The relationship between millisecond luminescence and fluorescence in tobacco leaves during the induction period.

Millisecond luminescence and fluorescence, from an intact tobacco (Nicotiana tabacum) leaf, were measured simultaneously during the induction period, as a function of the time. This was accomplished using a luminescence apparatus which separated out the faster luminescence components by subtraction of the accumulated slow-decaying ones. An antiparallel correlation between the two was observed, but only during a part of the induction period starting with the first fluorescence peak where the fluorescence decreases to a quasi plateau level. During this induction phase, luminescence rose very prominently to a maximum while fluorescence decreased. This correlation fits a linear dependence of the luminescence on the extent of RCs openness, as monitored by the photochemical quenching of the fluorescence. It may be concluded that during this induction phase, all other factors, which modulate luminescence (e.g. membrane potential), have become already steady and that the millisecond delayed luminescence reflects the photochemical reaction in an open center (i.e. with QA oxidized). This is further supported by steady-state experiments in thylakoid membranes. No correlations between luminescence and either momentary (F) or maximum (Fm) fluorescence during later induction phases can be pinpointed with confidence, although a trend of a parallel decrease at certain time intervals can be seen occasionally. Likewise, there is no relationship between the two in the very initial induction phase, during the rise of fluorescence from Fo to Fm, as noted earlier. This lack of correlation is presumably due to the dependence of luminescence on other parameters, which vary during these induction phases. The implications of these observations are discussed.