Isolation of mitotic chromosomes from partially synchronized carrot (D. carota) cell suspension cultures

UV-B-induced DNA damage mediates expression changes of cell cycle regulatory genes in Arabidopsis root tips

Even though a number of studies have shown that UV-B radiation inhibits plant growth and regulates the cell cycle progress, little is known about the molecular and cellular mechanisms. Here, we developed a synchronous root-tip cell system to investigate expression changes of cell cycle marker genes and DNA damage under UV-B radiation. Expression analysis of cell cycle marker genes revealed that G1-to-S transition in root-tip cells was accomplished within 6 h. In the in vivo synchronous root-tip cells, high level of UV-B radiation (0.45 W m(-2)) induced expression changes of the cell cycle regulatory genes. Genes involved in G1-to-S transition, Histone H4 and E2Fa, were down-regulated by UV-B radiation during 2-6 h; whereas transcripts for KRP2, a negative regulator of G1-to-S transition, were up-regulated by UV-B at 2 h. The peak time for transcript level of CYCD3;1, a positive factor in G1-to-S transition, was delayed by UV-B radiation. Interestingly, a medium level of UV-B radiation (0.25 W m(-2)) did not change the expression of these genes in root tip cells from wild type. However, cell cycle regulatory genes were greatly affected in uvh1 mutant, which exhibited higher content of cyclobutane pyrimidine dimers (CPDs). Ascorbic acid treatment did not change the expression pattern of cell cycle regulatory genes that were affected by high-level UV-B. Our results implied that UV-B-induced DNA damage results in the delay of G1-to-S transition of plant cell cycle. UV-B-induced G1-to-S arrest may be a protective mechanism that prevents cells with damaged DNA from dividing and may explain the plant growth inhibition under increased solar UV-B radiation.

In vitro nuclear reconstitution could be induced in a plant cell-free system

A cell-free system derived from carrot cell cytosol extract has been developed for reassembling nuclear structure around the added demembranated sperm chromatin of Xenopus. Morphological evidence suggests that reassembled nuclei display the typical characteristics of normal eukaryotic nuclei, such as double-layered nuclear membrane and nuclear pores. Micrococcal nuclease treatment indicates that remodeling of the demembranated sperm chromatin has occurred and the structure of nucleosome is formed during nuclear reconstitution. These data indicate that the nuclear reconstitution can be induced in cell-free systems from plants, and the self-assembly of the nucleus is ubiquitous in both animal and plant cells.

Cytological and molecular relationships between Larix decidua, L. leptolepis and Larix x eurolepis: identification of species-specific Chromosoms and synchronization of mitotic cells

The effects of different concentrations of hydroxyurea (HU) and aphidicolin (APH) on the mitotic index (MI) were compared in cells of embryogenic cultures of Larix decidua, L. leptolepis, and L. decidua x L. leptolepis (Larix x eurolepis). The highest enhancement of the MI was obtained with HU at 1.25 mM and 0.6% colchicine. In general the MI decreased with an increase of HU or APH concentration (over 1.25 mM for HU and 5 μM for APH). Detailed karyotype analyses were made on the somatic complement of L. decidua, L. leptolepis, and their hybrid. These karyotypes were asymmetrical and advanced, with the smaller chromosomes being more submedian than the larger ones. The topography of chromosome 7 of L. decidua and chromosome 9 of L. leptolepis was found to be the most significant cytotaxonomic characteristic in differentiating these two species. Cytological data indicate that Japanese larch (L. leptolepis) is phylogenetically closer to European larch (L. decidua) than the Siberian larch group (L. sibirica and L. sukaczewii). Chromosomes with unusually long kinetochores were found in both species and the hybrid. Hyperploid cells (2n = 25) were observed in the hybrid (Larix x eurolepis) material analyzed. A genomic L. decidua probe hybridized strongly to dots of DNA from L. leptolepis indicating that there is high sequence homology between these two species.

Preparation and flow cytometric analysis of metaphase chromosomes of tomato

A procedure for the preparation of tomato chromosome suspensions suitable for flow cytometric analysis is described. Rapidly growing cell suspension cultures of Lycopersicon esculentum cv VFNT cherry and L. pennellii LA716 were treated with colchicine to enrich for metaphase chromosomes. Metaphase indices between 20 and 35% were routinely obtained when cultures were exposed to 0.1% colchicine for 15-18 h after 2 days of subculture. Mitotic cells were isolated by brief treatment with cell wall digesting enzymes in a medium with low osmolarity (∼325 mOsm/kg of H52O). The low osmolarity medium was needed to avoid the chromosome clumping and decondensation seen in standard media. Suspensions of intact chromosomes were prepared by lysing swollen protoplasts in various buffers (MgSO4, polyamines, hexylene glycol, or KCl-propidium iodide) similar in contents to the buffers used to isolate mammalian chromosomes. For univariate flow cytometric analysis, chromosome suspensions were stained with a fluorescent DNA-binding stain (propidium iodide, Hoechst 33258, mithramycin, or chromomycin A3) and analyzed using an EPICS flow cytometer (Profile Analyzer or 753). Peaks for the chromosomes, chromatids, clumps of chromosomes, nuclei, and fluorescent debris were seen on a histogram of log of fluorescence intensity, and were confirmed by microscopic examination of the objects collected by flow-sorting. Chromosome suspensions prepared in MgSO4 buffer have the highest frequency of intact chromosomes and the least fluorescent cellular debris. Peaks similar to theoretical univariate flow karyotypes of tomato chromosomes were seen on the observed univariate flow karyotypes, but were not as well resolved. Bivariate flow analysis of tomato chromosome suspension using double-stain combination, Hoechst 33258 and chromomycin A3, and two laser beams showed better resolution of some chromosomes.

A comparison of the effects of various spindle toxins on metaphase arrest and formation of micronuclei in cell-suspension cultures ofNicotiana plumbaginifolia

The effects of the spindle toxins colchicine, oryzalin and amiprophos-methyl (APM) on metaphase arrest, chromosome scattering, and on the induction and yield of micronuclei were compared in suspension cells ofNicotiana plumbaginifolia (kanamycin-resistant "Doba" line). The inhibition of spindle formation is stronger with oryzalin and APM than with colchicine, which resulted in a more efficient accumulation of meta-phases with well-scattered chromosomes, allowing the isolation of single chromosomes. Further, APM and oryzalin treatments resulted in a higher frequency of micro-nucleated cells and greater yield of micronuclei than after colchicine treatment. The different actions of the chemicals on the functioning of the spindle, development of nuclear membranes around the chromosomes, formation of micronuclei and fusion of micronuclei, resulting in restitution nuclei, are discussed.

Induction of high mitotic index in Petunia suspension cultures by sequential treatment with aphidicolin and colchicine

Significantly higher than normal mitotic index (MI) values were induced in Petunia cell suspensions following treatments with colchicine, aphidicolin, drastic medium replacement, or a sequential application of aphidicolin and colchicine. This last treatment yielded the highest MI values: cells incubated with 30 μg/ml aphidicolin for 18 h, then cultured in drug-free medium for 8 h and finally exposed to 0.1% colchicine for 8 additional hours exhibited MI of 62.8% and 65.7% respectively, for the two cell lines in study.