Use of plastome and nuclear mutants of higher plants to study the genetic control of plastid formation and function.

We conducted comparative biochemical and electron-microscopic studies of several types of plastome and nuclear mutants of Antirrhinum majus and Pelargonium zonale. It was shown that specific blocking of the photosynthetic reaction occurs in plastome mutants of A. majus; Photosystem II was found to be damaged in the en:alba-1 mutant and photo-system I was affected in the en:viridis-1 mutant. The plastid mutations in these mutants caused loss of certain soluble lamellar proteins and pigment--protein complexes or a reduction in their content, which led to disappearance of photosynthetic activity. When the content of high-molecular ribosomal RNA in the leaves of normal and mutant P. zonale plants was compared, the normal plants were found to have four types of RNA: two types of cytoplasmic-ribosome RNA and two types of plastid-ribosome RNA. No plastid-ribosome RNA was detected in the mutant. These results were confirmed by electron-microscopic examination: no ribosomes were detected in the mutant plastids. Thus, use of plastome mutants made it possible to establish that the genetic information concentrated in the plastid DNA controls formation of ribosomes and lamellae in the chloroplasts and thus affects chloroplast photosynthetic function.