28
PNL Volume 15 1983
RESEARCH REPORTS
MORPHOGENETIC EFFECTS. AUXIN UPTAKE AND METABOLISM OF SOME PEA
VARIETIES AFTER ROOT APPLICATION OF AUXINS
Ingensiep, H. W. Institute of Genetics, University of Bonn
Federal Republic of Germany
Previously we proposed a system to test the effects of root applied
auxins on morphogenesis, auxin uptake, and metabolism of young pea
seedlings (1,2). The present paper summarizes the results of experi-
ments with six varieties of peas using the described test system
(Table 1). The varieties differed in seed color and weight and in
epicotyl length under uniform cultural conditions. Our hope was to find
some pea varieties that showed differences in response to root applica-
tion of auxins.
One-week-old pea seedlings were treated with the auxins 2,4-D,
2,4,5-T, NAA, and IAA (10~4M, 14C-labeled) for 24 hours via the roots
(10 ml medium per seedling). The loss of radioactivity in the medium
was measured and ethanolic extracts from the root tissue were analyzed
by thin layer chromatography (TLC). These experiments showed no sig-
nificant differences in uptake behavior, auxin metabolism, or
morphogenetic response among the varieties tested. All varieties showed
the following uptake behavior: The 2,4-D and 2,4,5-T uptake was very
low (about 10%), the uptake of NAA and IAA was very great (more than 30,
40%, respectively) under these conditions. The TLC-analysis of
ethanolic root extracts by autoradiography and the liquid scintillation
count data were in accord with the well-known explanation for this up-
take behavior: The 2,4-D and the 2,1,5-T radioactivity is only
represented by the spot of the free auxin. However, because the NAA and
IAA form conjugation products with aspartic acid the radioactivity ap-
pears in two spots, viz. the free auxin and amino acid-conjugation
products (NAA). Little difference in this reaction pattern was found
among the varieties.
The morphogenetic response among varieties was also sim:
The 2,1-D- and 2,4,5-T-treated seedlings were strongly inhibited in
their light dependent morphogenesis (tissue swelling, irregular lateral
roots, callus structures), while the NAA- or IAA-treated seedlings were
only slightly affected due to the metabolic inactivation of high amounts
of the free auxin. The results are summarized in Table 1.
These preliminary investigations confirm the view that the genes
which are involved in regulation of the endogenous auxin content (for
example for conjugating enzymes) seem to be very conservative within the
species. Further tests with other Pisum stocks are necessary to find
auxin-sensitive mutants, which differ in their response to auxins.
PNL Volume 15
1983
RESEARCH REPORTS 29
1. Ingensiep, H. W. , M. Hertl, and H. L. Jacobsen. 1981.
PNL 13:21-23.
2. Ingensiep, H. W. 1982. PNL 14:19-20.