EFFECT OF LIGHT ON THE BIOELECTRIC POTENTIALS OF ISOLATED ELODEA LEAVES

Abstract

The effect of light on electric potentials in isolated Elodea leaves was measured by a Compton quadrant electrometer. Both apical and basal leaves responded to the illumination of a spot at the apex by a large increase of P.D. between apex and base (apex positive), reaching a max. in about 7 min. of 75-100 mv. Under constant illumination the P.D. slowly fell. The fall of P.D. between the apical illuminated spot and the base of the leaf was linear; that is, the effect was transmitted without apparent loss to all regions. Upon cessation of illumination, the P.D. rapidly fell to the low level characteristic of the un-illuminated leaf, in a curve possessing constant individuality. Illumination of a medial spot also caused the apex to become more positive to the base, but to a lesser degree. Illumination of a basal spot caused the base to become positive to the apex; the curve corresponded exactly to the reverse of the curve obtained upon illumination of an apical point. But the regions at apex and base retain the original orientation of P.D., and only that of the middle of the leaf is reversed. Decrease of intensity of illumination seemed to have a small but constant effect, reducing the P.D.; but with increase of intensity no change of P.D. was observed.