Photosynthetic properties of two different soybean suspension cultures

The photosynthetic properties of two commonly used suspension cultured lines, embryogenic and photoautotrophic (PA, SB-1 line) cells of soybean [Glycine max (L.) Merr.] were characterized. We found that compared to the dark green PA cells, the light green embryogenic cells contained fewer and smaller plastids with less-developed thylakoid membranes. The embryogenic cells also contained much lower contents of both chlorophyll and the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) protein, an undetectable level of Rubisco small subunit protein, and a very low rate of photosynthesis. While the DNA contents of the nuclear genomes were similar in these two types of cultured cells, the embryogenic cells possessed a markedly lower content of plastid DNA. The 18-year-old PA suspension culture, SB-1, continues to evolve with higher Rubisco and plastid DNA contents than leaves, and with small decreases in nuclear DNA content that appears to mimic changes in chromosome numbers. These findings may prove useful in the application of plastid transformation, particularly when non-leaf or non-green tissues must be used as targets for transformation and plant regeneration.