Histological and Microchemical Studies of the Reactions of Tomato Plants to Indoleacetic Acid

Abstract

1. Tomato seedlings were decapitated above the second lobed leaf and a mixture of 20 mg. of indoleacetic acid in 1 gm. of lanolin was applied to the cut surface. Similarly, decapitated plants were kept as controls, either untreated or with pure lanolin applied to the cut surface. 2. Gross observations and histological and microchemical studies were made of treated and control material collected at frequent regular intervals for a period of 216 hours after treatment. 3. The internode terminated by the cut surface fails to enlarge after decapitation unless the cut surface is treated with indoleacetic acid-lanolin mixture. The internodes so treated enlarge at about the same rate as do the internodes below. 4. The first change observed after treatment was enlargement of cells of the epidermis and cortex. 5. Many of the tissues of the stem became meristematic in response to the treatment, although most of this activity was confined to a zone 0.5 to 2 mm. from the treated surface. Most parenchymatous cells in this zone underwent some divisions; the endodermal cells, external and internal phloem parenchyma, and pith cells adjacent to the internal phloem exhibited the greatest activity. There were, however, certain tissues comprising a small portion of the stem whose living cells showed little or no meristematic activity. These include epidermis, most of the pericycle, sieve tubes and companion cells, and internal fibers. 6. A ring of adventitious roots was formed around the stem as a result of activity in the external phloem. Portions of the active band of endodermal cells covered the tips of these roots as they pushed through the cortex. Another ring of adventitious roots was formed near the pith as a result of activity of cells of the internal phloem and adjacent pith. 7. Nitrates were more concentrated in the controls than in the stems treated with indoleacetic acid. The concentration of protein in the treated stems increased in those areas where cell divisions became most abundant. Starch disappeared from the cells of the treated stems as the tumors enlarged, but remained in the controls.