Studies on the adaptation of roots of Pisum satiuum to auxins and anti-auxins

Abstract

Evidence has been provided which decisively demonstrates that the Pisum Satiuum roots growing continuously in the inhibitory medium of 2,4-D and IAA become less sensitive to their inhibitory action and to the inhibitory action of the other growth substances (TIBA x CNB). The reduced sensitivity of IAA grown root sections to applied IAA may partly be due to the induced formation of the IAA-oxidizing enzymes which in fact lower the auxin level in the cells by oxidizing it.This, however, can not be the case with 2,4-D since there is no evidence that this compound can induce the formation of an adaptive oxidase. Furthermore, it has been found that IAA grown root sections are less sensitive to the inhibitory action of 2,4-D which can not be oxidized by the enzyme IAA-oxidase. It is therefore concluded that both IAA and 2,4-D induce basical changes in the constitution of the growth enzymes of the cells formed in their presence that they become less sensitive to their inhibitory action. As far as anti-auxins are concerned TIBA and DCA grown root sections also show much reduced sensitivity towards auxin IAA and this has been found to be explainablein the terms of the induced formation of adaptive oxidase already present. TIBA inhibition might be due to the increased destruction of endogenous auxin as the IAA root sections show less response to the inhibitory action of applied IAA. It is therefore suggested that the auxin in the normal root sections is at a sub-optimal level.Roots grown in the inhibitory medium of CNB show anincreased sensitivity towards applied IAA. There is alsono effect of CNB on the oxidase contents of roots grownin its solution. Furthermore, 2,4---D grown root sections are less sensitive to the inhibitory action of CNBindicating a direct antagonism by 2,4---D retained in their cells. The conclusion drawn from the above results is that IAA, 2,4-D, TIBA ana DCA reduce the sensitivity of the cells formed in their presence to their inhibitory action and to the inhibitory action of the other three. 2,4-D indicates a direct action on the growth system while IaA, TIBa and DCA may, in addition, cause an apparent loss of sensitivity to IAA by stimulating the production of oxidizing enzymes. CNB acts as an auxin antagonist to growth substances.