Effect of Zinc Nutritional Status on Growth, Protein Metabolism and Levels of Indole-3-acetic Acid and other Phytohormones in Bean (Phaseolus vulgaris L.)

Bean (Phaseolus vulgaris L. var. Prelude) plants were grownfor 17 d under controlled environmental conditions with variedZn supply in the nutrient solution. The concentrations of aminoacids; indole-3-acetic acid, IAA; abscisic acid, ABA; isopentenyladenine, I-Ade; isopentenyl adenosine, I-Ado; zeatin, Z; andzeatin riboside, ZR were determined in various shoot fractions. The growth of plants, especially shoot growth, was severelydepressed under conditions of Zn deficiency. Simultaneously,concentrations of soluble protein and chlorophyll decreased,whereas amino acid concentrations increased several-fold. Inthe Zn-deficient plants, the level of IAA in the shoot tipsand young leaves decreased to about 50% of that in Zn-sufficientplants. A similar decrease occurred in the ABA levels of shoottips. In contrast, Zn deficiency was without effect on cytokininlevels in the leaves. Re-supply of Zn to the deficient plantsfor up to 96 h significantly increased shoot growth, solubleprotein, and IAA levels up to the values of Zn-sufficient plants.Simultaneously, the concentration of amino acids dropped tolow levels. The effect of Zn nutritional status on the tryptophanlevel was parallel to that of most of the other amino acids.The results confirm the role of Zn in protein synthesis anddemonstrate that the decrease in IAA level in Zn-deficient plantsis not brought about by impaired synthesis of tryptophan. Itis also unlikely that in Zn-deficient plants the conversionof tryptophan to IAA is specifically inhibited. Key words: Indole-3-acetic acid, tryptophan, zinc deficiency