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PubMed2001

Guard cell abscisic acid signalling and engineering drought hardiness in plants.

Guard cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants through transpiration to the atmosphere. Guard cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of guard cell abscisic acid signalling have been discovered. The molecular understanding of the guard cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.

Abscisic Acid↗
PubMed2001

Plant evolution and development in a post-genomic context.

Large-scale gene-sequencing projects that have been undertaken in animals have involved organisms from contrasting taxonomic groups, such as worm, fly and mammal. By contrast, similar botanical projects have focused exclusively on flowering plants. This has made it difficult to carry out fundamental research on how plants have evolved from simple to complex forms - a task that has been very successful in animals. However, in the flowering plants, the many completely or partially sequenced genomes now becoming available will provide a powerful tool to investigate the details of evolution in one group of related organisms.

Biological Evolution↗
PubMed2001

Constitutive expression of Arabidopsis LEAFY or APETALA1 genes in citrus reduces their generation time.

Citrus trees have a long juvenile phase that delays their reproductive development by between 6 and 20 years, depending on the species. With the aim of accelerating their flowering time, we transformed juvenile citrus seedlings to constitutively express the Arabidopsis LEAFY (LFY) or APETALA1 (AP1) genes, which promote flower initiation in Arabidopsis. Both types of transgenic citrus produced fertile flowers and fruits as early as the first year, notably through a mechanism involving an appreciable shortening of their juvenile phase. Furthermore, expression of AP1 was as efficient as LFY in the initiation of flowers, and did not produce any severe developmental abnormality. Both types of transgenic trees flowered in consecutive years, and their flowering response was under environmental control. In addition, zygotic and nucellar derived transgenic seedlings had a very short juvenile phase and flowered in their first spring, demonstrating the stability and inheritance of this trait. These results open new possibilities for domestication, genetic improvement, and experimental research in citrus and other woody species.

Arabidopsis↗
PubMed2001

Hydrogen peroxide-induced changes in intracellular pH of guard cells precede stomatal closure.

Epidermal bioassay demonstrated that benzylamine, a membrane-permeable weak base, can mimick hydrogen peroxide (H2O2) to induce stomatal closure, and butyric acid, a membrane-permeable weak acid, can partly abolish the H2O2-induced stomatal closure. Confocal pH mapping with the probe 5-(and-6)-carboxy seminaphthorhodafluor-1-acetoxymethylester (SNARF-1-AM) revealed that H2O2 leads to rapid changes in cytoplasmic and vacuolar pH in guard cells of Vicia faba L, i. e. alkalinization of cytoplasmic areas occur red in parallel with a decrease of the vacuolar pH, and that butyric acid pretreatment can abolish alkalinization of cytoplasmic areas and acidification of vacuolar areas of guard cells challenged with H2O2. These results imply that the alkalinization of cytoplasm via efflux of cytosol protons into the vacuole in guard cells challenged with H2O2 is important at an early stage in the signal cascade leading to stomatal closure.

Benzopyrans↗
PubMed2004

Carbohydrate-binding modules: fine-tuning polysaccharide recognition.

The enzymic degradation of insoluble polysaccharides is one of the most important reactions on earth. Despite this, glycoside hydrolases attack such polysaccharides relatively inefficiently as their target glycosidic bonds are often inaccessible to the active site of the appropriate enzymes. In order to overcome these problems, many of the glycoside hydrolases that utilize insoluble substrates are modular, comprising catalytic modules appended to one or more non-catalytic CBMs (carbohydrate-binding modules). CBMs promote the association of the enzyme with the substrate. In view of the central role that CBMs play in the enzymic hydrolysis of plant structural and storage polysaccharides, the ligand specificity displayed by these protein modules and the mechanism by which they recognize their target carbohydrates have received considerable attention since their discovery almost 20 years ago. In the last few years, CBM research has harnessed structural, functional and bioinformatic approaches to elucidate the molecular determinants that drive CBM-carbohydrate recognition. The present review summarizes the impact structural biology has had on our understanding of the mechanisms by which CBMs bind to their target ligands.

Binding Sites↗
PubMed2002

Entopically additive expression of GLABRA2 alters the frequency and spacing of trichome initiation.

GLABRA2 (GL2)/ATHB-10 encodes a homeodomain protein that belongs to the homeodomain-leucine zipper family. Mutant studies have revealed that this gene is involved in trichome, root-hair and seed-coat development. We used reverse genetics to investigate the role of GL2 in trichome development. A transgene consisting of a GL2-coding fragment preceded by the cauliflower mosaic virus 35S promoter (35S::GL2) did not complement defects in the gl2-1 mutant. In the wild-type genetic background, 35S::GL2 caused gl2-mutant-like and scarcely viable phenotypes, suggesting that ectopic overexpression of GL2 interrupts endogenous GL2 function in trichome development and is toxic to plants. On the other hand, another GL2 transgene containing the GL2 promoter (pGL2::GL2) complemented the gl2-1 mutation. Entopically additive expression of GL2 by introduction of pGL2::GL2 in the wild-type genetic background noticably increased the number of trichomes and induced production of adjacent trichomes. Consistent with this result, gl2-1/+ heterozygous leaves, whose GL2 expression was expected to decrease, had fewer trichomes than +/+ leaves. These results indicate that GL2 quantitatively regulates the frequency of trichome initiation and is involved in determining trichome spacing.

Arabidopsis↗
PubMed2000

A xylem-specific cellulose synthase gene from aspen (Populus tremuloides) is responsive to mechanical stress.

Angiosperm trees accumulate an elevated amount of highly crystalline cellulose with a concomitant decrease in lignin in the cell walls of tension-stressed tissues. To investigate the molecular basis of this tree stress response, we cloned a full-length cellulose synthase (PtCesA) cDNA from developing xylem of aspen (Populus tremuloides). About 90% sequence similarity was found between the predicted PtCesA and cotton GhCesA proteins. Northern blot and in situ hybridization analyses of PtCesA gene transcripts in various aspen tissues, and PtCesA gene promoter-beta-glucuronidase (GUS) fusion analysis in transgenic tobacco, demonstrated conclusively that PtCesA expression is confined to developing xylem cells during normal plant growth. During mechanical stress induced by stem bending, GUS expression remained in xylem and was induced in developing phloem fibers undergoing tension stress, but was turned off in tissues undergoing compression on the opposite side of the bend. Our results suggest a unique role for PtCesA in cellulose biosynthesis in both tension-stressed and normal tissues in aspen, and that the on/off control of PtCesA expression may be a part of a signaling mechanism triggering a stress-related compensatory deposition of cellulose and lignin that is crucial to growth and development in trees.

Arabidopsis Proteins↗
PubMed2001

The shoot apical meristem restores its symplasmic organization during chilling-induced release from dormancy.

The shoot apex of overwintering perennials ceases its morphogenetic activity at the end of the growing season and transforms into a bud which is dormant and freezing-tolerant. In birch (Betula pubescens) these events are triggered by short photoperiod, and involve the production of 1,3-beta-D-glucan containing sphincters on the plasmodesmata. As a result, all symplasmic pathways shut down. Here we show that breakage of bud dormancy by chilling involves restoration of the symplasmic organization of the meristem. This restoration is likely to be mediated by 1,3-beta-D-glucanase, which was present in small spherosome-like vacuoles that arose de novo during dormancy induction. During chilling these vacuoles were displaced from the bulk cytoplasm to the cortical cytoplasm where they became aligned with the plasma membrane, often associated with plasmodesmata. At this stage the enzyme also appeared outside the vacuoles. During chilling, 1,3-beta-D-glucan disappeared from the plasmodesmal channels and wall sleeves, and the plasmodesmata regained the capacity for cell-cell transport, as demonstrated by microinjection of Lucifer Yellow CH and Fluorescein-tagged gibberellic acid. Collectively, the present experiments demonstrate that restoration of the symplasmic organization of the meristem is indispensable for the release of buds from dormancy and the assumption of a proliferation-competent state, and implicate 1,3-beta-D-glucanase action at the plasmodesmata. Based on these findings we propose a model for 'dormancy cycling' which depicts the meristem as passing through three sequential states of cellular communication with characteristic sensitivities to distinct environmental cues.

Cell Communication↗
PubMed2003

Antimicrobial activity of essential oils isolated from Portuguese endemic species of Thymus.

AIMS: Thymus species are wild species mostly found in the arid lands of Portugal. Possible antimicrobial properties of Thymus essential oils have been investigated. The chemical composition of the essential oils and the antimicrobial activity of Thymus mastichina (L) L. subsp. mastichina, T. camphoratus and T. lotocephalus from different regions of Portugal were analysed. METHODS AND RESULTS: Hydrodistillation was used to isolate the essential oils and the chemical analyses were performed by gas chromatography (GC) and GC coupled to mass spectrometry. The antimicrobial activity was tested by the disc agar diffusion technique against Candida albicans, Escherichia coli, Listeria monocytogenes, Proteus mirabilis, Salmonella spp. and Staphylococcus aureus. Pure linalool, 1,8-cineole and a mixture (1 : 1) of these compounds were included. Linalool, 1,8-cineole or linalool/1,8-cineole and linalool/1,8-cineole/linalyl acetate were the major components of the essential oils, depending on the species or sampling place. The essential oils isolated from the Thymus species studied demonstrated antimicrobial activity but the micro-organisms tested had significantly different sensitivities. CONCLUSIONS: The antimicrobial activity of essential oils may be related to more than one component. SIGNIFICANCE AND IMPACT OF THE STUDY: Portuguese endemic species of Thymus can be used for essential oil production for food spoilage control, cosmetics and pharmaceutical use. Further studies will be required to elucidate the cell targets of the essential oil components.

Acyclic Monoterpenes↗
PubMed2001

New antioxidant and antimicrobial ellagic acid derivatives from Pteleopsis hylodendron.

Bioassay-guided isolation of two new compounds, 3,4-methylenedioxy-3'-O-methyl-4'-O-glucoside ellagic acid (1) and the pteleoellagic acid derivative (2), from the stem bark of Pteleopsis hylodendron is reported along with 3,4-methylenedioxy-3'-O-methyl ellagic acid (3), 3,3'-di-O-methyl ellagic acid (4) and 3,3',4'-tri-O-methyl ellagic acid (5), which were obtained for the first time from this plant. The structures of these compounds were elucidated with the help of spectroscopic studies. Compounds 1 and 4 were found to have significant antioxidant activity, while compounds 1-4 showed antibacterial activity against different pathogenic bacteria.

Anti-Bacterial Agents↗
PubMed2001

A curcuminoid and sesquiterpenes as inhibitors of macrophage TNF-alpha release from Curcuma zedoaria.

Tumor necrosis factor-alpha (TNF-alpha) is one of the major mediators produced in activated macrophages which contribute to the circulatory failure associated with septic shock. In the course of screening marketed oriental anti-inflammatory herbal drugs for TNF-alpha antagonistic activity, a crude methanolic extract of the rhizomes of Curcuma zedoaria exhibited significant activity. The activity-guided fractionation and repetitive chromatographic procedures with the EtOAc-soluble fraction resulted in the isolation of three active compounds. They were identified as 1,7-bis(4-hydroxyphenyl)-1,4,6-heptatrien-3-one (1), procurcumenol (2) and epiprocurcumenol (3) by spectral data analysis. They inhibited the production of TNF-alpha by lipopolysaccharide (LPS)-activated macrophages from the results of bioassay (IC(50) values of 1 and 2 are 12.3 and 310.5 microM, respectively) and Western blot assay. These results imply that the traditional use of C. zedoaria rhizome as anti-inflammatory drug may be explained at least in part, by the inhibition of TNF-alpha production.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Essential oil composition and antimicrobial activity of three Zingiberaceae from S.Tomé e Príncipe.

The essential oil composition of three Zingiberaceae widely used as medicinal aromatic plants from S. Tomé and Príncipe: Aframomum danielli (Hook. f.) K. Schum., Curcuma longa L. and Zingiber officinale Rosc. was studied. Two samples of the essential oils from fruit of A. danielli and from rhizomes of the other two species, were obtained by hydrodistillation and analyzed by GC, GC-MS, and (13)C-NMR. The essential oil from fruits of A. danielli has been studied for the first time and was characterised by its high content of monoterpenes, with 1,8-cineole (25.5 - 34.4 %) the major constituent, followed by beta-pinene (14.1 - 15.2 %) and alpha-terpineol (9.9 - 12.1 %). Essential oils from the rhizomes of C. longa contained a lower content of ar-turmerone (4.0 - 12.8 %) than those reported in the literature for C. longa from other origins (24.7 - 31.4 %), whereas the results for Z. officinale essential oils were in accordance with the literature data. The essential oils of A. danielli and Z. officinale showed antimicrobial activity against all Gram-positive and Gram-negative bacteria tested, as well as against yeasts and filamentous fungi, using the agar diffusion method.

Anti-Bacterial Agents↗
PubMed2002

Variation in content of taxol and related taxanes in Eastern Himalayan populations of Taxus wallichiana.

Extraction and analysis of paclitaxel and other taxanes in bark, needle leaves and stem segments of male and female plants of Taxus wallichiana, representing several populations, indicate that significant variation in taxane content exists within the population. Bark accumulated maximum amount of paclitaxel in almost all plants. Populations located at higher altitude tended to accumulate more paclitaxel than lower altitude plants. Seasons in which samples were collected and plant age have also been shown to affect paclitaxel accumulation. No effects of plant sex on paclitaxel content of the plants analyzed were observed. Significant differences in baccatin-III and 10-deacetylbaccatin III content were found to exist in the trees analyzed in this study.

Asia, Western↗
PubMed2000

Plant organ size control: AINTEGUMENTA regulates growth and cell numbers during organogenesis.

The control of cell proliferation during organogenesis plays an important role in initiation, growth, and acquisition of the intrinsic size of organs in higher plants. To understand the developmental mechanism that controls intrinsic organ size by regulating the number and extent of cell division during organogenesis, we examined the function of the Arabidopsis regulatory gene AINTEGUMENATA (ANT). Previous observations revealed that ANT regulates cell division in integuments during ovule development and is necessary for floral organ growth. Here we show that ANT controls plant organ cell number and organ size throughout shoot development. Loss of ANT function reduces the size of all lateral shoot organs by decreasing cell number. Conversely, gain of ANT function, via ectopic expression of a 35S::ANT transgene, enlarges embryonic and all shoot organs without altering superficial morphology by increasing cell number in both Arabidopsis and tobacco plants. This hyperplasia results from an extended period of cell proliferation and organ growth. Furthermore, cells ectopically expressing ANT in fully differentiated organs exhibit neoplastic activity by producing calli and adventitious roots and shoots. Based on these results, we propose that ANT regulates cell proliferation and organ growth by maintaining the meristematic competence of cells during organogenesis.

Arabidopsis↗
PubMed2003

Origin of cortical microtubules organized at M/G1 interface: recruitment of tubulin from phragmoplast to nascent microtubules.

The origin of cortical microtubules (CMTs) was investigated in transgenic BY-2 cells stably expressing a GFP (green fluorescent protein) -tubulin fusion protein (BY-GT16). In a previous study, we found that CMTs were initially organized in the perinuclear regions but then elongated to reach the cell cortex where they formed bright spots, and that the appearance of parallel MTs from the bright spots was followed by the appearance of transverse MTs (Kumagai et al., Plant Cell Physiol. 42, 723-732, 2001). In this study, we investigated the migration of tubulin to the reorganization sites of CMTs at the M/G1 interface. After synchronization of the BY-GT16 cells by aphidicolin, the localization of GFP-tubulin was monitored and analyzed by deconvolution microscopy. GFP-tubulin was found to accumulate on the nuclear surface near the cell plate at the final stage of phragmoplast collapse. Subsequently, GFP-tubulin accumulated again on the nuclear surface opposite the cell plate, where nascent MTs elongated to the cell cortex. The significance of these observations on the mode of CMT organization is discussed.

Aphidicolin↗
PubMed2003

Construction of gene expression system in hop (Humulus lupulus) lupulin gland using valerophenone synthase promoter.

The promoter region of the valerophenone synthase (VPS) gene was isolated from hop (Humulus lupulus). VPS, a member of the chalcone synthase (CHS) super-family, catalyzes the biosynthesis reaction of the hop resin that significantly accumulates in the cone's secretory gland called the "lupulin gland". The typical H-box and G-box sequences, which exist in many plants' CHS promoters and act as cis-elements for tissue specificity, UV-light induction, etc., were not found in the isolated VPS promoter, although the H-box-like sequence (CCTTACC, CCTAACC) and the core sequence (ACGT) of the G-box were observed. The transformation experiment using the VPS promoter-UIDA gene fusion revealed that the promoter acts not only in the lupulin gland but also in the glands of leaf and stem. On the other hand, the VPS promoter activity was not induced by UV-irradiation.

Acyltransferases↗