Spikelet structure and development in Cyperoideae (Cyperaceae): a monopodial general model based on ontogenetic evidence

Background and Aims

In Cyperoideae, one of the two subfamilies in Cyperaceae, unresolved homology questions about spikelets remained. This was particularly the case in taxa with distichously organized spikelets and in Cariceae, a tribe with complex compound inflorescences comprising male (co)florescences and deciduous female single-flowered lateral spikelets. Using ontogenetic techniques, a wide range of taxa were investigated, including some controversial ones, in order to find morphological arguments to understand the nature of the spikelet in Cyperoideae. This paper presents a review of both new ontogenetic data and current knowledge, discussing a cyperoid, general, monopodial spikelet model.

Methods

Scanning electron microscopy and light microscopy were used to examine spikelets of 106 species from 33 cyperoid genera.

Results

Ontogenetic data presented allow a consistent cyperoid spikelet model to be defined. Scanning and light microscopic images in controversial taxa such as Schoenus nigricans, Cariceae and Cypereae are interpreted accordingly.

Conclusions

Spikelets in all species studied consist of an indeterminate rachilla, and one to many spirally to distichously arranged glumes, each subtending a flower or empty. Lateral spikelets are subtended by a bract and have a spikelet prophyll. In distichously organized spikelets, combined concaulescence of the flowers and epicaulescence (a newly defined metatopic displacement) of the glumes has caused interpretational controversy in the past. In Cariceae, the male (co)florescences are terminal spikelets. Female single-flowered spikelets are positioned proximally on the rachis. To explain both this and the secondary spikelets in some Cypereae, the existence of an ontogenetic switch determining the development of a primordium into flower, or lateral axis is postulated.     

Elucidating the microbial component of natural attenuation

Microbial reactions are a key determinant in natural attenuation. However, providing unequivocal evidence of the extent of their involvement is challenging. Several approaches are being developed to meet this challenge, including the use of contaminant-specific transformation products, carbon- or hydrogen-based stable isotopic analysis and reactive transport modeling. These approaches emphasize the ongoing need to integrate strategically between temporally and spatially variant geochemical conditions, the ecological characteristics of the resident microbial communities and their resultant pollutant-transformation capabilities.     

Cytokinin-deficient transgenic Arabidopsis plants show multiple developmental alterations indicating opposite functions of cytokinins in the regulation of shoot and root meristem activity

Cytokinins are hormones that regulate cell division and development. As a result of a lack of specific mutants and biochemical tools, it has not been possible to study the consequences of cytokinin deficiency. Cytokinin-deficient plants are expected to yield information about processes in which cytokinins are limiting and that, therefore, they might regulate. We have engineered transgenic Arabidopsis plants that overexpress individually six different members of the cytokinin oxidase/dehydrogenase (AtCKX) gene family and have undertaken a detailed phenotypic analysis. Transgenic plants had increased cytokinin breakdown (30 to 45% of wild-type cytokinin content) and reduced expression of the cytokinin reporter gene ARR5:GUS (beta-glucuronidase). Cytokinin deficiency resulted in diminished activity of the vegetative and floral shoot apical meristems and leaf primordia, indicating an absolute requirement for the hormone. By contrast, cytokinins are negative regulators of root growth and lateral root formation. We show that the increased growth of the primary root is linked to an enhanced meristematic cell number, suggesting that cytokinins control the exit of cells from the root meristem. Different AtCKX-green fluorescent protein fusion proteins were localized to the vacuoles or the endoplasmic reticulum and possibly to the extracellular space, indicating that subcellular compartmentation plays an important role in cytokinin biology. Analyses of promoter:GUS fusion genes showed differential expression of AtCKX genes during plant development, the activity being confined predominantly to zones of active growth. Our results are consistent with the hypothesis that cytokinins have central, but opposite, regulatory functions in root and shoot meristems and indicate that a fine-tuned control of catabolism plays an important role in ensuring the proper regulation of cytokinin functions.     

Palynological evolutionary trends within the tribe Mentheae with special emphasis on subtribe Menthinae (Nepetoideae: Lamiaceae)

The pollen morphology of subtribe Menthinae sensu Harley et al. [In: The families and genera of vascular plants VII. Flowering plants·dicotyledons: Lamiales (except Acanthaceae including Avicenniaceae). Springer, Berlin, pp 167–275, 2004] and two genera of uncertain subtribal affinities (Heterolamium and Melissa) are documented in order to complete our palynological overview of the tribe Mentheae. Menthinae pollen is small to medium in size (13–43 μm), oblate to prolate in shape and mostly hexacolpate (sometimes pentacolpate). Perforate, microreticulate or bireticulate exine ornamentation types were observed. The exine ornamentation of Menthinae is systematically highly informative particularly at generic level. The exine stratification in all taxa studied is characterized by unbranched columellae. Orbicules are consistently absent in Menthinae. Our palynological data are interpreted in a phylogenetic context at tribal level in order to assess the systematic value of pollen characters and to evaluate the existing molecular phylogenies for this group. Pollen morphology suggests Heterolamium as a close relative of subtribe Nepetinae and supports the molecular affinity of Melissa to subtribe Salviinae.     

Development of transgenic tobacco harboring a zeatin O-glucosyltransferase gene from Phaseolus

Summary Zeatin and its derivatives are major consituents of higher plant cytokinins. Metabolic steps modifying the isoprenoid side chain, such as O-glycosylation, are expected to have a direct bearing on cytokinin-mediated processes. To examine this possibility, transgenic tobacco plants were generated harboring a gene (ZOG1) encoding a zeatin O-glucosyltransferase from Phaseolus lunatus under the control of a constitutive (35S) and an inducible (Tet) promoter. The presence of the transgene resulted in elevated enzyme production and conversion of exogenous zeatin to its O-glucoside, confirming the expression of the ZOG1 gene in transgenic plants. Endogenous O-glucosylzeatin was increased from less than 1 pmol per g fresh weight in leaves and roots of controls to 26 and 68 pmol per g fresh weight in leaves and roots of 35S-ZOG1 transformants, respectively. In cytokinin/auxin interaction experiments, Tet-ZOG1 leaf discs, in the presence of tetracycline, required 10-fold higher zeatin concentrations for the formation of shoots and callus than the controls. In 35S-ZOG1 plants, developmental changes included adventitious root formation on the lower stems, shorter stature, and axillary shoot growth. Thus, increased zeatin O-glucosylation in detached, cytokinin-dependent tissues leads to a shift in the response to exogenous zeatin indicative of cytokinin sequestering. In whole plants the effect can simulate a reduction or a rise in cytokinin activity depending on the tissue and stage of development. The use of tissue- and stagespecific promoters in the future will allow more precise analyses and targeted growth alterations.     

Pharmacological modulation of prostaglandin production by phagocytic cells of the thymic reticulum in relation to immunoregulation

We cultured phagocytic cells derived from the thymic reticulum in order to study the regulation of prostaglandin (PG) production by antiinflammatory or immunostimulating agents. The kinetics of PGE₂, 6-keto-PGF_1α and PGF_2α production were measured by specific radioimmunoassays of the supernatants harvested from cells treated with dexamethasone, a steroidal antiinflammatory drug and by two non steroidal inhibitors (indomethacin and sulindac) or by various immunostimulating agents, one of them, RU 41740 is currently being used in humans. Our results revealed that ech of these drugs exerts a differential effect on the PG production, with a striking action on PGE₂ synthesis, a lesser effect on 6-keto-PGF_1α production and almost no effect on PGF_2α synthesis. The possible mechanisms responsible for this complex regulation of PG production are discussed.     

Fully automated measurements by light microscopy of tissue sections using a cellular array computer

Software was developed for the acquisition, segmentation and analysis of microscopic OD-images on a VICOM digital image processor, extended with a VISIOMORPH morphoprocessor board. The delineation algorithms for peroxisomes, lysosomes, and nuclei in liver, kidney, and adrenal gland sections start by thresholding the difference between the original image and a low pass filtered version. The resulting binary mask is then processed by morphological operations in order to produce an object overlay. The efficiency of the programs is evaluated by comparing delineated objects at different OD-levels, created by varying the stain or by multiplying the original pixel values with constant factors. Manual delineation on some images is also used as a reference. More complex algorithms are used for the delineation of muscle fibres in ATP-ase-stained sections and immunocytochemically labelled cells in monolayer preparations. Muscle images from parallel sections with different stainings are matched with a coordinate transform, enabling the transfer of the object mask from a single delineated image to the unprocessed images and thus obtain all necessary information for fibre classification. After segmentation, the OD-images and their object overlays are fed into a data extraction program, measuring for each delineated object user-selected features. Data are sent to a VAX for statistical interpretation.     

Optimal fed batch experiment design for estimation of monod kinetics of Azospirillum brasilense: from theory to practice

In this paper the problem of reliable and accurate parameter estimation for unstructured models is considered. It is illustrated how a theoretically optimal design can be successfully translated into a practically feasible, robust, and informative experiment. The well-known parameter estimation problem of Monod kinetic parameters is used as a vehicle to illustrate our approach. As known for a long time, noisy batch measurements do not allow for unique and accurate estimation of the kinetic parameters of the Monod model. Techniques of optimal experiment design are, therefore, exploited to design informative experiments and to improve the parameter estimation accuracy. During the design process, practical feasibility has to be kept in mind. The designed experiments are easy to implement in practice and do not require additional monitoring equipment. Both design and experimental validation of informative fed batch experiments are illustrated with a case study, namely, the growth of the nitrogen-fixing bacteria Azospirillum brasilense.     

Gaertnera and Pagamea: Genera Within the Psychotrieae or Constituting the Tribe Gaertnereae? A Wood Anatomical and Palynological Approach

The possible alliance between Gaertnera and Pagamea (Rubiaceae-Rubioideae), two genera from the Old and New World, respectively, is investigated on the basis of wood anatomy and pollen morphology. Nowadays, the main point of discussion about the taxonomic position of these genera is whether they belong to the Psychotrieae or constitute a tribe Gaertnereae characterised by their secondarily superior ovary and sheathing stipules. Both the wood and pollen of the genus pair are found to show specific features absent in other genera of the Psychotrieae, e.g. parenchyma bands in the xylem and endexine thickenings on the polar sites of the pollen apertures. Nevertheless Gaertnera and Pagamea share many other characters with the Psychotrieae. Wood and pollen convincingly demonstrate the very close affinity of the two genera. The sister pair differs in so many features from other Psychotrieae, that Gaertnera and Pagamea should constitute at least a subtribe Gaertnerinae, formally recognized here. The general lack of profound studies on the affinities within the very large tribe Psychotrieae makes further comments on the taxonomic relationships of the Gaertnerinae difficult.     

Mitogenic and antimitogenic effects of cholera toxin-mediated cyclic AMP levels in 3T3 cells

The effect of time-controlled exposures to cholera toxin (CT) on intracellular levels of cyclic AMP (cAMP) and on the proliferative response of serum-stimulated 3T3 cells was investigated. Continuous exposure to CT caused up to 8-fold raises in cAMP content and inhibited DNA replication by delaying G1-S transition and by reducing the fraction of cells committed to DNA replication. In contrast, short exposures to CT during G0-G1 transition increased the fraction of cells responding to serum stimulation and potentiated the serum-induced morphological changes in the cell monolayer. A short exposure during late G1 phase, however, inhibited the onset of DNA synthesis but had little effect on ongoing DNA replication. The results indicate that cAMP has diverse and opposite effects on two defined restriction points in cell cycle control. Cyclic AMP was positively involved in the acquisition of the state of competence by quiescent cells (G0-G1 transition) but antagonistic on the onset of DNA replication (G1-S transition) in committed cells. The observations reconcile a number of controversial conclusions regarding the role of cAMP in cell cycle control.