Stimulation of Growth in Zinc‐Deficient Corn Seedlings by the Addition of Tryptophan1

Abstract
L‐tryptophan added to the nutrient solution has been shown to eliminate retarded growth and deficiency symptoms resulting from omission of zinc in the growth of young corn seedlings (Zea mays L.). Compared to those which received zinc, seedlings treated with tryptophan had about a five‐fold reduction in tissue‐zinc content. No additive effect on growth was observed when tryptophan and zinc were supplied together. Addition of indole‐3‐acetic acid (IAA) failed to correct deficiency symptoms or restore growth rate in zinc‐deficient plants. The results indicated that optimal synthesis of tryptophan depended on suitable levels of zinc in the tissue and that the leaf‐streaking symptom was actually caused by low levels of this amino acid in the tissue under zincdeficient conditions.

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