Richard G. Jensen. Professor, Departments of Biochemistry and Plant Sciences. Ph.D., Brigham Young University.

• Office: Biologcal Sciences West, #531 (621-3489)
• e-mail: jensen@biosci.arizona.edu

Plant biochemistry, photosynthesis, plant salt and water stress, carbohydrates and polyols, and rubisco.

The metabolism of plants during water/salt stress constitutes the main research direction of the laboratory. Tobacco and arabidopsis have been transformed with selected foreign genes chosen to convey resistance to water and salt stress. The transformed plants synthesize polyol sugars, mannitol, sorbitol and ononitol (4-0 methyl myo-inositol), previously unseen in these plants. Using techniques of plant gene and transformation the effects of producing these polyols and the possible synergy of up to three polyols on plant growth and resistance to salt stress is being investigated. Seeds are generated by crossing and selfing to produce one or more of the three polyols. Experiments from this lab showed that tobacco transformed to produce mannitol did convey significant resistance to mature plants grown in salt at one-half of sea water. The sorbitol transformants act as if the amount of sorbitol produced was causing osmotic stress and reducing growth. The ononitol-producing plants make more of the methylated inositol when water stressed, even though there is no change in enzyme amounts during stress. The relative effects on growth and development are being observed and the resistance to stress determined. These experiments give insight into the potential these polyols might play in resistance to salt/water stress as a prelude toward rational design of stress resistance for economic crops.

That ononitol production is increased under water stress also indicates that tobacco is capable of supplying considerable amounts of myo-inositol upon demand. This also indicates that tobacco is capable of producing methyl groups during stress, probably coming from the photorespiratory carbon cycle. The genetics, molecular biology and biochemistry of inositol metabolism and the one-carbon cycle (including S-adenosylmethionine) are being studied.

Regulation of rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase) activity by fallover caused by the missfire products, xylulose 1,5-bisphosphate and 3-ketoarabinitol 1,5-bisphosphate, is being examined. HPLC techniques have been developed to accurately measure the CO2/O2 specificity and the missfire products. These biochemical characteristics are being determined from various rubiscos from different plant and algal sources and compared to the unique structure of that rubisco to determine how enzyme structure regulates enzyme activity.

Tarczynski, M.C., R.G. Jensen and H.J. Bohnert, "Expression of a Bacterial mtlD Gene in Transgenic Tobacco Leads to the Production and the Accumulation of the Sugar Alcohol, Mannitol." Proc.Natl.Acad.Sci. USA 89:2600-2604 (1992).

Adams, P., J.C. Thomas, D.M. Vernon, H.J. Bohnert and R.G. Jensen, "Distinct Cellular and Organismic Responses to Salt Stress". Plant Cell Physiol. 33:1215-1223 (1992).

Tarczynski, M.C., R.G. Jensen and H.J. Bohnert, "Stress Protection of Transgenic Tobacco by Production of the Osmolyte Mannitol" Science 259:508-510 (1993).

Vernon, D.M., M.C. Tarczynski, R.G. Jensen and H.J. Bohnert, "Cyclitol Production in Transgenic Tobacco" Plant Journal 4:199-205 (1993).

Adams, P., A. Zegeer, H.J. Bohnert and R.G. Jensen, "Anion Exchange Separation and Pulsed Amerometric Detection of Inositols from Flower Petals", Analyt. Biochem. 214:321-324 (1993).

Bohnert, H.J., J.C. Thomas, E.J. DeRocher, C.B. Michalowski, H. Breiteneder, D.M. Vernon, W. Deng, S. Yamada and R.G. Jensen, "Responses to Salt Stress in the Halophyte Mesembryanthemum crystallinum", In J. Cherry, Editor, Biochemical and Cellular Mechanisms of Stress Tolerance in Plants, NATO ASI Series, Vol. H 86, Springer Verlag, Berlin, pp. 415-428 (1994).

Bohnert, H.J., D.E. Nelson and R.G. Jensen, "Adaptations to Environmental Stresses", The Plant Cell 7:1099-1111 (1995).