Light driven scattering changes and increased 515 nm absorbance changes associated with fatty acid inhibition of photosynthesis in chlorella

Abstract

1. The size and time of half decay of the 515 nm positive and 475 nm negative light driven absorbance changes in Chlorella was considerably increased by 1 · 10 −4–5 · 10 −4 M lipoic, caprylic and iodoacetic acids and by 1 · 10 −5–8 · 10 −5 M nitrous acid. Salts of these acids at neutral pH, iodoacetamide and HCl did not affect the absorbance changes. 2. The absorbance changes were restored to their original size and photosynthetic CO 2 fixation partially restored on washing the cells free of lipoic acid. 3. Light driven absorbance changes at 350 nm (positive), 405 nm, 425 nm, 450 nm and 648 nm (all negative) were unchanged in magnitude on addition of acid but their decays were slowed. The greater part of the 515-475 nm changes is therefore not due to Chlorophyll b. 4. Addition of 10 −3 M caprylic, lipoic, iodoacetic acids, methyl octonoate and hexyl resorcinol caused slow reversible light driven scattering changes which were not associated with volume changes of the whole cell.