K. Chamberlain et al., PHLOEM TRANSLOCATION OF PYRIDINECARBOXYLIC ACIDS AND RELATED IMIDAZOLINONE HERBICIDES IN RICINUS-COMMUNIS, Pesticide science, 45(1), 1995, pp. 69-75
The movement of [C-14]pyridinecarboxylic acids was investigated in the
castor bean plant Ricinus communis L. after application by petiole in
jection. The three isomeric unsubstituted acids appeared in similar co
ncentrations in phloem sap taken from the upper main stem over a perio
d of 6 h after application, but nicotinic acid occurred at higher conc
entrations than its isomers in phloem sap from the lower stem indicati
ng better retention in the phloem sieve tubes. After 24 h, nicotinic a
cid had accumulated to a greater extent in the phloem sinks than had p
icolinic or isonicotinic acids. Phloem transport of substituted analog
ues, including dihalopyridinecarboxylic acids and imidazolinone herbic
ides, was measured in short-term tests, and attempts made to relate su
ch transport to the lipophilicity and pK(a) of the compounds. Analogue
s of the imidazolinone, imazapyr, were less well transported than imaz
apyr itself, and were also much less well taken up by barley roots fro
m nutrient solution compared to the herbicidal imidazolinone, and this
could explain their low herbicidal efficacy despite a high intrinsic
activity against the target enzyme acetolactate synthase.