Influence reciproque de quelques substances de croissance dans la culture de tissu de topinambour (Helianthus tuberosus L. var. Violet). I. Le comportament du milieu de culture

The influence of explants from tubers of Jerusalem artichoke on the culture medium was studied. Growth substances: indolyl-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic-acid (2,4-D) and naphthoxyacetic acid (NoxAA) rapidly disappeared from the medium as was shown in the ether extraction. When labelled IAA was introduced it appeared that a long extraction period with ether (48h) is necessary. IAA-1-14C decarboxylated more rapidly than IAA-2-14C. Thus all experiments were done with IAA-2-'4C. The culturing procedure was standardized: 30 ml medium (minerals of Heller, 2% glucose, 0.8% agar) containing 10 ppm IAA and about 1.2 xlO6 cpm IAA-2-I4C was used. Three cylindrical pieces of Jerusalem artichoke weighing each 160-180 mg were transferred to the medium. A device was made to avoid t4CQ2 losses. The disappearance of IAA from the medium was followed during 10 days. During the first 5 days the pH of the medium increased from 4.5 to 6.5. The IAA content decreased and this decrease continued and reached 50% after 10 days. This probably explains why the tissue can be transferred, after 10 days, to a medium without auxin and can continue its development. The decarboxylation of IAA, naturally taking place, is much (10 x) enhanced by the tissue. The problem now is, whether the tissue enhances the decarboxylation in the medium, or whether the tissue absorbs the intact IAA and secretes the decarboxylated product into the medium.