A. Szweykowska

Changes in enzyme activities accompanying cytokinin-induced formation of gametophore buds in Ceratodon purpureus

Summary During the first 24 hr of kinetin treatment a decrease in RNase and DNase activities occur in the protonema of Ceratodon purpureas . After a prolonged 5-day-long treatment, when the number and size of cytokinin-induced gametophore buds reach the maximum, the activities of RNase, acid phosphatase, and peroxidase increase considerably above control levels. In the case of peroxidase differential stimulation of some isoenzymes and induction of a new isoenzyme have been found. The results are interpreted as indicating the existence of two phases in cytokinin action on moss protonemata: a juvenile phase of promotion of growth and development, and a second phase of growth inhibition and enhancement of aging.

Effect of Cytokinins and Antibiotics on Chloroplast Development in Cotyledons of Cucumis sativus

Summary A description is given of changes which occured under the influence of cytokinins, chloramphenicol (CAP), eyeloheximide (CXD) and their combinations in chlorophyll synthesis and development of chloroplast structure in palisade parenchyma cells of cucumber cotyledons. Cytokinins distinctly promoted chlorophyll synthesis and chloroplast development, and the antibiotics inhibited these processes. The inhibiting activity of CXD was several times higher than that of CAP. Kinetin applied simultaneously with CAP only partially overcame its inhibitory effect, whereas in the case of CXD the overcoming was complete. It is suggested that the promotion by cytokinins of chloroplast development in cucumber cotyledons results mainly from their effect on protein synthesis occurring in the cytoplasm.

The Role of Cytokinins in the Development and Metabolism of Barley Leaves III. The Effect on the RNA Metabolism in Various Cell Compartments During Senescence

Summary The degradation of RNA in excised barley leaves in darkness mainly concerned the 25 S and 18 S rRNAs, whereas the 23 S and 16 S rRNAs were. rehtively stable. The cytokinin prevented an increase in the RNase activity and caused an increase in the RNA level and in the incorporation of 14 C-uracil into the cytoplasmic rRNAs, their precursors and the low molecular RNAs. There was no incorporation of the precursor into the 23 S and 16 S RNAs. Changes in RNA resulting from the senescence and from the cytokinin treatment occurred mainly in the cytoplasmic and nuclear cell fractions; they were relatively small or non-existent in the chloroplast fraction. It is concluded that changes in chloroplast structure during senescence of barley leaves are rather secondary results of processes occuring in other cell compartments. Also the retarding effect of cytokinin on the chloroplast senescence seems to be rather indirect and resulting inter alia from a protection of the RNA and a stimulation of its synthesis in the cytoplasm and nucleus.

The Role of Cytokinins in the Development and Metabolism of Barley Leaves: II. The Effect on the DNA-Dependent RNA Polymerase during Leaf Senescence

Summary The effect of a cytokinin, 6-isopentenylaminopurine, on the chromatin-bound RNA polymerase of excised, dark-incubated senescing barley leaves was investigated. During the course of 3 days of dark incubation, the enzyme activity was distinctly higher in the cytokinin-treated material than in that not having been treated. The increased activity was due primarily to the polymerase I, as judged by the isolation method employed and α-amanitin resistance. The relationship between the actions of cytokinin on the polymerase activity and on leaf senescence is discussed.

The effect of 3-Indolylacetic acid on the differentiation of plastids in callus culture ofCichorium intybus L.

SummaryThe effect of 3-indolylacetic acid (IAA) on structure of plastids in cells of callus developing on the phloem explants of chicory roots was investigated. In the absence of IAA the proplastids in the initial expiant developed into typical chloroplasts. The presence of increasing IAA concentrations in the medium resulted in a gradual reduction of the thylakoid system accompanied by an increasing starch content of the plastids. Depending on the IAA concentration used, various types of plastids from typical chloroplasts to typical amyloplasts were found. A possible relationship between auxins and sugar metabolism is indicated.

Effect of kinetin on the transcription activity of chromatin from cucumber cotyledons

Summary Three-day-old etiolated seedlings of Cucumis sativus L. cv. Monastyrski were sprayed with water or 0.1 mM kinetin solution, which led to an enhancement of expansion growth of the cotyledons. After 24 h in darkness, the cotyledons were harvested, chromatin was isolated and its transcription activity tested. Chromatin from kinetin-treated cotyledons exhibited higher activity, both endogenous and supported with exogenous Escherischia coli RNA polymerase, which pointed to a higher DNA template activity as compared with the untreated control. Addition of kinetin to the reaction mixture for RNA synthesis in vitro, as well as the presence of kinetin during homogenization of the cotyledons had no effect on the transcription activity of the chromatin. Kinetin inhibited elongation growth of the hypocotyls. Chromatin isolated from kinetin-treated hypocotyls displayed lower activity with respect to the untreated control. Also the presence of kinetin during hypocotyl homogenization led to a reduction of the transcriptional activity of the chromatin.

The Cell Division Response to Cytokinins in Isolated Cell Cultures of the Protonema of Funaria hygrometrica and its Comparison with the Bud Induction Response

Summary Several cytokinins and cytokinin-like adenine derivatives as well as other growth regulatory substances were tested for their effectiveness in promoting cell divisions in cultures of isolated protonema cells of Funaria hygrometrica in order to examine the specificity of the celldivision response and to compare it with the bud-induction effect. Several differences have been found between the two responses, first of all a lack of specificity of the cell-division response, and a strong inhibition of the protonemal cell divisions by 1-,3-,and 9-substituted adenine derivatives which with respect to the bud formation showed no inhibition or even (in the case of 1-isopentenyl- adenine) a slightly promoting effect. The possible role of cytokinins in the bud-induction is discussed, and it is suggested that they affect both the intensity of cell divisions occurring during this process as well as their orientation into a three-dimensional growth pattern of the gametophore buds. Only the latter effect, involving a morphogenetic rearrangement, is a specific one, whereas in the promotion of cell divisions the cytokinins can be replaced by other substances.

The ultrastructural aspects of the cytokinin-induced bud formation inCeratodon purpureus

SummaryThe fine structure of gametophore buds developing in response to a cytokinin treatment is described and compared with the results of biochemical and physiological investigations. In the early period of growth, the buds followed a regular pattern of development, with the differentiation of a tetrahedral apical cell at the 3-cell stage of the bud. After 6 and 48 hours of the cytokinin treatment, structural changes indicating an increased metabolic activity were found in the developing buds. Treatment for 5-days resulted in signs of degeneration in most of the bud cells. Nuclei and chloroplasts were the organelles most sensitive to the cytokinin. Among the structures described, complexes of minute, strongly osmiophilic globules, arranged in parallel rows between microfilaments were of particular interest. They seemed to appear temporarily in cells and they may constitute storage material for building structures at an appropriate stage of cell development.

Kinetin modifies the secondary structure of poly(A)RNA in cucumber cotyledons

Abstract Evidence has been obtained for a presence of double-stranded regions in poly(A)RNA from cucumber cotyledons, as well as for an engagement of the poly(A) segment in the formation of these regions. Kinetic treatment of the cotyledons leads to an increase in degree of the secindary structure of poly(A)RNA, to a slight increase in the length of the poly(A) tail and to a considerable decrease in its involvement in base pairing, thus making the poly(A) segments more ‘unmasked’.

A tRNA-Nucleotidyltransferase from Moss Protonema and Promotion of its Activity by Cytokinin

Summary In the protonema of Ceratodon purpureus the activity has been found of an enzyme which on the basis of a preliminary characteristics has been classified as tRNA-nucleotidyltransferase (EC 2.7.7.25) responsible for the synthesis of the terminal nucleotide sequence pCpCpA of the 3’-end of all active tRNA molecules. As a result of cytokinin (6-Δ2-isopentenylaminopurine) treatment an increase in enzyme activity occurs in the protonema after 1–3 hours of hormone action.