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CONSEQUENCES OF ALTERED GAS DIFFUSION RATES FOR CELL DIVISION AND SECONDARY METABOLITE PRODUCTION BY SOYBEAN (Glycine max) CELLS GROWN IN TISSUE CULTURE.  L.K. Tuominen¹ and M.E. Musgrave².   ¹Plant Biology Graduate Program and ²Biology Department, Univ. of Massachusetts, Amherst, MA 01003

   Observation of hypoxic responses in plants grown in spaceflight has led researchers to speculate that absence of buoyancy-driven convection in microgravity may limit gas exchange rates.  The purpose of this study was to understand how the rate of availability of oxygen and carbon dioxide to plant cells influences cell division and secondary metabolite production.  Callus culture of soybean (Glycine max (L.) Merr.) tissue provided a model system in which both processes could be readily quantified.  Aliquots of the synthetic cytokinin, 6-benzylaminopurine (BA), were added to tissue culture medium to stimulate different rates of cell division, quantified by fresh weight gain of the callus.  Similarly, liquid shake cultures derived from callus cells were induced to synthesize the plant estrogen diadzein (7,4’-dihydroxyisoflavone) by addition of BA.  Following extraction of the cells at 4C with ethanol, diadzein was quantified spectrophotometrically using peaks at 262 and 270 nm.  Synthetic atmospheres were devised as follows.   The control atmosphere provided to the cultures was 21% oxygen, 400 ppm carbon dioxide, and the balance nitrogen.   Replacement of nitrogen by helium in this system was used to increase the diffusion rate of oxygen, carbon dioxide and ethylene, thus making them more readily available to the plant tissues.   Conversely, replacement of nitrogen by argon slowed the diffusion rates of the metabolic gases.  Gases were sent through a humidifier before passing to test chambers.  Flow rate was sufficient to maintain the desired atmospheric composition in the chambers, as confirmed by gas chromatography.  For the cell division assay, treatment in the test gases lasted 28 days, while for the more rapid diadzein response, gas treatment lasted 72 h, with diadzein synthesis induced after 24 h.  The results are significant for spaceflight applications because they model diffusion rate effects on basic plant growth and metabolism.

(Supported by NASA grant NAG2-1375.)