The Boron Requirement and Cell Wall Properties of
Growing and
Stationary Suspension-Cultured
Chenopodium album L.
Cells |
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Authors: | Axel Fleischer Christine Titel and Rudolf Ehwald |
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Institution: | Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Institut für Biologie, Invalidenstrasse 42, 10115 Berlin, Germany |
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Abstract: | Suspension-cultured
Chenopodium album L. cells are capable of continuous,
long-term growth on a boron-deficient medium. Compared with cultures
grown with boron, these cultures contained more enlarged and detached
cells, had increased turbidity due to the rupture of a small number of
cells, and contained cells with an increased cell wall pore size. These
characteristics were reversed by the addition of boric acid (≥7
μm) to the boron-deficient cells. C. album
cells grown in the presence of 100 μm boric acid entered
the stationary phase when they were not subcultured, and remained
viable for at least 3 weeks. The transition from the growth phase to
the stationary phase was accompanied by a decrease in the wall pore
size. Cells grown without boric acid or with 7 μm boric
acid were not able to reduce their wall pore size at the transition to
the stationary phase. These cells could not be kept viable in the
stationary phase, because they continued to expand and died as a result
of wall rupture. The addition of 100 μm boric acid
prevented wall rupture and the wall pore size was reduced to normal
values. We conclude that boron is required to maintain the normal pore
structure of the wall matrix and to mechanically stabilize the wall at
growth termination.The ultrastructure and physical properties of plant cell walls are
known to be affected by boron deficiency (Kouchi and Kumazawa, 1976;
Hirsch and Torrey, 1980; Fischer and Hecht-Buchholz, 1985; Matoh et
al., 1992; Hu and Brown, 1994; Findeklee and Goldbach, 1996). Moreover,
boron is predominantly localized in the cell wall when plants are grown
with suboptimal boron (Loomis and Durst, 1991; Matoh et al., 1992; Hu
and Brown, 1994; Hu et al., 1996). In radish, >80% of the cell wall
boron is present in the pectic polysaccharide RG-II (Matoh et al.,
1993; Kobayashi et al., 1996), which is now known to exist as a dimer
that is cross-linked by a borate ester between two apiosyl residues
(Kobayashi et al., 1996; O''Neill et al., 1996). Dimeric RG-II is
unusually stable at low pH and is present in a large number of plant
species (Ishii and Matsunaga, 1996; Kobayashi et al., 1996, 1997; Matoh
et al., 1996; O''Neill et al., 1996; Pellerin et al., 1996; Kaneko et
al., 1997). The widespread occurrence and conserved structure of RG-II
(Darvill et al., 1978; O''Neill et al., 1990) have led to the
suggestion that borate ester cross-linked RG-II is required for the
development of a normal cell wall (O''Neill et al., 1996; Matoh, 1997).One approach for determining the function of boron in plant cell walls
is to compare the responses to boron deficiency of growing plant cells
that are dividing and synthesizing primary cell walls with those of
growth-limited plant cells in which the synthesis of primary cell walls
is negligible. Suspension-cultured cells are well suited for this
purpose because they may be reversibly transferred from a growth phase
to a stationary phase. Continuous cell growth phase is maintained by
frequent transfer of the cells into new growth medium (King, 1981;
Kandarakov et al., 1994), whereas a stationary cell population
is obtained by feeding the cells with Suc and by not subculturing them.
Cells in the stationary phase are characterized by mechanically
stabilized primary walls and reduced biosynthetic activity. Here we
describe the responses of suspension-cultured Chenopodium
album L. cells in the growth and stationary phases to boron
deficiency. These cells have a high specific-growth rate, no
significant lag phase, and reproducible changes in their wall pore size
during the transition from the growth phase to the stationary phase
(Titel et al., 1997). |
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