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Evolution of 'pollinator'- attracting signals in fungi.

Fungi produce a plethora of secondary metabolites yet their biological significance is often little understood. Some compounds show well-known antibiotic properties, others may serve as volatile signals for the attraction of insects that act as vectors of spores or gametes. Our investigations in an outcrossing, self-incompatible fungus show that a fungus-produced volatile compound with fungitoxic activities is also responsible for the attraction of specific insects that transfer gametes. We argue that insect attraction using this compound is likely to have evolved from its primary function of defence--as has been suggested for floral scent in the angiosperms. We, thus, propose that similar yet convergent evolutionary pathways have lead to interspecific communication signals in both fungi and plants.

Animals↗

Expression of ornithine decarboxylase is transiently increased by pollination, 2,4-dichlorophenoxyacetic acid, and gibberellic acid in tomato ovaries.

A cDNA encoding for a functional ornithine decarboxylase has been isolated from a cDNA library of carpels of tomato (Lycopersicon esculentum Mill.). Ornithine decarboxylase in tomato is represented by a single-copy gene that we show to be up-regulated during early fruit growth induced by 2,4-dichlorophenoxyacetic acid and gibberellic acid.

2,4-Dichlorophenoxyacetic Acid↗

Specific IgE to recombinant vegetal panallergen (rBet v 2) and fruit allergy in pollinic patients.

The presence of IgE antibodies to the allergens rBet v 1 and rBet v 2 was investigated in patients with known sensitization to ryegrass (Lolium perenne) and/or olive (Olea europaea) pollen, by comparing a group of 10 patients who had allergic symptoms after ingestion of fruits (A) with a group of 17 patients who had only seasonal respiratory symptoms (B). There was no significant difference between the two groups for total IgE. All patients showed specific IgE to both L. perenne and O. europaea. No specific IgE binding to rBet v 1 was detected in any patient. The incidence of the presence of IgE antibodies to rBet v 2 was 90% in the group with fruit allergy (A) and 35% in group B. We found a significant association between presence of IgE antibodies to rBet v 2 and fruit allergy (P = 0.007). Specific IgE values to O. europaea pollen were higher in the fruit-allergy group than the group without fruit allergy (P = 0.032). In conclusion, pollen-allergic patients with specific IgE to birch pollen profilin show a significantly elevated frequency of fruit allergy.

Adolescent↗

Amplified fragment length polymorphism linkage analysis of common buckwheat (Fagopyrum esculentum) and its wild self-pollinated relative Fagopyrum homotropicum.

Common buckwheat (Fagopyrum esculentum) (2n = 2x = 16) and Fagopyrum homotropicum (2n = 2x = 16) were mated in an interspecific cross and amplified fragment length polymorphism (AFLP) linkage maps were constructed by analyzing segregation in the F2 population. Six hundred and sixty-nine bands were identified using 20 AFLP primer combinations, of which 462 (69%) segregated in the F2 population. The map of F. esculentum has eight linkage groups with 223 markers covering a total of 508.3 cM. The map of F. homotropicum has eight linkage groups with 211 markers covering 548.9 cM. There was one to one correspondence of the esculentum and homotropicum linkage groups. Three morphological markers, distylous self-incompatibility, shattering habit, and winged seed, were located on the AFLP map. Distylous self-incompatibility and shattering habit are tightly linked to each other (1.3 cM) and are located near the center of linkage group 1. Winged seed is located on linkage group 4.

Chromosome Mapping↗

The mechanisms of pollination and fertilization in plants.

In flowering plants, pollen grains germinate to form pollen tubes that transport male gametes (sperm cells) to the egg cell in the embryo sac during sexual reproduction. Pollen tube biology is complex, presenting parallels with axon guidance and moving cell systems in animals. Pollen tube cells elongate on an active extracellular matrix in the style, ultimately guided by stylar and embryo sac signals. A well-documented recognition system occurs between pollen grains and the stigma in sporophytic self-incompatibility, where both receptor kinases in the stigma and their peptide ligands from pollen are now known. Complex mechanisms act to precisely target the sperm cells into the embryo sac. These events initiate double fertilization in which the two sperm cells from one pollen tube fuse to produce distinctly different products: one with the egg to produce the zygote and embryo and the other with the central cell to produce the endosperm.

Cell Communication↗

Post-pollination callose development in ovules of Rhododendron and Ledum (Ericaceae): zygote special wall.

In Rhododendron spp. and Ledum groenlandicum a callose wall is laid down around the zygote in the first 2 days after fertilization. The periodic acid/Schiff-positive, aniline blue-fluorescence-positive callosic wall is initiated adjacent to the degenerating synergid, extends to cover the entire zygote surface, and remains visible during the initiation of embryogeny as the zygote elongates before the first proembryonal division. Unfertilized ovules show eventual callose deposition in the ovule wall cells during senescence in undeveloped abscising pistils, but show no development of callose within the embryo sac. Possible roles of a zygote special callose wall are discussed.

Cell Wall↗