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

Abstract

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.have been many investigations on stress-induced ABA accumulation in leaves, few studies have examined endogenous ABA levels in plant roots. This paper reports enhanced ABA levels in roots of water-stressed wheat seedlings. Since ABA reportedly stimulates WGA synthesis in wheat roots (16), we further describe (a) the increase ofWGA content and synthesis in wheat seedling roots as a result of drought and osmotic stress, and (b) the inhibition of this stress-induced increase by fluridone, an inhibitor of ABA synthesis (2,4,5,14). MATERIALS AND METHODS Growth of Wheat SeedlingsWheat grains (Triticum aestivum L., cv Fidel) were surfacesterilized by consecutive treatments of 70% ethanol (3 min), sterile distilled water, 1% NaOCl (diluted commercial bleach, 30 min) and further washed in five changes of sterile distilled water. The grains were germinated under sterile conditions on moist filter paper in petri dishes (20 cm diameter), and incubated in the dark at 25C. Seedlings used for experiments were 2 d old and had three roots.

Leaf Abscission Induced by Ethylene in Water-Stressed Intact Seedlings of Cleopatra Mandarin Requires Previous Abscisic Acid Accumulation in Roots

“…3B) tion to ACC (Tudela and Primo-Millo, 1992), was actively transported through the xylem after rehydration. In roots, ABA synthesis induced by water stress (Cammue et al, 1989;Tardieu et al, 1992) andlor subsequent ABA transport from roots to shoots (Zeevaart and Boyer, 1984;Zhang and Davies, 1989;Neales and McLeod, 1991;Tardieu et al, 1991;Trejo and Davies, 1991) previously have been reported in a number of species. Water stress also induced ABA accumulation in leaves (Fig.…”

Maturation Proteins Associated with Desiccation Tolerance in Soybean

“…Exogenous ABA enhances expression of Lea proteins in seeds (1 1) as well as in vegetative tissue (5,19). Whether endogenous ABA induces expression of these genes in seeds is still debated (4).…”

“…In contrast, maturation proteins were induced under both conditions. We conclude that maturation proteins may contribute to desiccation tolerance of soybean seeds, though they may not be sufficient to induce tolerance by themselves.Like sugars, specific proteins are known to accumulate during late seed maturation (4,12,15), and some of these same proteins accumulate during drought stress of vegetative tissue (5,19). A role for this class of "late embryogenesis accumulating" (Lea) (9) or "maturation" (25) proteins in protecting against desiccation-induced damage has been proposed (2, 9) but correlations between protein level and desiccation tolerance have been reported only in developing barley seeds (3).…”

“…Like sugars, specific proteins are known to accumulate during late seed maturation (4,12,15), and some of these same proteins accumulate during drought stress of vegetative tissue (5,19). A role for this class of "late embryogenesis accumulating" (Lea) (9) or "maturation" (25) proteins in protecting against desiccation-induced damage has been proposed (2,9) but correlations between protein level and desiccation tolerance have been reported only in developing barley seeds (3).…”

Plant Lectins – More than Just Tools for Glycoscientists: Occurrence, Structure, and Possible Functions of Plant Lectins

“…With inhibition experiments using chitotriose which is one of the haptenic sugars of the lectin, it could be substantiated that the fungicidal action is due to the lectin [Broekaert et al, 1989]. Hevein, a protein that occurs in the latex of wounded rubber (H. brasiliensis) trees, is a further example of a chitin-binding protein that can inhibit fungal growth [van Parijs et al, 1991].…”