Characterization of a cytoplasmically inherited yellow foliar mutant (cyt-Y 3) in soybean

Genetic analysis of a yellow foliar mutant in soybean (Glycine max L. Merr.) showed maternal inheritance of the mutant phenotype designatedcyt-Y 3. The mutant was grown beside normal green sibs (cyt-G 3) under three different photosynthetic photon flux densities (PPFD), and samples were collected to determine pigment content and for electron microscopy analyses of plastid ultrastructure. The plastid ultrastructure ofcyt-Y 3 appeared normal at low PPFD and the carotenoid level ofcyt-Y 3 was also normal, but the chlorophyll content was only approximately one-third that ofcyt-G 3. Under medium and high PPFD,cyt-Y 3 plastids lacked a structured thylakoid, and total chlorophyll content was only 28% and 1% of normal, respectively; the carotenoid levels ofcyt-Y 3 also dropped to 33% and 2% of normal, respectively. These data indicate that the effect of high PPFD oncyt-Y 3 might result from a deficiency in a plastid membrane protein. The resulting changes in membrane configuration could then interfere with the accumulation or stabilization of chlorophylls and carotenoids, thereby resulting in the subsequent photooxidation of both at medium and high PPFD. This mutant could be useful in the study of thylakoid biosynthesis and pigment stabilization, or could provide a source of conditionally identifiable plastids for organelle segregation studies.