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At least 145 records · Page 8Linked to original sources

PubMed1985

Elevation in the Sucrose Content of the Shoot Apical Meristem of Sinapis alba at Floral Evocation.

Nanogram tissue samples from apical meristems of Sinapis alba were assayed for sucrose, total soluble hexosyl equivalents ( identical with glucose and fructose plus hexoses from sucrose hydrolysis), and total soluble glucosyl equivalents ( identical with glucose plus glucose from sucrose hydrolysis). On dry weight basis, sucrose concentration increased by more than 50% within 10 hours after the start of either a long photoperiod or a short photoperiod displaced by 10 hours in the 24-hour cycle (;displaced short day'). (These treatments induce flower initiation) Glucose and fructose concentrations were close to zero in vegetative meristems and remained low compared to sucrose in meristems of induced plants. Within a single meristem, the peripheral and the central zones had similar concentrations of sucrose. Our results indicate that an early physiological event in floral transition is the accumulation of sucrose in the meristem.

Journal Article↗

PubMed2000

Shoot organization genes regulate shoot apical meristem organization and the pattern of leaf primordium initiation in rice.

The mechanism regulating the pattern of leaf initiation was analyzed by using shoot organization (sho) mutants derived from three loci (SHO1, SHO2, and SHO3). In the early vegetative phase, sho mutants show an increased rate of leaf production with random phyllotaxy. The resulting leaves are malformed, threadlike, or short and narrow. Their shoot apical meristems are relatively low and wide, that is, flat shaped, although their shape and size are highly variable among plants of the same genotype. Statistical analysis reveals that the shape of the shoot meristem rather than its size is closely correlated with the variations of plastochron and phyllotaxy. Rapid and random leaf production in sho mutants is correlated with the frequent and disorganized cell divisions in the shoot meristem and with a reduction of expression domain of a rice homeobox gene, OSH1. These changes in the organization and behavior of the shoot apical meristems suggest that sho mutants have fewer indeterminate cells and more determinate cells than wild type, with many cells acting as leaf founder cells. Thus, the SHO genes have an important role in maintaining the proper organization of the shoot apical meristem, which is essential for the normal initiation pattern of leaf primordia.

Cell Division↗

PubMed1991

A Mutation in the Arabidopsis TFL1 Gene Affects Inflorescence Meristem Development.

We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfl1-1), that identifies a new genetic locus, TFL1. The tfl1-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. Inflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfl1-1 with the floral morphogenesis mutations apetala 1-1 (ap1-1), ap2-1, and agamous (ag) suggest that the tfl1-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the ap1-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfl1-1 ap1-1 double mutants. Our results suggest that tfl1-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.

Journal Article↗

PubMed1993

CLAVATA1, a regulator of meristem and flower development in Arabidopsis.

We have investigated the effects on plant development of mutations in the Arabidopsis thaliana CLAVATA1 gene. In clavata1 plants, vegetative, inflorescence and floral meristems are all enlarged relative to wild type. The apical meristem can fasciate in the more severe mutant alleles, and this fasciation can occur prior to the transition to flowering. Flowers of clavata1 plants can have increased numbers of organs in all four whorls, and can also have additional whorls not present in wild-type flowers. Double mutant combinations of clavata1 with agamous, apetala2, apetala3 and pistillata indicate that CLAVATA1 controls the underlying floral meristem structure upon which these homeotic genes act. Double mutant combinations of clavata1 with apetala1 and leafy indicate CLAVATA1 plays a role in establishing and maintaining floral meristem identity, in addition to its role in controlling meristem size. In support of this, RNA expression patterns of AGAMOUS and APETALA1 are altered in clavata1 flowers.

Arabidopsis↗

PubMed1984

Somatic chromosome counts from leaf meristems in the tribe Triticeae.

The Feulgen procedure was applied to chromosome preparations of leaf meristems from growing plants of wheat, barley, and wheat-wheatgrass hybrids. Leaf primordia from the base of secondary tillers were pretreated in cold water (overnight, 2 C), fixed in glacial acetic acid (20 min, 2 C), hydrolyzed in 1 N HC1 (14 min), stained in leuco-basic fuchsin (about 15 min) and squashed in 1% acetocarmine. The chromosome spreads from leaf meristems were generally superior to those of the root meristems of the same plant. Mitotic index in leaf meristems was higher than in root meristems in some species. The method appears useful for counting the chromosome number of growing plants, detecting chimeras, and verifying root tip chromosome counts.

Chromosomes↗

PubMed1978

Comparison of determined and undetermined meristems of Selaginella willdenovii Baker.

Three types of meristems from Selaginella willdenovii were compared. Undetermined dorsal branch junction meristems were aseptically cultured for 0, 1, 3, 5, and 7 days on Knop's medium prior to fixation. Root tips and shoot tips, which have meristems already determiend developmentally, were excised from intact plants and fixed immediately. The cellular ultrastructure of each meristem was studied showing some differences in chloroplast structure, microtubule deposition, vesicle formation, degree of vacuolation, and invaginations of the plasma membrane. Some of these features, such as microtubule deposition and vesicle formation and vacuolation could be attributed to the different developmental states of the meristems.

Cell Membrane↗

PubMed2003

MISSING FLOWERS gene controls axillary meristems initiation in sunflower.

The initiation and growth of axillary meristems are fundamental components of plant architecture. Here, we describe the mutant missing flowers (mf) of Helianthus annuus characterized by the lack of axillary shoots. Decapitation experiments and histological analysis indicate that this phenotype is the result of a defect in axillary meristem initiation. In addition to shoot branching, mutation affects floral differentiation. The indeterminate inflorescence of sunflower (capitulum) is formed of a large flat meristem which produces floret primordia in multiple spirals. In wildtype plants a bisecting crease divides each primordium in two distinct bumps that adopt different fate. The peripheral (abaxial) part of the primordium becomes a small leaf-like bract and the adaxial part becomes a flower. In the mf mutant, the formation of flowers at the axil of bracts is precluded. Histological analyses show that in floret primordia of the mutant a clear subdivision in dyads is not established. The primordia progressively bend inside and only large involucral floral bracts are developed. The results suggest that the MISSING FLOWERS gene is essential to provide or perceive an appropriate signal to the initiation of axillary meristems during both vegetative and reproductive phases.

Flowers↗

PubMed2004

Rescue of defective auxin-mediated gene expression and root meristem function by inhibition of ethylene signalling in sterol biosynthesis mutants of Arabidopsis.

The roles of sterols in plant development are not well understood, but evidence is emerging that they are required for cell division, polarity and patterning by mechanisms that are independent of brassinosteroids, of which they are precursors. Previous evidence shows that two sterol-defective mutants of Arabidopsis thaliana (L.) Heynh., hyd1 and fk(hyd2), are defective in root development. Here we show that the HYD1 gene, like the FK gene, is transcriptionally active in both primary and lateral root meristems, though not in the shoot apical meristem. The patterns of cell division during early stages of lateral root initiation in the hyd1 and fk(hyd2) mutants appear normal. Previous evidence also suggests that auxin and ethylene signalling is defective in the mutants. Here we show that the cytokinin- and ethylene-responsive ACS1::GUS reporter in the fk(hyd2) mutant responds to exogenous cytokinins but not to the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, indicative of normal cytokinin signalling but supporting the hypothesis that ethylene signalling is defective. The defective root meristem cell division activity and expression patterns of the auxin-regulated DR5::GUS and IAA2::GUS reporters can be rescued to a significant extent by the pharmacological or genetic inhibition of ethylene signalling, but not by treatment with aminoethoxyvinylglycine, an inhibitor of ethylene synthesis. This supports the emerging view that the hyd1 and fk(hyd2) mutants exhibit an enhanced and unregulated ethylene signalling activity, which accounts for at least part of the observed mutant phenotypes, including disrupted auxin signalling. The possible relationship between ethylene signalling, membrane sterols and meristem function is discussed.

Arabidopsis↗

PubMed2000

The frequency of plasmodesmata increases early in the whole shoot apical meristem of Sinapis alba L. during floral transition.

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem. The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at floral transition, there is an unfolding of a single field with increased plasmodesmatal connectivity, and (ii) this event is an early effect of the arrival at this meristem of the floral stimulus of leaf origin. Since (i) the wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al. 1998, Plant cell proliferation and its regulation in growth and development, pp. 67 78; Wiley), and (ii) the increase in frequency of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating the cell layers), it is concluded that the extra plasmodesmata seen at floral transition do not arise in the forming cell plate during mitosis and are thus of secondary origin.

Meristem↗

PubMed2005

Activation of the WUS gene induces ectopic initiation of floral meristems on mature stem surface in Arabidopsis thaliana.

A gain-of-function Arabidopsis mutant was identified via activation tagging genetic screening. The mutant exhibited clustered ectopic floral buds on the surface of inflorescence stems. The mutant was designated as sef for stem ectopic flowers. Our detailed studies indicate that the ectopic flower meristems are initiated from the differentiated cortex cells. Inverse PCR and sequence analysis indicated that the enhancer-containing T-DNA from the activation tagging construct, SKI015, was inserted upstream of the previously cloned WUS gene encoding a homeodomain protein. Studies from RT-PCR, RNA in situ hybridization and transgenic plant analysis further confirmed that the phenotypes of sef are caused by the overexpression of WUS. Our results suggest that overexpression of WUS could trigger the cell pluripotence and reestablish a new meristem in cortex. The type of new meristems caused by WUS overexpression was dependent upon the developmental and physiological stages of a plant. With the help of some undefined factors in the reproductive organs the new meristems differentiated into floral buds. In a vegetative growth plant, however, only the new vegetative buds can be initiated upon the overexpression of WUS. These studies provide new insights of WUS on flower development.

Arabidopsis↗

PubMed2006

How floral meristems are built.

The formation of flowers involves the activity of a genetic network that acts in meristems to specify floral identity. The main output of this network is the initiation of a developmental patterning program for the generation of floral organs. The first characteristic of meristem identity genes is their capacity to integrate the environmental and endogenous cues that regulate the onset of flowering. This mechanism synchronizes temporal and spatial information, ensuring that flowers arise in the correct location at the appropriate time. The second characteristic of this network is the mutual regulatory interactions established between meristem identity genes. These interactions provide flexibility and robustness against environmental noise and prevent reversion once the decision to flower has been made. Finally, the third feature is the overlap between the meristem identity and other developmental programs that operate simultaneously to regulate different aspects of the construction of flowers.

Body Patterning↗

PubMed2005

POL and related phosphatases are dosage-sensitive regulators of meristem and organ development in Arabidopsis.

CLAVATA1 (CLV1) regulates stem cell accumulation at Arabidopsis shoot and flower meristems. CLV1 encodes a receptor-like kinase, but very little is known about downstream signaling components of receptor-kinase signaling in plants. poltergeist (pol) mutants suppress the accumulation of stem cells that occur in clv mutants, and POL has been hypothesized to modulate CLV1 signaling. The POL gene, which encodes a functional protein phosphatase type 2C, is a member of a six-gene family in Arabidopsis. We have isolated loss-of-function alleles for each of the five POL-like genes (PLL1-PLL5). All gene family members, with the exception of PLL3, are expressed broadly within the plant, albeit at differing levels. We show that PLL1 regulates meristem development in parallel with POL. We observe a strong dosage sensitivity at the meristem for POL and PLL1 function in both loss- and gain-of-function analyses, suggesting that these proteins are rate-limiting modulators of stem cell specification. PLL genes also function outside of the meristem: POL and PLL1 regulate pedicel length in interaction with ERECTA, while PLL4 and PLL5 regulate leaf development. We observed no developmental role for either PLL2 or PLL3 based on single and double mutant analysis.

Alleles↗

PubMed2001

Cellular basis of shoot apical meristem development.

Shoot apical meristems are composed of proliferating, embryonic type cells, that generate tissues and organs throughout the life of the plant. This review covers the cell biology of the higher plant shoot apical meristem (SAM). The first section describes the molecular basis of plant cell growth and division. The genetic mechanisms, that operate in meristem function and the identification of several key regulators of meristem behavior are described in the second section, and intercellular communication and coordination of cellular behavior in the third part. Finally, we discuss some recent results that indicate interaction between the cellular regulators, such as the cell cycle control genes and developmental regulators.

Cell Differentiation↗

PubMed2000

The stem cell population of Arabidopsis shoot meristems in maintained by a regulatory loop between the CLAVATA and WUSCHEL genes.

The higher-plant shoot meristem is a dynamic structure whose maintenance depends on the coordination of two antagonistic processes, organ initiation and self-renewal of the stem cell population. In Arabidopsis shoot and floral meristems, the WUSCHEL (WUS) gene is required for stem cell identity, whereas the CLAVATA1, 2, and 3 (CLV) genes promote organ initiation. Our analysis of the interactions between these key regulators indicates that (1) the CLV genes repress WUS at the transcript level and that (2) WUS expression is sufficient to induce meristem cell identity and the expression of the stem cell marker CLV3. Our data suggest that the shoot meristem has properties of a self-regulatory system in which WUS/CLV interactions establish a feedback loop between the stem cells and the underlying organizing center.

Arabidopsis↗

PubMed2001

Termination of stem cell maintenance in Arabidopsis floral meristems by interactions between WUSCHEL and AGAMOUS.

Floral meristems and shoot apical meristems (SAMs) are homologous, self-maintaining stem cell systems. Unlike SAMs, floral meristems are determinate, and stem cell maintenance is abolished once all floral organs are initiated. To investigate the underlying regulatory mechanisms, we analyzed the interactions between WUSCHEL (WUS), which specifies stem cell identity, and AGAMOUS (AG), which is required for floral determinacy. Our results show that repression of WUS by AG is essential for terminating the floral meristem and that WUS can induce AG expression in developing flowers. Together, this suggests that floral determinacy depends on a negative autoregulatory mechanism involving WUS and AG, which terminates stem cell maintenance.

AGAMOUS Protein, Arabidopsis↗

PubMed1998

To be, or not to be, a flower--control of floral meristem identity.

Sexual reproduction in higher plants occurs within the flower, which develops from the floral meristem, a specialized form of lateral meristems. The decision to become a floral meristem is highly regulated, and several genes controlling this process have been isolated. Some of these genes were shown to promote the floral fate precociously and ectopically when expressed constitutively. Furthermore, studies indicate the commitment to the floral fate is not a single switch, but a condition acquired progressively. Finally, genes controlling flowering time, at least in part, act through the floral-meristem-identity genes, and such interactions occur at multiple levels.

Arabidopsis↗

PubMed2003

Shoot apical meristem maintenance: the art of a dynamic balance.

The aerial structure of higher plants derives from cells at the tip of the stem, in the shoot apical meristem (SAM). Throughout the life of a plant, the SAM produces stem tissues and lateral organs, and also regenerates itself. For correct growth, the plant must maintain a constant flow of cells through the meristem, where the input of dividing pluripotent stem cells offsets the output of differentiating cells. This flow depends on extracellular signaling within the SAM, governed by a spatial regulatory feedback loop that maintains a reservoir of stem cells, and on factors that prevent meristem cells from differentiating prematurely. The terminating floral meristem incorporates the spatial regulation scheme into a temporal regulation pathway involving flower patterning factors.

Arabidopsis↗

PubMed2000

A xenobiotic-stress-activated transcription factor and its cognate target genes are preferentially expressed in root tip meristems.

In plants, as-1-type cis elements and their trans-acting factors confer tissue-specific and signal-responsive activities to the promoters of several glutathione S-transferase (GST) genes. Regulation of as-1 is widely thought to involve trans-acting factors that belong to a family of basic/leucine-zipper 'TGA factors' that selectively bind this element. We have previously shown that TGA 1a, a highly conserved TGA factor of tobacco, enhances transcription through as-1 in response to xenobiotic-stress cues. To better understand the functional contribution of this transcription factor to the expression of as-1-regulated genes, we have studied its tissue- and cell-specific localization in tobacco seedlings. We show here that the relative amount of TGA1a transcripts expressed in roots and shoots correlate with the as-1-regulated, basal-level expression of a GUS transgene and two putative target GST genes. In situ hybridization of intact seedlings demonstrated that TGA1a and these GST genes are preferentially expressed in root tip meristems. Similar findings were made with a gene-specific probe for PG13, a homologue of TGA1a, demonstrating that both factors are likely to be present in the same root meristem cells. Furthermore, TGA1a protein was immunologically detected exclusively in the primary root and its meristem. Collectively, these studies suggest that TGA1a, and perhaps PG13, may contribute to the expression of GST isoenzymes, especially in root tip meristems. The biological significance of these observations is discussed.

Basic-Leucine Zipper Transcription Factors↗