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Environmental and Stress Physiology

Stress-Induced Accumulation of Wheat Germ Agglutinin and Abscisic Acid in Roots of Wheat Seedlings ¹

Laboratorium voor Plantenbiochemie K. U. Leuven, Willem De Croylaan, 42, B-3030 Leuven Belgium, MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824-1312

Wheat germ agglutinin (WGA) levels in roots of 2-day-old wheat seedlings increased up to three-fold when stressed by air-drying. Similar results were obtained when seedling roots were incubated either in 0.5 molar mannitol or 180 grams per liter polyethylene glycol 6000, with a peak level of WGA after 5 hours of stress. Longer periods of osmotic treatment resulted in a gradual decline of WGA in the roots. Since excised wheat roots incorporate more [³⁵S]cysteine into WGA under stress conditions, the observed increase of lectin levels is due to de novo synthesis. Measurement of abscisic acid (ABA) levels in roots of control and stressed seedlings indicated a 10-fold increase upon air-drying. Similarly, a five- and seven-fold increase of ABA content of seedling roots was found after 2 hours of osmotic stress by polyethylene glycol 6000 and mannitol, respectively. Finally, the stress-induced increase of WGA in wheat roots could be inhibited by growing seedlings in the presence of fluridone, an inhibitor of ABA synthesis. These results indicate that roots of water-stressed wheat seedlings (a) contain more WGA as a result of an increased de novo synthesis of this lectin, and (b) exhibit higher ABA levels. The stress-induced increase of lectin accumulation seems to be under control of ABA.

¹ Supported in part by grants of the National Fund for Scientific Research (Belgium) and by a grant (0056/88) from the North Atlantic Treaty Organization for collaboration between N. V. R. and W. J. P. W. J. P. is Senior Research Associate and W. F. B. is Research Assistant of this fund. B. P. A. C. and J. T. C. K. receive a fellowship of the Belgian Instituut tot Aanmoediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw (IWONL).