Auxin messenger

These observations are consistent with the conclusion that auxin treatment leads to the synthesis of BS cellulase, which then accumulates in smooth ER vesicles. There is direct evidence that the synthesis occurs in rough ER vesicles (11). Cellulase activity was shown (25) to increase in RNA-rich pea microsomes, provided these were isolated from auxin-treated tissue, when the preparations were incubated with ingredients necessary for carrying out protein synthesis in vitro. Messenger RNA (mRNA) from these microsomes has been translated in a different ribo-somal system and shown to synthesize BS cellulase protein (II). Thus, it is legitimate to use the term "induction to apply to the ability of auxin to evoke the appearance of mRNA for BS cellulase. 

Zurfluh, L.L., Guilfoyle, T.J. 1982. Auxin-induced changes in the population of translatable messenger RNA in elongating sections of syobean hypocotyl. Plant Physiol. 69 332-337. 

There is experimental evidence that herbicides with auxin action also interfere at the gene level in the specific protein synthesis of plants. According to the investigations of Hanson and Slife (1969) and Key (1969), this probably occurs by the abnormal enhancement of messenger RNA production. 

A variety of second messengers have been implicated in auxin signaling including phosphatidylinositol, calcium, and the products of phospholipase A (PLA) enzyme. Since most of these reports have been in the literature for some time, they will not be discussed here (see [47] for review). Recent reports have provided additional evidence for a role for PLA in auxin action. Earlier studies by Andre and Scherer [48] showed that auxin treatment resulted in an increase in PLA activity in a number of plant species suggesting that a product of this enzyme functions as a signaling molecule. Consistent with this possibility, inhibitors of mammalian PLA inhibit auxin-induced hypocotyl elongation in... 

The Second Messenger in Apical Dominance Controlled by Auxin... 

The existence of a closed circulatory system in higher animals provides the organism with an easy and efficient route for the transport of hormones from the site of synthesis to the target tissues. In plants some hormones appear to be transported directly in the vascular tissue for example, cytokinin, GA, and ABA move from the root to the shoot in the xylem GA moves out of young leaves in the phloem and ABA is transported out of wilting leaves in the phloem (Fig. 6.1). However, auxin is not transported directly in the vascular tissue, but instead appears to be transported in cells associated with the phloem (Fig. 6.1). Ethylene poses a special problem in that it is a diffusable gas. However, its precursor, 1-aminocyclopropane-l-carboxylic acid (ACC), is transported from the root to the shoot in the xylem. Therefore, using the traditional concept of a hormone as a translocated chemical messenger, ACC may be more aptly considered to be a hormone than ethylene. 

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