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The Role of EDTA in Lead Transport and Accumulation
by Indian
Mustard1
Andrew D. Vassil,
Yoram Kapulnik,
Ilya Raskin, and
David E. Salt*
AgBiotech Center, Rutgers University, Cook College, New Brunswick,
New Jersey 08903 (A.D.V., I.R.); Agronomy and Natural Resources
Department, The Volcani Center, Bet Dagan, 50250, Israel (Y.K.); and Chemistry Department, Northern Arizona University, Flagstaff,
Arizona 86011 (D.E.S.)
Indian mustard (Brassica
juncea) plants exposed to Pb and EDTA in hydroponic solution
were able to accumulate up to 55 mmol kg 1 Pb in dry shoot
tissue (1.1% [w/w]). This represents a 75-fold concentration of Pb
in shoot tissue over that in solution. A threshold concentration of
EDTA (0.25 mM) was found to be required to stimulate this
dramatic accumulation of both Pb and EDTA in shoots. Below this
threshold concentration, EDTA also accumulated in shoots but at a
reduced rate. Direct measurement of a complex of Pb and EDTA (Pb-EDTA)
in xylem exudate of Indian mustard confirmed that the majority of Pb in
these plants is transported in coordination with EDTA. The accumulation
of EDTA in shoot tissue was also observed to be directly correlated
with the accumulation of Pb. Exposure of Indian mustard to high
concentrations of Pb and EDTA caused reductions in both the
transpiration rate and the shoot water content. The onset of these
symptoms was correlated with the presence of free protonated EDTA
(H-EDTA) in the hydroponic solution, suggesting that free H-EDTA is
more phytotoxic than Pb-EDTA. These studies clearly demonstrate that
coordination of Pb transport by EDTA enhances the mobility within the
plants of this otherwise insoluble metal ion, allowing plants to
accumulate high concentrations of Pb in shoots. The finding that both
H-EDTA and Pb-EDTA are mobile within plants also has important
implications for the use of metal chelates in plant nutritional
research.
1
This research was supported by grants from the
U.S. Department of Agriculture (no. 96-35102-3838 to D.E.S.) and
Phytotech, Inc., to I.R.
*
Corresponding author; e-mail david.salt{at}nau.edu; fax
1-520-523-8111.
Plant Physiol. (1998) 117: 447-453
Copyright Clearance Center: 0032-0889/98/117/0447/07
© 1998 American Society of Plant Physiologists
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