Woody plants in boreal to arctic environments and high mountains survive prolonged exposure to temperatures below -40°C and minimum temperatures below -60°C, and laboratory tests show that many of these species can also survive immersion in liquid nitrogen at -196°C. Studies of biochemical changes that occur during acclimation, including recent proteomic and metabolomic studies, have identified changes in carbohydrate and compatible solute concentrations, membrane lipid composition, and proteins, notably dehydrins, that may have important roles in survival at extreme low temperature (ELT). Consideration of the biophysical mechanisms of membrane stress and strain lead to the following hypotheses for cellular and molecular mechanisms of survival at ELT: (1) Changes in lipid composition stabilize membranes at temperatures above the lipid phase transition temperature (-20 to -30°C), preventing phase changes that result in irreversible injury. (2) High concentrations of oligosaccharides promote vitrification or high viscosity in the cytoplasm in freeze-dehydrated cells, which would prevent deleterious interactions between membranes. (3) Dehydrins bind membranes and further promote vitrification or act stearically to prevent membrane-membrane interactions.

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Mid-domain effect (MDE) models predict that the random placement of species' ranges within a bounded geographical area leads to increased range overlap and species richness in the center of the bounded area. These models are frequently applied to study species-richness patterns of macroorganisms, but the MDE in relation to microorganisms is poorly understood. In this study, we examined the characteristics of the MDE in richness patterns of ectomycorrhizal (EM) fungi, an ecologically important group of soil symbionts. We conducted intensive soil sampling to investigate overlap among species ranges and the applicability of the MDE to EM fungi in four temperate forest stands along an elevation gradient on Mount Fuji, Japan. Molecular analyses using direct sequencing revealed 302 EM fungal species. Of 73 EM fungal species found in multiple stands, 72 inhabited a continuous range along the elevation gradient. The maximum overlap in species range and the highest species richness occurred at elevations in the middle of the gradient. The observed richness pattern also fit within the 95% confidence interval of the mid-domain null model, supporting the role of the MDE in EM fungal richness. Deviation in observed richness from the mean of the mid-domain null estimation was negatively correlated with some environmental factors, including precipitation and soil C/N, indicating that unexplained richness patterns could be driven by these environmental factors. Our results clearly support the existence of microbial species' ranges along environmental gradients and the potential applicability of the MDE to better understand microbial diversity patterns.

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Background Arabinogalactan proteins (AGPs) are complex proteoglycans of the cell wall found in the entire plant kingdom and in almost all plant organs. AGPs encompass a large group of heavily glycosylated cell-wall proteins which share common features, including the presence of glycan chains especially enriched in arabinose and galactose and a protein backbone particularly rich in hydroxyproline residues. However, AGPs also exhibit strong heterogeneities among their members in various plant species. AGP ubiquity in plants suggests these proteoglycans are fundamental players for plant survival and development. Scope In this review, we first present an overview of current knowledge and specific features of AGPs. A section devoted to major tools used to study AGPs is also presented. We then discuss the distribution of AGPs as well as various aspects of their functional properties in root tissues and pollen tubes. This review also suggests novel directions of research on the role of AGPs in the biology of roots and pollen tubes.

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The scaling of respiratory metabolism with body mass is one of the most pervasive phenomena in biology. Using a single allometric equation to characterize empirical scaling relationships and to evaluate alternative hypotheses about mechanisms has been controversial. We developed a method to directly measure respiration of 271 whole plants, spanning nine orders of magnitude in body mass, from small seedlings to large trees, and from tropical to boreal ecosystems. Our measurements include the roots, which have often been ignored. Rather than a single power-law relationship, our data are fit by a biphasic, mixed-power function. The allometric exponent varies continuously from 1 in the smallest plants to 3/4 in larger saplings and trees. Therefore, our findings support the recent findings of Reich et al. [Reich PB, Tjoelker MG, Machado JL, Oleksyn J (2006) Universal scaling of respiratory metabolism, size, and nitrogen in plants. Nature 439:457-461] and West, Brown, and Enquist [West GB, Brown JH, Enquist BJ (1997) A general model for the origin of allometric scaling laws in biology. Science 276:122 -126.]. The transition from linear to 3/4-power scaling may indicate fundamental physical and physiological constraints on the allocation of plant biomass between photosynthetic and nonphotosynthetic organs over the course of ontogenetic plant growth.

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Background and aims Silicon (Si) in plants provides structural support and improves tolerance to diseases, drought and metal toxicity. Shoot Si concentrations are generally considered to be greater in monocotyledonous than in non-monocot plant species. The phylogenetic variation in the shoot Si concentration of plants reported in the primary literature has been quantified. Methods Studies were identified which reported Si concentrations in leaf or non-woody shoot tissues from at least two plant species growing in the same environment. Each study contained at least one species in common with another study. Key results Meta-analysis of the data revealed that, in general, ferns, gymnosperms and angiosperms accumulated less Si in their shoots than non-vascular plant species and horsetails. Within angiosperms and ferns, differences in shoot Si concentration between species grouped by their higher-level phylogenetic position were identified. Within the angiosperms, species from the commelinoid monocot orders Poales and Arecales accumulated substantially more Si in their shoots than species from other monocot clades. Conclusions A high shoot Si concentration is not a general feature of monocot species. Information on the phylogenetic variation in shoot Si concentration may provide useful palaeoecological and archaeological information, and inform studies of the biogeochemical cycling of Si and those of the molecular genetics of Si uptake and transport in plants.

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