Bio-Optical Inferences from Chlorophyll a Fluorescence: What Kind of Fluorescence Is Measured in Flow Cytometry. (Reannouncement with New Availability Information).

摘要

A comparison is made of the in vivo Chl alpha fluorescence per cell measured by the flow cytometer (F sub cyt) and dark-adapted bulk fluorescence measured in a standard field fluorometer for the marine cryptomonad Chroomonas sp. (clone Chang 2). The bulk fluorescence protocol estimated the levels of the minimum (F sub o) and maximum (F sub max) fluorescence yields that are exhibited depending on the redox state of the photosystem 11 reaction center. Both F sub o and F sub max are known to be functions of cell irradiance history. During the illumination of control samples at growth irradiance (40 micro mol quanta m-2 s-1), F sub o, F sub max, and F sub cyt (EPICS V) all increased by about the same proportion. After exposure to photoinhibiting irradiance (1,700 micro mol quanta m-2 s-1), F sub max decreased and F sub o increased. Parameters of the photosynthesis-irradiance curve verified that photoinhibition had occurred, indicating less activity at all irradiances. In contrast to bulk fluorescence measurements, relative changes in F sub cyt in response to strong-irradiance treatment were much smaller than changes in F sub o and F sub max. We conclude that this is because F sub cyt, is intermediate between F sub o and F sub max. Multiple regression analyses suggest that, under the flow cytometry conditions used, F. exhibits -20% enhancement above F sub o, i.e. an average of 20% of the increase from F sub o to F sub max. Time scales of photosystem 11 primary photochemistry are consistent with this amount of fluorescence enhancement occurring over the residence time of the cell in the laser beam.