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Mimicry is the close resemblance of one living organism (the mimic) to another (the model), leading to misidentification by a third organism (the operator). Similar to other organism groups, certain species of plant-parasitic fungi are known to engage in mimetic relationships, thereby increasing their fitness. In some cases, fungal infection can lead to the formation of flower mimics (pseudo flowers) that attract insect pollinators via visual and/or olfactory cues; these insects then either transmit fungal gametes to accomplish outcrossing (e.g. in some heterothallic rust fungi belonging to the genera Puccinia and Uromyces) or vector infectious spores to healthy plants, thereby spreading disease (e.g. in the anther smut fungus Microbotryum violaceum and the mummy berry pathogen Monilinia vaccinii-corymbosi). In what is termed aggressive mimicry, some specialized plant-parasitic fungi are able to mimic host structures or host molecules to gain access to resources. An example is M. vaccinii-corymbosi, whose conidia and germ tubes, respectively, mimic host pollen grains and pollen tubes anatomically and physiologically, allowing the pathogen to gain entry into the host's ovary via stigma and style. We review these and other examples of mimicry by plant-parasitic fungi and some of the mechanisms, signals, and evolutionary implications.
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PMID:Mimicry in plant-parasitic fungi. 1655 49

The proportion of mimics and models is a key parameter in mimetic systems. In monoecious plants with self-mimicry pollination systems, the mimic-model ratio is determined by the floral sex ratio. While an equal sex ratio (1:1) could provide the perfect balance between pollen donors and stigma surfaces able to receive the pollen, an unequal ratio could increase pollination by production of a greater number of rewarding, model flowers. The aim of the present study is to test the differences in visitation frequency and reproductive rates of different mimic and model flower arrays in order to assess the efficacy of the mimetic system in a Begonia cucullata population. The frequencies of visitors to groups of flowers with three distinctive sex ratio arrays (male-biased, female-biased and equal ratio) were compared using a Bayesian approach. The reproductive outcomes were compared in order to detect advantages of particular sex ratios. Low visitation frequency was recorded in all arrays. Pollinators showed similar behaviour regardless of sex ratio; they tended to avoid female, rewardless flowers. Pollination quality was highest in the equal sex ratio array. The current study shows that sex ratio plays a critical role in the pollination of B. cucullata and that the efficacy of the self-mimicry system appears to be doubtful. Visitation frequency may be associated with visual or chemical cues that allow pollinators to recognize models and mimics, regardless of their frequency in the population.
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PMID:Effects of model-mimic frequency on insect visitation and plant reproduction in a self-mimicry pollination system. 2925 87

The monocot genus Aspidistra comprises rhizomatous perennials that are distributed in tropical to warm temperate regions of Asia. Little is known about the pollinators of almost all the species, probably due to the inconspicuous nature of Aspidistra flowers. Nevertheless, the unusual floral morphology suggests biotic pollination, since pollen grains are hidden under each flower's stigma. Aspidistra elatior has been suspected to have a very peculiar pollination ecology. So far, pollination by mollusks, crustaceans, or collembolans has been suspected. However, a recent study showed that A. elatior is mainly pollinated by species of fungus gnats in Kuroshima Island, southern Japan, which is its natural habitat. Here, we investigated the pollination ecology of A. elatior in Shiga Prefecture, central Japan, which is the introduced population, to reveal whether fungus gnats are also the main pollinator in the introduced population. Our study confirmed fungus gnats pollination in the investigated pollination. Furthermore, the main pollinators (i.e., Cordyla sixi and Bradysia sp.) are the same in both Kuroshima and Shiga Prefecture. Therefore, A. elatior mainly depends on a narrow taxonomic group of fungus gnats for pollination. In contrast, we failed to document any terrestrial amphipods visiting the A. elatior flowers, in spite of a relatively high fruit set in natural conditions. This fact will refute the amphipod pollination hypothesis proposed by previous studies. We consider that A. elatior is pollinated by fungus gnats through fungal mimicry, due to its superficial similarity to mushroom fruiting bodies and strong, musky floral scent.
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PMID:Specialized pollination by fungus gnats in the introduced population of Aspidistra elatior. 2931 35