Light-induced rapid absorption changes during photosynthesis

Rapid absorption changes can be induced by short light flashes in Ochromonas danica. The absorption change rises in 10⁻⁴ sec or less and has a half life of 35–40 msec. The complex difference spectrum has positive peaks at 443, 475, 505 and 580 mμ and negative peaks at 490 and 535 mμ.

The absorption change is very sensitive to physical treatments. Heating to 40° for 2 min or sonicating at 10 kcycles for 1 sec completely eliminates the signal.

The absorption change remains unaffected by resuspending the organism in a “starvation” medium or by making the medium anaerobic. The presence of several oxidants or reductants, KCN, and iodoacetamide has no noticeable effects on the absorption changes.

3-(3,4-dichlorophenyl)-1,1-Dimethylurea at 10⁻⁷ and 10⁻⁶M reduces the magnitude of the absorption change by 50 and 75%, respectively. A residual activity (about 20%) persists up to 0.5 mM 3-(3,4-dichlorophenol)-1,1-dimethylurea. 2,4-Dinitrophenol reduces the absorption change and accelerates the decay, whereas carbonyl cyanide m-chlorophenylhydrazone only lengthens the decay. H₂O₂ both reduces the magnitude of the absorption change and lenghtens the decay.