STIMULATION OF APPEARANCE OF EXTRAPLASTIDIC TETRAPYRROLES BY A PHOTOOXIDATIVE TREATMENT OF THE PLASTIDS

In the mustard seedling (Sinapis alba L.) the appearance of photodetec table phytochrome and synthesis of relatively abundant cytosolic hemop roteins (nitrite reductase, ascorbate peroxidase) are stimulated rathe r than impaired by a photooxidative treatment of the plastids. While t he ability to synthesize protoporphyrin IX from exogenous 5-aminolevul inic acid was preserved in the photooxidatively damaged plants, protoc hlorophyll and chlorophyll accumulation was no longer possible. It app ears from our data that in higher plants the pathway of tetrapyrrole s ynthesis up to protoporphyrin IX is not adversely affected by a photoo xidative treatment of the plastids that destroys the capacity of the o rganelle to synthesize chlorophyll.