Inhibition auxin transport

Inhibits auxin transport, apparently by binding with a carrier protein on the... 

Phytotropins are synthetic molecules which affect the tropic responses, inhibit auxin transport and bind to the receptor for 1-N-naphthylphthalamic acid (NPA) (10-1) [91-93]. For a recent review see [94]. A simple assay to detect and compare activities is measurement of antigravitropic activity on cress seedlings [95]. There are two phytotropin recognition sites on the NPA receptor, or two receptors, which recognize phytotropins... 

It is obvious that no single structure-activity correlation can encompass all molecules which can bind to the NPA receptor. It has been suggested that the receptor may be multifaceted [106], but there may also be multiple receptors. Compounds which interact with the NPA receptor(s) inhibit auxin transport and it can be classified as auxin transport inhibitors , but auxin transport inhibition need not be the, or the only, function of the receptor(s). Flavonoids have been proposed as the natural ligands, but there may be others and these need not act in the same way as the synthetic molecules [94]. There is much that is unknown about the role and function of NPA receptors. 

Naptalam seems to specifically inhibit auxin transport, and it must be concluded that different sites exist for auxin transport and other auxin-induced responses. 

Mathesius U, Schlaman FIRM, Spaink PIP, Sautter C, Rolfe BG, Djordjevic MA. 1998. Auxin transport inhibition precedes root nodule formation in white clover roots and is regulated by flavonoids and derivatives of chitin oligosaccharides. Plant J 14 23-34. 

Wasson AP, Pellerone FI, Mathesius U. 2006. Silencing the flavonoid pathway in Medicago truncatula inhibits root nodule formation and prevents auxin transport regulation by rhizobia. Plant Cell 18 1617-1629. 

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,... 

In some cases it might be desirable to inhibit ethylene synthesis chemically to prevent responses mediated by naturally produced ethylene or stress-produced ethylene. Although some substances do inhibit ethylene production modestly—e.g. TIBA (69)—no outstanding regulator of this nature has been discovered. Another possibility is to promote or inhibit ethylene action. Promotion can be accomplished by auxin transport inhibitors and GA in cases where auxins and ethylene have opposite effects 52, 53, 54, 55). Recently, silver ion was found to be a potent inhibitor of ethylene action (70). Ethylene action also can be inhibited by lowering the temperature and O2 level or increasing the CO2 level... 

Diflufenzopyr giving membrane disruption (1996) Inhibits the auxin transport 1999... 

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). 

Ethylene is a hydrocarbon plant hormone that comes from the methionyl moiety of S-adenosylmethionine. Ethylene stimulates fruit n 2 ripening and the aging of flowers, and it inhibits seedling growth. It also redirects auxin transport (another plant hormone) to promote transverse, rather than longitudinal, growth of plants. 

Triiodo Benzoic Acid (TIBA) 10-6 is unique. It can act as an auxin, anti-auxin and auxin transport inhibitor. It can inhibit in vitro auxin transport before binding to the NPA receptor is observed. It need not act by the same mechanism as phytotropins [96]. 

Auxin-transport inhibition was recently reported to interfere with the normal course of cellular development in the root apex. Roots of the tir3 mutant of Arabidopsis are believed to be affected in this way [79]. The primary root of the mutant has a meristem twice the length of wild-type (500 p,m compared to 250 p,m), suggesting that an altered auxin distribution within the root apex permitted more cells than normal to remain in a... 

The first study relates to the identification and design of novel herbicides and plant growth regulators that act by inhibiting polar transport of the plant hormone auxin (100). Previous studies (101) had identified seven auxin transport inhibitors, from which it was possible to describe a three-component... 

The growth of plants can be retarded by inhibiting the transport of the auxin, indol-3-ylacetic acid. Schneider (1964) prepared a series offluorene derivatives to produce dwarf varieties of economic plants. Another use of these morph-actins, as they are called, is to retard the growth of dicotyledonous weeds in a... 

The process of auxin transport can be inhibited by a group of synthetic compounds which bind to a specific cell membrane receptor. Several flavonoids, including quercetin (7), apigenin (5), and kaempferol (6), can specifically compete with one of the synthetic compounds, naphthylphthalamic acid, at micromolar levels for binding to the receptor and, thereby, perturb auxin transport in a variety of plant tissues (Jacobs and Rubery, 1988). Although quercetin (7) was highly active, a common quercetin glycoside, rutin (35) proved inactive. 

PCIB can therefore be either due to, a) a disruption of endogenous auxin transport, b) an inhibition of auxin synthesis and or accumulation, and c) competition for auxin-binding sites. Based on data available at present, these alternatives cannot be distinguished. 

NPA and other synthetic auxin transport inhibitors can block PAT when they are incorporated into the receiver blocks in a classical donor-to-receiver polar transport assay. Figure 4 shows that quercetin in receiver blocks can inhibit lAA arrival, but only for the first 2 h of the transport test. Thereafter, the radioactivity delivered to the receiver blocks is increased compared to controls. In some experiments lAA (or NAA) arrival in quercetin-containing receiver blocks is increased at earlier times. A crossover is never observed when NPA is used. Quercetin and other flavonoids bind strongly to cellulose [31 ] and, unlike NPA, do not diffuse away... 

It is possible to circumvent problems arising from quercetin s apparent immobility when added to the basal end of a transport segment, by applying it or N PA as small local doses half-way up 20 mm long hypocotyl segments (Table 4). With this method both substances can be seen to interrupt the lAA transport stream and to inhibit basipetal auxin transport. Attempts to demonstrate perturbation of seedling gravitropism by quercetin have so far been unsuccessful. 

---