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The calibration process is a crucial step in molecular dating and needs to be carefully designed in order to obtain reliable divergence time estimates. Forest (pp. 789–794) discusses various aspects of the calibration procedure, the potential pitfalls and the increasing number of new methods proposed to tackle the problems associated with this procedure.
Ortiz et al. (pp. 795–807) pay tribute to Professor Stanley J. Peloquin (1921–2008), who was an internationally renowned plant geneticist and breeder who made exceptional contributions to the quantity, quality and sustainable supply of food for the world from his innovative and extensive scientific contributions. Amongst other achievements, with co-workers he developed methods to use 2n gametes and haploids for breeding, and used them to move genes for important horticultural traits from wild tuber-bearing Solanum species to cultivated potato for the betterment of agriculture.
Focussing on the establishment of zygomorphy during development and on its evolution, Jabbour et al. (pp. 809–822) compare the floral developmental sequence of six species of Ranunculaceae. They elaborate a developmental model to break down the successive acquisitions of floral organ identities on the ontogenic spiral, giving clues to understanding this complex morphogenesis from an evo–devo point of view.
Flowers of the African parasitic plant genus Hydnora emerge from the ground and resemble a dead animal, both in colour and odour, which attracts carrion insects. Seymour et al. (pp. 823–832) find that the osmphores that produce the scent warm slightly, because of an elevated respiration rate. Compared to other thermogenic flowers, however, heat production is low and floral temperature is not regulated.
Physical dormancy (PY) in seeds of the Sapindaceae has been demonstrated in several different genera; however, the feature allowing eventual imbibition (the water gap) has not been identified. Turner et al. (pp. 833–844) investigate seed anatomy of Dodonaea petiolaris and identify the water gap as a small plug in the seed coat adjacent to the hilum and opposite the area where the radicle emerges; this forms a small region that blisters under stress. Similar blisters are observed in three other species in two different genera following treatment with hot water, indicating that a common morphological basis exists for regulating PY in many Sapindaceae.
Based on its floral syndrome, the Asian sacred lotus, Nelumbo nucifera, has long been predicted to be beetle-pollinated. By means of pollinator-exclusion, Li and Huang (pp. 845–851) confirm that beetles are effective pollinators in this thermoregulating plant, and hence are potential pollen vectors for outcrossing. However, other generalist insects can contribute to pollination in the wild where the beetles are absent, implying that contemporary pollinators may not reflect the predicted pollination syndrome. (Featured article in ContentSelect on p. v.)
Flavonoids have the potential to serve as antioxidants in addition to their function of UV screening in photoprotective mechanisms. Agati et al. (pp. 853–861) analyse the tissue-specific distribution of quercetin and luteolin derivatives in leaves of Ligustrum vulgare using fluorescence-microspectroscopy and multispectral-fluorescence micro-imaging. These flavonoids, which are effective antioxidants in vitro and in vivo, accumulate in the vacuole of palisade cells in response to natural sunlight, in the presence or absence of UV-radiation. These findings are consistent with a key antioxidant function of flavonoids in photoprotection.
Dendrobium species show tremendous morphological diversity and have a broad geographical distribution. Begum et al. (pp. 863–872) identify major repetitive and evolutionary diverged sequence families in a c0t-1 plasmid library of D. moschatum. Comparative fluorescent in situ hybridization of these repetitive sequences as well as rDNA probes on metaphase chromosomes of three Dendrobium species reveals a species-specific chromosomal organization, thus suggesting remarkable genomic diversification during Dendrobium speciation. (Featured article in ContentSelect on p. v.)
The increasing significance of Brachypodium distachyon as a model grass species emphasizes the need to understand the evolutionary relationships within this relatively small genus, most species of which have not been analysed cytogenetically. Wolny and Hasterok (pp. 873–881) determine that techniques such as FISH and GISH are suitable for comparative phylogenetic analyses and give interesting insights into the phylogenetic relationships between Brachypodium species.
Chaubert-Pereira et al. (pp. 883–896) introduce an integrative statistical model for forest tree growth that enables representation of growth phases (the ontogenetic component), the influence of climatic factors, and the growth-level deviations of each tree. On the basis of this model, they show that growth phases are not only defined by an average growth level but also by growth fluctuation amplitudes in response to climatic factors and inter-individual heterogeneity.
Is plant reproductive success simply a reflection of pollinator abundance? Jürgens et al. (pp. 897–912) study pollinator spectra, pollinia transfer and fruit set among three populations of Eulophia alta, a tropical terrestrial orchid. They find that pollinator composition affects reproductive success, because behavioral patterns of certain pollinators influence the performance of other pollinator species and hence plant reproductive success.
Floral development and anatomy of Salvadora and Dobera are investigated by Ronse De Craene and Wanntorp (pp. 913–923) to clarify morphology and the systematic position of the family. They find that the ovary is basically bicarpellate and pseudomonomerous with single locule and parietal placenta, and a short hypanthium is present in Salvadora. Salvadoraceae share morphological synapomorphies with Bataceae and Koeberliniaceae, supporting their close relationship.
Different populations of the xerohalophyte species Atriplex halimus exhibit different levels of resistance to salt and osmotic stress depending on the nature of the osmocompatible solute they accumulate. By examining responses of water-stress-resistant and salt-resistant populations, Hassine et al. (pp. 925–936) suggest that polyamines are involved in the salt excretion process and that ABA contributes to polyamine synthesis, as well as to the conversion from bound/conjugated to the free soluble forms of polyamine. (Featured article in ContentSelect on p. vi.)
The occurrence of nectaries in fruits is restricted to a minority of plant families and consistent reports of their occurrence are not found associated with Fabaceae. Paiva (pp. 937–944) describes the anatomical organization and ultrastructure of the pericarpial nectaries in Erythrina speciosa, and suggests that these small structures mediate a symbiotic relationship between ants and the plant, a role of many extrafloral nectaries.
Stinging nettle, Urtica dioica, is a dioecious herbaceous perennial characterized by rapid growth. Oñate and Munné-Bosch. (pp. 945–956) demonstrate that plant maturity reduces vegetative growth and that these effects are evident both in reproductive and non-reproductive shoots, but particularly in the former. Interestingly, the results are confirmed in plant cuttings, suggesting there is a control at the meristem (local) level.
Fruit set in indeterminate plant species largely depends on the balance between source and sink strength. Using six Capsicum cultivars, Wubs et al. (pp. 957–964) show that those with high individual fruit sink strength have large variations in week-to-week fruit set, and the source–sink ratio threshold for fruit set is higher for large-fruited cultivars than for small-fruited ones. Both individual fruit sink strength and the source–sink threshold for fruit set are thus needed to explain the differences observed between the patterns of fruit set.
Using flow cytometry and chromosome counts for Dianthus broteri, Balao et al. (pp. 965–973) describe the highest diversity of cytotypes known to date within the genus, with five ploidy levels being determined. Some of the cytotypes present remarkable internal genome size variation. The evolution of the complex within the Iberian Peninsula is discussed in terms of autopolyploidy, with primary and secondary contact zones.
Two inbred lines of Sorghum bicolor with contrasting patterns of dormancy release and sprouting behaviour are compared by Rodríguez et al. (pp. 975–985). They show that several ABA signalling genes together with ABI5 protein levels are regulated differently in the two lines, and involvement of these components in the expression of dormancy is related to the developmental stage. (Featured article in ContentSelect on p. vi.)
The costs of height-gain shape the way trees grow. Using diameter–height allometry and plant traits, Kooyman and Westoby (pp. 987–993) show that wood density and diameter contribute almost equally to height-gain in rainforest saplings in subtropical Australia. They suggest that wider diameters prevent main-stem breakage in the short term, and higher wood density provides stronger protective effects through time.
Population growth rates of epiphytic orchids differ among host trees, and ignoring these differences by using spatially averaged matrix models leads to strongly deviating predictions of population size when compared with use of metapopulation models. Winkler et al. (pp. 995–1004) use both types of analysis to study populations of epiphytic orchids, and suggest that a conflict exists between seed survival and colonization in metapopulations, with recolonization events increasing with dispersal distance but local fecundity decreasing.
Counting pollen grains in an accurate, efficient and cost-effective way has long been a logistical problem in the field of plant reproductive biology and ecology. Costa and Yang (pp. 1005–1010) describe a method to count pollen grains automatically from digital images using ImageJ, a Java-based image-processing program, and give a validation of the accuracy of this method.
Potamogeton belongs to the early divergent Potamogetonaceae and possesses inaperturate pollen, a type for which it has been suggested that there is a release of the constraint on tetrad shape. Nunes et al. (pp. 1011–1015) support this view and suggest that the lack of specific sites on which callose deposition is completed during microsporogenesis is a developmental reason for the lack of apertures in the pollen of this species. They also show that the inaperturate pollen of Potamogeton would be better classified as omniaperturate.