Growth of Parthenocissus tricuspidata tissue cultured on media containing aza analogues of indole-3-acetic acid & indole-3-propionic acid

Abstract

Several years ago, Robison and Robison (5) reported the synthesis of some compounds of biological interest. Among these were 7-aza-indole-3-acetic acid (AIAA) and 7-aza-indole-3-propionic acid (AIPA), aza analogues of indole-3-acetic acid (IAA), and indole-3-propionic acid (IPA). It was apparent that such compounds miglit be anti-metabolites of auxin, in the same manner that azaguanine has proved to be an inhibitor in guanine metabolism (2). For this reason, studies were begun of the effect of these compounds on normal and crown gall tissues of Parthenocissus. Although preliminary results indicated that these compounds might, indeed, be inhibitors, further study showed that they actually stimulated growth at certain concentrations (6). After initiating this study, Thimann (8) reported on the auxin activity of AIAA in Avena and Pisum; however, he did not report on the activity of AIPA. Since our results with regard to AIAA were in general agreement with Thimann's, it seemed even more appropriate to investigate the new compound, AIPA, and to extend the findings with AIAA to other plant tissues. Furthermore, this seemed especially desirable, since these compounds showed promise of being helpful in investigating the difference between normal and tumor tissues of Parthenocissus. One of the characteristics of the crown gall tissue is its ability to grow in culture in the absence of an exogenous auxin supply. The normal tissue must have auxin in the medium for growth. This difference in the two types of tissue has been the object of investigation for the last 10 years, and the possibilities for speculation have been narrowed. Several investigators have ruled out the possibility that the crown gall grows without auxin altogether (3, 4). Therefore, the only remaining possibilities are that the auxin is produced more rapidly in the crown gall, that it is destroyed less rapidly, or that the tumor has a much lower auxin requirement. Recently, Lipetz, and Galston (4) have shown that IAA oxidase can be obtained from the medium on which crown gall tissues are grown. Since this was not the case with the normal tissue, the fact suggested that the capacity of the crown gall to destroy auxin was higher than the normal and that the difference in the two tissues resulted from a higher auxin production in the tumor. However, the level of peroxidase was high in the normal tissue, and since this enzyme seems to be an essential part of the IAA oxidase system, the authors suggest that the oxidase activity in the intact normal cells may be quite high. The fact that it was possible to obtain inhibition of the growth of tumor tissue with the aza analogue of IPA suggested that it might be acting to block either the synthesis of auxin or its destruction. Therefore the investigation of the effects of the aza compounds was extended to their action on IAA oxidase from tumor tissue.