Chlorophyll B fluorescence and an emission band at 700 nm at room temperature in green algae

Chlorophyll (Chl) b is non-fluorescent in utio as it transfers excitation energy with 100% efficiency to Chl a [l-3]. There is no record of Chl b fluorescence in viva. We show here, for the first time, that Chi b is slightly fluorescent in vivo (at 660-665 nm) when the cells are exposed to bright light, or treated with DCMU (see footnote*); this emission was uncovered when we compared the ratios of <‘high” to “low” fluorescence yields as a function of the wavelength of light. In red algae, a new band around 693 nm, observed upon excitation with high intensity system II light, or with DCMU treatment, was suggested to originate in the energy trap of system II [4, 51. Earlier attempts in our laboratory by several investigators failed to reveal the presence of a similar band in green algae. We demonstrate here the existence of an emission band at about 700 nm in Chlorella and Chlamydomonas when we compare the ratios of “high” to “low” yield fluorescence as a function of the wavelength of light. We interpret the above findings as to be caused by a decrease in the efficiency of energy transfer from Chl b to ChI 12, and from Chl a molecules near the trap to the trap of system II, when the latter are closed at high light and in the presence of DCMU.