Ja. Cruz et al., Inhibition of plastocyanin to P-700(+) electron transfer in Chlamydomonas reinhardtii by hyperosmotic stress, PLANT PHYSL, 127(3), 2001, pp. 1167-1179
Oxygen electrode and fluorescence studies demonstrate that linear electron
transport in the freshwater alga Chlamydomonas reinhardtii can be completel
y abolished by abrupt hyperosmotic shock. We show that the most likely prim
ary site of inhibition of electron transfer by hyperosmotic shock is a bloc
kage of electron transfer between plastocyanin (PC) or cytochrome c(6) and
P-700. The effects on this reaction were reversible upon dilution of the os
molytes and the stability of plastocyanin or photosystem (PS) I was unaffec
ted. Electron micrographs of osmotically shocked cells showed a significant
decrease in the thylakoid lumen volume. Comparison of estimated lumenal wi
dth with the x-ray structures of plastocyanin and PS I suggest that lumenal
space contracts during HOS so as to hinder the movement of docking to PS I
of plastocyanin or cytochrome c(6).