Mechanical improvements for Arabidopsis guard cell impalement. (A) Double-barrelled microelectrodes pulled with settings for Vicia (above) and for Arabidopsis (below), in the latter case showing a 1–1.5o taper to the final 10 μm of the tip. The extreme tips of both microelectrodes are below the resolution of the light microscope. Scale bars, 10 μm. (B) A custom-built brace with a fixed clamp (fc) for one amplifier headstage and a second, adjustable clamp (ac) provided by a Narashige C2 micromanipulator. The entire brace is fixed to the lateral, rack-and-pinion coarse movement of a Huxley-type micromanipulator visible behind. Scale bar, 1 cm. (C) Halfcells of the Ag|AgCl-KCl type constructed (left) using 0.5 mm diameter Ag wire soldered to a 2-mm diameter socket threaded in a PTFE sleeve and fitted with silicon and glass tubing, and (right) using 0.5 mm diameter Ag wire soldered to a 2-mm diameter socket and press-fit with a silicon plug behind the tip segment of a 2-ml graduated polypropylene pipette tip. Scale bar, 1 cm. When backfilled with KCl electrolyte, the halfcells weigh 5.5 g (left) and 0.6 g (right). For general details of halfcell construction, see .