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PERMEABILITY LIMITS OF CELLWALLS INSUSPENSIONCULTURES -
PHYSIOLOGICALANDBIOTECHNOLOGICALASPECTS
CHRISTINETITEL ANDRUDOLF EHWALD
Humboldt University Berlin, Institute o fBiolog}’, Imalidenstr. 42, D -10115 Berlin,
Germany
In vitro cultures are widely used fo r investigation of the structure and
function o f the primary cell wall. Many investigations on the chemical
composition and the structural organization of cell wall polysaccharides and
the dynamical changes o f the wall during growth and differentiation have
been carried out with suspension cultured cells.
Primary cell walls behave as ultrafilters for macromolecules, this being
an important feature in physiological and biotechnological regard. In our
physiological investigations we concentrate on determination of permeability
limits of suspension cultured plant cells of different origin and under various
physiological conditions. For this purpose, a new method based on size
exclusion chromatography of polydisperse dextrans before and after
equilibration with the cells was used (Woehlecke, Ehwald 1995, Titel et al.
1997).The limiting pore size was determined for various suspension cultures
as mean size limit of dextran for permeation trough the cell wall. This value
was higher fo r investigated dicot cultures (2,5-4 nm) than fo r cultures o f
gram ineous species (1,7-3,2 nm). The accurate method allowed for
determination of physiologically mediated changes of the permeability limits
during a cultivation period when the cells undeigo characteristic morphological
and physiological alteration. In the phase o f intensive division growth the
mean size lim it is higher than in resting cells o f the stationary phase. This
characteristic change during batch culture seems to be correlated with the
growth mediated loss of matrix polymers to the medium. Using a special
cultivation regime and determining permeability lim its o f suspension cells
under these conditions a step forward to the understanding of boron action
in higher plants was done: In a semicontinuous culture where cells have
been kept at a high propagation rate by frequent dilution with fresh medium,
biomass growth and viability remains high over a long time even when boron
concentration was nearly zero. When these boron deficient suspensions
went over to the stationary phase they died as cells o f batch cultures did on
boron-free medium. Several findings demonstrate that the microelement is
necessary for cell wall stiffening processes occurring after the cells left the
division cycle. Change of the mean size lim it was an early event registered
within 5 min after addition of boron to deficient cultures. (Fleischer, Titel,
Ehwald 1997) Cell wall permeability may be of importance for biotechnological
application too, e.g. for non-destructive extraction o f secondary metabolites
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