Light affects the flux of Ca2+ from excised tomato leaves within four seconds

The flux of Ca²⁺ from excised tomato leaves, conditioned in100 mM KCI for 60 min, was shown to be affected by turning anincandescent light (32 µmol m^–2 s^–1) on oroff. Calcium concentrations were measured with a single junctioncombination electrode connected to a high impedence electrometeramplifier interfaced with a microcomputer. Net Ca²⁺ fluxes fromexcised leaves 30 s prior to and 30 s after turning on the lightwere 68 and 122pmol g ^–1 dry weight s ^–1 respectively.The Ca²⁺ fluxes for the 30 s prior to and 30 s after turningoff the light were 113 and 51 pmol g^–1 dry weight s^–1respectively. Close examination of the first 10 s after thelight was turned off showed that there was a 4 s delay in theflux of Ca²⁺ . The heat given off by the incandescent bulb hadno effect on Ca²⁺ flux during these short time periods. Theeffect of light on the Ca²⁺ flux was evident for at least 2h after the initial treatment. Key words: Ca²⁺, signalling, light, tomato