GENETICALLY CAUSED DIFFERENCES IN SOLUBLE AUXIN-BINDING: CORRELATION WITH INTERNODE LENGTH AND CALLUS FORMATION

PNL Volume 17 1985

RESEARCH REPORTS

GENETICALLY CAUSED DIFFERENCES IN SOLUBLE AUXIN-BINDING: CORRELATION

WITH INTERNODE LENGTH AND CALLUS FORMATION

Jacobsen, H.-J. Institute of Genetics

University of Bonn, Federal Republic of Germany

In tissue culture studies with crop plants, one often is confronted

with recalcitrant regeneration when hybrid lines or cultivars serve as

starting material. In pea, the use of defined mutants resulted in a

certain success of regenerating plants from callus tissues (7, 8) or

somatic embryos from calli transferred to liquid medium (4, 6). These

results indicate that success or failure of in vitro regeneration is

determined in part by the genotype. Since attempts to use the potential

of in vitro technology for crop improvement depend on the regeneration

of intact plants from isolated and selected cells or protoplasts, the

lack of complete understanding and control of this process is a key

problem in most important crops, e.g. large seeded legumes such as pea.

Thus, investigations were carried out in an attempt to correlate the

known genetic control of in vitro behavior with observations on the

molecular level of hormone recognition in plants.

The existence in pea of soluble cytoplasmic auxin-binding sites is

well established (1, 2, 3, 5). Epicotyls of etiolated pea seedlings

exhibit soluble auxin-binding with all characteristics required (or re-

ceptor function of these proteins. These proteins are a) specific for

auxins, b) have a high affinity to bind active auxins, and c) show a

time-dependent occurrence. One binding site (sABP1) is found in the

cytosol of etiolated pea seedlings aged 7 days or more; a second site

(sABP2) can be found in seedlings 9 days after germination (3). These

two binding sites can further be distinguished by their different pi and

their different dissociation constants.

In recent experiments it was demonstrated that in a recombinant

derived from a cross between mutant 489C and the initial line (DGV) the

second binding site was not expressed as in the parent lines (Fig. 1).

Both soluble auxin-binding sites evidently were present in each of the

two parental lines whereas only one was evident in recombinant R 1111.

The internode length of the recombinant is twice that of DGV but the

number of internodes is the same, so the height of the mutant in the

field is about double that of the initial line (Loennig, pers. comm.).

On the other hand, R 1111 reacts best in callus induction experiments.

While calli formed from explants of non-elongated internodes (6 mm) of

DGV and 489C after 3 days were 8.11 +/- 0.8 mm and 8.29 +/- 1.0 mm, the mean

length of these calli in the recombinant was 9.27 +/- 1.2mm. From these

data it is suggested that the different in vitro reaction reflects the

differences observed with the soluble auxin-binding kinetics.

1. Jacobsen, H.-J. 1981. Cell Biol. Intl. Rep. 5(8):768.

2. Jacobsen, H.-J. 1982. Physiol. Plant. 56:161-167.

3. Jacobsen, H.-J. 1984. Plant & Cell Phys. 25(6):867-873.

4. Jacobsen, H.-J. and W. Kysely. 1984. Plant Cell Tissue & Organ

Culture (In press).

5. Jacobsen, H.-J. and K. Hajek. 1985. Biol. Plant. (In press).

6. Kysely, W. 1985. PNL 17:38-39.

7. Malmberg, R. L. 1979. PNL 11:21-22.

8. Malmberg, R. L. 1982. PNL 14:39-40.

^1/Dedicated to Prof. Dr. W. Gottschalk on the occasion of his 65th

birthday.



	PNL Volume 17 1985	RESEARCH REPORTS 33



	Fig. 1. Scatchard plots showing apparent cooperative binding of NAA in the cytosols of etiolated seedlings from two parent lines ( Delta - DGV; x---x 489C) , and the absence of cooperativity in the recombinant R 11.11 (o---o) (epicotyls were from 10-day-old etiolated seedlings).