Afterglow thermoluminescence measured in isolated chloroplasts.

The thermoluminescence afterglow (AG) measured in plant leaves originates from the S(2)/S(3)Q(B)(-) charge pair recombination in photosystem II (PSII) initiated by reverse electron flow from stromal reductants to PQ and then to the Q(B) site in PSII centers that are in the S(2)/S(3)Q(B) state. In this study, we show that this luminescence, absent in isolated thylakoid membranes, can be measured in intact chloroplasts that retain their stromal content including the electron acceptor pool (oxidized ferredoxin/NADP(+)) of photosystem I. The properties of the chloroplasts AG emission is similar to the AG in leaves in terms of temperature maximum, period-four modulation, far-red light stimulation, and antimycin A inhibition.