Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0277787 (stigma)
 13,352 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Antral pressure was measured within the follicles of unstimulated ovaries in prepubertal pigs and following an ovulatory stimulus with exogenous gonadotropins. No increase in intrafollicular pressure (IFP) was observed as the time of ovulation approached. A wide range of IFP was noted within follicles of the unstimulated ovary. In many follicles IFP was greater than 30 cm H2O, suggesting that the antral fluid was not in hydrostatic equilibrium with the surrounding thecal capillaries. IFP of unstimulated follicles could be increased to more than 400 cm H2O by antral injection of mineral oil without follicular rupture--a demonstration of the need for stigma formation in the release of the ovum from the follicle. Stimulated follicles were found to be more distensible than unstimulated follicles. The follicles also fell into two groups--those in which sustained versus transient elevation in IFP occurred following oil injection. It is postulated that the follicle wall develops the ability to undergo stress relaxation during follicular maturation and that this process plays a role in regulating IFP.
 ...
PMID:Intrafollicular pressure within preovulatory follicles of the pig. 76 82

With the aid of osmium tetroxide vapour, dry pollen and pollen at various stages of hydration has been fixed anhydrously for examination with the transmission electron microscope (TEM). In addition to establishing features characteristic of grains at different states of hydration, this technique has enabled the detection of a superficial layer investing both the exine and the pollen coating. This layer, some 10 nm in depth, binds both lanthanum and Alcian Blue and is shown to be the first component of the pollen grain to make contact with the stigmatic pellicle. The use of vapour fixation has also rendered it possible to chart the passage of water into the pollen grains with great accuracy, for each level of hydration displays a strikingly different cytoplasmic organization. For example, dry pollen is characterized by the presence of unusual structures at the protoplast surface and large numbers of spherical fibrillar bodies, whilst the protoplast of hydrating pollen is conspicuously stratified and contains a peripheral layer of membranous cisternae, subjacent to which is a fibrillar matrix derived from the spherical bodies found in the dry grains. Vapour-fixed, fully hydrated pollen resembles conventionally fixed grains. The pollen coating appears electron-translucent after anhydrous fixation and contains discrete, slightly rounded bodies some 50 nm in diameter. The uptake of water by grains on the stigma is accompanied by conspicuous structural changes in this layer for, after a short period in contact with the papillar surface, the spherical bodies rapidly disappear and the coat becomes electron-opaque. Close examination of this 'converted' coating reveals the presence of membranous vesicles and other structural components.
 ...
PMID:Pollen-stigma interactions in Brassica. IV. Structural reorganization in the pollen grains during hydration. 352 12

The osmotic potential (psi pi) of the stigmatic papillar cells of Brassica oleracea is -14.8 bars. In laboratory conditions each cell transpires water at rates within the range from 3 X 10(-5) to 5 X 10(-5) mm3h-1. A small increase in transpiration rate is detected following cross-(compatible) but not self-(incompatible)pollination. No significant changes in psi pi occur following pollinations of either compatibility. Electron microscopy reveals an active papillar cytoplasm apparently secreting proteins into the cell wall via small vesicles. The cuticle is discontinuous and freeze-fracture techniques indicate that channels transverse the cell wall, suggesting a possible pathway for the movement of protein molecules of high molecular weight from the cytoplasm to the stigma surface. Analysis of electron-microscopic autoradiographs of mature, self-incompatible papillae following pulse-chase experiments with L-[3H]leucine and treatment with cycloheximide shows that protein molecules secreted into the cell wall may return to the cytoplasm at a later stage. The significance of these results is discussed in terms of current models of the pollen-stigma interaction in Brassica.
 ...
PMID:Pollen-stigma interactions in Brassica oleracea. I. Ultrastructure and physiology of the stigmatic papillar cells. 674 57

High-performance liquid chromatography with photodiode-array detection was used to separate picrocrocin (bitter-tasting component, glucoside of safranal), cis/trans-crocins (carotenoids, glucosyl esters of crocetin) and safranal (flavour, monoterpene aldehyde) of saffron. All components of pure red Greek saffron were extracted from dried stigma with 50% methanol. These compounds were detected, separated collected and identified simultaneously using a Merck LiChroCART 125-4 Superspher 100 RP-18 (4 microns) column and as mobile phase a linear gradient from 20% to 100% acetonitrile in water in 20 min with a detection wavelength at 308 nm.
 ...
PMID:Separation of picrocrocin, cis-trans-crocins and safranal of saffron using high-performance liquid chromatography with photodiode-array detection. 801 49

Plants distinguish among the pollen grains that land on the stigma, permitting only compatible pollen to fertilize egg cells. To investigate these cell-cell interactions, Arabidopsis mutations that affect pollen-pistil communication were isolated. A male-sterile mutation that disrupts pollen-pistil interactions by eliminating the extracellular pollen coat (tryphine) is described here. Stigma cells that contact the mutant pollen produce callose, a carbohydrate synthesized in response to foreign pollen. The mutant pollen fails to germinate because it does not absorb water from the stigma, yet germinates in vitro, indicating it is viable. The defect is also conditional; high humidity results in pollen hydration and successful fertilization. Analysis of mature, mutant pollen indicated that it is deficient in long-chain lipids and has none of the lipoidic tryphine normally present on its surface. Immature mutant pollen grains have aberrant tryphine that disappears during pollen development. The sterile plants also lack stem waxes, and pollen from other wax-defective (eceriferum) mutants with reduced fertility has few of the lipid droplets normally present in tryphine. These results demonstrate that tryphine is critical for pollen-stigma interactions and suggest that tryphine lipids are required for fertilization, either by directly signaling the stigma or by stabilizing other tryphine components.
 ...
PMID:A conditional sterile mutation eliminates surface components from Arabidopsis pollen and disrupts cell signaling during fertilization. 850 36

In higher plants, cell-cell recognition reactions taking place following pollination allow the selective restriction of self-pollination and/or interspecific pollination. Many of these systems function by regulating the process of water transfer from the cells found at the stigmatic surface to the individual pollen grain. Interspecific pollination studies on the cruciferous weed Arabidopsis thaliana revealed only a broad specificity of pollen recognition such that pollen from all tested members of the crucifer family were recognized, whereas pollen from almost all other species failed to hydrate. Genetic analysis of A. thaliana has identified three genes that are essential for this recognition process. Recessive mutations in any of these genes result in male sterility due to the production of pollen grains that fail to hydrate when placed on the stigma, but that are capable of hydrating and growing a pollen tube in vitro. Results from mixed pollination experiments suggest that the mutant pollen grains specifically lack a functional pollen-stigma recognition system. All three mutations described also result in a defect in the wax layer normally found on stems and leaves, similar to previously described eceriferum (cer) mutations. Genetic complementation and mapping experiments demonstrated that the newly identified mutants are allelic to the previously identified genes cer1, cer3 and cer6. TEM analysis of the ultrastructure of the pollen coating revealed that all of the mutant pollen grains bear coatings of normal thickness and that tryphine lipid droplets are missing in cer1-147, are reduced in size in cer6-2654 and appear normal in cer3-2186.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Identification of genes required for pollen-stigma recognition in Arabidopsis thaliana. 852 81

Self-incompatibility in Brassica refers to the rejection of self-related pollen and is mediated by a receptor protein kinase localized to the plasma membrane of the stigma epidermis in the flower. The recessive mutation mod eliminates self-incompatibility in the stigma. In mod mutants, self-compatibility was shown to be associated with the absence of transcripts encoded by an aquaporin-related gene. This observation suggests that a water channel is required for the self-incompatibility response of Brassica, which is consistent with the concept that regulation of water transfer from the stigma to pollen is a checkpoint in the early events of pollination in the crucifer family.
 ...
PMID:An aquaporin-like gene required for the Brassica self-incompatibility response. 917 Oct 60

Successful pollination and fertilization are absolute requirements for sexual reproduction in higher plants. Pollen hydration, germination and penetration of the stigma by pollen tubes are influenced by the exudate on wet stigmas and by the pollen coat in species with dry stigmas. The exudate allows pollen tubes to grow directly into the stigma, whereas the pollen coat establishes the contact with the stigma. Pollen tubes then grow into the papillae, which are covered by a cuticle. The components of the exudate or pollen coat that are responsible for pollen tube penetration are not known. To discover the role of the exudate, we tested selected compounds for their ability to act as functional substitutes for exudate in the initial stages of pollen-tube growth on transgenic stigmaless tobacco plants that did not produce exudate. Here we show that lipids are the essential factor needed for pollen tubes to penetrate the stigma, and that, in the presence of these lipids, pollen tubes will also penetrate leaves. We propose that lipids direct pollen-tube growth by controlling the flow of water to pollen in species with dry and wet stigmas.
 ...
PMID:Lipids are required for directional pollen-tube growth. 957 41

Pollen tubes navigate the route from stigma to ovule with great accuracy, but the cues that guide them along this route are not known. We reproduced the environment on the stigma of Nicotiana alata by immersing pollen in stigma exudate or oil close to an interface with an aqueous medium. The growth of pollen in this culture system mimicked growth on stigmas: pollen grains hydrated and germinated, and pollen tubes grew toward the aqueous medium. The rate-limiting step in pollen germination was the movement of water through the surrounding exudate or oil. By elimination of other potential guidance cues, we conclude that the directional supply of water probably determined the axis of polarity of pollen tubes and resulted in growth toward the interface. We propose that a gradient of water in exudate is a guidance cue for pollen tubes on the stigma and that the composition of the exudate must be such that it is permeable enough for pollen hydration to occur but not so permeable that the supply of water becomes nondirectional. Pollen tube penetration of the stigma may be the most frequently occurring hydrotropic response of higher plants.
 ...
PMID:Directional guidance of nicotiana alata pollen tubes in vitro and on the stigma 980 17

Chlamydodon mnemosyne, a brackish-water ciliate which feeds on cyanobacteria, is capable of sensing the direction of light. Cells are negatively phototactic in the well-fed state and tend to swim towards the light source when mildly starved. Severely starved cells normally fail to show phototactic responses. An autofluorescent substance, which is present in all life cycle stages, occurs in, or immediately beneath, the plasma membrane of this ciliate. It is located in the anterior left side of a cell, in the same region where mildly starved cells accumulate small orange globules that form a structure known as the stigma. The diameter of the whole area where the autofluorescent substance is located appears to be smaller than the stigma; typically, it consists of two rows of blue-green fluorescence, each row subdivided into 5-10 squares. Since the blue-green autofluorescence is excited by both blue (450-490 nm) and near-ultraviolet (340-380 nm) light, it possibly originates from flavin- and/or pterin-like molecules. We suggest that the autofluorescent substance located in or beneath the plasma membrane of Chlamydodon mnemosyne acts as a photoreceptor pigment in phototaxis and that photo-orientation of this ciliate is triggered by a combined mechanism involving the photoreceptor and either the stigma or a number of light-absorbing food vacuoles as a shading device.
 ...
PMID:Structure, fluorescent properties and proposed function in phototaxis of the stigma apparatus in the ciliate chlamydodon mnemosyne 1008 64


1 2 3 4 5 6 7 8 9 10 Next >>