Spatial origin of the extracellular ATP-induced cytosolic calcium signature in Arabidopsis thaliana roots: wave formation and variation with phosphate nutrition.

Extracellular ATP (eATP) increases cytosolic free calcium ([Ca2+ ]cyt ) as a specific second messenger 'signature' through the plasma membrane DORN1/P2K1 receptor. Previous studies revealed a biphasic signature in Arabidopsis thaliana roots that is altered by inorganic phosphate (Pi) deprivation. The relationship between the two phases of the signature and possible wave formation have been tested as a function of Pi nutrition. The bioluminescent aequorin and intensiometric GCaMP3 reporters were used to resolve the spatial origin of the eATP [Ca2+ ]cyt signature in Arabidopsis root tips. Application of eATP only to the root apex allowed [Ca2+ ]cyt wave resolution without the confounding effects of eATP delivery by superfusion. The first apical millimetre of the root generates the first [Ca2+ ]cyt increase by eATP, regardless of nutritional status. The second increase occurs sub-apically in the root hair zone, has some autonomy and is significantly reduced in Pi-starved roots. A significant component of the Pi-replete signature does not require DORN1/P2K1, but Pi-starved roots appear to have an absolute requirement for that receptor. Application of eATP specifically to the root apex provides evidence for cell-to-cell propagation of a [Ca2+ ]cyt wave that diminishes sub-apically. The apex maintains a robust [Ca2+ ]cyt increase (even under Pi starvation) that is the basis of a propagative wave, with implications for the ability of the root's eATP signalling systems to signal systemically. Partial autonomy of the sub-apical region may be relevant to the perception of eATP from microbes. eATP-induced [Ca2+ ]cyt increase may not have always have an obligate requirement for DORN1/P2K1.

Sensing glucose concentrations at GHz frequencies with a fully embedded Biomicro-electromechanical system (BioMEMS).

The progressive scaling in semiconductor technology allows for advanced miniaturization of intelligent systems like implantable biosensors for low-molecular weight analytes. A most relevant application would be the monitoring of glucose in diabetic patients, since no commercial solution is available yet for the continuous and drift-free monitoring of blood sugar levels. We report on a biosensor chip that operates via the binding competition of glucose and dextran to concanavalin A. The sensor is prepared as a fully embedded micro-electromechanical system and operates at GHz frequencies. Glucose concentrations derive from the assay viscosity as determined by the deflection of a 50 nm TiN actuator beam excited by quasi-electrostatic attraction. The GHz detection scheme does not rely on the resonant oscillation of the actuator and safely operates in fluidic environments. This property favorably combines with additional characteristics-(i) measurement times of less than a second, (ii) usage of biocompatible TiN for bio-milieu exposed parts, and (iii) small volume of less than 1 mm3-to qualify the sensor chip as key component in a continuous glucose monitor for the interstitial tissue.