The kinetics of P515 in relation to the lipid composition of the thylakoid membrane [Chloroplasts, spinach]

Flash-induced P515 absorbance changes have been studied in dark-adapted chloroplasts isolated from spinach plants grown under two different light intensities. The slow component (reaction 2), normally present in the P515 response of chloroplasts isolated from plants grown at an intensity of 60 W X m-2, was largely reduced in chloroplasts isolated from plants grown at an intensity of 6 W X m-2. This reduction of the slow component in the P515 response appeared to be coincident with an alteration in the lipid composition of the thylakoid membrane. Mainly the ratio monogalactosyldiacylglycerol to digalactosyldiacylglycerol appeared to be altered. In thylakoids from plants grown at 6 W X m-2, the ratio was approximately 35% lower than that of plants grown at 60 W X m-2. The amount of both cytochrome b563 and cytochrome f was largely reduced in chloroplasts isolated from plants grown at low light intensity. These results may indicate a possible correlation between structural organization of the thylakoid membrane and the kinetics of the flash-induced P515 response.