PLANT PHYSIOLOGY , Vol 114, Issue 3 887-892, Copyright © 1997 by American Society of Plant Biologists
Involvement of Thylakoid Overenergization in Tentoxin-Induced Chlorosis in Nicotiana spp
N. Holland, Y. Evron, MAK. Jansen, M. Edelman and U. Pick
Department of Plant Genetics, Weizmann Institute of Science, Rehovot 76100, Israel (N.H., M.E.)
The purpose of this work was to clarify the mechanism of tentoxin-induced
chlorosis in Nicotiana spp. seedlings. We found that chlorosis does not
correlate with the inhibition of chloroplast ATP synthesis in vivo, since
it occurs at tentoxin concentrations far higher than that required for the
inhibition of photophosphorylation measured in the same seedlings. However,
tentoxin-induced chlorosis does correlate with in vivo overenergization of
thylakoids. We show that tentoxin induces overenergization in intact plants
and isolated thylakoids, probably via multiple interactions with ATP
synthase. Furthermore, gramicidin D, a protonophore that relieves
overenergization, also relieves chlorosis. Two lines of evidence suggest
that reactive oxygen species may be involved in the process of chlorosis:
ascorbate, a quencher of oxygen radicals, significantly protects against
chlorosis, whereas transgenic Nicotiana spp. mutants overexpressing
chloroplast superoxide dismutase are partially resistant to
tentoxin-induced chlorosis. It is proposed that chlorosis in developing
seedlings results from overenergization of thylakoids, which leads to the
generation of oxygen radicals.
