Effects of post-translational modifications catalysed by pollen transglutaminase on the functional properties of microtubules and actin filaments

TGases (transglutaminases) are a class of calcium-dependent enzymes that catalyse the interactions between acyl acceptor glutamyl residues and amine donors, potentially making crosslinks between proteins. To assess the activity of apple (Malus domestica) pollen TGase on the functional properties of actin and tubulin, TGase was prepared from apple pollen by hydrophobic interaction chromatography and assayed on actin and tubulin purified from the same cell type. The enzyme catalysed the incorporation of putrescine in the cytoskeleton monomers. When tested on actin filaments, pollen TGase induced the formation of high-molecular-mass aggregates of actin. Use of fluorescein– cadaverine showed that the labelled polyamine was incorporated into actin by pollen TGase, similar to with guinea pig liver TGase. The pollen TGase also reduced the enzyme activity and the binding of myosin to TGase-treated actin filaments. Polymerization of tubulin in the presence of pollen TGase also yielded the formation of high molecular mass aggregates. Furthermore, the pollen TGase also affected the binding of kinesin to microtubules and reduced the motility of microtubules along kinesincoated slides. These results indicate that the pollen tube TGase can control different properties of the pollen tube cytoskeleton (including the ability of actin and tubulin to assemble and their interaction with motor proteins) and consequently regulate the development of pollen tubes

Ultrastructural characteristics of pollen development in Vitis vinifera L. (cv. Sangiovese)

Ultrastructural studies on the development of microspores to ripe pollen (cv. Sangiovese) showed that the diploid microsporocyte undergoes meiosis in order to form a tetrad of microspores sticked together by a callose wall. After callose digestion, 4 independent microspores were released. With successive growth, the single nucleus of each microspore undergoes an asymmetrical division forming the bicellular pollen grain (vegetative cells containing the generative cells). Only after pollination and pollen tube growth the two sperms will be formed. The mature pollen of Sangiovese is tricolpate; the exine is scabrate-verrucate in the equatorial zone and foveolate in the polar region

Uniform current in graphene strip with zigzag edges

Graphene exhibits zero-gap massless-Dirac fermion and zero density of states at E = 0. These particles form localized states called edge states on finite width strip with zigzag edges at E = 0. Naively thinking, one may expect that current is also concentrated at the edge, but Zarbo and Nikolic numerically obtained a result that the current density shows maximum at the center of the strip. We derive a rigorous relation for the current density, and clarify the reason why the current density of edge state has a maximum at the center.Comment: 5 pages, 3 figures; added references and corrected typos, to be published in J. Phys. Soc. Jpn. Vol.78 No.

Sequence analysis of a microsatellite and its flanking regions in intraspecific hybrids of grapevine (Vitis vinifera L.)

Microsatellite (MS) VVMD21 (BOWERS et al. 1999) was taken as a model to explore the molecular basis of polymorphism in a panel of 6 grapevine accessions (Vitis vinifera L.), consisting of Sangiovese and Cabernet Sauvignon and 4 F1 plants derived from crossing both varieties. The 12 alleles of both parents and the progeny were cloned and sequenced. The microsatellite repeat (AG)n>6 was found in each sequence, together with a poly-T rich region that showed irregularity. Furthermore, single nucleotide deletion or exchange (point mutations) were found in the microsatellite flanking regions

An extracellular transglutaminase is required for apple pollen tube growth

An extracellular form of the calcium-dependent protein-crosslinking enzyme TGase (transglutaminase) was demonstrated to be involved in the apical growth of Malus domestica pollen tube. Apple pollen TGase and its substrates were co-localized within aggregates on the pollen tube surface, as determined by indirect immunofluorescence staining and the in situ cross-linking of fluorescently labelled substrates. TGase-specific inhibitors and an anti-TGase monoclonal antibody blocked pollen tube growth, whereas incorporation of a recombinant fluorescent mammalian TGase substrate (histidine-tagged green fluorescent protein:His6– Xpr–GFP) into the growing tube wall enhanced tube length and germination, consistent with a role of TGase as a modulator of cell wall building and strengthening. The secreted pollen TGase catalysed the cross-linking of both PAs (polyamines) into proteins (released by the pollen tube) and His6-Xpr-GFP into endogenous or exogenously added substrates. A similar distribution of TGase activitywas observed in planta on pollen tubes germinating inside the style, consistent with a possible additional role for TGase in the interaction between the pollen tube and the style during fertilization

Ultrastructural Aspects of Unilateral Interspecific Incompatibility between Lycopersicum Peruvianum and L. Esculentum

SUMMARYObservations have been made, at the electron microscope, of the pollen tubes present in the styles of Lycopersicum esculentum and L. peruvianum after reciprocal crosses between the two species.The unilateral incompatibility barrier which isolates the two species when L. peruvianum is used as pistillate parent was then compared to the processes of pollen tube rejection which have been recently analysed (J. Cell Sci., 1972) after self-pollination in this self-incompatible species. Such a comparison, which was also carried out by means of fluorescence techniques, has permitted to find out that for both types of incompatibility the rejection process was characterised by a progressive disappearance of the callose-rich inner wall of the pollen tube and by an accumulation of bi-partite particles in the tube cytoplasm.In the case of unilateral incompatibility, however, the tube outer wall is gradually disaggregated while the callosic inner wall remains quite thick at the tube apex, becoming thinner and fin..

Chromosome numbers for the Italian flora: 6

In this contribution, new chromosome data obtained on material collected in Italy are presented. It includes three chromosome counts for Bupleurum baldense Turra, Colchicum lusitanum Brot., and Euphorbia gasparrinii Boiss. subsp. gasparrinii

Quenching of the quantum Hall effect in graphene with scrolled edges

Edge nanoscrolls are shown to strongly influence transport properties of suspended graphene in the quantum Hall regime. The relatively long arc length of the scrolls in combination with their compact transverse size results in formation of many nonchiral transport channels in the scrolls. They short-circuit the bulk current paths and inhibit the observation of the quantized two-terminal resistance. Unlike competing theoretical proposals, this mechanism of disrupting the Hall quantization in suspended graphene is not caused by ill-chosen placement of the contacts, singular elastic strains, or a small sample size