Donato Chiatante

Arrest of the Cell Cycle Induced by Dibutyryl-Camp and Sodium Butyrate in Root Meristems of Lettuce

SUMMARYDibutyryl-cAMP was supplied to seedlings of Lactuca sativa L. cv. Great Lakes 118, and its effect on the cell cycle in root meristems was compared to that of dibutyryl-cGMP and sodium butyrate. Dibutyryl-cAMP and sodium butyrate induced a sharp decrease in the labelling index, attributable to an arrest of the cell cycle in G1 and possibly G2, whereas dibutyryl-cGMP was ineffective. The use of dibutyryl-cAMP and sodium butyrate in studies on the control of cell cycle and cell differentiation in growing roots is suggested. Various hypotheses on the mode of action of dibutyryl-cAMP are also discussed.

Cell cycle arrest induced by theophylline in root meristem of Haplopappus gracilis

Theophylline, an inhibitor of cyclic nucleotide phosphodiesterase, induced a block of the cell cycle in G1, a temporary arrest in G2 and 70% decrease in the uptake of labelled thymidine in roots of Haplopappus. These effects are compared to those previously found with aminophylline and discussed in view of the possible involvement of cAMP in the regulation of the cell cycle in plants.

Phosphorylation of nuclear proteins and proliferation in root meristems of pea (Pisum sativum)

Protein kinase(s) and related endogenous substrates are present in nuclei of meristematic and adult root tissue of pea (Pisum sativum L., cv. Lincoln). The protein kinase(s) is bound to the chromatin and is not solubilized by 0.14 M NaCl, although such a salt concentration solubilizes a considerable number of endogenous substrates. Comparison of the electrophoretic patterns of phosphorylated nuclear proteins purified from quiescnt or actively proliferating meristematic root tissue reveals the existence of variations of phosphorylation. Differences exist also between the electrophoretic patterns of phosphorylated nuclear proteins extracted from differentiated or meristematic root tissue. The hypothesis that the variations of phosphorylation of particular proteins might be correlated with the state of proliferation and differentiation of the cell is presented.

Effect of benzyladenine on cell cycle in intact roots. A cytofluorimetric approach

Summary Cytofluorimetry following DAPI-staining of the nuclei was used, in combination with autoradiography, to study the effect of benzyladenine on the cell cycle in pea root meristems. When administered to roots of intact two-day-old seedlings, 30 µM benzyladenine induced in the terminal 2 mm a decrease in the labeling and mitotic indices and an increase in the number of nuclei in G2. At the same time, a rapid inhibition of root elongation was also observed. The shift of nuclei towards G2 was particularly evident in the second mm of the root tip zone. We suggest that the primary effect of this supraoptimal benzyladenine concentration might be the promotion of G 1 arrest. The increase of nuclei in G2 might be due to the effect of the G2-factor translocated from the cotyledons, level of which within the tip might increase as a consequence of the rapid inhibition of root elongation induced by the treatment.

Effect of Theophylline on Elongation and some Transport Processes in Embryos of Haplopappus gracilis.

In germinating embryos of Haplopappus gracilis, theophylline induced a FC-reversible inhibition of elongation and K(+) uptake. The possible action of theophylline on the proton pump and other transport processes is discussed and compared with the effects of its ethylenediamine salt, aminophylline.

Biochemical investigations of the nuclear proteins during the transition of root meristems from quiescent to proliferating state in Pisum sativum

Abstract The electrophoretic analysis of nuclear proteins extracted from root meristems at different times of germination puts in evidence the variations of content of specific proteins. Several nuclear proteins are phosphorylated by endogenous protein kinase and often the maximum rate of phosphorylation it has been observed in proteins present in the nucleus at low concentrations. Moreover also the phosphorylation rate of specific proteins changes at different times of germination. It is interesting the fact that both variations of concentration and phosphorylation in nuclear proteins occurr at the time when root meristems leave the quiescence to enter a proliferating state. We suggest that these variations play a role in this physiological event.

Inhibition of cotyledon greening by exogenous cytokinins and their correspondent ribosides in lettuce seedlings germinating in the light

Abstract Administration of exogenous cytokinins to lettuce seedlings germinating in the light, inhibits the accumulation of chlorophyll in the cotyledons. This action seems to be independent from the type of modification in N-6 or N-9 position of the purine ring of cytokinins. This fact suggests that the purine ring itself could be involved in this particular cytokinin action. The biochemical event(s) affected are unknown.