124
LUISE STANGE
during regeneration the content of UNA increases in the nuclei and the
cytoplasm of the cell poles. After treatment with méthylène blue and
trypaflavine no reaction occurs at the regenerating cell poles while a
distinct staining appears in a middle region of the cells where most of
the chloroplasts are assembled. I t is therefore assumed that metaphosphates formed in the chloroplasts are consumed at the regenerating
poles of the cells. In further experiments the cells were labelled with
32p o r 35g supplied as inorganic phosphate or sulphate. These isotopes
were almost exclusively incorporated at the poles of the regenerating
cells and later in the cell region where the new cell wall arises. These
results indicate an activation of metabolic processes in these cell regions.
Besides the cytochemical investigations already mentioned only very
few observations are available about metabolic changes in cells during
embryonization although knowledge about them would be very important. Increase in nuclear and nucleolar size and intensification of
stainability indicate increasing or renewed synthetic activity in the
nucleus. There is no doubt that synthesis of UNA is enhanced or renewed. I t can be expected from other investigations that synthesis of
deoxyribonucleic acid (DNA) also takes place during embryonization.
Determinations of the DNA-content in cells of permanent tissues have
shown that in diploid organisms these cells generally—apart from the
occurrence of endopolyploidy—have the diploid DNA-value which they
received at the last division (cf. Swann, 1958; Mazia, 1961). This indicates that they have not doubled their DNA but are held back at an
earlier point in the reproductive cycle. In radioautographic studies of a
population of dividing and non-dividing cells, Quastler and Sherman
(1959) found that the 'decision' to divide or to differentiate is made
shortly after division and long before the onset of DNA-synthesis.
In the liverwort Riella it is possible to cut a sufficient number of small
fragments out of the wings to get enough cell material for biochemical
investigations. When equal numbers of fragments of the same size are
cut for the samples, the results can be referred to a cell base. The first
changes can be assumed to be the same in all isolated cells, but not all
cells reach the stage of division. Experiments were carried out with
incorporation of
32
P into the cells to label the different organic phosphates (Stange, 1957). Under the experimental conditions employed,
nuclear divisions occur after about 36 h. At different time intervals after
isolation fragments were transferred to nutrient solution containing
32
P as K H 2 P 0 4 . After 6 h of incorporation the fragments were killed and
the phosphate fractionated by different extractions : (1) extraction with
cold 10% trichloroacetic acid; this fraction contained inorganic
phosphate, sugar phosphates and mono- and oligonucleotides ; (2)
extraction with cold 10% perchloric acid for 18 h to yield the fraction of
LUISE STANGE
during regeneration the content of UNA increases in the nuclei and the
cytoplasm of the cell poles. After treatment with méthylène blue and
trypaflavine no reaction occurs at the regenerating cell poles while a
distinct staining appears in a middle region of the cells where most of
the chloroplasts are assembled. I t is therefore assumed that metaphosphates formed in the chloroplasts are consumed at the regenerating
poles of the cells. In further experiments the cells were labelled with
32p o r 35g supplied as inorganic phosphate or sulphate. These isotopes
were almost exclusively incorporated at the poles of the regenerating
cells and later in the cell region where the new cell wall arises. These
results indicate an activation of metabolic processes in these cell regions.
Besides the cytochemical investigations already mentioned only very
few observations are available about metabolic changes in cells during
embryonization although knowledge about them would be very important. Increase in nuclear and nucleolar size and intensification of
stainability indicate increasing or renewed synthetic activity in the
nucleus. There is no doubt that synthesis of UNA is enhanced or renewed. I t can be expected from other investigations that synthesis of
deoxyribonucleic acid (DNA) also takes place during embryonization.
Determinations of the DNA-content in cells of permanent tissues have
shown that in diploid organisms these cells generally—apart from the
occurrence of endopolyploidy—have the diploid DNA-value which they
received at the last division (cf. Swann, 1958; Mazia, 1961). This indicates that they have not doubled their DNA but are held back at an
earlier point in the reproductive cycle. In radioautographic studies of a
population of dividing and non-dividing cells, Quastler and Sherman
(1959) found that the 'decision' to divide or to differentiate is made
shortly after division and long before the onset of DNA-synthesis.
In the liverwort Riella it is possible to cut a sufficient number of small
fragments out of the wings to get enough cell material for biochemical
investigations. When equal numbers of fragments of the same size are
cut for the samples, the results can be referred to a cell base. The first
changes can be assumed to be the same in all isolated cells, but not all
cells reach the stage of division. Experiments were carried out with
incorporation of
32
P into the cells to label the different organic phosphates (Stange, 1957). Under the experimental conditions employed,
nuclear divisions occur after about 36 h. At different time intervals after
isolation fragments were transferred to nutrient solution containing
32
P as K H 2 P 0 4 . After 6 h of incorporation the fragments were killed and
the phosphate fractionated by different extractions : (1) extraction with
cold 10% trichloroacetic acid; this fraction contained inorganic
phosphate, sugar phosphates and mono- and oligonucleotides ; (2)
extraction with cold 10% perchloric acid for 18 h to yield the fraction of