N. Holland et al., INVOLVEMENT OF THYLAKOID OVERENERGIZATION IN TENTOXIN-INDUCED CHLOROSIS IN NICOTIANA SPP, Plant physiology, 114(3), 1997, pp. 887-892
The purpose of this work was to clarify the mechanism of tentoxin-indu
ced chlorosis in Nicotiana spp, seedlings. We found that chlorosis doe
s not correlate with the inhibition of chloroplast ATP synthesis in vi
vo, since it occurs at tentoxin concentrations far higher than that re
quired 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 ov
erenergization 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 invo
lved in the process of chlorosis: ascorbate, a quencher of oxygen radi
cals, significantly protects against chlorosis, whereas transgenic Nic
otiana spp. mutants overexpressing chloroplast superoxide dismutase ar
e partially resistant to tentoxin-induced chlorosis. It is proposed th
at chlorosis in developing seedlings results from overenergization of
thylakoids, which leads to the generation of oxygen radicals.