Measurement of the fluorescence lifetime of chlorophyll a in vivo.

New measurements have been made of fluorescence lifetime (tau) of chlorophyll a in the algae Chlorella pyrenoidosa, Porphyridium cruentum, Anacystis nidulans, and in spinach chloroplast. tau-values of 0.6 and 0.7 nsec were obtained with green plants. Anacystis and Porphyridium gave a tau of 0.5 nsec. The previously described two stage decay of fluorescence in vivo in these organisms could not be confirmed. This observation could have been caused by a second wave of light emission from the exciting hydrogen lamp (not detected in earlier work). The lifetimes found in this study (calculated, as before, by the method of convolution integrals) were close to those found by other observers for "low" excitation intensities; the value first reported from this laboratory (1.0-1.7 nsec) may have corresponded to "high" excitation intensity.