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Transglycosylases remodel the plant cell wall during periods of growth or senescence by cutting a polysaccharide and attaching the newly created end to another polysaccharide. Schröder et al. (pp. 197–204) re-interpret the role of the hydrolytic enzyme endo-β-mannanase as a transglycosylase by analogy to the role of xyloglucan endotransglucosylase/hydrolase, the only other known transglycosylase in the cell wall.
Pollination drops of gymnosperms and nectar (mainly of angiosperms) are secretions related to plant reproduction. Although having very different functions they share strong similarities, although with significant differences. Nepi et al. (pp. 205–219) review these similarities and differences in the light of recent advances in the molecular biology and proteomics of these two secretions, emphasizing their biochemical and physiological complexity.
Floral elaiophores, secreting oil as a food-reward to pollinators, are widespread amongst orchids. In the Bifrenaria clade (Maxillariinae sensu lato), Davies and Stpiczyńska (pp. 221–234) show that elaiophores of Rudolfiella and Oncidiinae have similar anatomical organization, but the plastids that they contain are very different: Rudolfiella plastids resemble those in resin-secreting cells of Rhetinantha (Maxillariinae sensu stricto). Along with presence of palisade secretory cells, the observations have phylogenetic implications and support convergent evolution in response to pollinator pressures.
The inhibition of root elongation is the primary symptom of Al toxicity; however, the underlying basis of the process is unclear. Considering the multiple physiological and biochemical functions of pectin in plants, Li et al. (pp. 235–241) demonstrate that Al stress results in the disorganized distribution of homogalacturonan epitopes, which correlates well with Al-induced root growth inhibition in Zea mays.
In wheat, the number of fertile florets per spikelet is associated with ploidy level: 1–2 florets in diploids, 2–3 in tetraploids, and >3 in hexaploids. Shitsukawa et al. (pp. 243–251) demonstrate that the difference in the number of floret primordia in diploid, tetraploid and hexaploid wheats is caused by the heterochronic initiation of floret meristem development from the spikelet meristem.
Jacobs et al. (pp. 253–276) examine fruit and seed anatomy and morphology in 52 Dipsacalean taxa in combination with molecular data. Their phylogenetic analysis supports a close affinity between Lonicera plus Leycesteria and Symphoricarpos plus Triosteum. The results further provide support for a sister relationship of Heptacodium and the Linnina clade as opposed to Heptacodium and the Lonicera clade.
Transgenic Lotus japonicus, expressing the dominant insensitivity allele of the Arabidopsis ethylene receptor gene ETR1, are characterized by Lohar et al. (pp. 277–285). They find that nodule number is significantly increased due to higher infection success and an expanded radial zone of successful nodule initiation. Nodulation sensitivity to nitrate remains unaltered but lateral root numbers decrease, while bacteroid numbers/symbiosomes increase, suggesting early and late symbiosis effects of ethylene. (Featured article in ContentSelect on p. iii.)
Milbau et al. (pp. 287–296) show that seed germination in sub-arctic species will not only be affected by increasing summer temperatures, but also by colder soil temperatures during winter, which are the result of a reduced snow cover. The effects are mainly seen as changes in the timing of germination, whereas final germination percentages are less influenced. (Featured article in ContentSelect on p. iii.)
Nock et al. (pp. 297–306) show that wood density reflects differences in shade-tolerance in six tropical tree species, and that radial gradients are common. The findings suggest that a ‘whole-tree’ view of life history and biomechanics is important for understanding patterns and consequences of radial variation in wood density. Furthermore, the accuracy of estimates of stem biomass and carbon is improved by taking density variations into account.
Carnivorous plants of the genus Nepenthes grow in nutrient-poor, wet and sunny habitats and have evolved specialized traps – the pitchers. Pavlovič et al. (pp. 307–314) report that Nepenthes enhances its rate of photosynthesis as a result of increased nutrient acquisition from prey. So carnivory can provide a competitive advantage over non-carnivorous plants in nutrient-poor habitats.
Growth and maximization of artemisinin concentration in A. annua are manipulated by Davies et al. (pp. 315–323) by changing nutrient application. They find that nitrogen application rate has an optimum for maximal growth, while higher rates have no further effect but reduce artemisinin concentration. Maximization of artemisinin yield (amount per plant) requires optimization of leaf biomass through nitrogen supply. (Featured article in ContentSelect on p. iv.)
Pollen source affects the kernel oil concentration in maize through modifications of both the embryo/kernel ratio and the embryo oil concentration. Tanaka et al. (pp. 325–334) analyse the effects of pollen source on growth of kernel structures, embryo chemical allocation, and on histology of the embryos. The effects on both the embryo/kernel ratio and embryo chemical allocation seem to be related to the early-established sink strengths of the embryo, i.e. sink size and sink activity.
Du et al. (pp. 335–343) provide the first experimental evidence that arbuscular mycorrhizal fungi (AMF) can modify the effects of clonal integration on the plasticity and performance of the clonal species Trifolium repens (white clover) in heterogeneous environments. In particular, AMF may partly replace the effects and benefits of clonal integration in low-nutrient habitats, possibly more so where fungal species-richness is high.
Sun et al. (pp. 345–356) demonstrate that molybdenum regulates the expression of COR genes in ABA-dependent and ABA-independent pathways in winter wheat under low temperatures. Comparison of Mo-efficient and Mo-inefficient winter wheat cultivars suggests that Mo might regulate the ABA-dependent pathway of COR gene expression under low-temperature stress. Notably, the response of the ABA-dependent pathway to Mo is prior to that of the ABA-independent pathway. (Featured article in ContentSelect on p. iv.)