Photoautotrophic Growth of Soybean Cells in Suspension Culture

Abstract

Highly chlorophyllous photomixotrophic callus was visually selected from callus originating from soybean (G. max (L.) Merr. cv. Corsoy) cotyledon. Suspension cultures initiated from this callus became photoautotrophic under continuous light with an atmosphere of 5% CO2 (balance air). Dry wt increases of 1000-1400% in the 2-wk subculture period were observed. The cellular Chl [chlorophyll] content ranged 4.4-5.9 .mu.g .cntdot. mg-1 dry weight which is .apprx. 75-90% of the Chl content in soybean leaves under equivalent illumination (300 .mu. Einsteins/m2 .cntdot. s-1). No growth can be observed in the dark in sucrose-lacking medium or in the presence of 0.5 .mu.M 3-(3,4-dichlorophenyl)-1,1-dimethylurea, a concentration which does not inhibit heterotrophic growth (on sucrose). Photoautotrophic growth has an absolute requirement for elevated CO2 concentrations (> 1%). During the 14-day subculture period, growth (fresh wt and dry wt) is logarithmic. Photosynthesis quickly increases after day 4, reaching a peak of 83 .mu.mol CO2 incorporated per milligram Chl per hour while dark respiration decreases 90% from day 2 to day 6. The pH of the growth medium quickly drops from 7.0 to 4.5 before slowly increasing to 5.0 by day 14. At this pH range and light intensity (200-300 microEinsteins/m2 .cntdot. s-1), no O2 evolution could be detected althoguh at high pH and light intensity O2 evolution was recorded.