An analysis of H3-thymidine distribution throughout the vegetative meristem of Arabidopsis Thaliana (L.) heynh

High-resolution boundary analysis during Arabidopsis thaliana flower development

We report a comparative analysis of cell proliferation patterns during Arabidopsis flower development. Cell division was evaluated by a direct method, i.e. the 5-bromo-2'-deoxyuridine (BrdU) incorporation/immunodetection procedure. BrdU patterns in wild-type plants were correlated with the expression profiles of both several cell cycle genes involved in the control of the G(1)/S transition and cell cycle-related repressor genes, MSI4 and MSI5, encoding WD-repeat proteins. To evaluate how proliferation patterns arise with respect to boundaries and vice versa, the expression of a boundary gene, CUP SHAPED COTYLEDON (CUC)2, was determined. Combining these approaches, we demonstrate that boundaries between inflorescence and floral meristems and between floral whorls are narrow bands of non-dividing cells. In addition, we show that negative and positive regulators of cell proliferation are simultaneously and continuously expressed in dividing meristematic domains, being excluded from boundary cells. Finally, BrdU incorporation and CUC2 in situ hybridisation patterns were analysed in two mutant backgrounds, agamous (ag)-1 and superman (sup)-1, in order to assess changes in boundary establishment and different levels of indeterminacy under conditions of altered proliferation at the floral meristem centre.

[Nuclear criteria for complete dormancy in the shoot apex of Fraxinus excelsior L]

The cytohistological criteria for the vegetative shoot apex dormancy in Fraxinus excelsior L. have been quantitatively established with the aid of 3 techniques: historadiography after incorporation of [(3)H]thymidine, mitotic index and nuclear cytophotometry by the two wavelength method. Nuclear DNA content, mitotic activity and DNA synthesis were compared in 3 different zones(apical zone, lateralzone, rib meristem) of the dormant and non-dormant apices. The periodical break in morphogenetic activity, in contrast to the vegetative period (April to July), is characterized by the absence of zonation and by the fact that meristematic cells remain in the G1 phase of the mitotic cycle. In Fraxinus excelsior L., the meristem dormancy is complete (no DNA synthesis, no mitotic activity and no DNA content greater than 2C).