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Pyridine nucleotides are essential for electron transport and serve as co-factors in multiple metabolic processes in a variety of organisms. Hashida et al. (pp. 819–824) review progress in the developmental and stress-related roles of genes associated with NAD biosynthesis in plants. Special attention is given to assessments of cellular impacts through the modulation of NAD and NADP biosynthesis.
Life form, mating system and seed dispersal are important adaptive traits of plants. Yan et al. (pp. 825–834) describe how these traits influence the population genetic structure of M. ruthenica and M. lupulina, and emphasize their main effect on shaping genetic structure.
Isolation from pollen exchange between fragmented patches of L. borealis and the lack of compatible mates within them compromise reproductive success and prospects for recovery of this rare, clonal, self-incompatible plant. Scobie and Wilcock (pp. 835–846) show that the principal pollinators are small flies and pollen dispersal is limited, and that compatible mates must be situated in close proximity for successful seed production.
Porter et al. (pp. 847–858) reveal that Carica papaya's response to touch includes petiole cork outgrowths and decreased anthocyanin levels. However, only a few touch-regulated gene homologues were identified. The novel phenotypes and potentially fewer touch-regulated genes suggest that this tropical fruit tree, the fifth angiosperm to be sequenced, may serve as a complementary model for thigmomorphogenesis. (Featured article in ContentSelect on p. v.)
The major form of carbon storage in the stems of wheat is water-soluble carbohydrates (WSC; principally fructan and sucrose), which are later remobilized for grain filling. Scofield et al. (pp. 859–868) show that some starch also accumulates in stem parenchyma cells around anthesis, but decreases a few days later. The starch storage precedes the WSC, suggesting that it fulfils a different role.
More than six patterns of tetrasporic female gametophyte development have been described in angiosperms; however, the developmental basis for transitions among each of these ontogenies has never been explored within a phylogenetic context. Madrid and Friedman (pp. 869–884) examine female gametophyte development in Piper peltatum, and use these data to reconstruct the specific developmental processes responsible for female gametophyte structural diversification in the Piperaceae.
Using microsatellite markers, Byars et al. (pp. 885–899) examine the genetic structure of populations of Poa hiemata across altitudinal gradients in an alpine zone. The patterns of genetic variation suggest higher rates of gene flow among sites at similar altitudes than along vertical transects, a process that could assist adaptation to altitude: levels of gene flow along transects appear insufficient to prevent adaptive changes in morphological traits.
A nutrient addition experiment conducted by Ryan et al. (pp. 901–911) reveals that Ptilotus polystachyus, a perennial herb native to Australia, grows extremely well under low phosphorus conditions. When high levels of phosphorus are applied, P. polystachyus appears unable to down-regulate phosphorus uptake and concentrations of phosphorus in shoots approach 4% of dry weight; however, no symptoms of phosphorus toxicity are apparent.
A study of an agronomically relevant forage system by Frankow-Lindberg et al. (pp. 913–921) reveals that species diversity produces a strong positive yield effect, as well as reducing invasion by unsown species. Introducing a wide genetic diversity of two of the species involved had little impact on these ecosystem properties.
Excess copper is toxic to most plants and can cause a wide range of deleterious effects. Zhang et al. (pp. 923–930) use a proteomic approach to analyse Cu-stress-induced changes in the expression of low-molecular-weight proteins in germinating rice seed embryos. Thirteen of the proteins identified, including a metallothionein-like protein, a membrane-associated protein-like protein and a resistance protein, were upregulated by Cu stress. (Featured article in ContentSelect on p. v.)
Manganese hyperaccumulation is manifested in a small group of angiosperms that occur mainly in the Western Pacific region. Fernando et al. (pp. 931–939) screen selected eastern Australian species by analysing herbarium leaf-tissue samples. The resultant data reveal at least five new Mn hyperaccumulators, and support the hypothesis that foliar Mn levels may potentially be useful in resolving certain taxa. (Featured article in ContentSelect on p. vi.)
Only a few studies have investigated heritability in pollen performance and they have shown conflicting results. Using experimental crosses, Lankinen et al. (pp. 941–950) find that heritability and evolvability for pollen-tube growth rate are relatively high in a population of Collinsia heterophylla.
How does flower morphology change during the evolution of self-fertilization? Vallejo-Marín and Barrett (pp. 951–962) investigate flower morphology in tristylous Eichhornia paniculata and demonstrate that the transition to selfing is initiated through a reduction in the distance between sex organs. Plants display developmental instability in the production of ‘selfing flowers’ and this plasticity enables dynamic control of mating in uncertain environments. (Featured article in ContentSelect on p. vi.)
Polyploidy has long been recognized as an important force in plant evolution. Kolář et al. (pp. 963–974) investigate cytotype distribution in a taxonomically challenging diploid–polyploid complex, Knautia arvensis, in Central Europe. They find both primary and secondary contact zones and ploidy-specific reproductive barriers. The results indicate that the species provides a unique model system for studying evolutionary dynamics and cytotype interactions under natural conditions.
RPB2 gene evolution in the genus Hordeum is characterized by Sun et al. (pp. 975–983), and the sequences are used to reconstruct the phylogeny of the genus. They reveal that miniature inverted-repeat terminal elements and large indels have shaped the RPB2 loci between the Xu and H, I and Xa genomes. Maximum-parsimony analysis demonstrates that the four genomes can be subdivided into two groups.
The history of the expansion of Acrocentron, one of the largest sections of Centaurea, through the Mediterranean is investigated by Font et al. (pp. 985–997) who find that radiation followed two waves. Firstly in the late-Miocene, from Turkey to the Iberian Peninsula by the south, landmarked by relictic taxa in Sicily and North Africa, and secondly in the Holocene from the north Balkans along Eurasia, from Central Iberia to Kazakhstan.