Endogenous auxin, replacement

If auxin determinations are done by bioassay, the transport sections must be depleted of their endogenous auxin before the donors are applied. Usually, batches of ten or more sections are combined in order to collect enough auxin in a receiver for quantitative determinations. Van der Weij used three or more batches of coleoptile sections, and assayed for auxin in the receiver blocks at three or more intervals. Another method is to replace receiver blocks periodically with fresh (blank) agar blocks. The amounts of auxin in the respective receivers were then used for plotting and/or computing data (see Fig. 3.1). In order to guarantee a constant auxin concentration in the donors, they, too, were replaced periodically in longer experiments (see Sects. 3.3.3.4, 3.3.3.5). 

In studies of the basipetal auxin transport in flower stalks of Fritillaria, a method has been used which may be likely to estimate the in situ situation (Kaldewey 1968 b, 1971). The basic idea of this method was to replace the stream of endogenous auxin, delivered to the stalks by the bud or fruit (Kal-... 

It has been evidenced that auxin and ACC stimulate ethylene production in some lower plants, for example, in the moss Funaria hygrometrica and in the ferns Pteridium aquilinum and Matteuccia struthiopteris Moreover, ethylene synthesis via the ACC-dependent pathway and in the presence of endogenous ACC and its conjugate in marine unicellular Acetabularia algae was reported. Probably during the evolution of land plants, a relatively primitive pathway of ethylene production was replaced by the ACC-dependent synthesis pathway that now predominates. 

---