Translocation of Herbicides and Assimilates in Red Maple and White Ash

Loss of Picloram and 2,4,5-T from the Roots of Ash and Maple Seedlings

“…C) 4 -picloram loss through the roots increased over a 3-week period, with the exception of a slight decrease in the amount lost on the 6th and 16th day from the green ash. ,The total radioactivity in the white ash nutrient solution increased over the 9-day experiment.…”

Potential for Plant-Based Remediation of Pesticide-Contaminated Soil and Water using Nontarget Plants such as Trees, Shrubs, and Grasses

“…Other reasons for tolerance may include efficient translocation and detoxifying mechanisms, presence of detoxifying enzymes or plant compound (for example, benzoxazinone), and nonaccumulating capability of toxic metabolites (which is comparable to excreting toxic materials as a natural response by mammalian systems). On the other hand, the pesticide sensitivity of plants may be related to the following: (1) assimilation of pesticides in phloem vessels, thus injuring living cells, (2) sorption and binding of pesticides to roots and other plant material to reach toxic levels, (3) lack of metabolic capability to detoxify pesticides, (4) accumulation of toxic metabolites of pesticides, and (5) poor translocation and detoxifying mechanisms (Akinyemiju et al, 1983;Dhillion et al, 1968;Hamner and Tukey, 1946;Leonard et al, 1966;Norris and Freed, 1966a, 1966b, 1996cPallas, 1963;Sundaram, 1965;Wichman and Byrnes, 1975).…”

“…The study by Sundaram (1965) showed that in susceptible species where there is more phloem movement, the chemical is least mobile, whereas in the tolerant ones where the chemical moves in the xylem, it is most mobile. Longitudinal and radial investigation of herbicide movement in trees indicated that the killing action in sensitive trees is due to the retention of the herbicide by the phloem, and that its failure to kill tolerant trees is due to upward movement in the transpiration stream via the xylem (Sundaram, 1965 In the study of Leonard et al (1966), upward movement, presumably via the xylem after stem application, was appreciable, as indicated by the accumulation of herbicides, amitrole and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in the leaves following such application. Leonard et al (1966) concluded that absorption into living cells would be possible wherever contact with the herbicide occurs; symplastic transport then would be expected.…”

“…Passage of herbicides from cell walls into the cytoplasm of living cells of red maple might have been inhibited or limited by the cell membranes. If such absorption did occur, then possibly the 2,4,5-T became trapped within the living cells (perhaps vacuoles) in a manner that prevented its transport (Leonard et al, 1966;Pallas, 1963). In the study by Lund-Hoie (1969), phloem movement of simazine was ascribed limited importance because simazine may not be able to enter the symplast from the apoplast.…”

Import and unloading of 14C assimilate into mature leaves of Coleus blumei

“…As the expanding leaves grow older, they undergo a gradual transition to exporting status and, with the possible exception of rosette leaves (Thrower 1977), are considered to have lost the ability to import by the time they are fully expanded. A growing number of autoradiographic studies has shown, however, that mature leaves are capable of importing at least some material, especially if their sink strength is increased (usually by predarkening) and (or) competing sinks are removed (Thaine et al 1959;Thrower 1962Thrower , 1974Leonard et al 1966;Wu and 'Thrower 1973;Thrower and Thrower 1980;Blechschmidt-Schneider 1984;Blechschmidt-Schneider and Eschrich 1985). The imported label is confined largely to the major veins, with little reaching the minor veins and still less, if any, appearing in the mesophyll.…”