Thermoluminescence and temperature effects on delayed light emission (corrected for changes in quantum yield of fluorescence) in DCMU-treated algae.

( 1 ) The simultaneous measurements of delayed light emission (DLE) and chlorophyll (Chl) fluorescence yield in DCMU$ treated Chlorellu were made in the time range of I to I0 sec at various temperatures from 0 to 50°C. Similar measurements were made for DCMU treated thermophilic strain ofSynechococcus in the temperature range of 0 to 75°C. (2) Using the basic assumption that DLE is produced by the back reaction of primary photoproducts of system 11. and that two such reactions are required for it, a linear relationship between J+12 (where J is energy per unit time available for DLE) and time after illumination was derived. This second-order relationship was confirmed experimentally at several temperatures (T , 5", 10" and 15°C). From these analyses, reaction rate decay constants, at specific temperatures, were calculated. (3) An Arrhenius plot was made for these calculated rate constants. Its slope (8-10 kcal/ mole) agreed well with previous reports; however, it had a region of zero slope which occurred at the physiological temperature of the organisms used. (4) Thermoluminescence or temperature jump delayed light emission (TDLE) was measured using various temperature conditions and it was found that not only the magnitude of the temperature jump (AT), but the initial and final temperatures of the sample were important. For example, a temperature jump of 8°C from 2 to 10°C gave much higher T D L E than from 12 to 20°C. ( 5 ) Many properties e.g., magnitude, temperature dependence and time independence of TDLE could be explained by the DLE decay data (corrected for changes in fluorescence yield) and the kinetic analysis. (6) I t is suggested that, in addition to the back reaction of Z+ (the primary oxidized photoproduct of system 11) with Q(the primary reduced photoproduct of system I I ) , a reducing entity, beyond the sites of DCMU and antimycin a action, is somehow involved in the production of slow DLE. I N T R O D U C T I O N ONE OF the major goals of photosynthesis research is to understand how the electronic excitation energy, absorbed by chlorophyll (Chl) molecules, is converted into chemical energy. After the absorption of light the energy appears in various physical forms. The most immediate form is fluorescence which has a lifetime of 1 0-9 sec [ 1-51. The earliest evidence of a chemical form occurs in 10-2sec[6], the turnover time of the entire electron transport chain. The magnitude of these time differences implies the necessity *This research was supportedby NSFGB 19213 and 14176. t P. J . was supported by U.S.P.H.S. predoctoral traineeship in Biophysics. $Reprint requests should be addressed to Govindjee, Department of Botany, 297 Morrill Hall, University of Illinois, Urbana, Illinois 61801, U S A . $Abbreviations: Chl, chlorophyll; DCMU, 3-(3A-dichlorophenyl)-l .I-dimethylurea; DLE, delayed light emission: TDLE, temperature jump delayed light emission; Q, primary acceptor of electrons of system I I: Z, primary donor of electrons of system 11.