THE REDUCED PLASTID GENOME OF A NONPHOTOSYNTHETIC ANGIOSPERM OROBANCHE HEDERAE HAS RETAINED THE RBCL GENE

The holoparasitic Orobanchaceae (Orobanche hederae Duby and Orobanche minor Sm.), lack chlorophyll and obtain reduced carbon from their phot osynthetic hosts. Rubisco activity can be considered as non-existent a nd Rubisco protein is not detectable with immunological methods. Probe s representing the entire plastid genome of tobacco were used in South ern blot hybridizations to check roughly to what extent changes have o ccurred in plastid DNA. The Orobanche sp. plastid chromosome is only a bout one-half the size of a typical plastid genome. The inverted repea t region of the Orobanche sp. pt DNA is demonstrated to be more likely conserved whereas in the large single copy and in the small single co py large deletions have occurred. As the inverted repeat contains the genes encoding for ribosomal RNA, some ribosomal proteins and transfer RNA, Orobanche sp. might have retained a functional genetic apparatus in spite of the loss of the rpo genes. Most of the photosynthetic gen es are either absent or truncated, but using DNA amplification by poly merase chain reaction it was demonstrated that no deletion has occurre d in the coding region of the rbcL gene, although restriction patterns were shown to be different from those of tobacco rbcL gene. In this r espect, Orobanche sp. differ from Epifagus sp., an Orobanchaceae endem ic to the North American continent, the plastid genome of which has pr obably gone further in its reduction.