SUMMARYThe antagonism observed by Gross and Hess (Gross, E. and Hess, S. C. (1973) Arch. Biochem. Biophys. 159,[832][833][834][835][836] in the effect of monovalent and divalent cations on energy spillover between Photosystems I and II, as indicated by chlorophyll a fluorescence, was confirmed in spinach. Significant differences with oats, peas and lettuce were found using the same low salt method of preparation: the response to Na + and Ca 2+ was reversible, Ca 2÷ alone, when added first, produced a large (85 %) increase in the variable portion of the chlorophyll a fluorescence transient or the steady-state fluorescence, and Ca 2 + not only fully restored a Na ÷ induced inhibition of 680 nm fluorescence, but brought it above the original level. The fluorescence probes 1-anilinonaphthalene-8-sulfonate and N-phenyl-l-naphthylamine showed a rapid and a slower response, respectively, to the addition of mono-or divalent cations. Neither the structural changes responsible for the probe data, nor those leading to the measured cation stimulated changes in 90 ° light scattering could be precisely equated with any alteration of conformation involved in the chlorophyll spillover events.

No abstract

Liposomes made from phospholipids and containing sulforhodamine dye (1-50 mM) have been irradiated with nanosecond and picosecond laser pulses. Individual liposomes were locally heated by laser absorption of dye dimers during a single laser pulse, and heating was sufficient to release the liposome contents. The extent of dye release produced by a single laser pulse was shown to be quantitatively dependent on several interdependent variables, including dye concentration, liposome size, laser excitation parameters and initial temperature of the dye-liposome system. Fluorescence lifetime data having three components have been obtained and analyzed in terms of three dye environments. Quantitative estimates support a photo-induced thermal mechanism for liposome lysis and release of its contents. These results may be useful for laser induced delivery of therapeutic agents or other applications of lasers in biological systems. 4' SA'Aal D1tla

No abstract