Infloreszenz- und Blütenentwicklung bei der KugeldistelEchinops exaltatus (Asteraceae)

InEchinops the flowers are surrounded by several scales and initiated in an acropetal and spiral succession on a cone-like inflorescence axis (Figs. 1–6). The floral organs originate in the following sequence: petals—stamens—carpels—pappus. The petals arise from a meristematic rim and therefore are already interconnected when they arise as primordia. This sympetalous zone remains rather inconspicuous for a long period, but eventually, the elongated corolla tube is formed through intercalary growth in a ring zone. Thereby, the stamens are moved upwards and form ledges on the corolla tube (Fig. 34). In the inferior ovary the usual zones of the typical angiospermous gynoecium can be distinguished, namely a synascidiate, symplicate and hemisymplicate zone. The ovule is borne on carpellary tissue.

     

A new dimension to hummingbird-flower relationships

The close correspondence between the bills of hummingbirds and the lengths of the flowers they feed from has been interpreted as an example of coadaptation. Observations of birds feeding at flowers longer and shorter than their bills, however, and the lack of experimental evidence for any feeding advantage to short bills, seem to contradict this interpretation. I address this problem by considering a little-studied dimension of floral morphology: corolla diameter. In laboratory experiments on female ruby-throated hummingbirds (Archilochus colubris), probing abilities (maximum extraction depths) increased with increasing corolla diameter. Handling times increased with decreasing corolla diameter, resulting in handling time equivalents, i.e., flowers having the same handling times but different lengths and diameters. Longer-billed birds had greater maximum extraction depths and shorter handling times than shorter-billed birds at all corolla diameters greater than the width of the bill. In contrast, shorter-billed birds made fewer errors inserting their bills into narrow flowers. Hence, differences in bill lengths apparently are associated with trade-offs in foraging abilities, whereby longer-billed birds are able to feed at long flowers and may do so more quickly, whereas shorter-billed birds are able to feed more successfully at narrow flowers.     

Changes in density of chromatin in the meristematic cells ofSinapis alba during transition to flowering

Summary Changes in the density of nuclear chromatin in the shoot apical meristem ofSinapis alba L. during floral transition (floral evocation) are described using Feulgen-stained 2 m thick semi-thin sections and scanning cytophotometric techniques. In both G1 and G2 nuclei the chromatin becomes less heterogeneous and less dense in evoked meristems compared to vegetative meristems. When chromatin is resolved into two fractions the dispersed fraction increases relative to the condensed fraction at evocation. This decondensation process occurs earlier in G1 than in G 2 nuclei. These chromatin changes are presumably closely related to the dramatic stimulation of biosynthetic activity and cell division during floral transition.     

The pollination syndrome ofDeplanchea tetraphylla (Bignoniaceae)

The reproductive structures ofDeplanchea tetraphylla (Bignoniaceae) exhibit a significant number of unusual features: inflorescence with an apical platform; flowers yellow, short-tubed, strongly zygomorphic; mouth closed through lateral compression; stamens and style long-exserted, erect or slightly reclined; nectar dark brown, exposed in the spoon-shaped lowermost corolla lobe and apparently acting also as a visual cue. These features suggest a highly elaborate syndrome for bird pollination: the birds (probably lorikeets) perch on the inflorescence platform and bend downwards to take up the exposed nectar, thus touching the exserted anthers and stigmas with the throat or breast. The likely evolution of this syndrome by additive steps, effecting a change from head up to head down position of the pollinator, can be traced from the floral structure of the remaining four species of the genus.     

Induction,polarity and spatial control of cytokinesis in some abnormal subsidiary cell mother cells ofZea mays

Summary Cytokinesis in the subsidiary cell mother cells (SMCs) ofZea mays leaves grown in the presence of 5 mM of caffeine solution is usually partially inhibited. A continuous wall strip, resembling a portion of the subsidiary cell (SC) wall, is laid down in the preprophase microtubule band (PMB) cortical zone. Sometimes, the incomplete SC (SC) wall grows centripetally in the absence of a phragmoplast and the gap becomes smaller or closes. The SC nucleus escapes through the SC wall gap into the larger SMC compartment and may fuse with the other nucleus.The aberrant SMCs (a-SMCs) pass through another division cycle, reattempting to produce a SC. A typical PMB is found in the SC space, in the site of the previous PMB. Moreover, in some preprophase SMCs, the cytoplasm adjacent to the SC wall is traversed by a small number of microtubules. The preprophase nuclei are partly or totally separated from the PMB by the perforated SC wall and may lie far from the latter.Usually, one mitotic spindle is assembled. The cycling paired polarized nuclei appear to synchronize and their chromosomes line up together on a single metaphase plate. Although the mitotic spindle axis is diversely oriented, one of its poles tends to be stabilized in the proximity of the SC wall gap. These divisions separate abnormal cells. Most or all the cell plate edges fuse with wall regions far from the PMB cortical zone. However, when some of them approach the SC wall strips, they are attracted and intersect their rims. In rare occasions the cell plate, invading the SC space is guided by the PMB cortical zone to create a SC-like curved wall portion, in absence of a daughter nucleus.Observations show that the cell plate arrangement in redividing aberrant SMCs is not subjected to a strict spatial control. The disorder of polarization sequence generated by the SC wall ring and especially the perturbation of the spatial (and functional?) relationship between PMB-PMB cortical zone and the nucleus—mitotic spindle is a causal factor of the variable cell plate arrangements.     

Floral sexuality and breeding system in gum karaya tree, Sterculia urens

Comprehensive studies were carried out on phenology, floral sexuality, pollination biology, pollen-pistil interaction, breeding system and fruit and seed set on three populations of gum karaya tree (Sterculia urens). The species is andromonoecious and produces a large number of male and a limited number of bisexual (functionally female) flowers. The numbers of male and bisexual flowers varies not only between trees but also during the flowering period within a tree. Each male flower produces about 5000 fertile pollen grains. Neither in morphology nor in number, is there any difference between pollen grains in the bisexual and male flowers. However, pollen grains of bisexual flowers are completely sterile and incapable of siring any seeds. Their anthers, however, serve to attract pollinators; the emasculated bisexual flowers fail to do so. Thus S. urens is apparently andromonoecious but exhibits cryptic monoecy. That the species is self-incompatible was confirmed by controlled pollinations. The self-incompatibility is of the late-acting type and manifests after the entry of the pollen tube into the ovule. Apis indica is the only pollinator recorded by us and wind plays no role in pollination. The efficacy of pollination is low as only 56% of flowers were estimated to be pollinated. The pollen load on one-third the number of pollinated stigmas was lower than the number of ovules present. Fruit set under open pollination is poor and is highly variable from tree to tree (0.7–3.2%). Apart from pollination constraint, limited resource availability may also contribute to low fruit set.     

<Emphasis Type="Italic">In vitro</Emphasis> screening of sugarcane to evaluate smut susceptibility

Tissue-cultured plantlets of three sugarcane (Saccharum spp.) cultivars having a known field smut reaction were screened for susceptibility to Ustilago scitaminea H&P Sydow. Plantlets were inoculated with 0.5 l of a suspension of equally mixed quantities of plus and minus mating type sporidia of U. scitaminea at concentrations ranging from 1×10¹ to 1×10⁶ cells. Fungal sori (whips) were produced in cultivar N12 (intermediate) 6weeks following inoculation with 1×10⁵ mixed sporidia and thereafter in cultivar NCo310 (susceptible) but not in cultivar N19 (resistant). Sori bearing teliospores were produced up to 3months following inoculation and incubation at 26°C. No sori were produced at mixed sporidial concentrations lower than 1×10⁵cells. The in vitro soral production in cultivars N19, N12 and NCo310 was 0, 27.5 and 47.5% respectively. Plantlets inoculated with 1×105sporidia of only one mating-type did not produce sori in any of the three cultivars tested. Blind scoring of an unknown sugarcane cultivar by this method corresponded exactly with its field smut rating.     

Corolla and androecium development in someEudesmia eucalypts (Myrtaceae)

In the early stages of ontogeny, the corolline parts of theEudesmia eucalypts develop as compound structures directly comparable to the early stages of the petals ofAngophora and the bloodwood eucalypts, but with the onset of androecial formation a marked difference takes place. Rather than forming on the floral apex, the stamen primordia arise on the basal adaxial components of the young corolline parts; this basal component develops into the staminophore of the mature flower. The operculum consists only of the dorsal components of the corolline parts, the homologues of the dorsal keels of theAngophora petals. If the corolline parts remain more or less free in their early developmental stages, corresponding groups of stamens are produced. Early corolline continuity leads to a continuous ring of stamens. The staminophore is not an organ sui generis, but a derivative of the corolla. The bundles of stamens in some species are best referred to as epipetalous groups, not antepetalous fascicles.     

Floral sexual dimorphism and flower choice by pollinators in a nectarless monoecious vine Akebia quinata (Lardizabalaceae)

We investigated the pollination system and movement patterns of pollinators among flowers of the nectarless, monoecious vine Akebia quinata in natural populations and experimental floral arrays. Female flowers did not offer any rewards for pollinators and were larger than male flowers. Pollinators of A.quinata , such as small solitary bees and hoverflies, clearly discriminated between male and female flowers. Hoverflies always visited male flowers and rarely visited female flowers. In contrast, solitary bees tended to visit female flowers first when entering the array, but then switched to male flowers within the same foraging bout. This tendency disappeared when the sepal size of female flowers was experimentally reduced to the size of male flowers. Thus, observed non-randomness in flower choice by solitary bees may be caused by female>male sexual dimorphism and may increase the chance of cross-pollination and lower the probability of geitonogamous pollination in a single visit to a plant. Therefore, floral sexual dimorphism in A.quinata is considered to be an adaptation for deceptive pollination associated with discriminating pollinators.     

Oviposition choices by a pre-dispersal seed predator (Hylemya sp.)

Summary Although the importance of pollinators has most often been examined in the evolution of floral characters, seed predators may also play a role in shaping floral evolution. In this study, I examined the role of interplant distance, plant size, and flower morphology on Ipomopsis aggregatás (Polemoniaceae) attractiveness to a pre-dispersal seed predator, Hylemya sp. (Anthomyiidae) and to hummingbird pollinators. The attractiveness of I. aggregata individuals to Hylemya was nonlinearly related to interplant distance in experimental arrays. Clumped and highly dispersed plants were preyed upon more frequently than those at intermediate distances. I found no relationship between interplant distance and visitation rates by hummingbird pollinators in these experimental arrays. However, in natural populations studied, clumped plants were more frequently approached by hummingbirds than those growing more widely dispersed. Display size was unrelated to visitation by Hylemya on inflorescences I clipped and maintained as large, small and control. Display size was also unrelated to the total number of visits by hummingbird pollinators to each of these experimental plants, however large display plants were more likely to be visited first in any given visitation sequence. Of various morphological measurements, corolla length showed the strongest positive correlation with Hylemya egg presence. To the extent that plant spacing and morphology is correlated with pollinator visits and ultimate seed set, Hylemya could be choosing flowers optimally, and playing a role in the evolution of floral traits.     

Toxin-binding properties of cytochrome P450 in Saccharomyces cerevisiae and Kluyveromyces marxianus

Microsomes from Kluyveromyces marxianus GK1005 examined by carbon monoxide difference spectroscopy showed no evidence of cytochrome P450, in contrast to microsomes isolated from a control strain of Saccharomyces cerevisiae. Benzo[a]pyrene produced a typical Type I-binding spectrum with microsomes of both yeasts, with K _s values of 82 M (S. cerevisiae) and 70 M (K. marxianus). While aflatoxin B₁ generated a typical Type I-binding spectrum with microsomes from S. cerevisiae (K _s of 178 M), the toxin did not produce a recognisable binding spectrum with microsomes from K. marxianus.     

Fabrication of Stable Packed Capillary Reversed-Phase Columns for Protein Structural Analysis

Capillary column (320-m ID) liquid chromatography is an essential tool for the separation and concentration of low-picomole amounts of proteins and peptides for mass-spectrometric based structural analysis. We describe a detailed procedure for the fabrication of stable and efficient 50- to 180-m ID polyimide fused-silica columns. Columns were packed by conventional slurry packing with reversed-phase silica-based supports followed by column bed consolidation with acetonitrile and sonication. PVDF membrane or internal fused-silica particles were employed for column end-frit construction. The ability of these columns to withstand high back pressures (300–400 bar) enabled their use for rapid chromatography (>3400 cm/hr; i.e., 40 l/min for 200-m ID columns) and the loading of large sample volumes (up to 500 l). The accurate low flow rates (0.4–4.0 l/min) and precise gradient formation necessary to operate these columns were achieved by a simple modification of conventional HPLC systems [Moritz et al. (1992), J. Chromatogr. 599, 119–130]. Column performance was evaluated for ability to resolve low-fmol amounts of all components of a mixture of PTH-amino acids and to separate peptides for on-line LC/MS analysis of peptide mixtures derived from in situ digestion of 2-DE resolved protein spots.     

Colour saturation triggers innate reactions to flower signals: Flower dummy experiments with bumblebees

Summary Innate behavioural reactions, i.e. reactions of untrained, flower-naive bumblebees (Bombus terrestris L., B. lucorum L.; Apidae) were observed in flower dummy experiments. It was proven that an innate releasing mechanism responds to optical flower signals: the spectral purity of corolla colour was found to be crucial for far attraction toward flower dummies. During the subsequent near orientation, that is when a bumblebee finally reaches a flower dummy, the bumblebee's antennae contact the part of highest spectral purity while the bee is still in flight. Guides such as stamen patches present in the center of flower dummies are used only for near orientation. Flower dummies receiving the greatest number of antennae reactions at the guide were always those with low spectral purity in the surrounding background colour, high spectral purity at the corolla colour and highest spectral purity at the guide colour. In contrast, dominant wavelength and intensity of flower dummy colours had no detectable influence on innate behavioural reactions, while colour contrast had some. These results are interpreted as follows: orientation toward guides is based upon a gradient of centripetally increasing, bee-subjective colour saturation which directs the bumblebee's approach toward the center of the flower dummy where additional factors may contribute to stimulating the landing reaction.     

“Chromosome exo-skeleton” in plant cells visualized by scanning electron microscopy

Summary Cytoskeletons surrounding the chromosomes of the root tip cells ofPisum sativum and the generative cells ofAllamanda schottii were visualized using Triton X-100 extraction and scanning electron microscopy. The cytoskeleton surrounding the chromosome consisted of a reticulate network of fibres. This is the first report showing the existence of a chromosome exo-skeleton in plant cells.Abbreviations EGTA ethyleneglycol-bis-(-aminoethylether) N,N,N,N-tetraacetic acid - PIPES piperazine-N,N-bis-(2-ethanesulfonic acid)     

The flower biology ofCephalanthera longifolia (Orchidaceae)—pollen imitation and facultative floral mimicry

Solitary bees (Halictus sp.) were found to be the effective pollinators ofCephalanthera longifolia. In the same foraging flight the bees also visit flowers ofCistus salviifolius which has a similar colour pattern.Cephalanthera offers no reward to its pollinators, but orange papillae on its labellum successfully imitate pollen ofCistus. AsCephalanthera also attracts pollinators in the absence ofCistus, this is regarded as facultative floral mimicry.     

Meiotic studies ofElymus nutans andE. jacquemontii (Poaceae,Triticeae) and their hybrids withPseudoroegneria spicata and seventeenElymus species

Hybridizations ofElymus nutans andE. jacquemontii were carried out with one species ofPseudoroegneria (S genome), and 20Elymus species, each containing either of the SH, SY, SYH, or SYW genomes. Chromosome configurations were analysed at metaphase I of the two target taxa and their interspecific hybrids. It is concluded that (i)E. nutans is an allohexaploid containing the SYH genomes, andE. jacquemontii is an allotetraploid having the SY genomes; (ii) the genomic affinity is associated with the geographic distance between the species studied; (iii) minor genomic structural rearrangements have occurred within the hexaploid taxon ofE. nutans.     

A structural model for elongation factor 1 (EF-1) and phosphorylation by protein kinase CKII

EF-1a binds aminoacyl-tRNA to the ribosome with the hydrolysis of GTP; the complex facilitates the exchange of GDP for GTP to initiate another round of elongation. To examine the subunit structure of EF-1 and phosphorylation by protein kinase CKII, recombinant , , and subunits from rabbit were expressed in E. coli and the subunits were reconstituted into partial and complete complexes and analyzed by gel filtration. To determine the availability of the and subunits for phosphorylation by CKII, the subunits and the reconstituted complexes were examined as substrates for CKII. Formation of the nucleotide exchange complex increased the rate of phosphorylation of the subunit and reduced the Km, while addition of to or the complex inhibited phosphorylation by CKII. However, a had little effect on phosphorylation of . Thus, the and subunits in EF-1 were differentially phosphorylated by CKII, in that phosphorylation of was altered by association with other subunits, while the site on was always available for phosphorylation by CKII. From the availability of the subunits for phosphorylation by CKII and the composition of the reconstituted partial and complete complexes, a model for the subunit structure of EF-1 consisting of (22)2 is proposed and discussed.     

Dynamics of the cytoskeleton of epidermal cells in situ and in culture

Summary The cytoskeleton of primary tissue-culture cells from the epidermis of Xenopus laevis tadpoles was investigated by phase-contrast, immunofluorescence, and electron microscopy. The connection between the arrangement of different types of filaments and the mechanical properties of the epidermis is discussed. The bilayered epidermis attains stability from thick bundles of tonofilaments interconnecting the basal desmosomes. Twisting of tonofilaments around each other can explain the occurrence of elastic filamentous curls forming a meshwork braced between rows of small desmosomes in the apical region of the epidermis. Actin is arranged as a diffuse meshwork and sometimes forms bundles intermingling with tonofilament bundles. Surface membranes and rows of small desmosomes are delineated by actin and contain -actinin. Actin raises the tension for rounding and spreading of cells. Microtubules stabilize already well-developed lamellae.     

Maximum entropy approach to the determination of solution conformation of flexible polypeptides by global conformational analysis and NMR spectroscopy – Application to DNS1-c-[d-A2bu2, Trp4,Leu5]- enkephalin and DNS1-c-[d-A2bu2, Trp4, d-Leu5]enkephalin

A method is proposed to determine the conformational equilibrium of flexible polypeptides in solution, using the data provided by NMR spectroscopy and theoretical conformational calculations. The algorithm consists of the following three steps: (i) search of the conformational space in order to find conformations with reasonably low energy; (ii) simulation of the NOE spectrum and vicinal coupling constants for each of the low energy conformations; and (iii) determining the statistical weights of the conformations, by means of the maximum-entropy method, in order to obtain the best fit of the averaged NOE intensities and coupling constants to the experimental quantities. The method has been applied to two cyclic enkephalin analogs: DNS¹-c-[d-A₂bu²,Trp⁴,Leu⁵]enkephalin (ENKL) and DNS¹-c-[d-A₂bu²,Trp⁴,d-Leu⁵]enkephalin (ENKD). NMR measurements were carried out in deuterated dimethyl sulfoxide. Two techniques were used in conformational search: the electrostatically driven Monte Carlo method (EDMC), which results in extensive search of the conformational space, but gives only energy minima, and the molecular dynamics method (MD), which results in a more accurate, but also more confined search. In the case of EDMC calculations, conformational energy was evaluated using the ECEPP/3 force field augmented with the SRFOPT solvation-shell model, while in the case of MD the AMBER force field was used with explicit solvent molecules. Both searches and subsequent fitting of conformational weights to NMR data resulted in similar conformations of the cyclic part of the peptides studied. For both ENKL and ENKD a common feature of the low-energy solution conformations is the presence of a type II or type IV -turn at residues 3 and 4; the ECEPP/3 force field also gives a remarkable content of type III -turn. These -turns are tighter in the case of ENKL, which is reflected in different distributions of the d-A₂bu(NH)...d-A₂bu(CO) and d-A₂bu(NH)...Gly³(CO) hydrogen-bonding distances, indicating that the d-A₂bu(NH) amide proton is more shielded from the solvent than in the case of ENKD. This finding conforms with the results of temperature coefficient data of the d-A₂bu(NH) proton. It has also been found that direct (MD) or Boltzmann (EDMC) averages of the observables do not exactly conform with the measured values, even when explicit solvent molecules are included. This suggests that improving force-field parameters might be necessary in order to obtain reliable conformational ensembles in computer simulations, without the aid of experimental data.     

Homologues of a vacuolar processing enzyme that are expressed in different organs in Arabidopsis thaliana

Vacuolar processing enzymes (VPEs) are responsible for the maturation of seed proteins. These processing enzymes belong to a novel group of cysteine proteinases with molecular masses of 37 to 39 kDa. We isolated two genes of VPEs from a genomic library of Arabidopsis. The gene products were designated -VPE and -VPE, and they were 56% identical in terms of amino acid sequence. The amino acid sequences of -VPE and -VPE were also 55% and 67% identical to that of castor bean VPE, respectively. The gene for -VPE had 7 introns, while that of -VPE had 8 introns. Northern blot analysis revealed that -VPE is expressed in rosette leaves, cauline leaves and stems of Arabidopsis, while -VPE is predominantly expressed in the flowers and buds. Neither -VPE nor -VPE is expressed in the siliques. This result strongly suggests that the isolated genes encode isozymes of VPE that are specific to vegetative organs.