Translocation and Distribution of Picloram in Bean Plants Associated with Nastic Movements

Abstract

Abstract. Nastic responses in bean plants (Phaseolus vulgaris L. var. Black Valentine) occur rapidly when very low ooncentrations of picloram (4-amino-3,5,6-trichloropicolinic acid) are applied to the root systems. The distribution of pioloram associated with nastic responses was quantitatively determined in root-treated plants.Sixty-seven micrograms of 14C-labeled picloram and 72 sg of unlabeled picloram in 300 ml of nutrient solution were applied to roots of 9-day old bean plants growing in an environmental growth chamber at 240 and 56 % relative humidity. Plants were removed from the treatment solution after uptake periods of 3, 6, and 11 hr. Sections were excised from 10 locations on each plant and 14C content was determined by liquid scintillation techniques. As a qualitative indication of picloram mobility, additional plants were treated for 3 hr and subjected to autoradiographic analysis.The accumulation of picloram within various parts of the plant increased with treatment time. After 3 hr of picloram uptake, a curvature of 60 to 80°from vertical in the upper 50 to 60 mm of stem corresponded to an accumulation in that part of the plant of 0.300 (second internode sample) to 1.065 (terminal bud sample) ng of picloram per mg fresh weight. The appearance of hyponasty in the trifoliolate leaflets after 6 hr of treatment corresponded to a picloram concentration in the leaf of 0.803 to 0.855 ng per mg fresh weight.As evidenced by the 14C count data, the translocation of picloram from the roots to the apical part of the plant was very rapid. Picloram was preferentially accumulated in the terminal bud and first trifoliolate leaflets. Very little picloram was transported to the primary leaves and only at the longer treatment periods. Autoradiographs of plants treated for 3 hr showed a qualitatively similar distribution of ;4C in the plant.The herbicide picloram (4-amino-3,5,6-trichloropicolinic acid) has been characterized as comparable to 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxvacetic acid (2,4,5-T) in absorption anid translocation by plants and leachability from soils, but as more effective oni many broad-leaved plants (6). Distortions in growing tissue, growth promotion in stem sections, and other morphogenetic effects caused by picloram have also been reported (4, 5,6,12 Materials and MethodsBean plants (Phaseolus vulgaris L. var. Black Valentine) were germinated in sand, transferred to aerated half-strength Hoagland and Arnon's nutrient solution (7) and grown in a controlled environment growth chamber. Uniform plants in which the first trifoliolate leaf had just opened (9 days old) were selected for use. Experiments were conducted at 24 + 0.50°56 ± 4 % relative humidity and a 16-hr photoperiod of 1460 ft-c of illumination at plant top level provided by a mixture of fluorescent and incandescent lighting.Plants were treated by immersing the root systems in foil-covered pint jars containing 300 ml of 1 ptNi picloram in half-strength nutrient solution. PLANT PHYSIOLOGY were obtaine...

Uptake of picloram by roots of alfalfa and barley

“…These results are consistent with the findings of Reid and Hurtt (13), who observed preferential accumulation of root-absorbed picloram in apical regions of bean shoots. Presumably picloram is transported to fully expanded leaves via the xylem and, after entry into the assimilate stream, is redistributed to the meristematic region.…”

“…a Dotent root or foliar application (1, 8,13,15) and is neither readily metabolized in plants nor subject to rapid degradation by soil microorganisms (1 1, 15, 16, 18). In general, broadleaf plants are quite susceptible to the chemical, whereas grasses are resistant.…”

CONTROL OF REGENERATION IN ROOTS OF THE DEEP‐ROOTED WEED CHONDRILLA JUNCEA L.

“…Picioram inhibited bud formation further into the root than did 2,4-D Na (Tables 2 and 3, Fig. 1), which could result from picloram's superior auxin activity (Kefford & Caso, 1966;1972), its mode of translocation which appears different from that of 2,4-D (Merkle & Davis 1967; Reid & Hurst, 1969), or both.…”

Responses of Populus tremula to Picloram and Other Translocated Herbicides

“…While the response of the roots may be considered to be more or less directly related to the concentrations in the ambient solution, the responses of the shoots are due to translocated herbicide or, possibly, to injuries caused to the roots or to the conducting tissues. In leguminous species picloram has been shown to be rapidly taken up by the roots and translocated to the shoots (Reid andHurtt 1969, Baur andMorgan 1969). As judged from epinastic responses of the growing tops of the shoots of aspen plants picloram is also translocated very rapidly in this species.…”