are known to diminish the purple color of the complex
(Delhaize et al. 1993). Our results therefore suggest that
the roots of tea seedlings secrete Al-ligands, which have a
higher affinity for Al than for hematoxylin.
We previously reported the secretion of citrate, malate
and oxalate from tea roots after exposure to Al in
solution under aseptic conditions (Morita et al. 2001).
However, in that study, the possibility existed that
microorganisms were producing these organic acids in
the medium. We therefore employed aseptic conditions in
this study to examine whether low molecular weight
organic compounds produced by tea plant roots exhibited
Al-chelating ability. Although citrate, malate and
oxalate were secreted from tea roots in the treatment
medium, only the oxalate efflux increased in response to
an increase in the external Al concentration (Fig. 4a). The
secretion of oxalate from roots in response to Al
exposure has also been observed in other Al-accumulating
plant species, such as buckwheat (Ma et al. 1997a)
and tora (Colocasia esculenta L. cv. Lehua maoli) (Ma
and Miyasaka 1998). In this study, the amount of
oxalate secreted from tea roots ranged from 0.2 to
0.8 mmol h1 on a dry weight basis, which was somewhat
lower than that in buckwheat (1.0 to 1.5 mmol h1 on a
are known to diminish the purple color of the complex
(Delhaize et al. 1993). Our results therefore suggest that
the roots of tea seedlings secrete Al-ligands, which have a
higher affinity for Al than for hematoxylin.
We previously reported the secretion of citrate, malate
and oxalate from tea roots after exposure to Al in
solution under aseptic conditions (Morita et al. 2001).
However, in that study, the possibility existed that
microorganisms were producing these organic acids in
the medium. We therefore employed aseptic conditions in
this study to examine whether low molecular weight
organic compounds produced by tea plant roots exhibited
Al-chelating ability. Although citrate, malate and
oxalate were secreted from tea roots in the treatment
medium, only the oxalate efflux increased in response to
an increase in the external Al concentration (Fig. 4a). The
secretion of oxalate from roots in response to Al
exposure has also been observed in other Al-accumulating
plant species, such as buckwheat (Ma et al. 1997a)
and tora (Colocasia esculenta L. cv. Lehua maoli) (Ma
and Miyasaka 1998). In this study, the amount of
oxalate secreted from tea roots ranged from 0.2 to
0.8 mmol h1 on a dry weight basis, which was somewhat
lower than that in buckwheat (1.0 to 1.5 mmol h1 on a
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