Document Type

Thesis - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)




Zinc-deficient corn plants were obtained by raising seedlings in nutrient solution without added zinc. In the absence of zinc, retarded growth was evident after 16 days of germination. Interveinal chlorosis of the leaves was observed on plants grown in this nutrient solution without added zinc. Substitution of tryptophan for zinc in the nutrient solution without added zinc. Substitution of tryptophan for zinc in the nutrient solution during the first 19-day growth period, completely corrected the symptom of retarded growth and the other symptoms of zinc deficiency. This optimal growth and tryptophan was accomplished even with a five-fold reduction of tissue zinc when compared with zinc treatment. This result was interpreted to indicate that tryptophan synthesis required zinc. Substitution of indole acetic acid for zinc in the growth medium resulted on in a slight increase in dry weight yields when compared with the minus-zinc treatment. The lack of adequate response to supplemental IAA could be attributed to its inactivation by zinc-deficient plants. Dry yield data indicated that growth response was evident after 16 days of germination, but zinc application was shown to be essential by the sixth day of germination. Application after this data resulted in a reduced growth rate from which the plant did not recover after 18 days of growth. Therefore, zinc was clearly shown to be involved in the processes vital to growth. While it took 16 days for retarded growth to be evident in plants that received no zinc, a reduction in the heavy polysome population was observed on 4-day old seedlings growth under similar conditions. Therefore, it would seem that the accumulated growth resulting from the addition of zinc or tryptophan was reflected at the polysomal level at the early stages of development. The polysome studies thus gave added support to the growth data since they showed the same relationship between tryptophan and zinc treatments. As in the growth investigation the IAA-treatment was intermediate with the minus zinc treatment consistently the lowest. The additional support for the zinc-trypophan relationship was obtained in a series of tests with N-bromosuccinimide. The inactivation of tryptophan in plants grown in nutrient solution in which bromosuccinimide was added, resulted in characteristic zinc deficiency symptoms even with an adequate level of zinc in the tissue. In a polysome study a marked reduction in polysome yield due to this compound. These results demonstrated that zinc is necessary for tryptophan synthesis. It would appear that the role of tryptophan as a precursor for IAA synthesis is only a part of its complete function in corn plants.

Library of Congress Subject Headings

Corn -- Field experiments



Number of Pages



South Dakota State University