PNL Volume 14
Jacobsen, H. J. Institute of Genetics, University of Bonn
Federal Republic of Germany
Morphogenetic reactions of plant tissues to the application of cer-
tain types of phytohormone were shown to depend on (a) the plant's
genetic background and (b) the amount of free active hormone in the
cells. In the case of auxin effects in pea, we demonstrated that the
ability of intact pea seedlngs to reduce the auxin concentration by
oxidation (IAA) or conjugation (NAA) led to negligible morphogenetic
damages, while 2,4-D applied to the roots caused severe damage of the
seedlings because this growth regulator is metabolized to a much lesser
extent (1). On the other hand, we were able to demonstrate that the
fasciated mutant 489 C was able to form roots from auxin-induced callus,
while its initial line was not (2).
In a recent experiment, we tested the ability of a number of auxins
and so-called "non-active'' analogs on callus induction in epicotyl seg-
ments of the initial line (2 x 10 replications with 10~4 M of the
hormone, grown on Murashige/Skoog medium). The results, shown in
Table 1, were scored after 4 weeks in culture and are grouped in accord-
ance with the frequency of the parameter "%-callus induction".
Obviously, the phenoxy compounds 2,4-D, MCPA, and, surprisingly,
3,5-D were most effective in callus induction, while the other auxins
IBA, NAA, and IAA were less effective in this system at the applied
concentration. Compounds like 3,5-D, indole-3-acry lie acid, benzoic
acid, or indole-acetonitrile generally are referred to as "inactive"
auxins, where a behavioral pattern like that observed with 2-(2,4-
dichlorophenoxy)-proprionic acid would be expected. The effects on
callus induction or swelling of some of the explants were probably due
to interactions of these compounds with the reactions of the segments on
wounding. In any case, from the results of the present experiments no
PNL Volume 14
clear or definitive statement about the biological activity of an auxin-
analog could be made.
1. Ingensiep, H. W. , M. Herlt, and H.-J. Jacobsen. 1981.
Morphogenetic response, translocation and metabolism of root-applied
auxin in pea seedlings. PNL 13:21-23.
2. Jacobsen, H.-J., H. W. Ingensiep, M. Herlt, and M. L. H. Kaul.
1980. Tissue culture studies in Pisum sativum. In: Plant Cell
Cultures: Results and Perspectives. F. Sala, B. Parisi, R. Cella
and 0. Ciferi, editors. Elsevier/North Holland Biomedical Press,
Amsterdam, p. 319-324.