Photosynthetic Characteristics of a Photoautotrophic Cell Suspension Culture of Soybean

Abstract

ABSTRACrA soybean suspension culture (SB-P) which can grow photoautotrophically in 5% CO2 will not grow in ambient CO2 levels. This elevated CO2 requirement seems to be due to the additive effects of a number of factors. The in vivo activity of ribulose-1,5-bisphosphate carboxylase (RuBPcase) is much lower in the SB-P cells, compared to soybean plants. This may be due to the low light intensity used to culture the cells, which has been shown to decrease both the amount and activity in whole plants, resulting in a low rate of net photosynthesis. The RuBPcase activation level is also lowered in air CO2 levels. The presence of the liquid medium raises the cells CO2 compensation concentration (the CO2 concentration reached when the rates of CO2 fixed by photosynthesis and the CO2 respired by the cells are equal). These factors, coupled with the high respiratory loss of CO2 all contribute to reduced net photosynthesis in air, resulting in a photosynthetic capacity that is inadequate for cell survival. Active cell division, low photosynthetic capacity, elevated respiration, and a low ratio of RuBPcase(initial)/phosphoenolpyruvate carboxylase are traits that SB-P cells share with young leaf cells, indicating SB-P cell physiology may be comparable to that of young expanding leaves rather than to that of mature leaves. (pH 5.8), and 1.5 mm NaHCO3 in a final volume of 1 ml was added to the water-jacketed vessel and illuminated at a light intensity of 400 ME m-2 s-'. The evolution rate measurements were repeated three times.14CO2 Incorporation Experiments. Duplicate flasks of cell suspensions (pH 4.5) were combined and aliquots (950 ,ul) of cells, (7.0-11.4 mg fresh weight, 6-18 Mg Chl) and a stir bar were placed in serum stoppered 16 x 55 mm glass scintillation vials. Each assay was run in triplicate. The cells were stirred and gassed with CO2 free air at 26°C under a light intensity of 400 ,E m-2 s-' for 5 min. The assays were initiated by the simultaneous injection of 25 Ml of 205 mm bicarbonate (pH 9.3, 0.89 MCi Mmol-') and 50 Ml of 1.025 M Mes (pH 1.05) to adjust pH. The final concentrations were 5 mm bicarbonate and 50 mm Mes, at a pH of 4.5 which is near that of the culture conditions. After 5 min assays were terminated by the injection of 0.5 ml of 6 N acetic acid. Incorporation of '4CO2 in the dark was carried out in the same manner with the vials being wrapped in aluminum foil. Samples were dried at 60°C, 0.5 ml of 0.5 N HCI was added to dissolve the residue, S ml scintillation cocktail added, and the dpm were determined by liquid scintillation spectrometry.Infrared Gas Exchange Analysis. Plant Physiol. Vol. 84, 1987 gas mixtures were bubbled at 400 to 475 ml min-' through the illuminated (400 ,E m-2 s-') stirred cell suspensions. To measure dark respiration the tube containing the cells was covered with aluminum foil. All measurements were taken on duplicate aliquots of SB-P, repeated twice, and the numbers averaged.CO2 Compensation Concentration (r). The CO2 compensation concentration of the cells was measu...

Photosynthetic Carbon Metabolism in Photoautotrophic Cell Suspension Cultures Grown at Low and High CO2

“…This may reflect, in part, the health of the cells or the stage of the growth cycle (22). Dark respiration rates were generally higher than the 6 to 7 ,mol C/mg Chl h reported for a soybean leaf (19).…”

“…Soybean (Glycine max) cells and high C02-requiring cotton (Gossypium hirsutum) cells were grown at 5% C02 in a modified MS medium2 which contained thiamine and hormones as the only organic compounds (22). Cells were subcultured every 2 weeks.…”

“…Unlike a leaf, however, the majority of photoautotrophic cells require elevated levels of CO2 (1-5%) for growth (1 1, 17), and the successful establishment of a cotton cell line that grows at low CO2 (660 ,uL/L) (32) led us to investigate the differences in photosynthetic carbon metabolism between cotton cells grown at the culture room ambient level of 660 ,gL/L versus 5% CO2. A comparison was also made with two lines of soybean cells that grow at 5% CO2, which have been reported previously (10,22,23 …”

Photosynthetic Characterization of Photoautotrophic Cells Cultured in a Minimal Medium

“…The percent activation, ranging from 16 to 53% in these current experiments, has likewise been found to be lower compared with leaf cells. The activation of Rubisco for growth chamber grown spinach leaves was approximately 86%, and greenhouse grown soybean leaves were reported to be 95% activated (3,21,25). However, recent studies with the COT-P and SB 1-P cells demonstrated that Rubisco could be activated to higher levels of 93 to 94% with a 5-min preillumination prior to assaying for Rubisco activity (20).…”

Foliar and root Cu supply affect differently Fe- and Zn-uptake and photosynthetic activity in soybean plants

“…Volaina) were grown hydroponically in a growth chamber in half-Hoagland nutrient solution (Arnon, 1950) Cell suspension growth conditions.-Photosynthetic cell suspensions from soybean (Glycine max var. Corsoy) SB-P line were grown as described by Rogers et al (1987) with some modifications. These cell suspensions were established in our laboratory in 1990.…”