ABSORPTION AND CHLOROPHYLL a FLUORESCENCE CHARACTERISTICS OF TRIS-TREATED AND SONICATED CHLOROPLASTS

An a t tempt was made here to examine the three-light-reactions scheme of photosynthesis presented by Knaff and Arnon challenging the conventional Z-scheme. Tris-treated, sonicated chloroplasts (T20S2) -as used by the earlier workers -were prepared and their absorption, fluorescence action and emission spectra at 77°K were measured. This was done to test whether this treatment causes preferential loss of pigments of pigment system (PS) I; the latter could have led to an action spectrum of cytochrome b559 photooxidat ion matching that of PS II in Knaff and Arnon's work, and thus to their scheme. Results of room temperature absorption spectra, difference absorption spectra of normal minus T20 $2 chloroplasts, the ratios of chlorophyll a (Chl a) fluorescence intensity at 735 nm to that at 685 nm (F735/F685) at 77°K of both particles, and action spectra of Chl a fluorescence (F760) of thick samples, indicated that, indeed, there is a preferential loss of long wavelength forms of Chl a relative to other forms of Chl a in T2oS2 particles. Thus, it is likely that system IIa (according to Knaff and Arnon's terminology) may simply be system I wi thout the Chl a 690--700 (Chl a forms with " red" bands at 690--700 nm); this would make system I look like system II.