Ulvan, a sulfated polysaccharide from green algae, activates plant immunity through the jasmonic acid signaling pathway.

The industrial use of elicitors as alternative tools for disease control needs the identification of abundant sources of them. We report on an elicitor obtained from the green algae Ulva spp. A fraction containing most exclusively the sulfated polysaccharide known as ulvan-induced expression of a GUS gene placed under the control of a lipoxygenase gene promoter. Gene expression profiling was performed upon ulvan treatments on Medicago truncatula and compared to phytohormone effects. Ulvan induced a gene expression signature similar to that observed upon methyl jasmonate treatment (MeJA). Involvement of jasmonic acid (JA) in ulvan response was confirmed by detecting induction of protease inhibitory activity and by hormonal profiling of JA, salicylic acid (SA) and abscisic acid (ABA). Ulvan activity on the hormonal pathway was further consolidated by using Arabidopsis hormonal mutants. Altogether, our results demonstrate that green algae are a potential reservoir of ulvan elicitor which acts through the JA pathway.

Physiological and transcriptomic aspects of urea uptake and assimilation in Arabidopsis plants.

Urea is the major nitrogen (N) form supplied as fertilizer in agriculture, but it is also an important N metabolite in plants. Urea transport and assimilation were investigated in Arabidopsis (Arabidopsis thaliana). Uptake studies using (15)N-labeled urea demonstrated the capacity of Arabidopsis to absorb urea and that the urea uptake was regulated by the initial N status of the plants. Urea uptake was stimulated by urea but was reduced by the presence of ammonium nitrate in the growth medium. N deficiency in plants did not affect urea uptake. Urea exerted a repressive effect on nitrate influx, whereas urea enhanced ammonium uptake. The use of [(15)N]urea and [(15)N]ammonium tracers allowed us to show that urea and ammonium assimilation pathways were similar. Finally, urea uptake was less efficient than nitrate uptake, and urea grown-plants presented signs of N starvation. We also report the first analysis, to our knowledge, of Arabidopsis gene expression profiling in response to urea. Our transcriptomic approach revealed that nitrate and ammonium transporters were transcriptionally regulated by urea as well as key enzymes of the glutamine synthetase-glutamate synthase pathway. AtDUR3, a high-affinity urea transporter in Arabidopsis, was strongly up-regulated by urea. Moreover, our transcriptomic data suggest that other genes are also involved in urea influx.

New approach to measure protein binding based on a parallel artificial membrane assay and human serum albumin.

We report here a new, label-free approach to measure serum protein binding constants. The assay is able to measure HSA K d values in the milli-molar to micromolar range. The protein is not immobilized on any surface and the assay self-corrects for nonspecific adsorption. No mass balance is required to get accurate binding constants and it is not necessary to wait for equilibrium to extract the binding constant. The assay runs in a 96-well format using commercially available parts and is, therefore, relatively easy to implement and automate. As the chemical membranes used are not water permeable, there is no volume change due to the osmotic pressure and pretreatment (soaking) is not necessary. The concept can potentially be extended to other proteins and could thus serve as a label-free technique for general binding constant measurements.

High-throughput lipophilicity measurement with immobilized artificial membranes.

We report on a new, high-throughput assay designed to measure octanol/water partition coefficients in early drug discovery. The assay is carried out in 96-well microtiterplates and measures the diffusion of compounds between two aqueous compartments separated by a thin octanol liquid layer. Octanol/water partition coefficients are derived from the apparent permeability (P(a)) values using a calibration curve. The assay can measure partition coefficients within the range -2 to + 8; thus, a dynamic range of 10 log units can be covered in one single run. Unlike chromatographic methods, the technology is not restricted to neutral and weakly basic compounds, and, as no stationary phase is involved, the data can be strictly compared with values obtained from traditional methods such as shake-flask/HPLC or dual-phase potentiometric titration.

The algal polysaccharide carrageenans can act as an elicitor of plant defence.

• Effects of two algal polysaccharides, laminarin and carrageenans, on defence responses and signalling in tobacco plants is presented. A possible role as defence elicitors is important in the context of the use of algal extracts as plant protectants. • The effect of the extracts was assessed after infiltration of tobacco leaves, and compared to the effect of a known elicitor of Phytophthora parasitica var. nicotianae(Ppn). • Of the two algal polysaccharides, only carrageenans efficiently induced signalling and defence gene expression in tobacco leaves, as observed with Ppn elicitor. λ-carrageenan, with its high sulphate content, proved the most active. Defence genes encoding sesquiterpene cylase, chitinase and proteinase inhibitor were induced locally, and the signalling pathways mediated by ethylene, jasmonic acid and salicylic acid, were triggered. Some effects lasted for at least a week. • λ-Carrageenan can elicit an array of plant defence responses, possibly through an effect of its high sulphate content. This helps clarify the mechanism of plant protection by algal extracts.