The Biosynthesis of Indoleacetic Acid in the Styles and Ovaries of Tobacco Preliminary to the Setting of Fruit.

Abstract

Levels of free tryptophan in styles and ovaries of Nicotiana tabacum were followed. Immediately after pollination the level decreases in styles and then begins to rise beyond the amount found in styles of unpollinated flowers. Free tryptophan of the ovary increases 24 to 41 hrs. after pollination. Pollen tubes of tobacco can be grown in a liquid, sucrose-mineral soln. on a rotary shaker. Under such conditions they can convert supplemented tryptophan to a growth hormone. This is dependent upon time and concn. of substrate. The hormone of resting and germinating pollen was identified as indoleacetic acid (IAA) by paper chro-motography. IAA was also identified as the hormone produced by pollen tubes in the presence of tryptophan. Enzymatic activity as measured by the ability to convert tryptophan to IAA increases 3-fold in homogenates of pollen tubes as a result of 10 hrs. germination and 4-fold when pre-treated with tryptophan. The same enzyme system increases in activity in styles immediately after pollination and somewhat later in ovaries. It is concluded that the pollen tubes of tobacco supply to the style and ovaries additional amounts of enzymes which oxidize tryptophan to IAA and hence initiate fruit development.