A TECHNIQUE FOR PREVENTING INACTIVATION AT THE CUT SURFACE IN AUXIN DIFFUSION STUDIES

Abstract

THE INACTIVATION OF AUXIN at the cut surfaces of plant organs and in crushed tissue extracts has long been a well-known phenomenon. Thimann (1934) reported that water extractions of many plants yield little or no auxin, whereas chloroform extractions of the same plants give good yields. He showed that crushed leaf extracts inactivate added auxin rapidly and concluded that the reduced yields obtained from water extractions were the result of auxin inactivation in aqueous solution by an oxidative enzyme system in the tissues. Later Kornmann (1935) described the ability of basal parts of Avena coleoptiles, and also their tips, cylinders of Helianthus hypocotyl, buds of Pisuwn, Tradescantia, and Ephedra, and petioles of Lup,inus to inactivate auxin in agar blocks. Van Overbeek (1935) has reported the inactivation of growth substances in agar blocks by cylinders from the mesocotyls of maize and also by coleoptile tips of the same plant from which the auxin had previously been removed by diffusion. In both cases he found the inactivation to be greater in the dwarf nana variety than in the normal variety which he studied, and he associated the inactivation with catalase-peroxidase activity in the tissues. He showed (Van Overbeek, 1938) that increased yields from the coleoptile tips of normal maize seedlings could be obtained if the tips were given a preliminary diffusion on wet filter paper. This, he reported, reduced peroxidase activity at the cut surface. Larsen (1936) obtained similar auxin inactivation with epicotyls of Phaseolus multiflorus, both in diffusions and in the juice of the plant. He was able to trap the inactivating substance in agar blocks and subsequently to inactivate auxin freshly added to the blocks. He determined that the substance was thermolabile and later concluded (Larsen, 1940) that it was an oxidative enzyme. Fiedler (1936) also brought forward evidence to suggest cut-surface inactivation by showing that in some cases, the disappearance of auxin from roots could largely be prevented by coating the cut surfaces of roots with gelatin or lanolin. Several other workers, including De Haan and Gorter (1936), Gorter and Funk (1937), Van Raalte (1937) and Syre (1938) have recorded the ability of various plant organs to inactivate growth substances, both