CAN A PYRROLE DERIVATIVE BE SUBSTITUTED FOR IRON IN THE GROWTH OF PLANTS?

Abstract

In a preliminary note Pollacci and Oddo (4) discuss the presence of iron in the pigment of vertebrate blood and that of magnesium in the chlorophyll of green plants, and the fact that these metals are bound to organic complexes which yield similar pyrrole compounds on reduction. An experiment was described in which corn seedlings were grown in a nutrient solution lacking iron and in one containing a magnesium salt of pyrrole carbonic acid in place of iron. After 20 days' growth the corn plants in the solution containing the pyrrole salt were normally green and three times the size of the chlorotic plants grown without iron. In a more extensive paper (3) these investigators report normal growth and chlorophyll-development of 6 species of plants in solutions containing this pyrrole salt but lacking iron. From these experiments and from the analytical work of Willstatter (5, 6) upon the chemistry of chlorophyll the theory was advanced that iron functions as a catalyst in the formation of pyrrole groupings which go to make up the nucleus of the complex chlorophyll molecule. The Italian workers contend that, when the pyrrole group is supplied to plants in a form which can be used, iron becomes unnecessary for the formation of chlorophyll. The writer became interested in this subject through efforts to induce chlorophyll-development in some genetically yellow corn strains. It was soon apparent that considerable work would have to be done to secure positive results with normally green plants with a pyrrole salt substituted for iron. The main object of the present investigation therefore became an attempt to confirm the work of Pollacci and Oddo. The literature dealing with the physiological action of pyrrole compounds in relation to plants is very limited. Ciamician and Galizzi (i) report that pyrrole carboxylic acid and dimethyl-pyrrole dicarboxylic acid are not toxic to plants. R. Emerson of Harvard University, in a communication to the writer, states that 2-4-dimethyl-3-5-dicarbothoxy-pyrrole and 2phenoxy-pyrrole have been used in nutrient solutions for the growth of several species of plants with varying success. The magnesium salt of pyrrole carbonic acid used in these experiments, except for a small sample received from Prof. Oddo, was prepared by J. S. Chu 1 and the writer in the Organic Chemistry Laboratory of the