Inheritance of the reversal of O2 response of photosynthesis in a Flaveria linearis mutant

A mutant plant of Flaveria linearis Lag. expresses reversed O2 response of photosynthesis (i.e. its apparent photosynthesis is stimulated at atmospheric O2 levels). The objectives of this study were to determine the genetic inheritance of this trait and to investigate the biochemical mechanism for its expression. The mutant plant was crossed reciprocally with a plant of the closely related species Flaveria oppositifolia (DC.) Rydb. and also with another plant of F. linearis. Data on O2 inhibition of apparent photosynthesis were analyzed on F2 and F3 progeny from these F1 hybrids. In addition, test crosses (mutant x F1 hybrid) and S1 progeny from the mutant plant were also analyzed. All F1 hybrids expressed inhibition of apparent photosynthesis and their progeny segregated in acceptable 3:1 and 13:3 (normal:reversed) ratios. There was little effect of environment on expression of the reversed O2 response. Selected F2 plants and the original mutant plant produced progeny in normal:reversed ratios which indicated the trait is controlled by two major genes which show dominant and recessive epistasis. Plants with greater than 20 nanomoles per gram fresh weight per minute of fructose-1, 6-bisphosphatase activity in the cytosol had normal O2 response of photosynthesis. However, when plants had less than 20 nanomoles per gram fresh weight per minute of this enzyme activity in the cytosol, the O2 was normal in some and reversed in others. It is proposed that low fructose bisphosphatase activity in the cytosol is controlled by a recessive gene (fbp). A second dominant gene is speculated to be hypostatic to the normal fructose bisphosphatase gene and controls the expression of an unknown factor that determines whether O2 response of AP is reversed in the presence of fbp (i.e. when fructose bisphosphatase activity is low)