dry weight basis) treated with 50 mm AlCl3 in a 0.5mM
CaCl2 solution at pH 4.5 (Ma et al. 1997a), but considerably
higher than tora (around 0.01 mmol g1DWh1
on a dry weight basis) treated with 0.9mM AlCl3 in
nutrient solution at pH 4.0 (Ma and Miyasaka 1998).
These findings suggested that, like buckwheat, the roots
of tea plants have the ability to detoxify Al via the
secretion of oxalate.
Recent studies on the secretion of organic acids in
response to Al exposure have shown that there appear to
be two organic acid secretion mechanisms that differ
primarily on the basis of the timing of acid secretion
(Ma 2000). In Pattern †, no discernible delay is observed
between the addition of Al and the onset of secretion,
while in Pattern ††, organic acid secretion occurs several
hours after the initial Al exposure. In this study, the
secretion of oxalate from the roots of tea seedlings
increased within 1 h (Fig. 4b) suggesting that tea plants
employ a Pattern † secretion, which is the same pattern
used by buckwheat (Ma et al. 1997a). Our findings also
suggest that, in the process leading to the secretion of
organic acid anions in Pattern †, Al activates a
pre-existing anion channel on the plasma membrane
and that the induction of gene expression is not required
(Ma 2000; Ma et al. 2001). The precise mechanism of
oxalate secretion by tea plant roots is still unclear, and
further studies using anion channel inhibitors are
required to more closely examine the involvement of
anion channels in oxalate secretion.
dry weight basis) treated with 50 mm AlCl3 in a 0.5mM
CaCl2 solution at pH 4.5 (Ma et al. 1997a), but considerably
higher than tora (around 0.01 mmol g1DWh1
on a dry weight basis) treated with 0.9mM AlCl3 in
nutrient solution at pH 4.0 (Ma and Miyasaka 1998).
These findings suggested that, like buckwheat, the roots
of tea plants have the ability to detoxify Al via the
secretion of oxalate.
Recent studies on the secretion of organic acids in
response to Al exposure have shown that there appear to
be two organic acid secretion mechanisms that differ
primarily on the basis of the timing of acid secretion
(Ma 2000). In Pattern †, no discernible delay is observed
between the addition of Al and the onset of secretion,
while in Pattern ††, organic acid secretion occurs several
hours after the initial Al exposure. In this study, the
secretion of oxalate from the roots of tea seedlings
increased within 1 h (Fig. 4b) suggesting that tea plants
employ a Pattern † secretion, which is the same pattern
used by buckwheat (Ma et al. 1997a). Our findings also
suggest that, in the process leading to the secretion of
organic acid anions in Pattern †, Al activates a
pre-existing anion channel on the plasma membrane
and that the induction of gene expression is not required
(Ma 2000; Ma et al. 2001). The precise mechanism of
oxalate secretion by tea plant roots is still unclear, and
further studies using anion channel inhibitors are
required to more closely examine the involvement of
anion channels in oxalate secretion.
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