Movement 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... 

Analysis of tissues for lAA as determined by reverse isotope dilution assays reveals however, that brassinolide does not affect auxin uptake or auxin movement within the tissues (41). In this same study we also observed that bean internode sections treated with brassinolide contained significantly less lAA after 2 hours than tissues treated with lAA alone, even though BR potentiated lAA-induced growth by more than 400%. 

Another important factor of hormone-hormone interaction is the hormonal control of hormonal movement and polarity. Thus, various cytokinins have been reported to increase the polar movement of indole acetic acid and vice versa. Gibberellin treatment was shown also under cer- bain circumstances to increase the basipetal auxin movement. On the other hand, abscisic acid decreases the auxin movement and ethylene, according to some evidence, the gibberellin movement, perhaps through a promotion of conjugation of the auxins with aspartate and of the gibberellins with glucose (cf. Eef. 27). 

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...

One of the most potent factors in the regulation of lAA biosynthesis may be lAA itself. lAA appears to suppress its own biosynthesis in decapitated coleoptiles (Anker 1973), and certain auxin-induced modifications of growth patterns have been attributed in part to effects on endogenous auxin production (Evans and Schmitt 1975, Evans et al. 1977). Red light-induced suppression of auxin production in coleoptile tips may result from a suppression of auxin movement out of the tip leading to feedback inhibition of auxin biosynthesis (Huisinga 1976). 

Goldsmith MHM (1966 b) Maintenance of polarity of auxin movement by basipetal transport. Plant Physiol 41 749-754... 

Hertel R, Flory R (1968) Auxin movement in corn coleoptiles. Planta 82 123-144 Hertel R, Leopold AC (1962) Auxintransport und Schwerkraft. Naturwissenschaften 49 377-378... 

Krul WR (1977) Differences in velocity of auxin movement obtained by intercept and peak arrival methods. Physiol Plant 41 259-264 Krul WR, Colclasure GC (1977) Effect of galactose and other monosaccharides on lAA movement in bean hypocotyl segments. Physiol Plant 41 249-253 Kruszewski SP, Jacobs WP (1974) Polarity of thiamine movement through tomato petioles. Plant Physiol 54 310-311... 

Mai G (1934) Korrelationsuntersuchungen an entspreiteten Blattstielen mit lebenden Or-chideenpollinien als Wuchsstoffquelle. Jahrb Wiss Bot 79 681-713 Maravolo NC (1976) Polarity and localization of auxin movement in the hepatic Mar-chantia polymorpha. Am J Bot 63 526-531... 

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