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The glow curve of chloroplasts excited by continuous light of high intensity (500 W · m−2) at pH 7.5 during cooling from +2 to −80°C consisted of seven bands appearing at about −30°C (TL−30), −15°C (TL−10), +10°C (TL+10), +30°C (TL+30), +50°C (TL+50), +65°C (TL+65) and +85°C (TL+80), in which TL stands for thermoluminescence. In the pH range from 5.5 to 9.0 the peak positions of the TL−30, TL−10, TL+50, TL+65and TL+80bands were independent of pH. On the other hand the peak positions of the TL+10and TL+30bands were gradually shifted from +25 to −5°C and from +20 to +40°C, respectively, as the pH was decreased from 9.0 to 5.5. The same pH-induced shift (from +25 to −5°C) was observed for the TL+10band when electron transport was inhibited by DCMU. In dinoseb-treated chloroplasts the peak position of the main thermoluminescence band also exhibited pH dependency, and shifted from +20 to −20°C upon lowering the pH from 9.0 to 5.5. After the water-splitting system had been inactivated by Tris or NH2OH treatment no pH-induced shifts were observed in the peak positions of the thermoluminescence bands of DCMU and dinoseb-treated chloroplasts. The results suggest that the effect of pH on the thermoluminescence of untreated and inhibitor-treated chloroplasts is associated with protonation/deprotonation reactions occurring at the donor and acceptor sides of Photosystem II during the S1→ S2transition of the water-splitting system.

Following illumination at 200 K, the charge recombination reactions and the origin of the thermoluminescence (TL) bands appearing at about 0°C (Q band) and +50°C (C band) in the glow curve were investigated by comparative TL and EPR measurements in DCMU‐treated photosystem II particles. Decay half‐time measurements carried out at −25°C and +25°C, respectively, suggest that the S2state (multi‐line signal) undergoes charge recombination with the g= 1.9 form of the semiquinone‐iron complex, QA−·Fe2+, resulting in the appearance of the Q band, and that the g= 1.82 form of QA−·Fe2+back‐reacts with the oxidized tyrosine, YD+(Signal IIs), accounting for the generation of the C band.

Circular dichroism (c.d.) was measured for four chlorophyll-protein complexes, resolved from sodium dodecyl sulphate extracts of chloroplasts by electrophoresis in polyacrylamide gel containing Deriphat 160 (disodium N-dodecyl beta-imidopropionate), a zwitterionic detergent. The slowest-band (1) complex was found to be identical with the complex CP1 as found on electrophoresis in the presence of anion detergent, but it was in a much higher yield (30% of the chlorophyll a). In band-2 and -3 protein complexes a c.d. pattern described for the complex CP2 could be recognized. Another c.d. component of a split-exciton type with extrema at 680 (-) and 669 (+)nm, together with evidence of disorganized chlorophyll, was found in band-2, -3 and -4 complexes. When a barley (Hordeum vulgare) mutant lacking chlorophyll b was examined, only bands 1 and 4 were obtained, and the c.d. of the band-4 complex was much less affected by disorganized chlorophyll. C.D. spectra resembling that of this band-4 complex could be generated by subtracting the c.d. of complex CP1 from the c.d. of photochemically active mutant chloroplast fragments, or by subtracting the c.d. of complexes CP1 and CP2 from pea (Pisum sativum) chloroplast fragments. The Deriphat appears to have preserved at least to some extent a new type of chlorophyll a-protein complex.

In greening maize mesophyll, circular dichroism (c.d.) revealed the early formation of protein-chlorophyll complexes, followed by unorganized chlorophyll. The intense c.d. [Gregory & Raps (1974) Biochem. J. 142, 193-201] appeared later still, whereas membrane-membrane contact (stacking), measured from electron micrographs, appeared much earlier. Isolated grana, which still showed stacking, lost 92% of their original intense c.d.; intense c.d. is not therefore simply dependent on stacking.