhibited

(Fig. 2). This effect shows some

similarities to the morphology of

fasciated mutants and may be a hint

for the understanding the basic

mechanism leading to fasciation.

If colchicine under these conditions

acts mainly as MT-disorganizer, abnormal

formation of spindle or cortical micro-

tubules during cell division or growth

may play an important role during

the induction of the observed growth

aberrations in our plants.

On the other hand it is known that

auxins induce similar depolarized

growth in plants. The questions raised

are: What are the differences between

auxin-induced and colchicine-induced

morphogenetic aberrations leading

to the death of the plants and what

kinds of interaction exist?

Fig. 1. "C-tumors" induced by

colchicine.

PNL Volume 13 1981

RESEARCH REPORTS 19

Fig. 2. Effect of colchicine on shoot morphogenesis. Note swollen stem

and inhibited leaf development.

Our investigations revealed that the application of both 2,4-D and

colchicine to the roots leads to strongly inhibited root and shoot development.

We observed tissue swelling of the primary and lateral roots leading to rup-

tures, which often are observed for 2,4-D alone in this concentration range

(4). Some swelling occurred in the root tip region, but to a lesser degree

than in seedlings treated with colchicine alone (Fig. 3). Shoot morphogenesis

was similar to that of seedlings treated with colchicine alone, but the

inhibition appeared to be stronger. Typical 2,4-D effects such as induction

of lateral or adventitious roots and formation of callus-like structures were

not observed under these conditions. This demonstrates that the drastic

morphogenic effects of 2,4-D (4) were repressed by the joint treatment with

colchicine. A repression of auxin-induced growth by colchicine and other

MT-disorganizers has already been demonstrated with wheat coleoptile segments

(3). It is assumed that polymerization of MT-subunits is required for normal

growth to occur. The effect of both compounds on polarity of single cells

is known. In the case of colchicine it was clearly demonstrated that cells

of untreated controls stretch mainly in longitudinal axial directions, while

cells of colchicine treated roots expand transversely with a maximum in the

cortical tissue above the root tip (2). This observation, led Levan to con-

clude that a similar increase in cell size results in C-tumors just as in

auxin-induced enlargement. With respect to the biochemical action of colchi-

cine on the MT-organization, the present investigations confirm the hypothesis

that expression of normal and abnormal morphogenesis in plants depends on

the basic mechanism of MT-formation within the cell, which probably is

mediated somehow by intercellular regulators like auxins.

20 RESEARCH REPORTS PNL Volume 13 1981

1. Dustin, P. Microtubules. Springer, Berlin. 1978.

2. Levan, A. The macroscopic colchicine effect - a hormonic action?

Hereditas 28:1244. 1942.

3. Lawson, R. V. and R. L. Weintraub. Interactions of microtuble disorganizers,

plant hormones and red light in wheat coleoptile segment growth. Plant

Physiol. 55:1062-1066. 1975.

4. Ingensiep, H. W., et al. Morphogenetic response, translocation, and

metabolism of root-applied auxin in pea seedlings. PNL 13:21. 1981.

Fig. 3. Combined effect of colchicine and

2,4-D on root development.