Thermoluminescence in spinach chloroplasts and in Chlorella.

SUMMARY Preilluminated spinach chloroplasts and Chlorella pyrenoidosa, when subjected to a quick temperature jump of about 15 °, emit light. This thermoluminescence is observed both in normal and 3(3,4-dichlorophenyl)-l,l.dimethylurea.treated samples, but is absent when hydroxylamine is added to either of these samples. These results are explained in terms of a oack reaction of System II of photosynthesis. Isolated chloroplasts will emit light when subjected to acid-base pH transitions 1 and salt induced ionic transitions 2'3. In both cases light emission by the chloroplasts requires preillumination. This indicates that the pH and ionic transitions may be acting as a trigger to release stored light energy. We find that with a temperature jump of about 15 °, spinach chloroplasts that have been preilluminated will also emit light. Similar results have been found for the green alga Chlorella pyrenoidosa. The differences between our thermoluminescence experiments and those by Arnold and Sherwood 4 are discussed in this paper. We explain our results in terms of a back reaction of System II leading to light emission. Chlorella was grown as previously described s. Chloroplasts were isolated from spinach by the method outlined in ref. 2. The instrument assembled to measure the thermoluminescence was similar to that used by Mayne and Clayton I for measuring chemi. luminescence. A red cut off filter was placed before the photomultiplier to transmit chlorophyll emission. A 1-cm 2 glass cuvette was placed in a light tight box in front of a photomultiplier (EMI 9558 B). Two small holes were made on top of the box to atiow two hypodermic needles to extend to the bottom of the cuvette. An opening was made on the side of the box for the illumination of the sample. The intensity of the illuminating white light was 3.8.10 s ergs. cm-a • sec-~. The signal from the photomultiplier was displayed on a Tektronic 502 oscilloscope and was recorded on Polaroid 3000 film. The measurements Abbreviation: DCMU, 3(3,4-dichlorophenyl)-l,l-dimethylurea.