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PubMed1992

Low temperature between conditioning and challenge treatment prevents the 'adaptive response' of Vicia faba root tip meristem cells.

When the temperature during intertreatment time (2 h) between conditioning and challenge treatment of Vicia faba root tip meristems with either triethylenemelamine or maleic hydrazide was reduced from 24 degrees C to 12 degrees C no adaptive response occurred any more. The yield of metaphases with chromatid aberrations under these circumstances was similar to that observed after challenge treatment alone, i.e., no reduction occurred. This indicates that the metabolic state of the cells is of critical importance for the presence or absence of adaptive responses.

Adaptation, Physiological↗

PubMed1993

Combined application of MH and TEM for conditioning treatment simultaneously triggers two protective functions against induction of chromatid aberrations in Vicia faba root tip meristem cells.

Conditioning pre-exposure of Vicia faba root tip meristem cells to triethylenemelamine (TEM) does not trigger an adaptive response to maleic hydrazide (MH) and vice versa. Since TEM conditioning treatment can induce protective effects (as evident from the yield of metaphases with chromatid aberrations) against TEM challenging treatment and MH conditioning can trigger an adaptive response to MH challenging treatment, two different protective functions are apparently triggered in dependence on the agent used for conditioning pre-exposure. When a mixture of TEM and MH is being used for conditioning treatment, adaptive responses to both TEM and MH can simultaneously be induced and significantly reduce the yield of metaphases with chromatid aberrations observed after challenge treatment with TEM or MH.

Adaptation, Physiological↗

PubMed1985

Response of interphasic nucleoli to hypoxia in root meristems.

Hypoxia produces structural changes in interphasic nucleoli of Allium cepa L. root meristems. Following segregation, the fibrillar portion of nucleoli seems to be extruded in masses, accessory bodies, which stay in nucleoplasm. Such bodies apparently leave the fibrillar portion in places which seem to correspond to insertion areas of the nucleolar organizers in nucleoli. Reversal of these changes is rapidly obtained when oxygenation is restored. Accessory bodies differ from prenucleolar bodies since they are compact and homogeneous and they do not display segregation under hypoxia.

Cell Nucleolus↗

PubMed1989

Exponential pattern of cell age distribution in dividing cells of plant meristems.

In order to determine the pattern of cell age distribution in proliferating cells of Allium cepa roots we have measured by cytophotometry two cell size parameters, protein content and surface area projection, in cells that correspond to the entire proliferating population or only to the ana-telophase subpopulation. The size values of ana-telophase cells have been employed to construct theoretical size distributions for the entire proliferating cell population of the root meristem by assuming either a uniform or an exponential cell age distribution. Statistical comparison of theoretical distributions with the experimental one rules out a uniform cell age distribution and strongly favours an exponential age distribution similar to that found in bacteria.

Cell Division↗

PubMed1988

Effects of ethidium bromide and nalidixic acid pretreatment on the induction of chromatid aberrations by TEM and maleic hydrazide in Vicia faba main root meristems.

Pretreatment of Vicia faba main root meristems with ethidium bromide (EB) or nalidixic acid (NA) significantly reduced the yield of metaphases with chromatid aberrations induced by maleic hydrazide (MH), i.e., triggered clastogenic adaptation to MH. No such protection occurred when the alkylating agent triethylenemelamine (TEM) was used for challenge treatment. The differential response of pretreated cells to MH on the one hand (protection) and to TEM (no protection) on the other supports the conclusion that clastogenic adaptation is due to different inducible (repair?) functions, which eventually exert protection against clastogenic impacts.

Chromatids↗

PubMed1988

Induction of chromatid aberrations by TEM and maleic hydrazide is differently affected by pretreatment of Vicia faba root-tip meristems with methyl iodide.

Treatment of Vicia faba main root meristems with methyl iodide (MeI) 2 h before challenge treatment with triethylene melamine (TEM) significantly reduced the yield of metaphases with chromatid aberrations, i.e., resulted in clastogenic adaptation. Combined treatment with MeI and TEM increased the aberration yield; MeI treatment alone (10(-3) M, 0.5 h) was without clastogenic effect. No protective effects were observed after MeI pretreatment and challenge treatment by maleic hydrazide (MH). The data obtained in V. faba are compared to those previously reported for E. coli.

Chromatids↗

PubMed2000

Culture of red beet hairy roots by considering variation in sensitivity of tip meristems to hydraulic stress.

In the culture of red beet hairy roots in shaking flasks, a period for acclimation without lateral root generation existed at the early stage, and the root tip meristems containing growing points (GPs) were found to be damaged under an elevated shear stress condition. The loading experiments of shear stress to the hairy roots revealed that the GPs subjected to the acclimation acquired tolerance to shear stress, retaining relatively high viability of GPs up to 0.6N/m(2) of loaded shear stress. Next, the hairy roots after culture for 50h at 0.05N/m(2) of shear stress were exposed to conditions at various levels of shear stress in a single column reactor, and a relatively high growth rate was obtained in the vicinity of 1.0N/m(2) of shear stress. According to these results, two-stage cultures of hairy roots were then performed, which was comprised of a first stage for 50h at 0.05N/m(2) of shear stress for the prevention of decay of the GPs caused by hydraulic stress and a second stage for 110h at 1.0N/m(2) of shear stress for active elongation of the GPs with sufficient nutrient supply by regulation of the medium flow rate. The cell concentration ultimately reached 7.6kg dry cells/m(3), although no growth was observed in the case where the hairy roots did not undergo the first stage.

Journal Article↗

PubMed1999

Cell cycle synchronization in plant root meristems.

The analysis of structure and metabolism of a cell at a defined phase of cell cycle is often difficult because cell cycle progression in somatic tissues is asynchronous and only a fraction of cells are cycling. An elegant solution to obtain populations of cells enriched for single stage of the cell cycle is to impose the synchrony artificially. Different systems have been used to obtain synchronized populations of plant cells, including suspension-cultured cells, leaf mesophyll protoplasts and root tip meristems. Root tips have been frequently used in a variety of studies ranging from chromosome analysis to cell cycle and its regulation. Seedlings with actively growing roots may be obtained in most plant species, they are easy to handle, the experimental system is well defined, reproducible and can be easily modified for different species. This paper describes a protocol for cell cycle synchronization in root tips of Vicia faba, which is based on the use of DNA synthesis inhibitor hydroxyurea [18]. Modifications of the protocol for Pisum sativum, Medicago sativa, Hordeum vulgare, Secale cereale, Triticum aestivum, and Zea mays are also given. Flow cytometric data indicate that about 90% of root tip cells are synchronized. On average, mitotic indices exceeding 50% are obtained with the method. Synchronized cells may be accumulated at metaphase using a mitotic spindle inhibitor to achieve metaphase indices exceeding 50%.

Genes, cdc↗

PubMed1994

Co-suppression of the petunia homeotic gene fbp2 affects the identity of the generative meristem.

The function of the petunia MADS box gene fbp2 in the control of floral development has been investigated. Inhibition of fbp2 expression in transgenic plants by a co-suppression approach resulted in the development of highly aberrant flowers with modified whorl two, three and four organs. This mutant flower phenotype inherited as a single Mendelian trait. The flowers possess a green corolla which is reduced in size. Furthermore, the stamens are replaced by green petaloid structures and the inner gynoecial whorl is dramatically reduced. No ovules or placenta are formed and instead two new inflorescences developed in the axils of the carpels. These homeotic transformations are accompanied by a complete down-regulation of the petunia MADS box gene fbp6 which is highly homologous to the Arabidopsis and Antirrhinum genes agamous (ag) and plena (ple). In contrast to this, two other petunia MADS box genes, exclusively expressed in whorls two and three, are still transcribed. Our results indicate that the fbp2 gene belongs to a new class of morphogenesis genes involved in the determination of the central part of the generative meristem.

Amino Acid Sequence↗

PubMed1994

An approach towards genetically engineered cell fate mapping in maize using the Lc gene as a visible marker: transactivation capacity of Lc vectors in differentiated maize cells and microinjection of Lc vectors into somatic embryos and shoot apical meristems.

To establish a system for genetically engineered cell fate mapping, different vectors carrying the Lc gene, a member of the R gene family, were delivered into embryonic and meristematic cells of maize by the microinjection technique. Vectors in which the Lc cDNA is driven either by a constitutive promoter (CaMV 35S), with or without the Adh1 intron 1 of maize, or a tissue-specific promoter (phosphoenolpyruvate carboxylase, PEPC) as well as self-replicating wheat dwarf virus (WDV) vectors carrying a Lc-expression-cassette, have been tested. The ability of these vectors to transactivate was evaluated in mesophyll-derived protoplasts of the maize genotype appropriate for these microinjection experiments. The expression product of the introduced Lc gene can substitute for mutated R and B loci, resulting in anthocyanin production. Analogous results were obtained by microinjection into organized tissues, where transactivation of anthocyanin biosynthesis resulted in pigmented sectors in somatic embryos (B79) and in the leaves of plants regenerated from the cultivated shoot apical meristems (K55, r-g, b). The tissue-specific appearance of pigmented sectors in leaves, using the mesophyll-specific PEPC promoter suggests the possibility of using this approach for layer-specific cell fate studies. The presence of the introduced plasmids in leaves showing red sectors 20-30 days after injection was proven by PCR analysis.

Base Sequence↗

PubMed1996

The CER3 gene of Arabidopsis thaliana is expressed in leaves, stems, roots, flowers and apical meristems.

The eceriferum3 (cer3) locus encodes one of 21 gene products known to be involved in wax biosynthesis in Arabidopsis thaliana. Mutations at these loci are readily identified by their bright, dark-green stems when compared with the more glaucous wild-type plant. Clones of a gene which encodes a 795 amino acid open reading frame have been isolated by using plant DNA flanking the site of a T-DNA insertion in line BRL1. Molecular complementation of the cer3 mutant phenotype by clones of this gene establish that it corresponds to the CER3 gene. Although the 90 kDa predicted amino acid sequence of this gene shows no homology to any other known protein, the second exon of CER3 encodes a RRX12KK nuclear localization sequence (NLS). Southern blot and DNA sequence analysis revealed that the T-DNA is inserted 89 bp downstream of the translation termination codon of this gene. Northern blot hybridization of RNA isolated from the BRL1 mutant with the CER3 cDNA probe indicated that the transcript is absent in this mutant line. Unlike other CER genes that have been cloned to date, high levels of the CER3 transcript were found in all tissues from wild-type plants, that is, leaves, stems, roots, flowers, and apical meristems.

Amino Acid Sequence↗

PubMed1998

NEEDLY, a Pinus radiata ortholog of FLORICAULA/LEAFY genes, expressed in both reproductive and vegetative meristems.

The LEAFY/FLORICAULA genes from Arabidopsis and Antirrhinum are necessary for normal flower development and play a key role in diverse angiosperm species. A homologue of these flower meristem-identity genes, NEEDLY (NLY), has been identified in Pinus radiata. Although the NLY protein shares extensive sequence similarity with its angiosperm counterparts, it is lacking the proline-rich and acidic motifs thought to function as transcriptional activation domains. NLY already is expressed during vegetative development at least 5 years before the transition to the reproductive phase. Expression of NLY in transgenic Arabidopsis promotes floral fate, demonstrating that, despite its sequence divergence, NLY encodes a functional ortholog of the FLORICAULA/LEAFY genes of angiosperms. Expression of the LFY::NLY transgene can largely complement the defects in flower development caused by a severe lfy allele.

Amino Acid Sequence↗

PubMed2006

The production and release of living root cap border cells is a function of root apical meristem type in dicotyledonous angiosperm plants.

BACKGROUND AND AIMS: The root apical meristems (RAM) of flowering plant roots are organized into recognizable pattern types. At present, there are no known ecological or physiological benefits to having one RAM organization type over another. Although there are phylogenetic distribution patterns in plant groups, the possible evolutionary advantages of different RAM organization patterns are not understood. Root caps of many flowering plant roots are known to release living border cells into the rhizosphere, where the cells are believed to have the capacity to alter conditions in the soil and to interact with soil micro-organisms. Consequently, high rates of border cell production may have the potential to benefit plant growth and development greatly, and to provide a selective advantage in certain soil environments. This study reports the use of several approaches to elucidate the anatomical and developmental relationships between RAM organization and border cell production. METHODS: RAM types from many species were compared with numbers of border cells released in those species. In addition, other species were grown, fixed and sectioned to verify their organization type and capacity to produce border cells. Root tips were examined microscopically to characterize their pattern and some were stained to determine the viability of root cap cells. KEY RESULTS: The first report of a correlation between RAM organization type and the production and release of border cells is provided: species exhibiting open RAM organization produce significantly more border cells than species exhibiting closed apical organization. Roots with closed apical organization release peripheral root cap cells in sheets or large groups of dead cells, whereas root caps with open organization release individual living border cells. CONCLUSIONS: This study, the first to document a relationship between RAM organization, root cap behaviour and a possible ecological benefit to the plant, may yield a framework to examine the evolutionary causes for the diversification of RAM organization types across taxa.

Cucurbitaceae↗

PubMed1997

Genotoxicity of tetrodotoxin from puffer fish tested in root meristem cells of Allium cepa L.

Tetrodotoxin (TTX) extracted and purified from puffer fish Arothron nigropunctatus was tested for genotoxicity employing the root meristem cells of Allium cepa as the assay system. The genotoxicity endpoints investigated were mitotic index (MI), meta-anaphases with spindle aberrations, interphases with micronuclei (MNC) and sister chromatid exchanges (SCE) in metaphase chromosomes. The results demonstrated that TTX inhibited mitosis at concentrations of > or = 30 microM as evident by the fall of MI, but failed to induce MNC at significant levels at any of the concentrations tested (10-100 microM). TTX was thus proved to be neither clastogenic nor aneugenic in the present study. It was, however, noteworthy that TTX at far lower concentrations, 0.1-5.0 microM, significantly enhanced the frequencies of SCE which indicated possible interference of the toxin in DNA replication and repair.

Allium↗

PubMed1991

Upstream sequences of rice proliferating cell nuclear antigen (PCNA) gene mediate expression of PCNA-GUS chimeric gene in meristems of transgenic tobacco plants.

The transgenic tobacco plants have been generated that express the E. coli beta-glucuronidase (GUS) gene under control of the promoter from the rice proliferating cell nuclear antigen (PCNA, DNA polymerase auxiliary protein) gene. GUS expression detected in situ by staining with the chromogenic substrate, 5-bromo-4-chloro-3-indolyl-beta-D-glucuronide (X-Gluc), was restricted to meristems in the organs of the transgenic tobacco plants. This expression responded to the phytohormones which promote callus formation. Furthermore, in situ thymidine uptake showed that the GUS expression pattern corresponded well to the active sites of DNA synthesis. Deletion analysis of the 5' upstream sequence confined the GUS expression pattern to a fragment extending 263 bp upstream of the transcription start site of the rice PCNA gene. Thus, we have identified this fragment as a main regulatory element of the rice PCNA gene promoter.

Blotting, Northern↗

PubMed1974

Autoradiographic Examination of Meristems of Intact Boron-deficient Squash Roots Treated with Tritiated Thymidine.

Intact roots of boron-sufficient squash (Cucurbita pepo L.) plants, plants entering boron deficiency, and plants recovering from boron deficiency were exposed to tritiated thymidine at the end of the treatment period to label the replicating DNA of root tip cells. Using histological sections, autoradiographs of intact root meristems were prepared. The labeling pattern in +B root tips revealed the presence of a well defined quiescent center. The ability of root tip cells to incorporate label is correlated with the total root elongation during the -B treatment period. A greater amount of total root elongation during boron deficiency and recovery reflects the fact that root tip cells have retained their ability to synthesize DNA and enter mitosis for a longer time. In roots recovering from boron deficiency, cells of the quiescent center were seen to play no part in the recovery process in roots treated for as long as 20 hours in a -B nutrient solution. They were inactive before, during, and after the -B treatment. Cessation of mitosis occurs as early as 6.5 hours after boron is withheld from the nutrient solution while DNA synthesis can occur for as long as 20 hours after withholding boron. It was concluded that boron is essential for continued DNA synthesis and mitotic activity. The absence of boron results in the cessation of mitosis and DNA synthesis within 20 hours from the time boron is withheld.

Journal Article↗

PubMed1983

Endogenous levels of abscisic Acid and decanoic Acid in dutch iris bulbs and the influence of abscisic Acid and decanoic Acid on iris meristems cultured in vitro.

Abscisic acid (ABA) and decanoic acid inhibited shoot elongation and floral development of Dutch iris (Iris hollandica Hoog. cv Ideal) meristems cultured in vitro. No synergism with respect to inhibition of leaf growth between ABA and decanoic acid was observed. With monthly harvest dates, from July 10, 1981 to October 10, 1981, there was a progressive decrease in endogenous level of free ABA in ;Ideal' iris bulbs. Bulbs subjected to a full set of the usual preplanting storage conditions flowered, on average, 46 days after planting versus 194 days after planting for bulbs planted directly after harvest. ABA levels at harvest were 4- to 5-fold those after the preplanting storage treatment. In general, ABA levels did not correlate well with the length of time from planting until flowering of iris bulbs. Endogenous decanoic acid levels did not follow any pattern with respect to harvest date or postharvest treatment. After the postharvest high temperature treatment, there was about a 3-fold increase in nonscale decanoic acid concentration. Decanoic acid levels, in nonscale tissue, remained high after each of the other postharvest treatments. It is concluded that there is no good evidence to support the contention that either ABA or decanoic acid is directly involved in iris bulb dormancy.

Journal Article↗

PubMed1986

Quantitative Measurements of Hexokinase Activity in the Shoot Apical Meristem, Leaf Primordia, and Leaf Tissues of Dianthus chinensis L.

Hexokinase was measured by quantitative histochemical techniques in the apical meristem, primordia, and leaves of Dianthus chinensis L. The structural stages of development in the leaves sampled were determined by light and scanning electron microscopy. The results showed that activity decreased from the youngest primordia (1500 millimoles per kilogram dry weight per hour) to the mature leaves (200 millimoles per kilogram dry weight per hour) and that an intermediate leaf, the fourth youngest, showed the same declining pattern from its base to its tip. Surface views and measurements of these leaves revealed their basipetal maturation as seen by cell size, stomatal development, trichome differentiation, cuticular appearance, and leaf thickness. The intermediate leaf showed features representative of several stages in structural differentiation. It was concluded that the changes in hexokinase activity among the leaves of a shoot and within an individual leaf are similar and correlate with the degree of structural differentiation of the leaves.

Journal Article↗