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PubMed2005

Allelopathic effects of volatile monoterpenoids produced by Salvia leucophylla: Inhibition of cell proliferation and DNA synthesis in the root apical meristem of Brassica campestris seedlings.

Salvia leucophylla, a shrub observed in coastal south California, produces several volatile monoterpenoids (camphor, 1,8-cineole, beta-pinene, alpha-pinene, and camphene) that potentially act as allelochemicals. The effects of these were examined using Brassica campestris as the test plant. Camphor, 1,8-cineole, and beta-pinene inhibited germination of B. campestris seeds at high concentrations, whereas alpha-pinene and camphene did not. Root growth was inhibited by all five monoterpenoids in a dose-dependent manner, but hypocotyl growth was largely unaffected. The monoterpenoids did not alter the sizes of matured cells in either hypocotyls or roots, indicating that cell expansion is relatively insensitive to these compounds. They did not decrease the mitotic index in the shoot apical region, but specifically lowered mitotic index in the root apical meristem. Moreover, morphological and biochemical analyses on the incorporation of 5-bromo-2'-deoxyuridine into DNA demonstrated that the monoterpenoids inhibit both cell-nuclear and organelle DNA synthesis in the root apical meristem. These results suggest that the monoterpenoids produced by S. leucophylla could interfere with the growth of other plants in its vicinity through inhibition of cell proliferation in the root apical meristem.

Brassica↗

PubMed1981

Protein synthesis during the onset of cell proliferation in root meristems.

Dormant meristems of Allium cepa L. root begin to sprout as soon as the water and temperature conditions are right. These cell systems offer many advantages when studying the earliest metabolic events related with the onset of the cell proliferating activity. By electrophoresis in SDS polyacrylamide gels the soluble protein fraction from meristems with increasing imbibition times was analysed. There are qualitative constancy and quantitative differences between electrophoretic patterns from dormancy to steady state conditions. It is suggested that polypeptide 8a, approximately 80,000 daltons in molecular weight, be considered an indicator of proliferative activity in the meristem.

Cell Division↗

PubMed1989

Cell lineage patterns in the shoot meristem of the sunflower embryo in the dry seed.

We mapped the fate of cells in the shoot meristem of the dry-seed embryo of sunflower, Helianthus annuus L. cv. Peredovic, using irradiation-induced somatic sectors. We analyzed 249 chlorophyll-deficient or glabrous (hairless) sectors generated in 236 plants. Most sectors observed in the inflorescence extended into vegetative nodes. Thus cell lineages that ultimately gave rise to reproductive structures also contributed to vegetative structures. No single sector extended the entire length of the shoot. Thus the shoot is not derived from one or a few apical initials. Rather, the position, vertical extent, and width of the sectors at different levels of the shoot suggest that the shoot is derived from three to four circumferential populations of cells in each of three cell layers of the embryo meristem. Sectors had no common boundaries even in plants with two or three independent sectors, but varied in extent and overlapped along the length of the shoot. Thus individual cells in a single circumferential population behaved independently to contribute lineages of different vertical extents to the growing shoot. The predicted number of circumferential populations of cells as well as the apparent cell number in each population was consistent with the actual number of cells in the embryo meristem observed in histological sections.

Cell Count↗

PubMed2000

Histone deacetylase inhibitors and cell proliferation in pea root meristems.

The histone deacetylase (HDA) inhibitors, trichostatin A (TSA) and HC toxin halt mitosis in cultured root meristems of Pisnum sativum, while the anti-protozoan HDA inhibitor apicidin is ineffective. Two-dimensional PAGE of proteins from root meristems exposed to TSA and HC toxin did not show significant differences compared to controls, although a previously tested HDA inhibitor, butyrate, exhibited dramatic variations in its protein profile. Northern analysis of butyrate- and TSA-treated root meristems indicated that non-proliferating cells are expressing significant amounts of transcripts of the known cell proliferation associated genes: histone H2A, MAP kinase, cycA2:1 and cdc2. Western analysis reveals the presence of hyperacetylated nuclear proteins in HDA-inhibitor treated cells. These results suggest that the HDA inhibitors, butyrate and TSA, halt mitosis without down-regulating genes that typically have low or nonexistent expression levels in non-dividing cells.

Cell Division↗

PubMed2000

A floret by any other name: control of meristem identity in maize.

The life of a plant unfolds as a series of developmental stages, with each stage defined by changes in meristem identity. In maize, there are several distinct stages: the transition from vegetative growth to flowering, the elaboration of the inflorescence, and the formation of flowers. Progress in understanding meristem identity and function has been made by analyzing maize mutants with defects at each of these stages. Recently cloned genes suggest that, although the molecular mechanisms controlling floral organ identity are conserved in maize and other model species, the control of meristem identity during earlier developmental stages might be less conserved.

Genes, Plant↗

PubMed1997

Effect of Water Stress on Cortical Cell Division Rates within the Apical Meristem of Primary Roots of Maize.

We characterized the effect of water stress on cell division rates within the meristem of the primary root of maize (Zea mays L.) seedlings. As usual in growth kinematics, cell number density is found by counting the number of cells per small unit length of the root; growth velocity is the rate of displacement of a cellular particle found at a given distance from the apex; and the cell flux, representing the rate at which cells are moving past a spatial point, is defined as the product of velocity and cell number density. The local cell division rate is estimated by summing the derivative of cell density with respect to time, and the derivative of the cell flux with respect to distance. Relatively long (2-h) intervals were required for time-lapse photography to resolve growth velocity within the meristem. Water stress caused meristematic cells to be longer and reduced the rates of cell division, per unit length of tissue and per cell, throughout most of the meristem. Peak cell division rate was 8.2 cells mm-1 h-1 (0.10 cells cell-1 h-1) at 0.8 mm from the apex for cells under water stress, compared with 13 cells mm-1 h-1 (0.14 cells cell-1 h-1) at 1.0 mm for controls.

Journal Article↗

PubMed2000

A DEFICIENS homolog from the dioecious tree black cottonwood is expressed in female and male floral meristems of the two-whorled, unisexual flowers.

We isolated PTD, a member of the DEFICIENS (DEF) family of MADS box transcription factors, from the dioecious tree, black cottonwood (Populus trichocarpa). In females, in situ hybridization experiments showed that PTD mRNA was first detectable in cells on the flanks of the inflorescence meristem, before differentiation of individual flowers was visually detectable. In males, the onset of PTD expression was delayed until after individual flower differentiation had begun and floral meristems were developing. Although PTD was initially expressed throughout the inner whorl meristem in female and male flowers, its spatial expression pattern became sex-specific as reproductive primordia began to form. PTD expression was maintained in stamen primordia, but excluded from carpel primordia, as well as vegetative tissues. Although PTD is phylogenetically most closely related to the largely uncharacterized TM6 subfamily of the DEF/APETELA3(AP3)/TM6 group, its spatio-temporal expression patterns are more similar to that of DEF and AP3 than to other members of the TM6 subfamily.

Amino Acid Sequence↗

PubMed1997

Photo and hormonal control of meristem identity in the Arabidopsis flower mutants apetala2 and apetala1.

We have analyzed the contributions of phytochrome and gibberellin signal transduction to the control of flower meristem identity in the Arabidopsis mutants apetala1 (ap1) and apetala2 (ap2). ap1 flowers are partially defective for the establishment of flower meristem identity and are characterized by the production of ectopic secondary or axillary flowers and by branching. Axillary flower production is also induced in ap2-1 flowers by short-day photoperiod and is suppressed by hy1, a mutation blocking phytochrome activity. The production of axillary flower by ap2-1 is also suppressed by exogenous gibberellins and by spindly (spy), a mutation that activates basal gibberellin signal transduction in hormone-independent manner. Ectopic axillary flower production and floral branching by ap1 flowers are also suppressed by spy. We conclude that gibberellins promote flower meristem identity and that the inflorescence-like traits of ap2-1 and ap1-1 flowers are due in part to SPY gene activity.

Arabidopsis↗

PubMed2000

POLTERGEIST functions to regulate meristem development downstream of the CLAVATA loci.

Mutations at the CLAVATA loci (CLV1, CLV2 and CLV3) result in the accumulation of undifferentiated cells at the shoot and floral meristems. We have isolated three mutant alleles of a novel locus, POLTERGEIST (POL), as suppressors of clv1, clv2 and clv3 phenotypes. All pol mutants were nearly indistinguishable from wild-type plants; however, pol mutations provided recessive, partial suppression of meristem defects in strong clv1 and clv3 mutants, and nearly complete suppression of weak clv1 mutants. pol mutations partially suppressed clv2 floral and pedicel defects in a dominant fashion, and almost completely suppressed clv2 phenotypes in a recessive manner. These observations, along with dominant interactions observed between the pol and wuschel (wus) mutations, indicate that POL functions as a critical regulator of meristem development downstream of the CLV loci and redundantly with WUS. Consistent with this, pol mutations do not suppress clv3 phenotypes by altering CLV1 receptor activation.

Arabidopsis↗

PubMed2000

A test of the reserve meristem hypothesis using Verbascum thapsus (Scrophulariaceae).

The reserve meristem hypothesis predicts that latent meristems may act as a bet-hedging strategy given high-cost, predictable herbivory. Under this hypothesis, damage to a plant should elicit greater branching. This prediction was tested in Verbascum thapsus with three experiments manipulating the intensity and type of damage to reproductive tissue. In the first experiment, seed set was prevented in the treatment group by stigma excision and lanolin application to 80% of the flowers of each plant. In the second experiment, a minimum of two mating pairs of weevils were added to treated plants prior to the onset of flowering. In the third experiment, all fruits were sliced lengthwise twice. All three treatments significantly reduced seed set. In the first two experiments, treated plants significantly increased degree of branching (branch number and total branch length). This supports the reserve meristem hypothesis as an explanation for greater branching in larger plants of V. thapsus. Interestingly, the fruit destruction experiment failed to elicit a branching response, which suggests that the timing of damage is important.

Journal Article↗

PubMed2002

Induction of premature mitosis in root meristem cells of Vicia faba and Pisum sativum by various agents is correlated with an increased level of protein phosphorylation.

The intra-S-phase checkpoint response to hydroxyurea (HU)-mediated arrest of DNA replication was analysed in root meristems of two legumes, Pisum sativum and Vicia faba. The obtained results suggest that a molecular signal which invokes mechanisms allowing the cells to override the S-M dependency control system may be generated by caffeine (CF) and a number of alternative, yet related chemical agents, benzyl-6-aminopurine (BAP), 2-aminopurine (2-AP), and 6-dimethylaminopurine (DMAP). A variety of aberrant mitotic divisions included chromosomal breaks and gaps, lost and lagging chromatids and chromosomes, acentric fragments, chromosome bridges and micronuclei. Furthermore, similar effects induced by sodium vanadate, an inhibitor of protein phosphatases, extend the number of inhibitors capable of inducing premature chromosome condensation (PCC) in root meristem cells, as well as the range of possible regulatory pathways leading to the transition from S-phase arrest towards abnormal mitosis. Until preprophase, FITC-conjugated monoclonal antibodies (alpha-Y(a)b-FITC) that specifically recognize phosphorylated form of threonine indicate no evident cell cycle-dependent changes in an overall phosphorylation status of root meristem cells in the control plants. Irrespective of the stage of interphase, alpha-Y(p)ab-FITC was localized basically in the cytoplasm, whereas nuclear staining was considerably weaker, with a significant fluorescence confined merely to nucleolar regions. The intensity of alpha-Y(p)ab-FITC staining in HU/CF-treated seedlings was found higher than that in the control plants (with the exception of G2 cells), suggesting a general increase in the level of protein phosphorylation, a physiological response mediated probably by an enhanced activity of the cdc-like protein kinase(s).

Antibodies, Monoclonal↗

PubMed1979

[Electron microscopic study of the mitochondria in the apical meristem of a wheet shoot in ontogeny].

The mitochondria of apical meristem cells in the wheat (Triticum aestivum L.) shoot were studied during ontogenesis using electron microscope and morphometrical methods. Changes in their structure were followed from the juvenile mitochondria of the seed embryonic ear cells. The parameters of the "average" mitochondrion, such as profile area, outer membrane length, were shown to differ relatively weakly during the periods with different meristem activity. Changes in the internal structure of the mitochondria having the developed system of crystae in the actively growing apices and those with weakly developed crystae in the resting seed or low active "waiting meristem" are much more pronounced. The relative volume of mitochondria, their number per unit of cytoplasm volume and total length of membranes suffer relatively insignificant changes during the vegetative phase and increase markedly during the prefloral phase when the apex is preparing itself for generative differentiation.

Microscopy, Electron↗

PubMed2026

Genome-Wide Analysis of Triticum aestivum Root Meristem Growth Factor (RGF) Gene Family Highlights TaRGF5 as a Putative Component of Root-Associated Signaling.

Wheat (Triticum aestivum), a key global crop, faces rising drought stress that limits root growth and water uptake. Root meristem growth factors (RGFs) are small peptides that regulate root stem cell maintenance, meristem activity, and lateral root formation in model plants, yet the RGF gene family remains unexplored in wheat. Here, we performed a comprehensive genome-wide analysis of the TaRGF gene family, identifying 15 genes distributed across the A, B, and D subgenomes and classified into five homeologous groups (TaRGF1-TaRGF5), predominantly located on chromosomes 2 and 6. All TaRGFs contained a characteristic RGF motif, with dibasic cleavage sites and Asp-Tyr motifs indicating conserved maturation mechanisms. Based on the phylogenetic analysis, the TaRGF5 homeologs showed the highest similarity to Arabidopsis thaliana RGF5. Tested RNA-seq data revealed predominantly root-enriched expression for all TaRGF genes, with TaRGF5 exhibiting the most root-preferential and downregulation under drought stress. Quantitative real-time PCR (qRT-PCR) confirmed that drought stress suppressed the expression of TaRGF5A, TaRGF5B, and TaRGF5D in roots of wheat cultivar Sids-13 across all time points, unlike the higher accumulation seen in controls. Promoter analysis predicted a unique BES1 transcription factor binding site exclusively in TaRGF5B, linking brassinosteroid signaling to peptide-mediated root regulation. Structural modeling and molecular docking predicted an interaction between wheat TaRGF5 homeologs and root growth factor-insensitive receptor kinase (TaRGI3), characterized by conserved sulfotyrosine-mediated binding and favorable interaction energetics. Based on this characterization of the wheat RGF gene family, particularly the potential role of TaRGF5 in root development and drought-adaptation signaling, we propose targeting this gene for functional analysis to improve wheat resilience under water-limited conditions.

Triticum↗

PubMed2002

Cell lineage dynamics in stratified shoot apical meristems.

We devise a stochastic and spatially explicit model for the dynamics of the initials cells in a stratified shoot apical meristem (SAM). The meristem is composed of three layers with seven initials per layer. We investigate the probability and number of divisions for a mutant lineage to either reach fixation or becoming purged through selection or drift. In contrast to previous studies our results show that the functional organization of the initials in stratified SAMs acts as an efficient purging mechanism particularly of deleterious mutations. All mutants are rapidly purged when deleterious. The probability of fixation for mutants with a higher fitness than the wild type increases linearly up to 70%. The median number of divisions to fixation of both genotypes is insensitive to the mutant's fitness. The median number of divisions to wild-type fixation is less than 100, with the upper quartile below 200. The largest number of divisions to wild-type fixation are in the order of 100 000 divisions. Our results indicate that the spatial organization of SAM enables the efficient purging of mutant lineages, particularly if they are deleterious. On the other hand, long-lived chimeric stages are common when mutant lineages succeed to overcome the initial numerical disadvantage.

Cell Division↗

PubMed1998

Patterning the floral meristem.

Flowers are reproductive structures unique to the angiosperms. Flowers, which develop from small mounds of cells called floral meristems, show a number of universal patterns such as the arrangement of organs of different type along the floral axis. However, other conserved patterns, such as floral asymmetry, are merely conserved within different subgroups. This review discusses the emerging picture of early operating developmental mechanisms, which pattern floral meristems along the radial and dorsiventral axes, and of later-acting ones, which pattern tissue differentiation within floral organs.

Body Patterning↗

PubMed1996

Benzylaminopurine induces phenocopies of floral meristem and organ identity mutants in wild-type Arabidopsis plants.

Arabidopsis thaliana (L.) Heynh. has been used as a model system to investigate the regulatory genes that control and coordinate the determination, differentiation and morphogenesis of the floral meristem and floral organs. We show here that benzylaminopurine (BAP), a cytokinin, influences flower development in Arabidopsis and induces partial phenocopies of known floral homeotic mutants. Application of BAP to wild-type inflorescences at three developmental stages results in: (i) increase in floral organ number; (ii) formation of abnormal floral organs and (iii) induction of secondary floral buds in the axils of sepals. These abnormalities resemble the phenotypes of mutants, clv1 (increase in organ number), ap1, ap2, ap3 (abnormal floral organs) and ap1 (secondary floral buds in the axils of first-whorl organs). In addition, BAP induces secondary floral buds in the axils of perianth members of ap2-6, ap3-1 and ag mutants, and accentuates the phenotype of the ap2-1 mutant to resemble the ap2-6 mutant. These observations suggest that exogenous BAP suppresses the normal functioning of the genes for floral meristem identity and thereby affects flower development and the later stages of floral organ differentiation.

Arabidopsis↗

PubMed2003

Inheritance of plant regeneration from maize (Zea mays L.) shoot meristem cultures derived from germinated seeds and the identification of associated RAPD and SSR markers.

The inheritance of shoot regeneration through shoot-tip meristem culture derived from maize seedling was evaluated, and the markers (RAPD and SSR) associated with this regeneration character were identified both in a group of North American maize inbreds and a crossing population. A discrete distribution of percent regeneration and no. of shoots per explant was observed in the inbred group and the F(2) population. The results suggested that this regenerable trait was controlled by several major genes. Five RAPD markers were identified to be relevant to percent regeneration in maize shoot-tip culture system. One RAPD marker and three SSR markers were associated with no. of shoot per explant and its relevant traits. Of them marker BC603-1600 explained 18% of the variation for no. of shoot per explant and 16% of the variation for callus size. The BC603-1600 was sequenced and assigned in linkage group 7 based on a NCBI blast search. The information provided here should benefit to determine the genetic mechanisms involved in the maize regeneration response related to shoot meristem culture pathway and benefit to select high regenerable germplasm by using marker assisted selection.

Analysis of Variance↗

PubMed2003

Rescue of shoot apical meristems of chrysanthemum by culturing on root tips.

A new method to regenerate plants from leaf primordia-free shoot apical meristem domes (LP-free SAMs) was developed by establishing the meristem dome on the cut surface of root tips. Ten days after culture, the viable rate of LP-free SAMs of chrysanthemum 'Piato' attached to chrysanthemum root tips was >40%. Shoot regeneration was not observed from LP-free SAMs without the root tips. When LP-free SAMs of chrysanthemum were transferred to root tips of either petunia, cabbage, or carnation, the highest shoot regeneration rate was observed with cabbage root tips. Microscopic observation documented that the LP-free SAM temporarily adhered to the cut surface of the root tip of cabbage.

Botany↗