Generally, Al is known to induce (1, 3)--glucan
(callose) synthesis in roots, and callose formation may
be a potent parameter affecting Al toxicity and tolerance
(Wissenmeier et al. 1992; Zhang et al. 1994; Horst 1995;
Sivaguru et al. 2000). However, the callose content in
root tips of tea plants exposed to Al was lower than it
was in the root tips of plants cultured in media without
Al (Lian et al. 1998). Furthermore, tea root growth is
stimulated by the presence of Al (Konishi et al. 1985).
Eklund and Eliasson (1990) suggested that callose may
itself be a factor in preventing the ‘‘wall-loosening
process’’ and, consequently, cell wall extension.
Recently, caffeine was found to completely prevent the
deposition of callose in the cell plates of cultured tobacco
cells (Yasuhara 2005). In this study, the observation that
caffeine concentration of the treatment medium
increased within 60 min of Al exposure (Fig. 5) suggests
that the secretion of caffeine from tea roots might be
activated by Al or Al-oxalate complexes. These findings
suggest that the secretion of caffeine by tea roots
observed in this study may have stimulated root
growth through the inhibition of callose deposition in
the root tips. Thus, in order clarify the role of caffeine
secretion in the roots of tea plants, it will be necessary to
estimate whether Al exposure and other plant stressors
Generally, Al is known to induce (1, 3)--glucan
(callose) synthesis in roots, and callose formation may
be a potent parameter affecting Al toxicity and tolerance
(Wissenmeier et al. 1992; Zhang et al. 1994; Horst 1995;
Sivaguru et al. 2000). However, the callose content in
root tips of tea plants exposed to Al was lower than it
was in the root tips of plants cultured in media without
Al (Lian et al. 1998). Furthermore, tea root growth is
stimulated by the presence of Al (Konishi et al. 1985).
Eklund and Eliasson (1990) suggested that callose may
itself be a factor in preventing the ‘‘wall-loosening
process’’ and, consequently, cell wall extension.
Recently, caffeine was found to completely prevent the
deposition of callose in the cell plates of cultured tobacco
cells (Yasuhara 2005). In this study, the observation that
caffeine concentration of the treatment medium
increased within 60 min of Al exposure (Fig. 5) suggests
that the secretion of caffeine from tea roots might be
activated by Al or Al-oxalate complexes. These findings
suggest that the secretion of caffeine by tea roots
observed in this study may have stimulated root
growth through the inhibition of callose deposition in
the root tips. Thus, in order clarify the role of caffeine
secretion in the roots of tea plants, it will be necessary to
estimate whether Al exposure and other plant stressors
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