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At least 19 recordsLinked to original sources
PubMed2001

UV-excited chlorophyll fluorescence as a tool for the assessment of UV-protection by the epidermis of plants.

Recently, a new method for estimating epidermal transmission of UV radiation in higher plants has been proposed. The empirical evidence for the usefulness of this method is reviewed here. Direct comparison with spectroscopically determined epidermal transmission yielded equivalent results. A linear correlation to the concentration of epidermal screening compounds has been shown. Relating UV-A and UV-B absorbance allowed some preliminary conclusions about the chemical nature of the screening compounds. A new portable apparatus is presented for the first time, which allows the non-destructive assessment of UV-A screening even under field conditions. Repeated measurements on identical leaves over a time-course of 6 d demonstrated a strong age-dependence in the capacity for the synthesis of UV-A screening compounds upon exposure to UV-B radiation. It is concluded that the new method may provide a valuable tool for the investigation of the acclimation of plants to UV-B radiation and, when accompanied by HPLC analysis, of the reaction of phenolic metabolism to environmental stimuli.

Acclimatization↗
PubMed2006

Functional aspects of cell patterning in aerial epidermis.

Plants have evolved epidermal cells that have specialized functions as adaptations to life on land. Many of the functions of these specialized cells are dependent, to a significant extent, on their arrangement within the aerial epidermis. Considerable progress has been made over the past two years in understanding the patterning mechanisms of trichomes and stomata in Arabidopsis leaves at the molecular level. How universal are these patterning programmes, and how are they adjusted to meet the changing functions of specialized epidermal cells in different plant organs? In this review, we compare the patterning of stomata and trichomes in different plant species, describe environmental and developmental factors that alter cell patterning, and discuss how changes in patterning might relate to cell function. Patterning is an important aspect to the functioning of aerial epidermal cells, and a greater understanding of the processes that are involved will significantly enhance our understanding of how cellular activities are integrated in multicellular plants.

Cell Movement↗
PubMed2003

How do cells know what they want to be when they grow up? Lessons from epidermal patterning in Arabidopsis.

Because the plant epidermis is readily accessible and consists of few cell types on most organs, the epidermis has become a well-studied model for cell differentiation and cell patterning in plants. Recent advances in our understanding of the development of three epidermal cell types, trichomes, root hairs, and stomata, allow a comparison of the underlying patterning mechanisms. In Arabidopsis, trichome development and root epidermal patterning use a common mechanism involving closely related cell fate transcription factors and a similar lateral inhibition signaling pathway. Yet the resulting patterns differ substantially, primarily due to the influence of a prepattern derived from subepidermal cortical cells in root epidermal patterning. Stomatal patterning uses a contrasting mechanism based primarily on control of the orientation of cell divisions that also involves an inhibitory signaling pathway. This review focuses on comparing and contrasting these patterning pathways to identify and illustrate general themes that may be broadly applicable to other systems. Where these pathways occur in the same tissue, interaction and competition between these pathways is also discussed.

Arabidopsis↗
PubMed1997

Developmental regulation of cell interactions in the Arabidopsis fiddlehead-1 mutant: a role for the epidermal cell wall and cuticle.

Although the plant epidermis serves primarily a protective role, during plant development some epidermal cells specialize, becoming competent to interact not only with pollen but also with other epidermal cells. In the former case, these interactions mediate recognition, germination, and pollen growth responses and, in the latter case, result in interorgan fusions which, most commonly, alter floral architecture in ways that are thought to promote reproductive success. In either case, all of the initial signaling events must take place across the cell wall and cuticle. In Arabidopsis, mutation of the FIDDLEHEAD gene alters the shoot epidermis such that all epidermal cells become competent to participate in both types of interactions. In fdh-1 mutants, epidermal cells manifest not only a contact-mediated fusion response but also interact with pollen. Since carpel epidermal derivatives manifest both of these properties, we postulated that fdh-1 epidermal cells were ectopically expressing a carpel-like program. In this report we demonstrate that manifestation of the fdh-1 phenotype does not require the product of the AGAMOUS gene, indicating that the phenotype is either independent of the carpel development program or that fdh-1 mutations activate a carpel-specific developmental program downstream of the AG gene. Furthermore, we demonstrate that plants bearing mutations in the fdh-1 gene show significant changes in cell wall and cuticular permeability. Biochemical analyses of the lipid composition of the crude cell wall fraction reveal that fdh-1 cell walls differ from wild-type and manifest significant changes in high-molecular-weight lipid peaks. These results suggest that cell wall and cuticular permeability may be important determinants in developmental signaling between interacting cells and implicate lipids as important factors in modulating the selectivity of the permeability barrier presented by the epidermal cell wall and cuticle.

Arabidopsis↗
PubMed2000

Differentiation in plant epidermal cells.

The plant epidermis is a multifunctional tissue playing important roles in water relations, defence and pollinator attraction. This range of function is performed by a number of different types of specialized cells, which differentiate from the early undifferentiated epidermis in adaptively significant patterns and frequencies. These various cells show different degrees of morphological specialization, but there is evidence to suggest that even the less specialized cell types may require certain signals to ensure their correct differentiation and patterning. Epidermal cells may potentially adopt certain fates through a cell lineage based mechanism or a cell interaction mechanism. Work on stomatal development has focused on the cell lineage mechanism and work on trichome differentiation has focused on the cell interaction model. Recent work on the Arabidopsis trichome suggests that interactions between neighbouring cells reinforce initial differences, possibly in levels of gene expression or cell cycle stage, to commit cells to different developmental programmes. In this review these mechanisms are explored in a number of specialized cell types and the further interactions between different developmental programmes are analysed. It is in these interactions between differentiating cells adopting different cell fates that the key to the patterning of a multifunctional tissue must lie.

Arabidopsis↗
PubMed2005

Polar localizing class V myosin chitin synthases are essential during early plant infection in the plant pathogenic fungus Ustilago maydis.

Fungal chitin synthases (CHSs) form fibers of the cell wall and are crucial for substrate invasion and pathogenicity. Filamentous fungi contain up to 10 CHSs, which might reflect redundant functions or the complex biology of these fungi. Here, we investigate the complete repertoire of eight CHSs in the dimorphic plant pathogen Ustilago maydis. We demonstrate that all CHSs are expressed in yeast cells and hyphae. Green fluorescent protein (GFP) fusions to all CHSs localize to septa, whereas Chs5-GFP, Chs6-GFP, Chs7-yellow fluorescent protein (YFP), and Myosin chitin synthase1 (Mcs1)-YFP were found at growth regions of yeast-like cells and hyphae, indicating that they participate in tip growth. However, only the class IV CHS genes chs7 and chs5 are crucial for shaping yeast cells and hyphae ex planta. Although most CHS mutants were attenuated in plant pathogenicity, Deltachs6, Deltachs7, and Deltamcs1 mutants were drastically reduced in virulence. Deltamcs1 showed no morphological defects in hyphae, but Mcs1 became essential during invasion of the plant epidermis. Deltamcs1 hyphae entered the plant but immediately lost growth polarity and formed large aggregates of spherical cells. Our data show that the polar class IV CHSs are essential for morphogenesis ex planta, whereas the class V myosin-CHS is essential during plant infection.

Aminoglycosides↗
PubMed1995

The too many mouths and four lips mutations affect stomatal production in Arabidopsis.

Stomata regulate gas exchange through the aerial plant epidermis by controlling the width of a pore bordered by two guard cells. Little is known about the genes that regulate stomatal development. We screened cotyledons from ethyl methanesulfonate-mutagenized seeds of Arabidopsis by light microscopy to identify mutants with altered stomatal morphology. Two mutants, designated too many mouths (tmm) and four lips (flp), were isolated with extra adjacent stomata. The tmm mutation results in stomatal clustering and increased precursor cell formation in cotyledons and a virtual absence of stomata in the inflorescence stem. The flp mutation results in many paired stomata and a small percentage of unpaired guard cells in cotyledons. The double mutant (tmm flp) exhibits aspects of both parental phenotypes. Both mutations appear to affect stomatal production more than patterning or differentiation. tmm regulates stomatal production by controlling the formation, and probably the activity, of the stomatal precursor cell.

Arabidopsis↗
PubMed2002

Photosynthetic oxygen evolution at low water potential in leaf discs lacking an epidermis.

Land plants encountering low water potentials (low psiw) close their stomata, restricting CO2 entry and potentially photosynthesis. To determine the impact of stomatal closure, photosynthetic O2 evolution was investigated in leaf discs from sunflower (Helianthus annuus L.) plants after removing the lower epidermis at low psiw. Wounding was minimal as evidenced by O2 evolution nearly as rapid as that in intact discs. O2 evolution was maximal in 1% CO2 in the peeled discs and was markedly inhibited when psiw was below -1.1 MPa. CO2 entered readily at all psiw, as demonstrated by varying the CO2 concentration. Results were the same whether the epidermis was removed before or after low psiw was imposed. Due to the lack of an epidermis and ready movement or CO2 through the mesophyll, the loss in O2 evolving activity was attributed entirely to photosynthetic metabolism. Intact leaf discs showed a similar loss in activity when measured at a CO2 concentration of 5%, which supported maximum O2 evolution at low psiw. In 1% CO2, however, O2 evolution at low psiw was below the maximum, presumably because stomatal closure restricted CO2 uptake. The inhibition was larger than in peeled discs at psiw between -1 and -1.5 MPa but became the same as in peeled discs at lower psiw. Therefore. as photosynthesis began to be inhibited by metabolism at low psiw, stomatal closure added to the inhibition. As psiw became more negative, the inhibition became entirely metabolic.

Carbon Dioxide↗
PubMed2005

A guard-cell-specific MYB transcription factor regulates stomatal movements and plant drought tolerance.

Stomatal pores located on the plant epidermis regulate CO(2) uptake for photosynthesis and the loss of water by transpiration. The opening and closing of the pore is mediated by turgor-driven volume changes of two surrounding guard cells. These highly specialized cells integrate internal signals and environmental stimuli to modulate stomatal aperture for plant survival under diverse conditions. Modulation of transcription and mRNA processing play important roles in controlling guard-cell activity, although the details of these levels of regulation remain mostly unknown. Here we report the characterization of AtMYB60, a R2R3-MYB gene of Arabidopsis, as the first transcription factor involved in the regulation of stomatal movements. AtMYB60 is specifically expressed in guard cells, and its expression is negatively modulated during drought. A null mutation in AtMYB60 results in the constitutive reduction of stomatal opening and in decreased wilting under water stress conditions. Transcript levels of a limited number of genes are altered in the mutant, and many of these genes are involved in the plant response to stress. Our data indicate that AtMYB60 is a transcriptional modulator of physiological responses in guard cells and open new possibilities to engineering stomatal activity to help plants survive desiccation.

Adaptation, Physiological↗
PubMed2006

Trichomes: different regulatory networks lead to convergent structures.

Sometimes, proteins, biological structures or even organisms have similar functions and appearances but have evolved through widely divergent pathways. There is experimental evidence to suggest that different developmental pathways have converged to produce similar outgrowths of the aerial plant epidermis, referred to as trichomes. The emerging picture suggests that trichomes in Arabidopsis thaliana and, perhaps, in cotton develop through a transcriptional regulatory network that differs from those regulating trichome formation in Antirrhinum and Solanaceous species. Several lines of evidence suggest that the duplication of a gene controlling anthocyanin production and subsequent divergence might be the major force driving trichome formation in Arabidopsis, whereas the multicellular trichomes of Antirrhinum and Solanaceous species appear to have a different regulatory origin.

Anthocyanins↗
PubMed1999

Inhibitory effects of Sudanese plant extracts on HIV-1 replication and HIV-1 protease.

Forty-eight methanol and aqueous extracts from Sudanese plants were screened for their inhibitory activity on viral replication. Nineteen extracts showed inhibitory effects on HIV-induced cytopathic effects (CPE) on MT-4 cells. The extracts were further screened against HIV-1 protease (PR) using an HPLC assay method. Of the tested extracts, the methanol extracts of Acacia nilotica (bark and pods), Euphorbia granulata (leaves), Maytenus senegalensis (stem-bark) and aqueous extracts of A. nilotica (pods) and M. senegalensis (stem-bark) showed considerable inhibitory effects against HIV-1 PR. Inhibitory principles were isolated from M. senegalensis and their activities were also discussed.

Anti-HIV Agents↗
PubMed1999

Effects of aqueous extracts from Quercus ilex L. root bark, Punica granatum L. fruit peel and Artemisia herba-alba Asso leaves on ethanol-induced gastric damage in rats.

The gastroprotective effect of tannic acid and the aqueous extract of Quercus ilex L. root bark, Punica granatum L. fruit peel and Artemisia herba-alba Asso leaves was investigated in the rat against ethanol-induced damage. Tannic acid, Q. ilex and P. granatum extracts gave 100% precipitation of ovine haemoglobin in vitro, whereas A. herba-alba extract was devoid of any protein-binding property. Oral administration of these plant extracts or tannic acid induced a significant decrease in gastric lesions (47.7%-76%). The observed protection was more pronounced when the test solution was given at the same time with ethanol, except for Q. ilex extract. The acid content of the stomach was significantly increased by P. granatum (368%) and A. herba-alba (251%) extracts prepared in ethanol. It is suggested that monomeric and polymeric polyphenols can strengthen the gastric mucosal barrier.

Algeria↗
PubMed1999

Effects of Daniellia oliveri bark on isolated rat bladder.

The stem bark of Daniellia oliveri was screened phytochemically and a methanol extract prepared.-Condensed tannins, saponins, cyanogenetic and cardiac glycosides were identified in the crude drug. The cardiac glycoside components in the methanol extract were precipitated with acetone to yield a reddish-brown residue. The n-butanol soluble fraction of an aqueous solution of this residue tested positive for cardiac glycosides and was shown by TLC to contain steroidal compounds. This fraction was subjected to pharmacological studies on isolated rat bladder smooth muscle. It had no effect on purinergic neurotransmission but was a noncompetitive antagonist for muscarinic receptors.

Animals↗
PubMed1999

Effects of Daniellia oliveri stem bark and leaf extracts on rat skeletal muscle.

The stem bark and leaves of Daniellia oliveri were screened phytochemically and the effects of their respective methanol extracts on the skeletal muscle of rats were investigated using the isolated phrenic nerve hemidiaphragm muscle preparation. Both were found to contain tannins, cardiac and saponin glycosides. In addition, the bark, but not leaves, contained cyanogenetic glycosides. The methanol extracts were found to possess neuromuscular blocking properties. The leaf extract appeared to act primarily by inhibiting the influx of extracellular Ca(2+) principally by inhibiting K(+) channels. The inhibitory action of the bark extract appeared to be mediated by interference with transmitter release and an action on multiple sites.

Animals↗
PubMed1999

Some pharmacological and toxicological studies on Balanites aegyptiaca bark.

The aqueous extract of Balanites aegyptiaca bark, which is used in Sudanese folk medicine in the treatment of jaundice, was without effect when studied on rabbit intestine, rabbit aortic strip, rat stomach strip, rat uterus and rat phrenic nerve-diaphragm in a dose up to 10 mg/mL gut bath. In a larger dose (25 mg) the extract decreased significantly the contractility and the rate of the isolated perfused rabbit heart. Administration of the aqueous extract to biliary duct-ligated rats, showed a dose-dependent significant decrease in serum bilirubin level. The chronic and subchronic toxicity investigations indicate the safety of the aqueous extract at a dose level which showed a significant decrease in serum bilirubin level in experimental obstructive jaundice in rats.

Animals↗
PubMed2004

A subclass of myosin XI is associated with mitochondria, plastids, and the molecular chaperone subunit TCP-1alpha in maize.

The role and regulation of specific plant myosins in cyclosis is not well understood. In the present report, an affinity-purified antibody generated against a conserved tail region of some class XI plant myosin isoforms was used for biochemical and immunofluorescence studies of Zea mays. Myosin XI co-localized with plastids and mitochondria but not with nuclei, the Golgi apparatus, endoplasmic reticulum, or peroxisomes. This suggests that myosin XI is involved in the motility of specific organelles. Myosin XI was more than 50% co-localized with tailless complex polypeptide-1alpha (TCP-1alpha) in tissue sections of mature tissues located more than 1.0 mm from the apex, and the two proteins co-eluted from gel filtration and ion exchange columns. On Western blots, TCP-1alpha isoforms showed a developmental shift from the youngest 5.0 mm of the root to more mature regions that were more than 10.0 mm from the apex. This developmental shift coincided with a higher percentage of myosin XI /TCP-1alpha co-localization, and faster degradation of myosin XI by serine protease. Our results suggest that class XI plant myosin requires TCP-1alpha for regulating folding or providing protection against denaturation.

Actins↗
PubMed2004

Green fluorescent protein fusions to Arabidopsis fimbrin 1 for spatio-temporal imaging of F-actin dynamics in roots.

The visualization of green fluorescent protein (GFP) fusions with microtubule or actin filament (F-actin) binding proteins has provided new insights into the function of the cytoskeleton during plant development. For studies on actin, GFP fusions to talin have been the most generally used reporters. Although GFP-Talin has allowed in vivo F-actin imaging in a variety of plant cells, its utility in monitoring F-actin in stably transformed plants is limited particularly in developing roots where interesting actin dependent cell processes are occurring. In this study, we created a variety of GFP fusions to Arabidopsis Fimbrin 1 (AtFim1) to explore their utility for in vivo F-actin imaging in root cells and to better understand the actin binding properties of AtFim1 in living plant cells. Translational fusions of GFP to full-length AtFim1 or to some truncated variants of AtFim1 showed filamentous labeling in transient expression assays. One truncated fimbrin-GFP fusion was capable of labeling distinct filaments in stably transformed Arabidopsis roots. The filaments decorated by this construct were highly dynamic in growing root hairs and elongating root cells and were sensitive to actin disrupting drugs. Therefore, the fimbrin-GFP reporters we describe in this study provide additional tools for studying the actin cytoskeleton during root cell development. Moreover, the localization of AtFim1-GFP offers insights into the regulation of actin organization in developing roots by this class of actin cross-linking proteins.

Actins↗
PubMedDate not supplied

Supercritical fluid extraction of naringin from the peel of Citrus paradisi.

The highest yield (14.4 g/kg) of naringin, the major flavonoid from the peel of Citrus paradisi L., that could be achieved by supercritical fluid extraction was obtained using supercritical carbon dioxide modified with 15% ethanol and fresh (rather than dried) peels at 95 bar and 58.6 degrees C. This yield is higher than that attained by the conventional technique of maceration, and close to those obtained by reflux and Soxhlet methods. Furthermore, supercritical fluid extraction consumes less solvent and provides a shorter extraction time than conventional extraction methods.

Chromatography, Supercritical Fluid↗