LIGHT ABSORPTION BY PIGMENTS in vivo 1841 



and of photochemical reaction could be carried out more easily than in 

 whole cells (e. g., by using ferricyanide as Hill oxidant and a potentio- 

 metric method for reduction measurement). Similar curves were found 

 for the response of the two rates to changes in light intensity. The lumi- 

 nescence reached a maximum at 35° C, in common with photosynthesis 

 and Hill reaction. The luminescence had two pH optima — at pH 5.2 

 and 8.8, with a minimum at pH 6.7, which is not in agreement with Hill 

 reaction data (chapter 35, section B5). 



The luminescence of spinach chloroplast preparations decayed in the 

 same way (fig. 37C.23A) as that of the luminescence of Chlorella and of 

 leaves of spinach and mustard (half-time of decay, about 3 min.). Mustard 

 chloroplasts, washed only once, showed a different behavior, with a long 

 luminescence "tail." Luminescence of the chloroplasts (similarly to their 

 Hill reaction) showed no induction period, while one was present in Chlorella 

 luminescence (as well as in photosynthesis). Carbon dioxide had no 

 effect on the luminescence of chloroplasts (in contrast to that of Chlorella). 

 Dinitrophenol, cyanide and azide inhibited the chemiluminescence of 

 chloroplast material much less than that of Chlorella; the same was true 

 of the relative effect of the last two (but not of the first one) of these 

 inhibitors on the Hill reaction and on photosynthesis. Hydroxylamine 

 inhibited the chemiluminescence of chloroplasts much stronger than that 

 of Chlorella. 



Arnold and Davidson (1954) improved the measurements so as to ob- 

 tain a reliable spectral distribution curve of the luminescence. It proved 

 identical with that of chlorophyll fluorescence in vivo. They estimated 

 that each Chlorella cell emits, per second, about 33 quanta of delayed 

 luminescence (at the beginning of the decay curve, at 25° C). 



6. Light Absorption by Pigments in vivo 

 (Addendum to Chapter 22) 



(a) Absorption Spectra of Leaves and Algae 



The previously unpublished investigation by Loomis and co-workers 

 (1941), from which figures 1, 14, 30, 31, and 33 in chapter 22 had been 

 taken, has since appeared (Moss and Loomis 1952). The paper contains 

 some additional information. Fig. 37C.24 shows reflection and absorption 

 spectra of leaves of four species. Ficus leaves — thick and dark green — 

 absorb the most and reflect the least; cabbage leaves, with a highly re- 

 flecting surface layer, show the opposite behavior. A similar difference 

 often exists between the upper and the lower surface of the same leaf; 

 the lower, tomentuous surface reflects 2-3 times more light than the upper 

 surface, and correspondingly less of the light falling onto it is absorbed. 



