PLANT PHYSIOLOGY , Vol 102, Issue 2 467-472, Copyright © 1993 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Compartmentation Analysis of Paraquat Fluxes in Maize Roots as a Means of Estimating the Rate of Vacuolar Accumulation and Translocation to Shoots
J. M. DiTomaso, J. J. Hart and L. V. Kochian
Department of Soil, Crop and Atmospheric Sciences, Cornell University, Ithaca, New York 14853 (J.M.D., J.J.H.)
Efflux analysis conducted after five loading periods of various lengths (2,
6, 12, 18, or 24 h) was used to investigate uptake, compartmentation, and
translocation of [14C]paraquat in maize (Zea mays L.) seedlings. The time
course for net paraquat uptake (paraquat concentration in uptake solution =
25[mu]M) into maize roots was linear (56.7 nmol g-1 root fresh weight h-1)
for 24 h. Estimates of changes in paraquat content in the vacuole,
cytoplasm, and cell wall after 2-, 6-, 12-, 18-, and 24-h loading periods
indicated that the cell wall saturated rapidly, whereas accumulation of
paraquat into the vacuole increased linearly (12.4 nmol g-1 root fresh
weight h-1) over 24 h. In contrast to vacuolar accumulation, cytoplasmic
paraquat content appeared to approach saturation. The half-time for
paraquat efflux from the cell wall (16.6 min [plus or minus] 1.2 SD) and
cytoplasm (58.8 min [plus or minus] 8.9 SD remained relatively constant
regardless of the length of the loading period, whereas the half-time for
efflux from the vacuole was considerably longer and increased linearly with
increased loading time (6.1-18.7 h). The time course for paraquat
translocation to the shoot was linear within a 24-h exposure to
radiolabeled herbicide, but translocation did not begin until 5 h after
initiation of treatment. The experimental approach used in these
experiments provides a valuable method for examining the movement of
paraquat in maize seedlings. Results indicate that the herbicide slowly
accumulates in the vacuole of root cells but is also translocated to the
shoot.
