Effects of Linolenic Acid on the Spectral Properties and Picosecond Fluorescence of Pea Chloroplasts

Linolenic acid induces changes in the absorption spectrum and in the picosecond fluorescence of pea chloroplasts. The effects of linolenic acid are dependent on concentration and time. Linolenic acid increases the fluorescence life time of chloroplasts at room temperature. The contribution of the slow fluorescence component relative to the fast component is increased almost 10 fold in the presence of 0.5 m M linolenic acid. The synergistic action of digitonin and linolenic acid increases the ratio of “closed” to “open” traps in the photosynthetic units. Upon addition o f 0.5 m M linolenic acid there are increases in absorbance at 676 and 436 nm, and decreases in absorbance at 705 and 496 nm. Some of the spectral changes have a biphasic character, they reach a maxi um um after about 30 min then start to reverse. Based on the spectral changes at 496 and 705 nm it appears that linolenic acid has at least two effects, e. it modifies the thylakoid membrane and secondarily decreases the concentration of P 700, respectively.