REGENERATION IN LOWER PLANTS
143
nature of the correlation system between leaf and stem (von Maltzahn,
1962; cf. Table V). Regeneration from two-thirds leaves attached to a
stem segment was increased in older plants, in which antheridia formation at the gametophore apex took place and, concomitantly, the apical
growth of the gametophore ceased. Regeneration was also promoted
when the plants were decapitated 1-3 days before the stem segment
with the attached two-thirds leaf was isolated. When intact gametophores were grown on medium containing twice the normal ammonium
nitrate concentration, regenerations from the two-thirds leaves attached
to a stem segment was greatly increased. Higher concentrations of
ammonium nitrate had apparently toxic effects on the cells of the leaf.
Stem segments with attached two-thirds leaves were planted on agar
medium with various concentrations of kinetin added. Only the region
near the wound surface of the two-thirds leaves was in contact with the
medium. On the medium without kinetin almost no regeneration
occurred from the attached leaves, but under the influence of kinetin
concentrations of 10
-8
to 10~
6
g/ml the number of regenerative protonemata per attached two-thirds leaves was markedly increased (von
Maltzahn, 1961). Kinetin is known to have a strong effect on the
directional transport of soluble nitrogenous compounds (cf. Richmond
and Lang, 1957; Mothes, 1961); its localized application to excised
tobacco leaves led to localized accumulation and retention of soluble
nitrogen compounds and to RNA and protein synthesis (Wollgiehn,
1961). Von Maltzahn assumes that accumulation of substances necessary
for renewed synthetic activities lead to regeneration. In the intact plant
these substances are transported along a heteropolar axis to sites of
incorporation at the apical pole. Removal of this centre of growth
activity is believed to result in a lowering of the steepness and final disappearance of gradients along the heteropolar axis of the plant until
new centres of gradient fields are established in the form of secondary
sites of incorporation. Although the present writer is inclined to agree
with these ideas (Stange, 1957), it must be remembered, as already
mentioned, that regeneration, like all growth processes, must be dependent on a supply of precursors and energy. From the extensive work
of Skoog and collaborators with tobacco tissue (cf. Skoog and Miller,
1957) it is known that quantitative interactions between IAA and
kinetin and between these and other factors play an important role in
the regulation of growth. Possibly, the experimental results with
Splachnum could also be explained by assuming that an interaction
occurs between kinetin and some inhibiting substance derived in this
case from the stem cells.
In summary, the mechanism by which embryonization of permanent
cells is brought about is still by no means clear. Much more information
E 2
A.M.4
143
nature of the correlation system between leaf and stem (von Maltzahn,
1962; cf. Table V). Regeneration from two-thirds leaves attached to a
stem segment was increased in older plants, in which antheridia formation at the gametophore apex took place and, concomitantly, the apical
growth of the gametophore ceased. Regeneration was also promoted
when the plants were decapitated 1-3 days before the stem segment
with the attached two-thirds leaf was isolated. When intact gametophores were grown on medium containing twice the normal ammonium
nitrate concentration, regenerations from the two-thirds leaves attached
to a stem segment was greatly increased. Higher concentrations of
ammonium nitrate had apparently toxic effects on the cells of the leaf.
Stem segments with attached two-thirds leaves were planted on agar
medium with various concentrations of kinetin added. Only the region
near the wound surface of the two-thirds leaves was in contact with the
medium. On the medium without kinetin almost no regeneration
occurred from the attached leaves, but under the influence of kinetin
concentrations of 10
-8
to 10~
6
g/ml the number of regenerative protonemata per attached two-thirds leaves was markedly increased (von
Maltzahn, 1961). Kinetin is known to have a strong effect on the
directional transport of soluble nitrogenous compounds (cf. Richmond
and Lang, 1957; Mothes, 1961); its localized application to excised
tobacco leaves led to localized accumulation and retention of soluble
nitrogen compounds and to RNA and protein synthesis (Wollgiehn,
1961). Von Maltzahn assumes that accumulation of substances necessary
for renewed synthetic activities lead to regeneration. In the intact plant
these substances are transported along a heteropolar axis to sites of
incorporation at the apical pole. Removal of this centre of growth
activity is believed to result in a lowering of the steepness and final disappearance of gradients along the heteropolar axis of the plant until
new centres of gradient fields are established in the form of secondary
sites of incorporation. Although the present writer is inclined to agree
with these ideas (Stange, 1957), it must be remembered, as already
mentioned, that regeneration, like all growth processes, must be dependent on a supply of precursors and energy. From the extensive work
of Skoog and collaborators with tobacco tissue (cf. Skoog and Miller,
1957) it is known that quantitative interactions between IAA and
kinetin and between these and other factors play an important role in
the regulation of growth. Possibly, the experimental results with
Splachnum could also be explained by assuming that an interaction
occurs between kinetin and some inhibiting substance derived in this
case from the stem cells.
In summary, the mechanism by which embryonization of permanent
cells is brought about is still by no means clear. Much more information
E 2
A.M.4