Uptake of picloram by roots of alfalfa and barley

Abstract

MORRISON, I. N., and W. H. VANDEN BORN. 1975. Uptake of picloram by roots of alfalfa and barley. Can. J. Bot. 53: 1774-1785. Uptake of [14C]picloram (4-amino-3,5,6-trichloropicolinic acid) from culture solution by alfalfa (Medicago scrti\.o L.) and barley (Hordeirm tzrrlgare L.) seedlings was investigated to determine to what extent passive and (or) active mechanisms are involved in the uptake of the herbicide by roots of intact plants. The roots of both species had similar absorption patterns consisting of rapid initial uptake lasting 1 to 2 h, followed by continuing absorption at a markedly lower rate during the rest of a 12-h treatment period. Initial uptake both by roots and whole plants was not significantly reduced by 1.0 mM NaN,, whereas continuing absorption was depressed by this inhibitor. Q,, values were 1.4foralfalfaand 1 .O for barley forthe first 1-2 hof uptake, whereas for subsequent periods the values were consistently greater than 2.0. Evidently. uptake during the initial phaseof entry is governed by passive processes, while continuing absorption iscontrolled, at least in part. by active mechanisms. Much of the picloram taken up by alfalfa and barley roots during a4-h treatment period was released rapidly tounlabelled nutrient solution. Uptake by both species was decreased in the dark and enhanced in the presence of sucrose. The results of inhibitor studies suggest that picloram absorption by alfalfa plants is more dependent on a supply of metabolic energy than is uptake by barley plants. In most instances, total accumulation of piclolam in 4 h was much greater in alfalfa plants than in barley plants of nearly equivalent mass. This difference may account for at least part of the difference in susceptibility of alfalfa(sensitive) and barley (tolerant) to the herbicide. Alfalfa roots always contained a much greater proportion of the total amount of picloram in the plant than did barley roots.

Mechanisms of Herbicide Absorption Across Plant Membranes and Accumulation in Plant Cells

“…Similarly, imidazolinone uptake was inhibited with sodium azide, sodium cyanide, and 3-(3,4-dichlorophenyl)-l-ldimethylurea (DCMU) 4 (77); and picloram uptake was inhibited by sodium azide and sodium arsenate (43). In contrast, KCN (100) and DNP (44) did not affect 2,4-D uptake nor did sodium azide affect picloram absorption (60). Uptake of 2,4-D and 2,4,5-T was independent of available energy as tested by addition of CCCP, M^-dicyclohexylcarbodiimide (DCCD) 4 , and leci thin (89).…”

Plant Uptake, Transport and Metabolism

“…A reduction in phytotoxicity of the herbicide MCPB applied in darkness has been attributed to reduced translocation in the dark compared to in the light [62]. Root uptake and transport of other chemicals, including picloram [63], have also been shown to be less in darkness than in light. As would be expected, any factor or combination of factors which increase the transpiration rate of plants including high light intensity and low relative humidity is apt to increase the apoplastic movement of xenobiotics whether they are applied to roots or leaves.…”

The Antagonistic Action of 2,4-D and Bromoxynil on Glyphosate Phytotoxicity to Barley (Hordeum vulgare)

“…Glyphosate at rates as low as 0.21 kg/ha controls volunteer cereals as well as broadleaf weeds such as wild turnip (Brassica campestris L.) (4). Other broadleaf weeds, however, such as wild buckwheat (Poly gonum convolvulus L.) 3 , are more tolerant to this rate of glyphosate. When glyphosate is mixed with certain herbicides that are relatively inexpensive and effective for broadleaf weed control, there is a delay in glyphosate phytotoxicity to the grass weeds (4).…”