Analysis of the spatial expression pattern of seven Kip related proteins (KRPs) in the shoot apex of Arabidopsis thaliana.

Background And Aims: Kip-related-proteins (KRPs), negative regulators of cell division, have recently been discovered in plants but their in planta function is as yet unclear. In this study the spatial expression of all seven KRP genes in shoot apices of Arabidopsis thaliana were compared.

Methods: In situ hybridization analyses were performed on longitudinal sections of shoot apices from 2-month-old Arabidopsis plants.

Cytokinin levels in leaves, leaf exudate and shoot apical meristem of Arabidopsis thaliana during floral transition.

Understanding the complete picture of floral transition is still impaired by the fact that physiological studies mainly concern plant species whose genetics is poorly known, and vice versa. Arabidopsis thaliana has been successfully used to unravel signalling pathways by genetic and molecular approaches, but analyses are still required to determine the physiological signals involved in the control of floral transition. In this work, the putative role of cytokinins was investigated using vegetative plants of Arabidopsis (Columbia) induced to flower synchronously by a single 22 h long day.

Cell division and morphological changes in the shoot apex of Arabidopsis thaliana during floral transition.

Eight-week-old vegetative plants of Arabidopsis thaliana, ecotype Columbia, were induced to flower by a single long day (LD). In this experimental system, it is known that the last component of the floral stimulus moves from the leaves to the apex 24-36 h after the start of the LD, and the first floral meristem is initiated by the shoot apical meristem (SAM) at 44-56 h (Corbesier et al., 1996, The Plant Journal 9: 947-952).

Altered cell cycle distribution, hyperplasia, and inhibited differentiation in Arabidopsis caused by the D-type cyclin CYCD3.

CYCD3;1 expression in Arabidopsis is associated with proliferating tissues such as meristems and developing leaves but not with differentiated tissues. Constitutive overexpression of CYCD3;1 increases CYCD3;1-associated kinase activity and reduces the proportion of cells in the G1-phase of the cell cycle. Moreover, CYCD3;1 overexpression leads to striking alterations in development.

In situ localisation of cytokinins in the shoot apical meristem of Sinapis alba at floral transition.

In plants of Sinapis alba L. induced to flower by one long day (LD), previous work showed that the phloem sap feeding the shoot apex is enriched in cytokinins of the isopentenyladenine (iP)-type between 9 and 25 h after start of the LD [P. Lejeune et al.

Control of proliferation, endoreduplication and differentiation by the Arabidopsis E2Fa-DPa transcription factor.

New plant cells arise at the meristems, where they divide a few times before they leave the cell-cycle program and start to differentiate. Here we show that the E2Fa-DPa transcription factor of Arabidopsis thaliana is a key regulator determining the proliferative status of plant cells. Ectopic expression of E2Fa induced sustained cell proliferation in normally differentiated cotyledon and hypocotyl cells.

Cytokinin and gibberellin activate SaMADS A, a gene apparently involved in regulation of the floral transition in Sinapis alba.

In plants of Sinapis alba induced to flower by one long day, the MADS box gene, SaMADS A, is expressed initially in the central corpus (L3 cells) of the shoot apical meristem (SAM), about 1.5-2 days before initiation of the first floral meristem. We have combined a physiological approach by testing the effects of three putative floral signals on SaMADS A expression in the SAM of S.

Expression of CKS1At in Arabidopsis thaliana indicates a role for the protein in both the mitotic and the endoreduplication cycle.

Although endoreduplication is common in plants, little is known about the mechanisms regulating this process. Here, we report the patterns of endoreduplication at the cellular level in the shoot apex of Arabidopsis thaliana L. Heynh.

Cytokinin activation of Arabidopsis cell division through a D-type cyclin.

Cytokinins are plant hormones that regulate plant cell division. The D-type cyclin CycD3 was found to be elevated in a mutant of Arabidopsis with a high level of cytokinin and to be rapidly induced by cytokinin application in both cell cultures and whole plants. Constitutive expression of CycD3 in transgenic plants allowed induction and maintenance of cell division in the absence of exogenous cytokinin.

Characterization of SaMADS D from Sinapis alba suggests a dual function of the gene: in inflorescence development and floral organogenesis.

SaMADS D gene of Sinapis alba was isolated by screening a cDNA library from young inflorescences with a mixture of MADS-box genes of Antirrhinum majus (DEF, GLO, SQUA) as probe. Amino acid sequence comparison showed a high degree of similarity between the SaMADS D and AGL9, DEFH200, TM5, FBP2 and DEFH 72 gene products. Analysis of the SaMADS D gene expression by in situ hybridization reveals a novel expression pattern for a MADS-box gene and suggests a dual function for this gene: first, as a determinant in inflorescence meristem identity since it starts to be expressed directly beneath the inflorescence meristem at the time of initiation of the first floral meristem, is no longer expressed in the inflorescence meristem forced to revert to production of leafy appendages, and is expressed again when the reverted meristem resumes floral meristem initiation, and, second, as an interactor with genes specifying floral organ identity since it is expressed in the floral meristem from the stage of sepal protrusion.

The Arabidopsis cyclin-dependent kinase gene cdc2bAt is preferentially expressed during S and G2 phases of the cell cycle.

Cell cycle progression is regulated by cyclin-dependent kinases (CDKs). Arabidopsis thaliana contains two cdk genes, cdc2aAt and cdc2bAt. This paper compares the developmental and cell cycle phase-dependent transcription of both cdk genes.

Design in Arabidopsis thaliana of a synchronous system of floral induction by one long day.

A system of one-shot induction of flowering in Arabidopsis thaliana, ecotype Columbia, is described. Plants from vernalized seeds are grown for 2 months in 8 h short days at an irradiance of 48 mumol m-2 sec-1 (fluorescent light only). At that age they can be induced to flower by exposure to either a single long day or a single displaced short day.

High-yield isolation of protoplasts from microgram amounts of shoot meristematic tissues and rapid DNA content determination by flow cytometry.

This paper describes a novel approach to rapid cell-cycle analysis of shoot meristematic cells. The method involves fixation and disaggregation of meristems into protoplast suspension and flow-cytometric analysis of these protoplasts stained with fluorescent dyes. We have developed a procedure for a high-yield isolation of protoplasts allowing an accurate flow-cytometric analysis with a few micrograms of meristem tissues.

Activation of replicon origins as a possible target for cytokinins in shoot meristems of Sinapis.

Whilst the cytokinins are important promoters of plant cell division in vitro and in vivo, their mode of action remains unknown. Here we report the results of a study showing that a single application of a low dose of a cytokinin to the shoot apical meristem of Sinapis alba L. activates new replicon origins in chromosomal DNA, resulting in the halving of replicon size, and synchronizes the activation of replicon origins.

DNA fiber replication during a morphogenetic switch in the shoot meristematic cells of a higher plant.

Chromosomal DNA fiber replication was investigated in the shoot meristem of mustard plants during the morphogenetic transition from the leaf-forming (vegetative) to the flower-forming (evoked) condition. The replicon size, determined using the modal class, was 15 micron in the vegetative meristem and shifted to 7.5 micron in the evoked meristem.

Changes in cell-cycle duration and growth fraction in the shoot meristem of Sinapis during floral transition.

The cell-cycle duration and the growth fraction were estimated in the shoot meristem of Sinapis alba L. during the transition from the vegetative to the floral condition. Compared with the vegetative meristem, the cell-cycle length was reduced from 86 to 32 h and the growth fraction, i.

Occurrence of two cell subpopulations with different cell-cycle durations in the central and peripheral zones of the vegetative shoot apex of Sinapis alba L.

The cell-cycle duration and the growth fraction were estimated in the vegetative shoot apical meristem of Sinapis alba L. The length of the cell cycle was about 86 h, i.e.

Appearance of specific antigenic proteins in the maturing sexual organs of Sinapis flowers.

Three proteins specific to the flowering state were found in Sinapis by immunological techniques. Two of these are specific to the stamen and one to the pistil. By the use of a histoimmunofluorescence technique their localization in the developing flower primordia and in the apex was examined during the transition to flowering.

Flowering in Xanthium strumarium: INITIATION AND DEVELOPMENT OF FEMALE INFLORESCENCE AND SEX EXPRESSION.

Vegetative plants of Xanthium strumarium L. grown in long days were induced to flower by exposure to one or several 16-hour dark periods. The distribution of male and female inflorescences on the flowering shoot was described, and a scoring system was designed to assess the development of the female inflorescences.

Appearance and disappearance of proteins in the shoot apical meristem of Sinapis alba in transition to flowering.

Vegetative plants of Sinapis alba L. grown under short days were induced to flower by exposure to one long day or continuous long days. Irrespective of the number of long days, the first flower primordia were initiated by the shoot apical meristem 60 h after the start of the inductive treatment.

Cytokinin as a Possible Component of the Floral Stimulus in Sinapis alba.

Results of previous investigations indicated that one of the early and essential events occurring in the apical meristem of Sinapis alba L. during the transition to flowering is the release to mitosis of the G(2) nuclei; the trigger to mitosis is generated in the leaves and its movement out of the leaves begins around 16 hours after the start of the inductive treatment. The mitotic wave in the meristem culminates 10 hours later.