Chromatic Transients in the Photosynthesis of a Green Alga.

Abstract

Photosynthesis in the marine alga Ulva lobata was measured amperometrically by a polarized platinum electrode in direct contact with the tissue. Transient variation of O2 evolution occur on alternating exposures to light of certain wave lengths, without intervening dark periods. (Light intensities are adjusted to give equal steady-state rates of photosynthesis.) On passing from 540 m[mu] (absorbed by chlorophylls) to 490 m[mu] (absorbed largely by carotenoids), there is increased O2 evolution, followed by a depression and finally recovery to the steady state. On return to 540 m[mu] there is a depression and quick recovery. Effects similar to those at 490 m[mu] occur also on going from 688 m[mu] to 640 or 650 m[mu] (absorbed by chlorophyll b), with recovery at 688 m[mu] (absorbed by chlorophyll a). It is suggested that light absorption by carotenoids or chlorophyll b produces an enhanced photosynthesis quickly followed by increased O consumption (respiration of newly produced substrates, or photo-oxidation), with later partial recovery. This persists briefly into the chlorophyll a absorption period.