Polarity auxin

Another area in which Arabidopsis genetics is proving to be useful is the study of the proposed role of flavonoids in regulating auxin transport. Several years ago, Jacobs and Rubery published the first evidence that flavonoids could specifically compete with naphthylphthalamic acid for binding to the auxin efflux carrier in etiolated zucchini hypocotyls.35 This finding was somewhat controversial, however, and no additional evidence for the connection between flavonoids and auxin transport was reported for some time. Brown et al. have now used Arabidopsis flavonoid mutants to generate new evidence in support of a role for flavonoids in the regulation of polar auxin movement.6 These experiments took... 

To determine whether the reduced polar auxin transport observed in IFS knockdown plants was causal to the absence of nodulation, the authors conducted... 

Galweiler L, Guan C, Muller A, Wisman E, Mendgen K, Yephremov A, Palme K. 1998. Regulation of polar auxin transport by AtPINl in Arabidopsis vascular tissue. Science 282 2226-2230. 

Muday GK, DeLong A. 2001. Polar auxin transport Controlling where and how much. 

The inhibition of growth by ethylene in subhook regions of etiolated pea seedlings is largely due to reduction in the polar auxin transport system which supplies auxin to the cells (42,... 

A new class of plant auxin herbicides are the phytotropins, exemplified by the semicarbazone diflufenzopyr [148], Diflufenzopyr is a systemic herbicide for the selective control of broadleaf and perennial weeds in corn. Unlike the early auxin herbicides, such as 2,4-d and dicamba, which acted as mimics of indole-3-acetic acid, phytotropins prevent polar auxin transport in sensitive plants, causing stunting and loss of tropic response [149],... 

Keith and Baker (1966) found that naptalam strongly inhibits the transport and function of the basipetal polar auxin, 4-(indol-3-yl)acetic acid (lAA). 

Long-distance lAA transport from the apex downwards occurs at least partly in the phloem. Short-distance transport occurs by a process called polar auxin transport [45]. This involves a symmetrical uptake of lAA into cells up a pH gradient, coupled with unidirectional efflux of lAA from the basal end of cells. Auxin is removed from the... 

In gravistimulated roots pretreated with EGTA, there was little or no polar auxin movement across the caps. Polar auxin movement was restored by treatment with Ca prior to gravistimulation (Table 2). These results are in agreement with Koning s conclusion that the cap is the site of initial auxin redistribution, and they suggest that Ca is important to the auxin distribution mechanism. 

Table 2. Elfects of EGTA and calcium on gravi-in-duced polar auxin movement across the caps of maize roots...

Powerful synthetic Polar Auxin Transport Inhibitors (PATIS) have been available for many years and have proved valuable investigative tools [35]. They... 

Fig. 4. Effects of quercetin on polar auxin transport by zucchini hypocotyl segments. Data are counts per min collected in the pooled receivers of quintuplicate samples over the half-hour periods shown and for the period from 2 to 3 h of transport. Open panels control treatment, shaded panels quercetin...

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