Abstract
We describe a novel experimental strategy that makes use of the conditional flu mutant of Arabidopsis thaliana, which makes it possible to induce the release of singlet oxygen in a controlled and noninvasive manner.
The flu mutant accumulates protochlorophyllide in the dark. Following a dark-to-light shift generation of singlet oxygen starts within the first minute of illumination and was shown to be confined to plastids. Immediately after the shift mature plants stopped growing, while seedlings bleached and died. These responses do not result merely from physicochemical damage. Instead they reflect the activation of distinct stress response programs, as indicated by the recovery of more than 30 second-site suppressors mutations that abrogate the reactions. Two distinct signal transduction pathways were defined, which diverged from a single genetic locus, Executor 1 (Ex1), that is indispensable for the processing and transmission of the initial stress signal.
