The morphology and activity of the extrafloral nectaries in Reynoutria × bohemica (Polygonaceae).

Reynoutria × bohemica is an invasive species causing significant damage to native ecosystems in North America and Europe. In this work, we performed an in-depth micromorphological characterisation of the extrafloral nectaries (EFN), during their secretory and post-secretory phases, in combination with field monitoring of nectary activity over time and the qualitative pool of insect visitors. EFN consist of secretory trichomes and vascularised parenchyma. Polysaccharides, lipids and proteins were histochemically detected in all trichome cells; phenolic substances were detected in parenchyma cells. Our data indicate that all nectary regions are involved in nectar production and release, constituting a functional unit. Moreover, the main compound classes of nectar and their transfer change over time: first, granulocrine secretion for sugars prevails, then eccrine secretion of the lipophilic fraction takes place. Active nectaries are mainly located in the apical portion of the stem during the growth phase (April-May), when we detected the highest number of individuals visited by ants; from mid-August onwards, during flowering, the number of active nectaries declined then ceased production (September), with a concomitant decrease in visits by the ants. The spectrum of nectar-foraging ants mainly included representatives of the genera Formica, Lasius and Camponotus. Reynoutria × bohemica produces an attractive secretion able to recruit local ants that may potentially act as 'bodyguards' for protecting young shoots, reducing secretions during the blooming stage. This defence mechanism against herbivores is the same as that displayed by the parental species in its native areas.

Cytomorphological investigations in Oxyria digyna Hill. from the Kashmir Himalaya, India.

In the present paper, detailed cytomorphological investigations in Oxyria digyna Hill. from Kashmir Himalaya-India have been reported for the first time. All the of 14 investigated populations of O. digyna are diploid based on x = 7. Out of these in two populations 0-2B chromosomes have been recorded for the first time while 6 populations differed significantly in their meiotic characteristics. Meiotic abnormalities during male meiosis observed include inter PMC chromatin transfer (cytomixis). Non-synchronous disjunction of some bivalents, laggards and bridges at anaphases and telophases. Consequent to these meiotic anomalies, microsporogenesis in meiocytes is abnormal resulting in to dyads, triads and polyads with or without micronuclei. The overall effect is seen in reduced pollen fertility. Unreduced pollen grains were observed in some populations, which differed significantly in their size compared to the normal (reduced) pollen grains. It is observed that a smaller frequency of pollen grains differed morphologically in Aharbal and Yosmarg populations. The remaining eight populations showed regular meiotic course, normal microsporogenesis and high percentage of pollen fertility (95.09-99.09%).

Ecological functions and differentially expressed transcripts of translucent bracts in an alpine 'glasshouse' plant Rheum nobile (Polygonaceae).

The molecular basis of many physiological and/or phenotypic adaptations of alpine plants remains largely unknown. The upper leaves of what are termed "glasshouse plants" have been transformed into translucent bracts that cover their inflorescences. This change in appearance is believed to allow such plants to maintain normal sexual reproduction under very cold conditions. Thus, it is hypothesized that the foliar roles of these bracts have been altered as an adaptation to alpine environments. In the present study, a test of this hypothesis revealed distinct physiological and anatomical differences (especially related to photosynthesis) between the bracts and normal leaves in one 'glasshouse' species, Rheum nobile Hook. f. and Thomson. A cDNA-AFLP analysis, was conducted to identify candidate genes involving differential expression in bracts and normal leaves, detected 323 (5.4%) transcript-derived fragments (TDFs) that were differentially expressed (up- or down-regulated) among 6,000 TDFs recovered. In total, 110 differentially expressed TDFs were sequenced, of which 52 were homologous to genes reported from other plants. More than half of the candidate genes represented by the unidentified TDFs may be specific to the Rheum lineage or have arisen through adaptive processes in alpine plants. All putative genes involved in photosynthesis had been down-regulated, while those related to stress and defense response were up-regulated in the bracts. These differentially expressed genes are highly congruent with physiological and anatomical differences between the bracts and normal leaves, indicating that they are associated with functions that confer a physiological advantage in alpine conditions.

Investigating cytoskeletal function in chloroplast protrusion formation in the arctic-alpine plant Oxyria digyna.

Arctic and alpine plants like Oxyria digyna have to face enhanced environmental stress. This study compared leaves from Oxyria digyna collected in the Arctic at Svalbard (78 degrees N) and in the Austrian Alps (47 degrees N) at cellular, subcellular, and ultrastructural levels. Oxyria digyna plants collected in Svalbard had significantly thicker leaves than the samples collected in the Austrian Alps. This difference was generated by increased thickness of the palisade and spongy mesophyll layers in the arctic plants, while epidermal cells had no significant size differences between the two habitats. A characteristic feature of arctic, alpine, and cultivated samples was the occurrence of broad stroma-filled chloroplast protrusions, 2 - 5 microm broad and up to 5 microm long. Chloroplast protrusions were in close spatial contact with other organelles including mitochondria and microbodies. Mitochondria were also present in invaginations of the chloroplasts. A dense network of cortical microtubules found in the mesophyll cells suggested a potential role for microtubules in the formation and function of chloroplast protrusions. No direct interactions between microtubules and chloroplasts, however, were observed and disruption of the microtubule arrays with the anti-microtubule agent oryzalin at 5 - 10 microM did not alter the appearance or dynamics of chloroplast protrusions. These observations suggest that, in contrast to studies on stromule formation in Nicotiana, microtubules are not involved in the formation and morphology of chloroplast protrusions in Oxyria digyna. The actin microfilament-disrupting drug latrunculin B (5 - 10 microM for 2 h) arrested cytoplasmic streaming and altered the cytoplasmic integrity of mesophyll cells. However, at the ultrastructural level, stroma-containing, thylakoid-free areas were still visible, mostly at the concave sides of the chloroplasts. As chloroplast protrusions were frequently found to be mitochondria-associated in Oxyria digyna, a role in metabolite exchange is possible, which may contribute to an adaptation to alpine and arctic conditions.

Sex chromatin and nucleolar analyses in Rumex acetosa L.

Rumex acetosa (sorrel) is a dioecious plant with a XX/XY1Y2 sex chromosome system. Both the Y chromosomes are nearly entirely heterochromatic and it has been hypothesised that they can persist as chromocenters in male interphase nuclei. Using specific antibodies against 5-methylcytosine and histone H4 acetylated at terminal lysine 5, global levels of DNA methylation and histone acetylation were studied on the sex chromosomes and autosomes of both sexes. The heterochromatic Y chromosomes did not display a higher methylation level compared to the autosomes. The only prominent hypermethylation signals were found at two nucleolar organising regions located on the autosome pair V, as confirmed by in situ hybridisation with 25S rDNA probe and staining. Immuno-analysis of DNA methylation on female and male interphase nuclei neither revealed any sex-specific differences. Two active (silver-positive) nucleoli and two likely inactive nucleolar organising regions (displaying prominent methylation signals) were found in both sexes. In a fraction of nuclei isolated from leaf cells, two peripheral bodies strongly positive for 4',6-diamidino-2-phenylindole were observed only in males, never in females. These heterochromatin regions were depleted in histone H4 acetylation at terminal lysine 5 and corresponded, according to in situ hybridisation with a Y-chromosome-specific repetitive probe, to the two Y chromosomes. We conclude that the peripheral condensed bodies observed exclusively in male nuclei represent the constitutive heterochromatin of the Y chromosomes which is characterised by a substantial histone H4 underacetylation.

The potential role of orbicules as a vector of allergens.

BACKGROUND: In the locules of anthers of flowering plants, tiny (1.5-2 microm) granules of sporopollenin may occur next to the pollen grains. Those granules, called orbicules, mostly occur on the radial and innermost tangential wall of secretory tapetum cells. METHODS: We have investigated the presence of orbicules in 15 important European allergenic species with scanning electron microscopy (SEM). RESULTS: Orbicules were present in all species investigated of the families Betulaceae, Chenopodiaceae, Fagaceae, Poaceae, Polygonaceae, and Urticaceae. However, in the Asteraceae and Oleaceae species studied, orbicules were lacking. In all Chenopodiaceae, Poaceae, and Urticaceae species, orbicules were attached to the pollen exine. These observations indicate the possibility of the dispersal of orbicules into the atmosphere during anthesis. CONCLUSIONS: The hypothesis of the potential role of orbicules as possible important vectors of allergens is put forward, based on the comparison of our results with recent literature about the evidence of allergenic activity in the smaller micronic atmospheric aerosol fraction. Our results provide evidence that an in-depth investigation of the sites of allergens across the whole anther is required. We suggest that allergen researchers apply immunoelectron microscopy on whole anthers to determine whether orbicules possess allergens.