Transcript Poster on Crotalaria juncea presented at the 2010 meeting of the

Phytotoxicity of 2-Amino-5-Hydroxyhexanoic Acid
G. Leather, R. Hanshaw, T. West, and T. Palmatory
West Virginia University
ABSTRACT
A non-protein amino acid, 2-amino-5-hydroxyhexanoic
acid (5-HNL), extracted from Crotalaria juncea (sunn
hemp, var. Tropic Sun) seeds inhibits the growth of
many agronomical important weeds at low dosage
levels. This compound is unique among allelochemicals
in that when topically applied to weeds that reproduce
by root buds, the treated plants symptomatically lose
chlorophyll (bleach) and plantlets from the root buds
are also devoid of chlorophyll, indicating translocation
of the compound (source to sink). When compared to
the organic herbicide, Amitrole (3-amino-1,2,4-triazole),
a carotenoid synthesis inhibitor, in a Lemna obscura
bioassay, 50μM of the 5-HNL inhibited growth of Lemna
to the same extent as 100μM of Amitrole. Lemna minor
was more sensitive to the 5-HNL in bioassay with a 90%
inhibition of growth at 12μM. The in vitro deamination
of poly-L-lysine by nitrite at low pH, produces 5-HNL and
the 6-hydroxy (6-HNL) isomer along with the isomer
chlorosubstitution products (5-CNL & 6-CNL). We are
currently assessing if the in vitro produced 5-HNL has
the same level of phytotoxicity as the in vivo produced
5-HNL and if any of the other products of poly-L-lysine
deamination are phytotoxic.
INTRODUCTION
Sunn hemp seeds contain a potent allelochemical 2-amino-5-hydroxyhexanoic acid (5-HNL)
Extracts of Crotalaria juncea seeds inhibited the
growth of Sinapis arvensis seedlings (4).
The isolation of a non-protein amino acid (5-hydroxy
norleucene) from the seeds of sunn hemp was first
reported by Pant and Fales in 1974 (1). Wilson & Bell (2)
found that 5-HNL was phytotoxic to lettuce in bioassays.
Leather et al. (3) demonstrated the allelopathic nature
of sunn hemp on Euphorbia esula and found that an
extract of the sunn hemp seeds inhibited the growth of
Lemna sp. in bioassay. Other allelopathic effects were
reported by Cole (4). Recently, Adler and Chase (5)
compared the allelopathic potential of sunn hemp to
other leguminous cover crops. The results reported here
suggest that with additional research, 5-HNL may be
useful in agriculture weed control.
Lemna minor bioassay used to determine the
phytotoxicity of 5-HNL
Differential inhibition of L. minor and L. obscura by 5-HNL
Leafy spurge
One droplet containing 5-HNL placed
on the terminal bud stopped growth
of plant and affected the plants
emerging from root buds.
Untreated plant
Extracts of Crotalaria juncea inhibited the growth
of Euphorbia esula seedlings (3,4).
CANADA THISTLE
Untreated plant
One droplet containing 5-HNL placed
on the terminal bud stopped growth
and affected the plants emerging
from root buds
INFLUENCE OF AMITROLE (3-amino-1,2,4-triazole) AND 5-HNL
ON LEMNA OBSCURA
LITERATURE CITED
1. Pant, R. & H.M. Fales. 1974. Phytochem. 13:1626 – 1627.
2. Wilson, M.F. & E.A. Bell. 1979. Phytochem. 18:1883-1884.
70
3. Leather, G.R., Yang, S.M., & W.M. Dowler. 1989. Proceed.
Leafy Spurge Sym. PP. 46-50.
60
4. Cole, S.D. 1991. Thesis, U. South Dakota. 74 pgs.
50
5. Adler, M.J. & C.A. Chase. 2007. HortSci. 42:289-293.
40
AM 100μM
CJ 50μM
30
20
10
0
Frond #
Frond wt.
Anthocy.