Azospirillum brasilense ameliorates the response of Arabidopsis thaliana to drought mainly via enhancement of ABA levels

Production of phytohormones is one of the main mechanisms to explain the beneficial effects of plant growth‐promoting rhizobacteria (PGPR) such as Azospirillum sp. The PGPRs induce plant growth and development, and reduce stress susceptibility. However, little is known regarding the stress‐related phytohormone abscisic acid (ABA) produced by bacteria. We investigated the effects of Azospirillum brasilense Sp 245 strain on Arabidopsis thaliana Col‐0 and aba2‐1 mutant plants, evaluating the morphophysiological and biochemical responses when watered and in drought. We used an in vitro‐grown system to study changes in the root volume and architecture after inoculation with Azospirillum in Arabidopsis wild‐type Col‐0 and on the mutant aba2‐1, during early growth. To examine Arabidopsis development and reproductive success as affected by the bacteria, ABA and drought, a pot experiment using Arabidopsis Col‐0 plants was also carried out. Azospirillum brasilense augmented plant biomass, altered root architecture by increasing lateral roots number, stimulated photosynthetic and photoprotective pigments and retarded water loss in correlation with incremented ABA levels. As well, inoculation improved plants seed yield, plants survival, proline levels and relative leaf water content; it also decreased stomatal conductance, malondialdehyde and relative soil water content in plants submitted to drought. Arabidopsis inoculation with A. brasilense improved plants performance, especially in drought.     

Wavelength dependence of the fluorescence emission under conditions of open and closed Photosystem II reaction centres in the green alga Chlorella sorokiniana

The fluorescence emission characteristics of the photosynthetic apparatus under conditions of open (F₀) and closed (F_M) Photosystem II reaction centres have been investigated under steady state conditions and by monitoring the decay lifetimes of the excited state, in vivo, in the green alga Chlorella sorokiniana. The results indicate a marked wavelength dependence of the ratio of the variable fluorescence, F_V = F_M − F₀, over F_M, a parameter that is often employed to estimate the maximal quantum efficiency of Photosystem II. The maximal value of the F_V/F_M ratio is observed between 660 and 680 nm and the minimal in the 690–730 nm region. It is possible to attribute the spectral variation of F_V/F_M principally to the contribution of Photosystem I fluorescence emission at room temperature. Moreover, the analysis of the excited state lifetime at F₀ and F_M indicates only a small wavelength dependence of Photosystem II trapping efficiency in vivo.     

SVCT2 transporter expression is post‐natally induced in cortical neurons and its function is regulated by its short isoform

Different studies have demonstrated the importance of micronutrients, such as vitamins, for normal adult brain function and development. Vitamin C is not synthesized in the brain, but high levels are detected in this organ because of the existence of specific uptake mechanisms, which concentrate ascorbic acid from the bloodstream to the cerebrospinal fluid and then into neurons and glial cells. Two different isoforms of sodium–vitamin C cotransporters (SVCT1 and SVCT2) have been cloned. SVCT2 expression has been observed in the adult hippocampus and cortical neurons by in situ hybridization. In addition, the localization of SVCT2 in the rat fetal brain has been studied by immunohistochemistry and in situ hybridization, demonstrating that SVCT2 is highly expressed in the ventricular and subventricular areas of the brain cortex. However, there are currently no immunohistochemical data regarding SVCT2 expression and function in the post‐natal brain. Therefore, we analyzed SVCT2 expression in the developing brain cortex of mice, and demonstrated an increase in SVCT2 mRNA in mice at 1–15 days of age. The expression of a short isoform, SVCT2sh, was also detected within the same period. SVCT2 expression was concentrated in neurons within the inner layer of the brain cortex. Both SVCT2 isoforms were coexpressed in N2a cells to obtain functional data. Fluorescence resonance energy transfer analysis revealed a molecular interaction between SVCT2wt and SVCT2sh. Finally, differences in transport ratios suggested that SVCT2sh expression inhibited ascorbic acid uptake in N2a cells when both isoforms were coexpressed.

     

The interplay between multiple predators and prey colour divergence

Evolutionary divergence in the coloration of toxic prey is expected when geographic variation in predator composition and behavior favours shifts in prey conspicuousness. A fundamental prediction of predator‐driven colour divergence is that the local coloration should experience lower predation risk than novel prey phenotypes. The dorsal coloration of the granular poison frog varies gradually from populations of conspicuous bright red frogs to populations of dull green and relatively cryptic frogs. We conducted experiments with clay models in four populations to examine the geographic patterns of taxon‐specific predation. Birds avoided the local phenotype while lizards consistently selected for decreased conspicuousness and crab predation did not depend on frog coloration. Importantly, birds and lizards favoured low conspicuousness in populations where relatively cryptic green morphs have evolved. This study provides evidence for the interplay among distinct selective pressures, from multiple‐predator taxa, acting on the divergence in protective coloration of prey species. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 580–589.