title: Effects of sodium and magnesium cations on the "dark-" and light-induced chlorophyll a fluorescence yields in sucrose-washed spinach chloroplasts.
abstract: The effects of Na plus and Mg-2 plus on the "dark" level (O level) and light-induced (P level) fluorescence in sucrose-washed spinach clhoroplasts were studied. Low concentrations of NaCl (2-10 mM) cause a significant decrease in both the O and P levels in the chlorophyll fluorescence transient. The effect on the O level may reflect changes in the bulk chlorophyll a. At 77 degrees K NaCl increases the F735/F685 emission peak ratio in dark-adapted and preilluminated chloroplasts, but has no significant effect on this ratio in sucrose-washed Photosystem II particles. This evidence is consistent with a sodium-induced excitation-energy distribution in favor of Photosystem I. In the presence of MgCl2, with or without NaCl, there is a slight decrease in the O and P level fluorescence as compared with the salt-free control, but an increase as compared with the NaCl-treated sample. Magnesium appears to override the sodium-induced changes. At low temperatures in chloroplasts and Photosystem II particles, MgCl2 has different effects on the F735/F685 ratio apparently depending on the state of the membrane. Magnesium, however, always induces an increase in the F695/F685 ratio. These results suggest that magnesium may influence Photosystem II reaction centers as well as energy distribution between the two photosystems.
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D003624:Darkness; D007700:Kinetics; D008027:Light; D008274:Magnesium / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism; D010785:Photophosphorylation / Q000187:drug effects*; D010944:Plants; D012964:Sodium / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D002734:Chlorophyll; D012964:Sodium; D008274:Magnesium; D010100:Oxygen