NUTRIENT DEFICIENCIES AND GROWTH HORMONE CONCENTRATION IN HELIANTHUS AND NICOTIANA

Abstract

THE RELATION of mineral nutrients to the production of growth hormone in plants pertains directly to the problem of plant development. Shoot tips are the main centers of growth in higher plants; they are also the main centers of hormone production. The continuous initiation and subsequent expansion of new organs in such regions depends upon the successful mobilization of the raw materials needed for growth; likewise, the continued production of hormone depends upon the presence of the proper raw materials. Studies on the growth hormone content of Helianthus and Nicotiana (Avery, Burkholder, and Creighton, 1936) have shown (1) that the hormone is scarcely detectable in the absence of supplied nitrogen; (2) that, within certain limits, hormone concentration is in proportion to the amount of nitrate supplied to plants grown in sand culture; (3) that shoot tips of Nicotiana grown in field experimental fertilizer plots exhibit no relationship between miiieral deficiencies and hormone content. From the latter it was concluded that the degree of deficiency observable in field-grown material was not sufficient to decrease the content of growth promoting substances in shoot tips. Before further studies on this subject were undertaken, the necessity became clear for establishing the relationship between mineral nutrition and growth hormone production with plants grown under controlled conditions in sand cultures. INVESTIGATION.-Growth hormone concentration in relation to varied proportions of nutrient ions.-The relationship of growth hormone concentration to varied nutrient ion proportions was studied in Helianthus annunts L. grown in sand cultures. In this work, a nine-salt solution was employed so that it was possible to vary in any single series of solutions the concentration of any cation or anion over a wide range without extensively altering the relation of the concentrations of the ions of opposite charge to each other (Beckenbach, Wadleigh and Shive, 1936). A list of the salts employed and the amounts used for making up the different culture solutions may be found in table 1. The nine salts containing the essential elements-nitrogen, phosphorus, potassium, calcium, magnesium, sulphur-were used in amounts appropriate to yield nutrient solutions with five of the ions in arbitrary standard concentration for each series of solutions, and one selected ion was varied so as to give relative concentrations as follows: times the standard, 1 (standard), 0.1, 0.02, 0.01 times the standard, and none. For example, the 4 nitrogen culture solution contained times as much