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Environmental factors greatly impact plant gene expression and concentrations of cellular metabolites such as sugars and amino acids. Hummel et al. (pp. 1–7) discuss the role of sucrose signalling in the translational control of bZIP11 and the regulation of ribosomal biogenesis in response to metabolic changes and stress conditions.
Nitric oxide (NO) is an indispensable signal molecule involved in various physiological functions, and may regulate the activity of nitrate reductase (NR) in plant roots. Jin et al. (pp. 9–17) show that a low concentration of NO stimulates NR activity of tomato roots, and increasing NO concentration increases NR activity in roots fed with 0·5 mm nitrate but decreases it at 5 mm nitrate. (Featured article in ContentSelect on p. iii.)
Ge et al. (pp. 19–31) demonstrate that the chromosomes belonging to the three different genomes in synthetic Brassica allohexaploids show contrasting stabilities in crosses with Orychophragmus violaceus where chromosomes are eliminated. This is thought to be affected by nucleolar dominance, with only rRNA genes from B. nigra being expressed in all allohexaploids and complex hybrids.
When studying the widespread phenomenon of nectar-robbing and its consequences, Zhang et al. (pp. 33–39) find that attention needs to be paid to the mating system of the host plants. Examining nectar-robbing by Bombus pyrosoma among three sympatric host species of Corydalis, they find that it can have variable effects on female plant reproduction, which can be explained, at least in part, by whether the species is an obligate or facultative outcrosser.
Within the species of Marantaceae characterized by an explosive pollination mechanism, Ley et al. (pp. 41–56) describe four distinct floral syndromes in Africa (approx. 40 species). Their detection of a diverse pollinator fauna, including first records of bird-pollination in these species, and observations of specific adaptations between flowers and pollinators lead to the hypothesis that pollinators have played an important role in the speciation of this family.
Probert et al. (pp. 57–69) report that seed longevity in air-dry storage is correlated with seed structure and climate of origin. Rapid ageing of 195 diverse species indicates that seeds with small embryos from cool, moist regions tend to be shorter-lived than seeds with large embryos from warm, dry regions. This understanding will improve the management of conservation collections. (Featured article in ContentSelect on p. iii.)
In order to gain a better understanding of clonal life-history, Araki et al. (pp. 71–79) explore demography, growth patterns and spatial distributions of ramets within genets for a rhizomatous clonal herb, Convallaria keiskei. Field monitoring of genotypically identified ramets demonstrates that ramet performance regulates genet dynamics and distribution, which are different among genets.
Apomixis may be transferred into sexual populations via the pollen function. Hörandl and Temsch (pp. 81–89) test this hypothesis by experimental crossings of diploid sexual plants and polyploid apomictic pollen donors of the Ranunculus auricomus complex. Flow cytometric seed screening reveals that introgression of apomixis is inhibited by seed abortion and also by induced selfing (mentor effects) of sexual individuals. Sexuality cannot be replaced by apomixis.
The preservation of phytoliths in fossil records makes them a tool to study early plant communities, with ancient types being compared with living morphotypes. Mercader et al. (pp. 91–113) examine samples from 90 species from Mozambique, producing the most extensive phytolith key for any African ecoregion. Local woody species are hypervariable silica producers and their phytolith morphotypes are highly polymorphic; nonetheless, some have taxonomic significance in a number of families and orders.
Ageing effects may be due to dysfunction, but other causes cannot be excluded in plants. Van Dijk (pp. 115–124) shows that in sea beet, Beta vulgaris, a species with a variable life span, there is a decline in seed production and root growth in the last year of life, whatever the life span, but that plants flower about 1·3 days later each year over their whole lifetime. (Featured article in ContentSelect on p. iv.)
Zarrei et al. (pp. 125–142) present phylogenetic analyses for 142 in-group taxa of Gagea and Lloydia (Liliaceae) using nrITS and plastid sequences. The results support the monophyly of Gagea/Lloydia collectively and provide the basis for a new classification of Gagea. Incongruence between plastid and nrITS trees is potentially due to ancient hybridization and/or paralogy of ITS rDNA.
Besnard et al. (pp. 143–160) report a comprehensive phylogeny of the olive genus, and find that polyphyly indicates the necessity of revising the current taxonomic boundaries of Olea. Phylogenetic dating indicates that the main lines of evolution in this genus were promoted by major Tertiary climatic shifts; in particular, diversification within the olive section (characterized by a dense abaxial indumentum) was concomitant with the aridification of Africa in the Late Miocene.
Nuclear genome size variation is studied within a phylogenetic framework in Hieracium subgen. Hieracium (Asteraceae) by Chrtek et al. (pp. 161–178). They find that species of western-European origin have significantly lower genome size than those of eastern-European origin, which correlates with two major phylogenetic clades based on ETS sequences.
Coniferous forests populated polar regions 140–50 million years ago when atmospheric CO2 was at least double that of the present-day. Llorens et al. (pp. 179–188) investigate how the interaction between a CO2-rich atmosphere and variations in daylight might have influenced water use of these conifers. Although plant water-use efficiency is improved by CO2-enrichment, transpiration is relatively insensitive to atmospheric CO2. (Featured article in ContentSelect on p. iv.)
Measuring the aluminium uptake rate across the plasma membrane of intact root cells is crucial for understanding the mechanisms and time course of Al toxicity in plants, requiring high spatial and temporal resolution. Babourina and Rengel (pp. 189–195) find that fluorescent lifetime imaging analysis of the fluorescence of Al–lumogallion complexes can be used to reliably quantify Al uptake in the cytoplasm of intact root cells of Arabidopsis during the initial stages of stress.