LIGHT AFFECTS THE FLUX OF CA2+ FROM EXCISED TOMATO LEAVES WITHIN 4 SECONDS

The flux of Ca2+ from excised tomato leaves, conditioned in 100 mM KCl for 60 min, was shown to be affected by turning an incandescent light (32 mu wol m(-2) s(-1)) on or off, Calcium concentrations were measur ed with a single junction combination electrode connected to a high im pedence electrometer amplifier interfaced with a microcomputer. Net Ca 2+ fluxes from excised leaves 30 s prior to and 30 s after turning on the light were 68 and 122 pmol g(-1) dry weight s(-1), respectively. T he Ca2+ fluxes for the 30 s prior to and 30 s after turning off the li ght were 113 and 51 pmol g(-1) dry weight s(-1), respectively. Close e xamination of the first 10 s after the light was turned off showed tha t there was a 4 s delay in the flux of Ca2+. The heat given off by the incandescent bulb had no effect on Ca2+ flux during these short time periods. The effect of light on the Ca2+ flux was evident for at least 2 h after the initial treatment.