Effects of culture conditions on isolated microspore response of barley cultivar Igri

Pretreatment of anthers in mannitol prior to isolation of microspores by glass rod homogenization was effective for in vitro induction of embryogenesis in barley cv. Igri. A procedure for separation of viable microspores using centrifugation on 20% maltose was developed. The concentration of microspores was important and greatly increased the number of developing structures. Initial culture of microspores on FHG medium containing 62 g l^-1 maltose, 4.4 M (1 mg l^-1) BA and 200 g l^-1 Ficoll-400 resulted in high frequencies of plant regeneration. Albino plant frequency was correlated to length of time in culture. Stock plant condition appeared to be a major factor influencing induction frequency. From 868 to 1738 green plants per 100 anthers were produced. The number of calli and embryos obtained and the number of green plantlets regenerated were improved by increasing the Ficoll concentration from 100 g l^-1 to 400 g l^-1 during the culture period compared to continuous culture on FHG Ficoll 200 g l^-1.Abbreviations BA benzyladenine     

Characterisation of protoplasts from hypocotyls of Helianthus annuus in relation to their tissue origin

Cells and protoplasts isolated from three different tissues of sunflower hypocotyls and cultured either in liquid or agarose medium were compared in terms of their volume, DNA content, division potential and embryoid formation. Epidermal and external cortical cells differ from other tissue cells by their small size, their weak response to plasmolysis and their low DNA content (around 1C). They contribute only very weakly to the dividing protoplast population. In contrast, protoplasts from cortical and medullar cells both have similar division potential, reaching 50%. The nuclear DNA content of these two cell types, as well as their corresponding protoplasts, has a 2C value, taking root tip cells in G0 phase as standard. The culture conditions induce the same specific response in protoplasts isolated from both tissues: exclusively loose colony formation in liquid medium, and mainly production of embryoids in agarose medium.     

Ultra-violet photoreceptors in the animal kingdom: their distribution and function

Until very recently, the role of ultra-violet (UV) colour perception in vertebrate and invertebrate vision has largely been ignored. However, in the past few years, a host of detailed information has become available on the widespread distribution of UV receptors in different species - from insects to mammals - and the important functions they seem to play in navigation, foraging, intraspecies communication and the control of circadian rhythms.     

Rainfall and flowering synchrony in a tropical shrub: Variable selection on the flowering time ofErythroxylum havanense

Summary We tested the adaptive significance of flowering synchrony by means of a quantitative analysis of selection and by flowering induction experiments with the deciduous shrubErythroxylum havanense. Temporal schedules of flower and fruit production were determined for a local population (in three sites) in a Mexican seasonal forest for 2 years (1987–1988). The consequences of natural variation in flowering time (flowering initiation day) on maternal reproductive success (fecundity) were evaluated. We observed high levels of inter- and intraindividual flowering synchrony in 1987, but not in 1988 and this contrast was related to differences in rainfall patterns between the two years. A significant proportion (15.4%) of the phenotypic variation in flowering initiation day was accounted for by environmental variance. The expression of phenotypic variance of flowering time and, consequently, the opportunity for selection to act, are controlled by annual variation in rainfall. Despite the between-year difference in flowering synchrony, we detected a relatively intense directional selection on flowering initiation day in both years, but selection coefficients were of opposite sign (standardized directional gradients were –0.326 and 0.333 for 1987 and 1988, respectively). For both years there was a significant relationship between individual relative fitness and the number of neighbouring flowering plants in a given day, suggesting positive frequency-dependent selection.     

Analysis of spatial and semporal organization in a salmonid brook in relation to physical factors and macrophytic vegetation

Four compartments of a salmonid brook were studied in consecutive sections either at sector scale or at facies scale: physical features, water quality, macrophytes and salmonids. The most important factor in the spatial and temporal organisation was the longitudinal zonation assessed by the four compartments. It was mainly shown by a gradient of the length of the morphodynamic sequence and of the facies width, of the pH and the conductivity and of macrophyte cover. It induced a colonisation by older trout in the downstream part of the brook where growth was better and shelter given by the bankside vegetation was more abundant. There were also greater densities of other age-classes upstream, with a correlation between salmon and rock shelter. Furthermore, the second factor corresponded to the flow characteristics and a granulometry gradient. The third factor corresponded chiefly to lighting, salmon numbers and densities. Salmonids showed a temporal stability from spring to autumn,and an opposition between growth and density. Six clusters of sectors defined functional entities. With regard to the 3—dimensitnal structure of the brook, the special pattern of each compartment shows its contribution to the functioning of the whole. Taking into account the scale of the study, the coexistence between trout and salmon did not show a competition between the two species, but rather a spatial partition, thanks to thehheterogenity inside each sector. We concluded on the necessity of studying sympatry at the facies scale to assess the role of habitat factors as regulators of carrying capacity.     

Induced conformational states of amphipathic peptides in aqueous/lipid environments.

Specific conformational effects have been reported for amphipathic model peptides upon binding of defined hydrophobic domains to nonpolar stationary phases during reversed-phase high performance liquid chromatography (RP-HPLC). Such induced conformations are found to be especially pronounced for peptides that are amphipathic in an alpha-helical conformation. Such induced amphipathic conformations resulted in substantially later elution than predicted using amino acid-based retention coefficients. In the present study, the induced conformational behavior of model peptides observed during RP-HPLC was correlated with their secondary structure as determined by circular dichroism (CD) spectroscopy in both aqueous solution and C18-mimetic environments. The experimental retention times of the peptides studied were found to correlate with their CD spectra in the presence of lipids, whereas a poor correlation was observed with their CD spectra in the presence of trifluoroethanol. A new approach was developed to evaluate the induction of secondary structure in peptides due to interactions at aqueous/lipid interfaces, which involves the measurement of the CD ellipticities of peptides bound to a set of C18-coated quartz plates. An excellent correlation was found in this environment between the RP-HPLC retention times and CD ellipticities of the bound peptides.