REGENERATION IN L O W E R PLANTS
125
ribonucleic acids ; (3) digestion with diastase to remove the phosphate of
the starch ; (4) extraction with 5% perchloric acid, twice 20 min at 70° C ;
this fraction contained the deoxyribonucleic acids. The determination
of radioactivity in the different fractions at different time intervals after
isolation of the cells showed a steep increase for the uptake of phosphate
between 12 and 36 h. This increase occurred in all fractions at the same
time, although the different samples were not taken close enough on the
time scale to reveal smaller differences. Nevertheless, it can be concluded from the results that in the isolated cells fundamental changes in
phosphate metabolism, including RNA and DNA, take place. These
results could be confirmed by determinations of the ultravioletabsorption in cold and hot perchloric acid extracts. An increase in
ultraviolet absorption occurred in both fractions after about 10 h of
isolation of the cells, indicating synthesis of RNA and DNA.
2. The Dependence of the Changes on the Age of the Cell
When in differentiation a cell has interrupted its cycle of growth and
division, its final destiny is to age and to die. This fate of a cell can only
be avoided by the process of embryonization. Investigations on the
potentialities for regeneration of cells in progressing stages of development and age may give information about the nature of progressing
differentiation.
Several authors investigated the regenerative power of successive
leaves of increasing age isolated along the axis of the gametophore of
mosses. Gemell (1953) used the moss Atrichum undulatum to test the
effects of leaf age on its power of regeneration. The criterion for the
regenerative power was the percentage of leaves producing 'regenerated
plants'. The results show that there was a decrease with age in the
ability of leaves to regenerate new plants. However, the 'percentage
regeneration' did not fall steadily with the age of the leaf but in the
lower half of the gametophore a significant rise of the curve was observed, followed by another decline. Working with leaves of Funaria
hygrometrica isolated successively from the tip to the base of the gametophore, Bopp (1955) determined the number of regenerative protonemata per leaf as a measurement for the number of cells growing out
of the leaf. The regenerative power of the leaves decreased from the
apex to the middle region of the gametophore, where a clear minimum
was found, and increased from here toward the base reaching the same
or higher values as at the apex. The same course of the curve was found
after different regeneration times. No explanation can be given for this
behaviour. However, such results cannot be taken as evidence against
a dependence of regenerative processes on the age of the cells. It is
questionable if the percentage of regenerating leaves and even the
125
ribonucleic acids ; (3) digestion with diastase to remove the phosphate of
the starch ; (4) extraction with 5% perchloric acid, twice 20 min at 70° C ;
this fraction contained the deoxyribonucleic acids. The determination
of radioactivity in the different fractions at different time intervals after
isolation of the cells showed a steep increase for the uptake of phosphate
between 12 and 36 h. This increase occurred in all fractions at the same
time, although the different samples were not taken close enough on the
time scale to reveal smaller differences. Nevertheless, it can be concluded from the results that in the isolated cells fundamental changes in
phosphate metabolism, including RNA and DNA, take place. These
results could be confirmed by determinations of the ultravioletabsorption in cold and hot perchloric acid extracts. An increase in
ultraviolet absorption occurred in both fractions after about 10 h of
isolation of the cells, indicating synthesis of RNA and DNA.
2. The Dependence of the Changes on the Age of the Cell
When in differentiation a cell has interrupted its cycle of growth and
division, its final destiny is to age and to die. This fate of a cell can only
be avoided by the process of embryonization. Investigations on the
potentialities for regeneration of cells in progressing stages of development and age may give information about the nature of progressing
differentiation.
Several authors investigated the regenerative power of successive
leaves of increasing age isolated along the axis of the gametophore of
mosses. Gemell (1953) used the moss Atrichum undulatum to test the
effects of leaf age on its power of regeneration. The criterion for the
regenerative power was the percentage of leaves producing 'regenerated
plants'. The results show that there was a decrease with age in the
ability of leaves to regenerate new plants. However, the 'percentage
regeneration' did not fall steadily with the age of the leaf but in the
lower half of the gametophore a significant rise of the curve was observed, followed by another decline. Working with leaves of Funaria
hygrometrica isolated successively from the tip to the base of the gametophore, Bopp (1955) determined the number of regenerative protonemata per leaf as a measurement for the number of cells growing out
of the leaf. The regenerative power of the leaves decreased from the
apex to the middle region of the gametophore, where a clear minimum
was found, and increased from here toward the base reaching the same
or higher values as at the apex. The same course of the curve was found
after different regeneration times. No explanation can be given for this
behaviour. However, such results cannot be taken as evidence against
a dependence of regenerative processes on the age of the cells. It is
questionable if the percentage of regenerating leaves and even the