Do plant mites commonly prefer the underside of leaves?

The adaxial (upper) and abaxial (lower) surfaces of a plant leaf provide heterogeneous habitats for small arthropods with different environmental conditions, such as light, humidity, and surface morphology. As for plant mites, some agricultural pest species and their natural enemies have been observed to favor the abaxial leaf surface, which is considered an adaptation to avoid rain or solar ultraviolet radiation. However, whether such a preference for the leaf underside is a common behavioral trait in mites on wild vegetation remains unknown. The authors conducted a 2-year survey on the foliar mite assemblage found on Viburnum erosum var. punctatum, a deciduous shrub on which several mite taxa occur throughout the seasons, and 14 sympatric tree or shrub species in secondary broadleaf-forest sites in Kyoto, west–central Japan. We compared adaxial–abaxial surface distributions of mites among mite taxa, seasons, and morphology of host leaves (presence/absence of hairs and domatia). On V. erosum var. punctatum, seven of 11 distinguished mite taxa were significantly distributed in favor of abaxial leaf surfaces and the trend was seasonally stable, except for Eriophyoidea. Mite assemblages on 15 plant species were significantly biased towards the abaxial leaf surfaces, regardless of surface morphology. Our data suggest that many mite taxa commonly prefer to stay on abaxial leaf surfaces in wild vegetation. Oribatida displayed a relatively neutral distribution, and in Tenuipalpidae, the ratio of eggs collected from the adaxial versus the abaxial side was significantly higher than the ratio of the motile individuals, implying that some mite taxa exploit adaxial leaf surfaces as habitat.     

Fungal entomopathogens as endophytes: can they promote plant growth?

Two experimental replicates were conducted to test whether strains of Beauveria brongniartii (BIPESCO2 and 2843) and Metarhizium brunneum (BIPESCO5) can endophytically colonise Vicia faba plants and improve their growth by comparing them with an endophytic strain of B. bassiana (NATURALIS^®). The plants were inoculated through foliar spray and the effect of inoculation on plant height, leaf pair number, fresh root and shoot weights was measured at 7 and 14 days post inoculation (dpi). Endophytic colonisation of different plant parts with the tested fungal strains were confirmed 7 and 14?dpi through re-isolation of inoculated fungi onto selective media and subsequent Simple Sequence Repeat (SSR) marker-based genetic identification. All tested strains were able to endophytically colonise leaves, stems, and even roots of inoculated plants 7 and 14?dpi, but per cent colonisation varied significantly among strains and plant parts within each sampling date. Foliar inoculation of plants with the tested strains increased plant height, leaf pair number, fresh shoot and root weights; however the increase was not always consistent across sampling dates in both experimental replicates. This study provides the first evidence for the endophytic colonisation of plants with two strains of B. brongniartii, an important biocontrol agent of Melolontha melolontha and other scarab beetles in several European countries, and thus extends previous reports on the ability of entomopathogenic fungi to act as endophytes. It also presents possible explanations for the lack of consistency in the plant growth promotion obtained by the foliar inoculation of entomopathogenic fungi.     

Do rivers function as corridors for plant dispersal?

Abstract. We evaluated the importance of dispersal for species frequencies and distribution by comparing dispersal properties of vascular plant species with their frequencies along river banks. We assumed that species with long-floating seeds would be more frequent than species with short-floating seeds. We compiled data on frequencies of vascular plants and their dispersal properties from ten rivers in northern Sweden and compared these with boreal forests and grasslands in the same region. In all rivers, but in none of the reference areas, there was a positive relationship between floating capacity and frequency of species. A comparison of floating capacity between species with and without certain dispersal devices showed that seeds of vegetatively dispersed species had higher floating capacities than other seeds. For other dispersal categories (animal and wind dispersal), floating time did not differ from contrast groups. The results indicate that water dispersal has a certain role in structuring the riparian flora, and provide a basis for explaining species distribution patterns from dispersal characteristics. They also suggest that continuous river corridors are important for maintaining regional biodiversity.     

Do infants associate spiders and snakes with fearful facial expressions?

Do infants preferentially learn to fear stimuli that represent an ancestral danger? This question was addressed using event-related brain potentials in 9-month-old infants (N = 38). In Experiment 1, infants saw fearful and neutral faces gazing towards spiders and flowers. Then spiders and flowers were presented again without faces. Infants responded with increased attention (signaled by the Negative central, Nc component) to stimuli associated with fear. In particular, spiders that were gaze-cued with a fearful as compared to a neutral expression elicited an increased Nc response. In Experiment 2, targets were snakes and fish. Snakes elicited increased Nc amplitude compared to fish irrespective of emotion condition. Results speak to the evolution-based fear-relevance of spiders and snakes. Our findings provide partial support for social fear learning and preparedness theory (Experiment 1) and non-associative accounts of fear acquisition (Experiment 2). We conclude that both kinds of fear acquisition seem to play a role in early human development.     

Do tomatoes on the plant behave as climacteric fruits?

I considered the possibility that changes in fruit photosynthesis obscure the occurrence of the climacteric rise in respiration in tomato fruits attached to the plant. Internal CO₂ and ethylene concentrations in tomatoes ( Lycopersicon esculentum Mill. cv. OH 7814) were analyzed after direct sampling through polyethylene tubes implanted in the external pericarp. Fruits which were shaded with aluminium foil contained up to 60 ml 1⁻¹ CO₂, until the internal ethylene concentration exceeded 1 μl l⁻¹, when CO₂ concentration declined to below 40 ml l⁻¹; the CO₂ concentration in fruits exposed to light only occasionally exceeded 40 ml 1⁻¹. The internal CO₂ concentration of detached fruits first declined and then increased along with ethylene concentration, as expected for the climacteric. Detached green fruits under continuous low photosynthetic photon flux density (100 μmol m⁻² s⁻¹) contained almost no internal CO₂ and produced no CO₂. Changes in photosynthesis and an associated CO₂-generating system in green fruits are thought to obscure the climacteric rise in tomato fruits developing on the plant.     

Do genetic predictors of pain sensitivity associate with persistent widespread pain?

Genetic risk factors for pain sensitivity may also play a role in susceptibility to chronic pain disorders, in which subjects have low pain thresholds. The aim of this study was to determine if proposed functional single nucleotide polymorphisms (SNPs) in the GTP cyclohydrolase (GCH1) and μ opioid receptor (OPRM1) genes previously associated with pain sensitivity affect susceptibility to chronic widespread pain (CWP). Pain data was collected using body manikins via questionnaire at three time-points over a four year period from subjects aged 25-65 in the North-West of England as part of a population based cohort study, EPIFUND. CWP was defined at each time point using standard criteria. Three SNPs forming a proposed "pain-protective" haplotype in GCH1 (rs10483639, rs3783641 and rs8007267) and two SNPs in OPRM1 (rs1777971 (A118G) and rs563649) were genotyped in cases with persistent CWP (CWP present at ≥2 time-points) and controls who were pain-free at all time-points. The expectation-maximisation algorithm was used to estimate haplotype frequencies. The frequency of the "pain-protective" (CAT - C allele of rs10483639, A allele of rs3783641 and T allele of rs8007267) haplotype was compared to the frequency of the other haplotypes between cases and controls using the χ² test. Allele frequencies and carriage of the minor allele was compared between cases and controls using χ² tests for the OPRM1 SNPs. The frequency of the proposed GCH1 "pain-protective" haplotype (CAT) did not significantly differ between cases and controls and no significant associations were observed between the OPRM1 SNPs and CWP. In conclusion, there was no evidence of association between proposed functional SNPs, previously reported to influence pain sensitivity, in GCH1 and OPRM1 with CWP. Further evidence of null association in large independent cohorts is required to truly exclude these SNPs as genetic risk factors for CWP.     

Do detached root-cap cells influence bacteria associated with maize roots?

Abstract. A model rhizosphere has been used which consisted of detached root-cap cells of maize in their surrounding root-cap mucilage on the surface of Noble agar. These cells were co-cultured for periods up to 32 d with eight different bacterial isolates from soil-grown roots and surrounding soil and two laboratory cultures. Cap cells were unaffected by the bacteria. There were five different type-specific responses of the bacteria in proximity to the cap cells. There were, strong growth inhibition ( Rhizobium sp. and Escherichia coli ), strong stimulation ( Pseudomonas fluorescens , laboratory strain), mixed weak inhibition or stimulation ( Pseudomonas fluorescens , field isolate), early inhibition followed by strong stimulation then spore formation ( Bacillus spp.), no effect ( Streptomyces sp. and Cytophaga sp.). It is concluded that detached root-cap cells are actively involved in the establishment of characteristic rhizosphere bacterial microflora.     

Do roots mind the gap?

Aims

Roots need to be in good contact with the soil to take up water and nutrients. However, when the soil dries and roots shrink, air-filled gaps form at the root-soil interface. Do gaps actually limit the root water uptake, or do they form after water flow in soil is already limiting?

Methods

Four white lupins were grown in cylinders of 20 cm height and 8 cm diameter. The dynamics of root and soil structure were recorded using X-ray CT at regular intervals during one drying/wetting cycle. Tensiometers were inserted at 5 and 18 cm depth to measure soil matric potential. Transpiration rate was monitored by continuously weighing the columns and gas exchange measurements.

Results

Transpiration started to decrease at soil matric potential ψ between ?5 kPa and ?10 kPa. Air-filled gaps appeared along tap roots between ψ?=??10 kPa and ψ?=??20 kPa. As ψ decreased below ?40 kPa, roots further shrank and gaps expanded to 0.1 to 0.35 mm. Gaps around lateral roots were smaller, but a higher resolution is required to estimate their size.

Conclusions

Gaps formed after the transpiration rate decreased. We conclude that gaps are not the cause but a consequence of reduced water availability for lupins.     

Do females preferentially associate with males given a better start in life?

A poor start in life owing to a restricted diet can have readily detectable detrimental consequences for many adult life-history traits. However, some costs such as smaller adult body size are potentially eliminated when individuals modify their development. For example, male mosquitofish (Gambusia holbrooki) that have reduced early food intake undergo compensatory growth and delay maturation so that they eventually mature at the same size as males that develop normally. But do subtle effects of a poor start persist? Specifically, does a male''s developmental history affect his subsequent attractiveness to females? Females prefer to associate with larger males but, controlling for body length, we show that females spent less time in association with males that underwent compensatory growth than with males that developed normally.     

Can fungal endophytes fast-track plant adaptations to climate change?

Rapid climate change threatens plant communities. While many studies address the impact of climate change on plants and mechanisms of their resilience to climate stressors, the role of the plant microbiome in aiding plants' adaptation to climate change has been less investigated. We argue here that fungal endophytes, an important constituent of the plant microbiome, may be key to the ability of plants to adapt to climatic stressors. The rapid adaptive response of endophytes coupled with their ability to ‘transfer’ resistance to their hosts may fast-track plants' adaptation to climate change. We briefly review the importance of Class 3 fungal endophytes of terrestrial plants and discuss how they may accelerate adaptations to climate change in crops and natural plant communities and call for efforts directed at improving the understanding of fungal endophyte-facilitated plant health. Such information could aid in devising improved strategies for mitigating climate change effects on plant communities.     

Do high-tannin leaves require more roots?

The well-known deceleration of nitrogen (N) cycling in the soil resulting from addition of large amounts of foliar condensed tannins may require increased fine-root growth in order to meet plant demands for N. We examined correlations between fine-root production, plant genetics, and leaf secondary compounds in Populus angustifolia, P. fremontii, and their hybrids. We measured fine-root (<2mm) production and leaf chemistry along an experimental genetic gradient where leaf litter tannin concentrations are genetically based and exert strong control on net N mineralization in the soil. Fine-root production was highly correlated with leaf tannins and individual tree genetic composition based upon genetic marker estimates, suggesting potential genetic control of compensatory root growth in response to accumulation of foliar secondary compounds in soils. We suggest, based on previous studies in our system and the current study, that genes for tannin production could link foliar chemistry and root growth, which may provide a powerful setting for external feedbacks between above- and belowground processes.     

Can Epichloë endophytes enhance direct and indirect plant defence?

Induced or constitutive production of secondary metabolites is a successful plant defence strategy against herbivores which can be mediated by plant associated micro-organisms. Several grass species can be associated with an endophytic fungus of the genus Epichloë which produces herbivore toxic or deterring alkaloids. Besides these direct defences, herbivorous insects are controlled via indirect plant defence mechanisms by attracting predators. Recent studies indicate that Epichloë endophytes can improve the grass emitted volatile organic compounds towards herbivore deterrence. Due to their defensive mutualistic function, we hypothesize that Epichloë altered plant volatiles can attract aphid predators and contribute to an increased indirect plant defence. With a common garden study, we show that hoverfly (Syrphidae) larvae and pupae were more abundant on endophyte-infected plants compared to uninfected plants. Our results indicate that the Epichloë endophyte provides, besides direct defence (alkaloid), indirect plant defence by improving the plant odor attracting more olfactory foraging aphid predators. Future research is needed in order to understand: (I) whether endophyte-mediated changes in plant volatiles are induced herbivore specific, (II) whether there is a trade-off between endophyte-mediated direct and indirect plant defence, (III) whether the endophyte produces volatiles or induces a change in plant-derived volatiles, (IV) the role of plant signals in endophyte-mediated plant defence.     

A role for haemoglobin in all plant roots?

Abstract. We have found haemoglobin in plant roots whereas previously it has been recorded only in nitrogen fixing nodules of plants. Haemoglobin occurs not only in the roots of those plants that are capable of nodulation but also in the roots of species that are not known to nodulate. We suggest that a haemoglobin gene may be a component of the genome of all plants. The gene structure and sequence in two unrelated families of plants suggests that the plant haemoglobins have had a single origin and that this origin relates to the haemoglobin gene of the animal kingdom. At present we cannot completely rule out the possibility of a horizontal transfer of the gene from the animal kingdom to a progenitor of the dicotyledonous angiosperms but we favour a single origin of the gene from a progenitor organism to both the plant and animal kingdoms. We speculate about the possible functions of haemoglobin in plant roots and put the case that it is unlikely to have a function in facilitating oxygen diffusion. We suggest that haemoglobin may act as a signal molecule indicating oxygen deficit and the consequent need to shift plant metabolism from an oxidative to a fermentative pathway of energy generation.     

Denitrification by plant roots? New aspects of plant plasma membrane-bound nitrate reductase

A specific form of plasma membrane-bound nitrate reductase in plants is restricted to roots. Two peptides originated from plasma membrane integral proteins isolated from Hordeum vulgare have been assigned as homologues to the subunit NarH of respiratory nitrate reductase of Escherichia coli. Corresponding sequences have been detected for predicted proteins of Populus trichocarpa with high degree of identities for the subunits NarH (75%) and NarG (65%), however, with less accordance for the subunit NarI. These findings coincide with biochemical properties, particularly in regard to the electron donors menadione and succinate. Together with the root-specific and plasma membrane-bound nitrite/NO reductase, nitric oxide is produced under hypoxic conditions in the presence of nitrate. In this context, a possible function in nitrate respiration of plant roots and an involvement of plants in denitrification processes are discussed.     

Do strigolactones contribute to plant defence?

Strigolactones are multifunctional molecules involved in several processes outside and within the plant. As signalling molecules in the rhizosphere, they favour the establishment of arbuscular mycorrhizal symbiosis, but they also act as host detection cues for root parasitic plants. As phytohormones, they are involved in the regulation of plant architecture, adventitious rooting, secondary growth and reproductive development, and novel roles are emerging continuously. In the present study, the possible involvement of strigolactones in plant defence responses was investigated. For this purpose, the resistance/susceptibility of the strigolactone‐deficient tomato mutant Slccd8 against the foliar fungal pathogens Botrytis cinerea and Alternaria alternata was assessed. Slccd8 was more susceptible to both pathogens, pointing to a new role for strigolactones in plant defence. A reduction in the content of the defence‐related hormones jasmonic acid, salicylic acid and abscisic acid was detected by high‐performance liquid chromatography coupled to tandem mass spectrometry in the Slccd8 mutant, suggesting that hormone homeostasis is altered in the mutant. Moreover, the expression level of the jasmonate‐dependent gene PinII, involved in the resistance of tomato to B. cinerea, was lower than in the corresponding wild‐type. We propose here that strigolactones play a role in the regulation of plant defences through their interaction with other defence‐related hormones, especially with the jasmonic acid signalling pathway.     

Do plant species with high relative growth rates have poorer chemical defences?

1. Most theories of plant strategies assume the presence of certain 'trade-offs'. One such evolutionary trade-off assumes a decrease in growth rate with increasing investment in chemical defences in species adapted to different levels of habitat fertility.
2. To test this hypothesis, we grew 31 herbaceous species of Asteraceae under controlled conditions of temperature (25 °C), humidity (80%), light (500 μmol m^–2 s^–1) and photoperiod (16 h day^–1) in a modified Hoagland hydroponic solution. The plants grew from seed for 35 days post-germination and were harvested at 14, 21, 28 and 35 days. Relative growth rate (RGR) was calculated as well as a general measure of potential phytochemical toxicity (LC₅₀) using an alcohol extraction of secondary compounds followed by Brine Shrimp bioassay and an assay of total phenolics.
3. The interspecific correlation between RGR and the potential phytochemical toxicity was weak and non-significant ( r _S = 0·12, P = 0·53). The correlation between RGR and total phenolics was weak, positive but significant ( r _S = 0·40, P = 0·03).
4. These results suggest that such an evolutionary trade-off does not exist in this group of Asteraceae.