IV. The effect of auxin on RNA and protein synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Requirement for RNA and protein synthesis ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Action of auxin on RNA polymerase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Binding of auxin to chromatin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Binding of auxin to RNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Auxin and enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Auxin induced enzyme synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Auxin and ribonuclease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 The effect of enzymes on growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Probable absence of involvement of polysaccharidases . . . . . . . . . . . . . . . 148 Protein synthesis and wall extensibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Current theories on the mode of action of auxin

The RNA molecules are stable under physiological conditions, and can be broken down in vivo only by enzymatic hydrolysis All RNA molecules are subject to hydrolytic breakdown; this makes their turnover possible The hydrolytic breakdown of RNA, in addition to the regulation of RNA synthesis at the transcriptional level, plays a major role in the selection of those molecular 
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Table 1
Classification of RNA-splitting enzymes

species of RNA which are needed by the cell at a given moment of its development Therefore, a thorough knowledge of the RNA-splitting enzymes in pivotal for the understanding of a number of regulatory and developmental processes in which RNA molecules are involved

Ribonucleases and Ribonucleic Acid Breakdown

Exogenous application of hormones is one of the most common methods in research into the mode of action of such substances. The rationale behind such approaches is based mainly on the idea of replacement of the endogenous, naturally occurring hormone by an exogenous hormone, the level of which may be controlled and its effect monitored. This is fairly easily accomplished in animal systems, where the gland synthesizing a particular hormone can be dissected out and the target tissue monitored after application of the exogenous hormone via the blood stream. This is rarely easy and often impossible to achieve with plant material because in most instances any given hormone may be produced in more than one location within the plant. Furthermore, the same organ or cell which produces the hormone may also be the target.

Molecular effects of hormone treatment on tissue.

Ribonucleases in vascular plants: cellular distribution and changes during development

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Morphology, RNase and transaminase of root protoplasts

In Lens root tips, a direct proportionality between RNA and auxin levels and inverse proportionality between RNA content and RNase activity were found. IAA treatment of the Lens seedlings causes, in the root, both an increase of RNA and auxin content and a decrease of RNase activity. Addition of IAA to the excised roots produces an inhibition of both the decrease of the RNA levels and an inhibition of the increase of the RNase activity. The action of IAA on growth, related to the control of the RNA metabolism is discussed.

Ribonuclease Activity and Auxin Effects in the Lens Root

The correlation between auxin and RNA metabolism was investigated in lentil roots. IAA and NAA both cause a considerable rise in the RNA level of germinating lentil roots, though no effect of IAA was found on the DNA level. In untreated germinating roots various sections were isolated and a direct relation found between RNA and auxin content, and an indirect relation between RNA content and auxin oxidase activity.



In excised roots, incubated for 24 hours, the loss of RNA is paralleled by a loss of endogenous auxin. Excised roots treated with 10−4M IAA or M 10−4 NAA loose little RNA.



The findings suggest that in lentil roots the RNA levels may be controlled by auxin levels, which in turn may be controlled by the levels of auxin oxidase.

R. Braun

Papers

Ribonuclease Activity and Auxin Effects in the Lens Root

The Interrelation of RNA, Auxin and Auxin‐oxidases in Lentil Roots