Biosintesi Delle Indolauxine Acide in Plantule di Orzo Marcato con C14: Effetti Dell'irraggiamento Sui Semi (Riassunto)

Abstract

Biosynthesis of acid indolauxins in young barley plants labelled with C¹⁴. Effects of irradiation on seeds. — With this preliminary research we wanted to begin the study of the setting-up of a system in order to mark young plants cultivated in several groups and kept under the same growth conditions. This apparatus has been utilized for the first time to study the irradiation effect of barley seeds on the biosynthesis of the acid indolderivates (PIA, BIA, IAA). The data in literature on the effect of radiations on the indolauxin-synthesis are barely uniform and we can summarize them so: Skoog (1935) has demonstrated that the auxin content of irradiated plants decreases already at very small doses; the results have been reached by the biological test and seem to be barely reproducible.

Afterwards, Gordon (1957) has confirmed the Skoog's data about different species of plants remarking that also with small doses of radiations the quantity of free auxins decreases quickly soon after irradiation. Gordon has also utilized for his experiments the biological test.

The author, supposing that the free auxins of plants were prevalently IAA, has irradiated IAA solutions: the results have pointed out that the molecule of this auxin is not particularly radiosensible. From these results Gordon concluded that in irradiate plants the decrease of IAA was not given to a direct action of irradiations of the molecule, but to a decrease of its biosyntesis. This assumption has also been maintained by Gordon on account of the results of a further experiment: giving triptophane to sprouts of irradiated seedlings of peas the author remarked a lessening of the IAA synthesis as the doses of irradiation increased. He demonstrated, by another experiment made on omogenates, that radiations caused a rent at the enzyme level which turnes the indolacetic aldeid into acid. On the other hand the data obtained by Gordon on the radiosensibility of IAA aqueous solutions are in opposition to the ones got by Skoog by experiments in vitro and by Cervigni and Belli (1962) which confirmed Skoog's data. These A.A. have demonstrated that the results obtained by Gordon are contestable on account of the analytical technique used. It is well known that seed irradiation causes an evident lessening of growth in young plants development. This phenomenon at least on one side might be connected with an alteration of the metabolic system, which causes the growth regulators synthesis, as the indolauxin.

This experiment wants to bring a contribution to the study of this important problem.

In this first experiment barley has been chosen because the irradiation of the seed at the employed doses. (7,5 and 15 Kr of X rays) does not causes a lessening of the germinability, while it does effect the growth.

Young plants derived from irradiated seeds and from the control ones, on the seventh day from the sowing were put into contact with an atmosphere of C¹⁴O₂ for 42 hoūrs. From the experimental data it has resulted that the synthesis of indolderivates acid in young plants originated from irradiated seeds does not decrease. On the contrary it seems that at least as far as the leaves are concerned there is a greater synthesis by increasing the irradiation dose.

If these first results will be confirmed by further experiments, we can think that the lessening of growth caused by irradiation it does not depend on the decreased synthesis of the acid auxins group, as Gordon and others stated, but rather on the alteration of other regulator systems, strictly connected with the plant's development. It cannot also be excluded that the lessening of growth caused by irradiation, may be attributed to a less sensibility of the tissues to the acid indolauxins.