Fluorescence characteristics of lyophilized maize chloroplasts suspended in buffer.

Fluorescence transients were measured in lyophilized maize chloroplasts (suspended in Tris-maleate buffer (pH 6.6)) after extraction with heptane. (The fluorescence characteristics before extraction were qualitatively similar to those in the fresh chloroplasts.) The initial fluorescence level (m) in the (dry) heptane-extracted sample remained the same as in the unextracted material, but the variable fluorescence (Am) was drastically diminished. A portion of variable fluorescence, however, could be restored by adding Na2S204. If the heptane extraction was made in the presence of water (wet), the m level was almost as high as (or higher than) the final level (M) of the unextracted sample, and Am was reduced. The " je t " of 02 (that measures the pool size of the intersystem intermediate A) and the "microjet" (that measures the pool size of the reaction center complex E), present in the unextiacted samples, were absent in both types of extracted samples. Some of the above data may be interpreted in a hypothesis in which two quenchers (Q1 and Q2) control the fluorescence (0 -+ P) of chloroplasts--the reduction of Qx being responsible for the rapid and that of Q~ ior the slow fluorescence rise.