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Susan A. Dunford Associate Professor University of Cincinnati Department of Biological Sciences, ML006 810 Rieveschl Hall Cincinnati, Ohio 45221-0006 Phone (513) 556-9728, FAX (513) 556-5299 email Susan.Dunford@UC.Edu	Back to Scientists

Research Interests

Phloem and xylem transport in higher plants and plant water relations Past research topics include: petiole cooling and its effect on phloem transport rates; the nature of phloem loading in sugar beet (with Donald Geiger, University of Dayton); the measurement of phloem turgor pressure (with Martin Zimmermann, Harvard University); water relations of phloem and xylem in forest trees; and drought tolerance. Current research is a collaborative project with Dr. Valerie Pence at the Center for Research of Endangered Wildlife, Cincinnati Zoo and Botanical Garden. This work concerns abscisic acid (ABA), which is a plant stress hormone, and desiccation tolerance in liverworts.

Phloem and xylem transport in higher plants and plant water relations

When Marchantia polymorpha is grown on a medium containing abscisic acid (10 microMolar), the hormone affects Marchantia's water relations but does not alter its desiccation tolerance. (See figures below.)

Marchantia was grown on ABA for 1 week then rapidly dried for two hours. The plant lost water somewhat more slowly during desiccation due to the ABA treatment. However, ABA had no effect on survivability, and both control and ABA-treated tissues died when they were returned to a control medium after drying.

In contrast, when Riccia fluitans is treated in the same fashion, ABA increases Riccia's desiccation tolerance but does not affect its rate of drying. (See figures at right.)

Further research has shown that the increase in desiccation tolerance induced in Riccia by ABA is accompanied by a three-fold increase in the concentration of soluble sugars and a decrease in the proportion of reducing sugars. A 12-hour treatment with ABA is sufficient to bring about a significant increase in survivability following rapid desiccation of Riccia , with a 20-hour treatment resulting in 100% survivability.

Future research questions include: what are the soluble sugars that increase as Riccia becomes desiccation tolerant? can desiccation tolerance be induced in Riccia by slower drying? if so, do ABA and soluble sugars increase during this treatment? do specific proteins, which appear in a number of seeds and plants as desiccation tolerance is induced, appear in Riccia also?

The ultimate issues are how all these factors interrelate in desiccation tolerance, what role they play in the survival of this liverwort in nature, and how these mechanisms in liverworts relate to those in other classes of plants.

Selected Publications

• Redella, S., Dunford, S.A. and Pence, V. 1997. Desiccation tolerance and ABA in selected thalloid liverworts. Plant Physiol. 114S: 108.
• Dunford, Susan. 1998. Transport in th Phloem. In: L. Taiz and E. Zeiger, eds., Plant Physiology, Second Ed. Benjamin/Cummings, Menlo Park.
• Dunford, Susan A. and Pence, Valerie C. 1998. Survival of Riccia fluitans L. following rapid or gradual drying. Final Program, Annual meeting of the American Society of Plant Physiologists. Abstract 458, p.106.
• Plair, Bernadette L., Pence, Valerie C., and Dunford, Susan A. 1998. The effect of abscisic acid on desiccation tolerance and soluble sugars in the liverwort Riccia fluitans L. Final Program, Annual meeting of the American Society of Plant Physiologists. Abstract 461, p.106.

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