Binding of β-indoleacetic acid with proteins of plants and possible physiological significance of this process

Abstract

Investigations were carried out on the action of IAA on the cell enlargement process by the interaction of proteinous substances. Experiments were performed with French bean (Phasolus vulgaris) hypocotyls, bean steems (Vicia faba) and bean roots as well as with wheat (Triticum aestivum) coleoptiles. The binding of IAA with proteins takes place with different intensities in the upper and lower halves of French bean hypocotyls, bean stems and roots kept in a horizontal position. This process takes place several times more intensively in the lower halves of the hypocotyls and stems than in the upper ones. In the case of bean roots howevery the amount of IAA bound into proteins was several times higher in the upper half than in the lower one. It shows that there is a direct ratio between the cell elongation process and the quantity of bound IAA. The main quantity binds with conjugated proteins — desoxyribonucleoproteins (about 70%) and with ribonucleoproteins (about 20%). Bound IAA is absent in the fractions of globulins, albumens, glutelins, and glucoproteins. IAA binds with the nucleic part of the desoxyribonucleoprotein and ribonucleoprotein molecules. It should be assumed that IAA binds with DNA and RNA by a chemical link because it does not chip off when the specimens of nucleic acid are purified by repeated dialysis, dissolution, re-precipitation or by washing with non-labelled IAA. Under the conditions under which stimulation for binding IAA with DNA and RNA was found, also a stimulation of the incorporation of various amino acids — 14C into proteins have been found, i. e. in the lower half of wheat coleoptiles and French bean hypocotyls the incorporation of amino acids into proteins has been increased. In bean roots, the cell growth of which was stimulated in the upper half, the quantity of glycine incorporated into protein increases in the upper half, too. These results support the opinion that the essence of the primary step of the induction of the growth acceleration process by means of IAA is most likely connected with the interaction of IAA by binding with DNA and RNA. This interaction can lead to results in protein synthesis probably enzyme synthesis, and cell enlargement.