From near extinction to diversification by means of a shift in pollination mechanism in the gymnosperm relict Ephedra (Ephedraceae,Gnetales)

Pollination in gymnosperms is usually accomplished by means of wind, but some groups are insect‐pollinated. We show that wind and insect pollination occur in the morphologically uniform genus Ephedra (Gnetales). Based on field experiments over several years, we demonstrate distinct differences between two Ephedra species that grow in sympatry in Greece in pollen dispersal and clump formation, insect visitations and embryo formation when insects are denied access to cones. Ephedra distachya, nested in the core clade of Ephedra, is anemophilous, which is probably the prevailing state in Ephedra. Ephedra foeminea, sister to the remaining species of the genus, is entomophilous and pollinated by a range of diurnal and nocturnal insects. The generalist entomophilous system of E. foeminea, with distinct but infrequent insect visitations, is in many respects similar to that reported for Gnetum and Welwitschia and appears ancestral in Gnetales. The Ephedra lineage is well documented already from the Early Cretaceous, but the diversity declined dramatically during the Late Cretaceous, possibly to near extinction around the Cretaceous–Palaeogene boundary. The clade imbalance between insect‐ and wind‐pollinated lineages is larger than expected by chance and the shift in pollination mode may explain why Ephedra escaped extinction and began to diversify again.     

The phytoplasma associated with purple woodnettle witches'‐broom disease in Taiwan represents a new subgroup of the aster yellows phytoplasma group

In October 2013, a new disease affecting purple woodnettle, Oreocnide pedunculata, plants was found in Miaoli County, Taiwan. Diseased plants exhibited leaf yellowing and witches'‐broom symptoms. Molecular diagnostic tools and electron microscopic cell observation were used to investigate the possible cause of the disease with a specific focus on phytoplasmas. The result of polymerase chain reaction with universal primer pairs indicated that phytoplasmas were strongly associated with the symptomatic purple woodnettles. The virtual restriction fragment length polymorphism (RFLP) patterns and phylogenetic analysis based on 16S rDNA and ribosomal protein, rplV‐rpsC region revealed that purple woodnettle witches'‐broom phytoplasma (PWWB) belongs to a new subgroup of 16SrI and rpI group and was designated as 16SrI‐AH and rpI‐Q, respectively, herein. RFLP analysis based on tuf gene region revealed that the PWWB belongs to tufI‐B, but phylogenetic analysis suggested that PWWB should be delineated to a new subgroup under the tufI group. Taken together, our analyses based on 16S rRNA and rplV‐rpsC region gave a finer differentiation while classifying the subgroup of aster yellows group phytoplasmas. To our knowledge, this is the first report of a Candidatus Phytoplasma asteris‐related strain in 16SrI‐AH, rpI‐Q and tufI‐B subgroup affecting purple woodnettle, and of an official documentation of purple woodnettle as being a new host of phytoplasmas.     

The red imported fire ant,Solenopsis invicta,modifies predation at the soil surface and in cotton foliage

Red imported fire ants, Solenopsis invicta, are generalist predators that can have major impacts on foliar arthropod communities in agricultural systems; however, their effects as predators at the soil surface have not been adequately characterized. We examined the contribution of fire ants to predation at the soil surface and in cotton foliage at two sites and over the course of two field seasons in Georgia, using egg masses of the beet armyworm, Spodoptera exigua. To assess interactions between fire ants and other arthropod species, we also measured the densities of edaphic predators and honeydew‐producing hemipterans at both sites. The sites occurred in different growing regions (Piedmont and Coastal Plain), and allowed us to characterize the importance of fire ants as predators under different climatic and soil conditions. Fire ant suppression decreased egg predation at both field sites, and predation by fire ants at the soil surface was equal to if not greater than that in cotton foliage. However, the impact of fire ants on predation varied between sites, likely due to differences in climate and the composition and activity of the extant arthropod communities. Our study also indicates that fire ant suppression is associated with decreases in the density of honeydew‐producing insects, and increasing abundance of whiteflies on the plants coincided with a decrease in egg predation at the soil surface. This finding suggests the mutualism between ants and whiteflies may lead to a shift in predation intensity from edaphic towards plant‐based food webs.     

The fungal cultivar of leaf‐cutter ants produces specific enzymes in response to different plant substrates

Herbivores use symbiotic microbes to help derive energy and nutrients from plant material. Leaf‐cutter ants are a paradigmatic example, cultivating their mutualistic fungus Leucoagaricus gongylophorus on plant biomass that workers forage from a diverse collection of plant species. Here, we investigate the metabolic flexibility of the ants’ fungal cultivar for utilizing different plant biomass. Using feeding experiments and a novel approach in metaproteomics, we examine the enzymatic response of L. gongylophorus to leaves, flowers, oats or a mixture of all three. Across all treatments, our analysis identified and quantified 1766 different fungal proteins, including 161 putative biomass‐degrading enzymes. We found significant differences in the protein profiles in the fungus gardens of subcolonies fed different plant substrates. When provided with leaves or flowers, which contain the majority of their energy as recalcitrant plant polymers, the fungus gardens produced more proteins predicted to break down cellulose: endoglucanase, exoglucanase and β‐glucosidase. Further, the complete metaproteomes for the leaves and flowers treatments were very similar, while the mixed substrate treatment closely resembled the treatment with oats alone. This indicates that when provided a mixture of plant substrates, fungus gardens preferentially break down the simpler, more digestible substrates. This flexible, substrate‐specific enzymatic response of the fungal cultivar allows leaf‐cutter ants to derive energy from a wide range of substrates, which likely contributes to their ability to be dominant generalist herbivores.     

Phenotypic and molecular analyses of leaf rust resistance in some Iranian wheat genotypes

Host resistance is the most sustainable method of controlling leaf rust which can be achieved through exploring resistance genes by gene postulation and/or molecular markers. The experiment was conducted to postulate leaf rust resistance genes in 20 Iranian wheat cultivars using 10 Puccinia triticina pathotypes. Six sequence-tagged site and sequence-characterised amplified region markers were also used to detect the genes Lr9, Lr10, Lr19, Lr24, Lr26 and Lr37. The genes Lr3a, Lr3Ka, Lr10, Lr15, Lr19, Lr26, Lr28, Lr30 and Lr27 + Lr31 genes were postulated to be present either singly or in combination. The cultivars Toos and Dabira were found to have no effective seedling resistance gene(s); The former was shown to carry none of the genes, while the latter carried Lr10, Lr24 and Lr37 based on molecular markers. It was not possible to postulate resistance genes in Sirvan, Backcross Roshan, Zagross and Chamran cultivars. However, molecular association indicated the presence of Lr19, Lr10 and Lr24 in Sirvan, Backcross Roshan, and Chamran, respectively while none in Zagross.     

Species traits and environmental characteristics together regulate ant‐associated biodiversity

Host‐associated organisms (e.g., parasites, commensals, and mutualists) may rely on their hosts for only a portion of their life cycle. The life‐history traits and physiology of hosts are well‐known determinants of the biodiversity of their associated organisms. The environmental context may strongly influence this interaction, but the relative roles of host traits and the environment are poorly known for host‐associated communities. We studied the roles of host traits and environmental characteristics affecting ant‐associated mites in semi‐natural constructed grasslands in agricultural landscapes of the Midwest USA. Mites are frequently found in ant nests and also riding on ants in a commensal dispersal relationship known as phoresy. During nonphoretic stages of their development, ant‐associated mites rely on soil or nest resources, which may vary depending on host traits and the environmental context of the colony. We hypothesized that mite diversity is determined by availability of suitable host ant species, soil detrital resources and texture, and habitat disturbance. Results showed that that large‐bodied and widely distributed ant species within grasslands support the most diverse mite assemblages. Mite richness and abundance were predicted by overall ant richness and grassland area, but host traits and environmental predictors varied among ant hosts: mites associated with Aphaenogaster rudis depended on litter depth, while Myrmica americana associates were predicted by host frequency and grassland age. Multivariate ordinations of mite community composition constructed with host ant species as predictors demonstrated host specialization at both the ant species and genus levels, while ordinations with environmental variables showed that ant richness, soil texture, and grassland age also contributed to mite community structure. Our results demonstrate that large‐bodied, locally abundant, and cosmopolitan ant species are especially important regulators of phoretic mite diversity and that their role as hosts is also dependent on the context of the interaction, especially soil resources, texture, site age, and area.     

Growth and biomass turnover ofHydrocharis dubia L. cultured under different nutrient conditions

Growth of a floating-leaved plant,Hydrocharis dubia L., was examined under varying nutrient conditions between 0.3 and 30 mgN l⁻¹ total inorganic nitrogen.H. dubia plants cultured under the most nutrient-rich condition showed the highest maximum ramet density (736 m⁻²), the highest maximum biomass (80.4 g dry weight m⁻²), and the highest total net production (185 g dry weight m⁻² in 82 days). Plants under nutrient-poor conditions had a relatively large proportion of root biomass and a small proportion of leaves with a long life span. Compared with other floating-leaved and terrestrial plants, the maximum biomass ofH. dubia was relatively small. This, and the rapid biomass turnover, was related to the short life span of leaves (13.2–18.7 days) and large biomass distribution to leaves.     

The effect of chemical stress on the polypeptide composition of the intercellular fluid of barley leaves

The effect of chemical stress on the polypeptide composition of the intercellular fluid of barley (Hordeum vulgare L.) and tomato (Lycopersicon esculentum Mill.) leaves has been studied. In some dicotyledonous plant species, including tomato, exposure to chemical stress leads to the denovo synthesis of intercellular proteins known as pathogenesis-related proteins which have been implicated to be part of a defence mechanism. In barley, however, no such changes in the polypeptide composition of the intercellular fluid could be detected. On the other hand, similar stress conditions induce in barley a strong accumulation of mRNA encoding leaf-specific thionins. These barley thionins represent a novel class of cell-wall proteins toxic to phytopathogenic fungi and are possibly involved in the defence mechanism. These proteins could not be detected in tomato plants. In contrast to the pathogenesis-related proteins of dicotyledonous plants, the leaf-specific thionins of barley are not present in the intercellular fluid of leaves. These results indicate that barley may have evolved a different mechanism to cope with the presence of stress.Abbreviations PAGE polyacrylamide gel electrophoresis - PR pathogenesis-related - SDS sodium dodecyl sulfate     

Separating the contribution of the upper and lower mesophyll to photosynthesis in Zea mays L. leaves

The appearance of transverse sections of maize leaves indicates the existence of two airspace systems serving the mesophyll, one connected to the stomata of the upper epidermis and the other to the stomata of the lower surface, with few or no connections between the two. This study tests the hypothesis that the air-space systems of the upper and lower mesophyll are separated by a defined barrier of measurable conductance. A mathematical procedure, based on this hypothesis, is developed for the quantitative separation of the contributions made by the upper and lower halves of the mesophyll to carbon assimilation using gasexchange data. Serial paradermal sections and three-dimensional scanning-electron-microscope images confirmed the hypothesis that there were few connections between the two air-systems. Simultaneous measurements of nitrous-oxide diffusion across the leaf and of transpiration from the two surfaces showed that the internal conductance was about 15% of the maximum observed stomatal conductance. This demonstrates that the poor air-space connections, indicated by microscopy, represent a substantial barrier to gas diffusion. By measuring the CO₂ and water-vapour fluxes from each surface independently, the intercellular CO₂ concentration (c _i) of each internal air-space system was determined and the flux between them calculated. This allowed correction of the apparent CO₂ uptake at each surface to derive the true CO₂ uptake by the mesophyll cells of the upper and lower halves of the leaf. This approach was used to analyse the contribution of the upper and lower mesophyll to CO₂ uptake by the leaf as a whole in response to varying light levels incident on the upper leaf surface. This showed that the upper mesophyll was light-saturated by a photon flux of approx. 1000 mol·m^-2·s^-1 (i.e. about one-half of full sunlight). The lower mesophyll was not fully saturated by photon fluxes of nearly double full sunlight. At low photon fluxes the c _i of the upper mesophyll was significantly less than that of the lower mesophyll, generating a significant upward flux of CO₂. At light levels equivalent to full sunlight, and above, c _i did not differ significantly between the two air space systems. The physiological importance of the separation of the air-space systems of the upper and lower mesophyll to gas exchange is discussed.Abbreviations and symbols A net leaf CO₂ uptake rate - A _upper ^app. and A _lower ^app. net rates of CO₂ uptake across the upper and lower surfaces - A _upper and A _lower derived net rates of CO₂ uptake by the upper and lower mesophyll - A _upward net flux of CO₂ from the lower to upper mesophyll - c _a, c _{a, upper} and c _{a, lower} the CO₂ concentrations in the air around the leaf above the upper surface and below the lower surface - c _N2O the concentration of N₂O in the air around the leaf - c _i, c _{i, upper} and c _{i, lower} the mesophyll intercellular CO₂ concentration of the whole leaf, the upper mesophyll and the lower mesophyll - g _i leaf internal conductance to CO₂ - g _s, g _{s, lower} and g _{s, upper} the stomatal conductance of the whole leaf, the lower surface and the upper surface - g the total conductance across the leaf - Q the photosynthetically active photon flux density