Chloroplasts are not fixed organelles and are capable of not only moving toward a brighter area in a cell, but can also avoid strong light and move away from the light source (called high-fluence-rate response or chloroplast avoidance movement). However the physiological importance of this phenomenon has remained unclear. In the December 19/26 Nature, Masahiro Kasahara and colleagues at the National Institute for Basic Biology, Okazaki, Japan, show that photosynthesis is more susceptible to photodamage in the absence of chloroplast avoidance movement than with it (Nature, 420:829-832, December 19/26, 2002).

Kasahara et al. used different classes of Arabidopsis mutant cells defective in chloroplast avoidance movement. They observed that these mutants are more susceptible to damage in high light than wild-type plants. In addition, they showed that damage of the photosynthetic apparatus and subsequent bleaching of leaf color and necrosis occurred faster under high light conditions in...

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