Genetic analysis of photosynthesis

Abstract

It is now possible to select mutations of nuclear genes controlling various steps of the light reaction of photosynthesis in higher plants. Forty-nine such mutants, which were not previously available for the study of photosynthesis, have been isolated on the basis of their high level of chlorophyll fluorescence or their ability to withstand treatment of the photodynamic inhibitor, diquat. Diquat requires photosynthetic activity in order to kill plants and therefore mutants of photosynthesis survive. Full green seedling lethal photosynthesis mutants of Zea mays have been isolated which have near normal chloroplast ultrastructure. Using standard measurements of photosynthetic reactions we have characterized the first series of these mutants to the single protein involved. Among those now identified, one is missing the NADP+ reductase enzyme (hcf-1); another has lost cytochrome f(hcf-2); and one has no high potential cytochrome b[subscript 559] (hcf-3). There is also indication that hcf-4 does not have the ATP synthesis enzymes for non-cyclic photophosphorylation. These maize mutants are now being applied to basic studies of the pathway of photosynthetic electron transport and phosphorylation. Unique information gained in this way may have application to our understanding of photosynthetic control in an important food plant species.