Distribution of loosely-bound calcium in the vegetative and generative cells of the pollen grains in Chlorophytum elatum

We used chlorotetracycline fluorescence, alizarin staining and potassium pyroantimonate methods, as well as X-ray microanalysis, to demonstrate the differential localization of Ca2+ during pollen maturation. Level of loosely-bound Ca2+ ions was higher in the generative cell than in the vegetative cell of the mature pollen grain which is one of the symptoms of metabolic differentiation of the two sister cells. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gibberellin-like substances and indole type auxins in developing grains of normal- and high-lysine genotypes of barley

Changes in gibberellin-like activity and content of indole type auxins were investigated during grain development of the two high-lysine barley (Hordeum vulgare L.) genotypes Sv 73608 and Risø 1508, and their corresponding normal cultivars Mona and Bomi. A peak in gibberellin-like activity was found in developing grains of the normal cultivars about 18 days after anthesis, whereas the grains of the high-lysine genotypes showed a two to five times higher maximum about 3–4 days later. The auxin content of the cultivar Bomi showed a maximum between the 22nd and the 29th day after anthesis, whereas, throughout their development the grains of the mutant Risø 1508 exhibited only about ¹/10 of the maximum level of auxin found in the grains of Bomi. The normal cultivar Mona also displayed higher contents of auxin than the high-lysine genotypes Sv 73608, particularly at the later stages of grain growth, but the differences in concentration were considerable smaller than for the pair ‘Bomi’—‘Risø 1508’. It is suggested that auxins play an important role in the development of barley grains.     

Natural and experimental hybridization inArmeria (Plumbaginaceae):A. villosa subsp.carratracensis

An experimental crossing program was carried out in order to test the hypothesis thatArmeria villosa subsp.carratracensis, a serpentine endemic from Southern Spain, is of hybrid origin. Fruit-set and mainly pollen stainability data in artificial hybrids demonstrate that internal interspecific barriers are weak. Two generations of backcrossing with the two putative parents —A. colorata andA. villosa subsp.longiaristata— can restore pollen stainability to an average of 83.2 and 68.7, respectively. A morphometric analysis of 148 specimens belonging to parental species, different artificial hybrid generations and wild putative hybrid race shows that (1) morphological characters have a strong genetic basis and thus are good markers in identifying hybrids and introgression inArmeria; (2) artificial backcrossing produces in morphometrical characters a variation which conforms in both trend and magnitude to what is commonly attributed in the wild to introgression; (3) the position of the putative hybrid race is intermediate between the two parental species used in the program. These results are in accordance with the hypothesis of hybrid origin ofA. villosa subsp.carratracensis. Natural and experimental hybridization inArmeria, I     

The use of Callitriche for water quality determination can be misleading: An example from the Po Valley in Northern Italy

In the context of the European Water Framework Directive (2000/60), aquatic macrophytes have become important elements for ascribing the correct ecological value to water systems. Callitriche includes macrophyte species which are widespread and particularly sensitive to environmental cues. High plasticity and morphological variability of these plants have carried to great difficulties in their correct taxonomic determination. Diverse populations of Callitriche of the Po Valley (Northern Italy) have been studied. Plants of Callitriche spp. were collected in Northern Italian rivers with mesotrophic and eutrophic waters and their morphological, karyological, and molecular features were analyzed. Populations with a different chromosome number equal to 10, 18, or 20 were found. Chloroplast rbcL DNA showed the presence of three different sequences. Moreover, the presence of heterozygous rDNA-ITS sequences suggests the existence of a considerable number of hybrids. At ecological level, only one taxon lives in eutrophic waters, while all the others live in mesotrophic ones. Different morphological characters and chromosome set suggest the presence of a new taxon among Italian Callitriche populations. In conclusion, this research underlines that the possibility of Callitriche taxon misclassification, using only the “canonical” macro-morphological approach, is significant and that the incorrect determination of these plants would lead to erroneous evaluation of water quality.     

Aerobiological survey in L'Aquila (Italy) throughout 1988 to 1990

Summary Airborne pollens were sampled in L'Aquila (Italy) throughout 1988 to 1990. Our data indicate that the flowering seasons of pollens mostly accounting for airborne concentrations are somewhat unique as compared to other Mediterranean areas. The prolonged season of Cupressaceae as well as the two different flowering seasons of Oleaceae, namely ofFraxinus, Ligustrum andOlea europaea, respectively, were the most relevant findings of our study. Furthermore, it is also worth to note thatParietaria judaica could be detected during the study period throughout March to June, but not in late summer and early autumn, as expected.Moreover, we evaluated the frequency of different pollen sensitizations in 2813 patients requiring medical care during the study period because of allergic diseases, such as conjunctivitis, oculorhinitis, and bronchial asthma. Our data demonstrate that both Compositae and Urticaceae proved to be the most allergenic pollens despite the low airborne concentrations detected. Finally, a relevant finding was the highOlea sensitization among patients with bronchial asthma.     

Pollen–pollen interactions in Betula pendula in vitro

Direct pollen interactions, as well as interactions mediated by a recipient, can have a remarkable influence on pollen fertilization ability. Under conditions of pollen competition it could be advantageous if pollen grains interfered with the germination of other pollen. The aim of this study was to find out if there are direct negative or positive pollen–pollen interactions between pollen grains from genetically slightly different donors. The in vitro germinability of the pollen from several Betula pendula Roth clones was investigated. The pollen interactions between the clones were examined pairwise by using equal pollen mixtures. In three of the eight cases the germination percentage of the pollen mixture was significantly higher than the average germination percentage of the separate clones that formed the mixture, which indicates some type of interaction between the pollen populations. We found only positive interactions between the pollen of clones. This study also documented density-dependent germination of pollen grains in vitro (=pollen population effect). Adding an aqueous pollen extract to the incubation medium increased the germination percentages of poorly germinating pollen and small pollen populations. Germination-stimulating effects were found to exist both with fresh and dead pollen. Such direct pollen–pollen interactions could be explained by specific water-soluble substances diffusing from pollen grains.     

Putative proteaceous elements of the Lomatites-type reinterpreted as new Berberis of the European Tertiary

 A characteristic xeromorphic foliage occurring in the European Tertiary was originally identified as a Proteaceae according to gross morphology, and compared with Grevillea L. and Lomatia L. (Grevillea kymeana Unger, Lomatites aquensis Saporta). On the basis of venation patterns and phyllotaxy, these elements are now reinterpreted as extinct species of Berberis L. (Berberidaceae): Berberis andreanszkyi spec. nov. occurring in the Upper Oligocene (Eger – Wind brickyard), and the Middle Miocene (Erdbénye) of Hungary, and Berberis kymeana (Unger) comb. nov. (syn. Lomatites aquensis Saporta) known from the Lower Miocene of Greece (Kymi) and the Oligocene of France (Aix-en-Provence, Manosque/Bois d'Asson, Cérestre, Bonieux). The associated vegetation reflects warm-temperate to subtropical subhumid climatic conditions. Extant barberries with similar foliage occur in the Himalayas and China today. Received April 3, 1999 Accepted September 25, 2000     

Floral bagging differentially affects handling behaviours and single-visit pollen deposition by honey bees and native bees

1. Measurements of pollinator performance are crucial to pollination studies, enabling researchers to quantify the relative value of different pollinator species to plant reproduction. One of the most widely employed measures of pollinator performance is single-visit pollen deposition, the number of conspecific pollen grains deposited to a stigma after one pollinator visit. To ensure a pollen-free stigma, experimenters must first bag flowers before exposing them to a pollinator. 2. Bagging flowers, however, may unintentionally manipulate floral characteristics to which pollinators respond. In this study, we quantified the effect of bagging on nectar volume in watermelon (Citrullus lanatus) flowers, and how this affects pollinator performance and behaviour. 3. Experimental bagging resulted in roughly 30-fold increases in nectar volume relative to unmanipulated, open-pollinated field flowers after only a few hours. Honey bees, but not native bees, consistently displayed elevated handling times and single-visit pollen deposition on unmanipulated bagged flowers relative to those from which we removed nectar to mimic volumes in open-pollinated flowers. 4. Furthermore, we identify specific bee foraging behaviours during a floral visit that account for differences in pollen deposition, and how these differ between honey bees and native bees. 5. Our findings suggest that experimental bagging of flowers, without accounting for artificially accumulated nectar, can lead to biased estimates of pollinator performance in pollinator taxa that respond strongly to nectar volume. We advise that pollination studies be attentive to nectar secretion dynamics in their focal plant species to ensure unbiased estimates of pollinator performance across multiple pollinator species.