g., Krey and Govindjee 1964; Govindjee and Briantais 1972). Further, #Small molecule library supplier randurls[1|1|,|CHEM1|]# due to the closure of PS II under these conditions, Govindjee and Briantais were also able to see chlorophyll b fluorescence due to reduced energy transfer from it to chlorophyll a! When discussing this last point Govindjee was keen to point out that this has not been exploited in current studies and deserves to be pursued for kinetic changes in photosynthesis. 4. Understanding of the mechanism of thermoluminescence

and delayed light emission in photosynthetic systems: beyond William Arnold Govindjee is known for his insight into the mechanism of delayed light emission (or delayed fluorescence) and

thermoluminescence. William Arnold, a former student of Robert Emerson, had not only discovered, in 1932, the concept of the “Photosynthetic Unit” with Emerson, but, in 1951, with Bernard Strehler, he discovered delayed light emission, while investigating the possible synthesis of ATP by plants (Strehler and Arnold 1951), and later, in 1957, he discovered the phenomenon of thermoluminescence (afterglow) with Helen Sherwood (Arnold and Sherwood 1957). Mar and Govindjee Chk inhibitor (1971) discovered that preilluminated spinach chloroplasts and Chlorella pyrenoidosa, when given a quick temperature jump of about 15 °C, emitted light. This thermoluminescence was present both in normal and DCMU-treated samples, where electron transport to PS I was blocked, but was absent when hydroxylamine, which blocks electron transport on the donor side of PS II, was added to these samples. These results were explained not in terms of Arnold’s theory of electron–hole reactions, but in terms of a back reaction of PS II of photosynthesis. This, it seems, was the beginning of Govindjee’s thoughts on thermoluminescence and his recognition Protirelin that Arnold’s theory was

in need of revision. Certainly Govindjee returned to this question when, almost 10 years later, he went to BARC (Bhabha Atomic Research Centre) in Trombay, Bombay (now Mumbai), India, to study thermoluminescence, discovering with V.G. Tatake, P.V. (Raj) Sane and coworkers abnormally large activation energies, using the well-known Randall-Wilkins theory (Tatake et al. 1981). This was an untenable situation, and it led him to approach Don DeVault (co-discoverer, with Britton Chance, of electron tunneling), who was also at Urbana, Illinois, to help him write the equations and theory, using the detailed scheme of PS II reactions that Govindjee presented to him.