TITLE	Effect of sorbitol induced osmotic stress on the changes of carbohydrate and free amino acid pools in sweet potato cell suspension cultures
AUTHOR	Heng-Long Wang Institute of Biological Chemistry, Academia Sinica, P. O. Box 23-106, Taipei, Taiwan 107, Republic of China Ping-Du Lee Biochemistry Laboratory, Department of Agricultural Chemistry, National Taiwan University, 1 Roosevelt Road Section 4, Taipei, Taiwan 107, Republic of China Li-Fei Liu Department of Agronomy, National Taiwan University, 1 Roosevelt Road Section 4, Taipei, Taiwan 107, Republic of China Jong-Ching Su Institute of Biological Chemistry, Academia Sinica, P. O. Box 23-106, Taipei, Taiwan 107, Republic of China
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ABSTRACT	The effects of osmotic stress induced by 0.6 M sorbitol on the cell growth and on the quantitative and qualitative changes in carbohydrates and free amino acids in suspended cells of sweet potato (Ipomoea batatas) were analyzed. Cells transferred into medium without (normal treatment) or with (stress-shocked treatment) 0.6 M sorbitol added, and cells consecutively subcultured under high stress conditions (stress-adapted treatment) were compared. Stress-shocked cells showed cell growth retardation and the induction of plasmolysis. Stress-adapted cells had a shorter lag phase in growth than the stress-shocked, and showed a normal morphology, albeit the size appeared slightly smaller than normal cells. Under the stress-shocked condition, the size of the amino acid pool (µmole/g fresh weight) increased fourfold relative to the control and stress-adapted cells. The levels of alanine and glutamic acid and its derivatives were especially high, indicating that the changes in the intensity of glycolysis have influenced the amino acid pool. Although the proline level showed a fivefold increase when stress-shocked, proline made up only about 1.5% of total amino acids, and thus did not seem to play an osmotic regulatory function. Among the carbohydrates, sucrose content was high in both stress-shocked and stress-adapted cells. Starch accumulated heavily in stress-shocked cells, but not in normal or stress-adapted cells, although the latter maintained a higher background level of starch. It is tempting to speculate that sucrose serves as a compatible solute, and starch synthesis from sucrose plays a pivotal role in moderating the hyperosmotic condition. The accumulated starch contained less amylose than the ordinary tuberous root starch, indicating that the pathway of starch synthesis was somewhat altered in the stress-shocked cells.
KEYWORD	Compatible solute; Free amino acid; Ipomoea batatas; Osmotic stress; Starch; Sucrose; Suspended cells;
ARTICLE INFO	Botanical Bulletin of Academia Sinica, Volume 40 Number 3 July 1999, page 219-225, 7 pages
PUBLISHER	Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan, Republic of China