A new minimal synthetic medium for germ-tube production in Candida albicans

A new minimal synthetic medium, with low amount of glucose, without aminoacids, vitamins and neutral pH, which induces germ-tubes production in Candida albicans, is reported in this work. The results indicate a perfect agreement between the germ-tube test performed with the standard method in human or animal serum and this test performed in minimal synthetic medium. In this medium the germ-tube test for the presumptive identification of Candida albicans can be performed with the same formality, time and reproducibility as those in human or animal serum. This constitutes an interesting finding because it is easy to prepare, to store and is highly reproducible.     

Oxypetalum banksii subsp. banksii: a taxon of Asclepiadaceae with an extragynoecial compitum

 The floral morphology of seven Oxypetalum species and, in particular, the spatial relationship between the five stigmatic chambers and two separate ovaries of their flowers with respect to transmission of the pollen tube are studied. In all species, except O. banksii subsp. banksii, floral morphology is similar to that in other Asclepiadeae, and the flowers pollinated with one pollinium develop only one follicle, which means compitum absence. In O. banksii subsp. banksii flowers, the secretory interstaminal tissue lines the inner walls of the stigmatic chambers as in the other species studied, but it also reaches the upper part of the inner surface of the filament tube, where it surrounds the styles, an unprecedented feature for Asclepiadaceae. This tissue secretes nectar and mucilage; the latter acts as transmitting medium for the growth of pollen tubes from pollinia inserted and hydrated in stigmatic chambers (“hyperstigmas”). Mucilage also functions as an extragynoecial compitum: in flowers pollinated with one pollinium both carpels develop into a follicle. Received August 28, 2001; accepted April 9, 2002 Published online: October 14, 2002 Addresses of the authors: Milene Faria Vieira (e-mail: mfvieira@mail.ufv.br), Departamento de Biologia Vegetal, Universidade Federal de Vi?osa, 36571-000, Vi?osa, Minas Gerais, Brazil. George John Shepherd, Departamento de Botanica, Instituto de Biologia, Universidade Estadual de Campinas, C.P. 6109, 13083-970, Campinas, S?o Paulo, Brazil.     

Second-messenger-induced signalling events in pollen tubes of Papaver rhoeas

A role for cytosolic free Ca²⁺ (Ca²⁺_i) in the regulation of growth of Papaver rhoeas pollen tubes during the self-incompatibility response has recently been demonstrated [Franklin-Tong et al. Plant J. 4:163–177 (1993); Franklin-Tong et al. Plant J. 8:299–307 (1995); Franklin-Tong et al. submitted to Plant J.]. We have investigated the possibility that Ca²⁺_i is more generally involved in the regulation of pollen tube growth using confocal laser scanning microscopy (CLSM). Data obtained using Ca²⁺ imaging, in conjunction with photolytic release of caged inositol 1,4,5-trisphosphate [Ins(1,4,5)P₃], point to a central role of the phosphoinositide signal transduction pathway in the control of Ca²⁺ fluxes and control of pollen tube growth. These experiments further revealed that increases in cytosolic levels of Ins(1,4,5)P₃ resulted in the formation of distinct Ca²⁺ waves. Experiments using the pharmacological agents heparin, neomycin and mastoparan further indicated that Ca²⁺ waves are propagated, at least in part, by Ins(1,4,5)P₃-induced Ca²⁺ release rather than by simple diffusion or by “classic” Ca²⁺-induced Ca²⁺ release mechanisms. We also have data which suggest that Ca²⁺ waves and oscillations may be induced by photolytic release of caged Ca²⁺. Ratio-imaging has enabled us to identify an apical oscillating Ca²⁺ gradient in growing pollen tubes, which may regulate normal pollen tube growth. We also present evidence for the involvement of Ca²⁺ waves in mediating the self-incompatibility response. Our data suggest that changes in Ca²⁺_i and alterations in growth rate/patterns are likely to be closely correlated and may be causally linked to events such as Ca²⁺-induced, or Ins(1,4,5)P₃-induced wave formation and apical Ca²⁺ oscillations.Presented at the 1997 SEB Annual Meeting: Interactive MultiMedia Biology - Experimental Biology Online Symposium, Canterbury, 7-11 April     

Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

Mediolateral patterning of somites: multiple axial signals, including Sonic hedgehog, regulate Nkx-3.1 expression

The axial structures, the notochord and the neural tube, play an essential role in the dorsoventral patterning of somites and in the differentiation of their many cell lineages. Here, we investigated the role of the axial structures in the mediolateral patterning of the somite by using a newly identified murine homeobox gene, Nkx-3.1, as a medial somitic marker in explant in vitro assays. Nkx-3.1 is dynamically expressed during somitogenesis only in the youngest, most newly-formed somites at the caudal end of the embryo. We found that the expression of Nkx-3.1 in pre-somitic tissue explants is induced by the notochord and maintained in newly-differentiated somites by the notochord and both ventral and dorsal parts of the neural tube. We showed that Sonic hedgehog (Shh) is one of the signaling molecules that can reproduce the effect of the axial structures by exposing explants to either COS cells transfected with a Shh expression construct or to recombinant SHH. Shh could induce and maintain Nkx-3.1 expression in pre-somitic mesoderm and young somites but not in more mature, differentiated ones. The effects of Shh on Nkx-3.1 expression were antagonized by a forskolin-induced increase in the activity of cyclic AMP-dependent protein kinase A. Additionally, we confirmed that the expression of the earliest expressed murine myogenic marker, myf 5, is also regulated by the axial strucutres but that Shh by itself is not capable of inducing or maintaining it. We suggest that the establishment of somitic medial and lateral compartments and the early events in myogenesis are governed by a combination of positive and inhibitory signals derived from the neighboring structures, as has previously been proposed for the dorsoventral patterning of somites.     

Study of the pollen emissions of Urticaceae, Plantaginaceae and Poaceae at five sites in western Spain

A comparative study is presented of the pollen emissions of Urticaceae, Plantaginaceae and Poaceae, collected during 1995 with Hirst samplers (Burkard or Lanzoni) at five sites in western Spain: two Mediterranean sites located in the south (Huelva and Seville) and three Atlantic sites in the north (Orense, Vigo and Santiago). The annual pollen of Poaceae and Plantaginaceae collected in the Atlantic cities was found to be twice that in the Mediterranean sites, and the total amount of Urticaceae was higher at sites with an urban environment and subject to sea influence (Vigo, Huelva and Seville). At all the sites, the start of the main pollination periods (MPP) took place in the following order: Urticaceae, Plantaginaceae and Poaceae. It was also observed that the MPP of these three pollen types began earlier in Huelva and Seville, where the mean temperatures necessary for the beginning of pollen emissions are recorded very early. Regarding the variation in pollen concentrations throughout the year, Urticaceae presented peaks of maximum concentration in March (Huelva, Seville, Vigo and Orense) and June (Santiago); Plantaginaceae in March (south) and June (north); and Poaceae in May (south) and June–July (north). At northern sites, pollen emissions of Urticaceae and Plantaginaceae continued throughout the summer, while in the south they decreased considerably from May onwards. From the allergenic point of view, the indices of reactivity described for Urticaceae and Poaceae were exceeded more often at northern sites, in particular at Vigo. The meteorological conditions associated with periods of highest pollen emission of these three herbaceous types are a rise in mean temperature, light or absent rainfall, and abundant sunshine. The statistical correlations between pollen emissions and meteorological factors were not well-defined, either for the stations or for all the taxa, although they were clearer for the Atlantic cities and for Urticaceae.     

An 11400 year paleoecological history of a British chalk grassland

The first broad-based, paleoecological analysis of a sedimentary sequence on the British chalk, dating to the terminal Pleistocene, reveals a history of climatic, vegetational and faunal change. The past co-occurrence of currently allopatric species among molluscs, beetles and plants supports hypotheses of the impermanence of communities. Modern pollen rain data are utilized to refine the ecological interpretation of the fossil pollen data. The presence of the Windermere Interstadial (Allerod) and the Loch Lomond re-advance (Younger Dryas) are represented by decreased abundances of arboreal taxa and increased representation of cold grassland elements. Open grassland habitats appear to have been a continuous landscape element, at least locally, since the late-glacial period on the northern British chal Mands, although their species composition has changed greatly in the last 11400 yr.     

Membrane flow in plants: preparation and kinetics of labelling of plasma membranes from growing pollen tubes of tobacco

Summary Growing pollen tubes of tobacco germinated in suspension culture, were labelled with [³H]leucine and after varying times of chase with unlabelled leucine at 23, 16, or 4°C, were separated into plasma membrane-enriched and plasma membrane-depleted fractions by aqueous two-phase partition. At 23°C, the specific radioactivity of the plasma membrane increased with time to a maximum at 60 min. At 16°C and 4°C, labelling of the plasma membrane was respectively 40% and 10% that at 23°C. However, if labelling was at 23°C and subsequent transfer was at 4°C, plasma membrane labelling was much less affected and labelling of the plasma membrane was 60% that at 23°C. Additionally, quantitation of various morphological parameters revealed no accumulations of 50–70 nm transition vesicles in the space between endoplasmic reticulum and cis Golgi apparatus that might suggest formation of a low temperature compartment similar to those described for mammalian cells and tissues. Similarly, growth of pollen tubes was reduced but not blocked even at temperatures of 12°C. The results suggest that tube elongation is accompanied by a steady state flow of membranes to the cell surface that is relatively insensitive to interruption by low temperatures. Whereas leucine incorporation is reduced by low temperature even at 16°C, the flow pathway to the cell surface, including the endoplasmic reticulum to Golgi apparatus transfer step, as well as elongation growth does not exhibit a pronounced low temperature block in this tip growing system.