Auxin inhibition

Anai T, Aizawa H, Ohtake N, Kosemura S, Yamamura S, Hasegawa K (1996) A New Auxin-Inhibiting Substance, 4-0-6,7-dimethoxy-2-benzoxazolinone, From Light-Grown Maize Shoots. Phytochemistry 42 273... 

Kosemura, S., Emori, H., Yamamura, S., Anai, T., and Aizawa, H. 1995. Isolation and characterization of 4-chloro-6,7-dimethoxybenzoxazolin-2-one, a new auxin-inhibiting benzoxazolinone from Zea mays. Chem. Lett., 1053-1054... 

Anai, T., Aizawa, H., Ohtake, N., Yamamura, S., and Hasegawa, K. 1996. A new auxin-inhibiting substance, 4-CI-6,7-dimethoxy-2-benzoxazolinone, from light grown maize shoots. Phytochemistry 42, 273-275... 

The influence of different growth hormones on C. roseus plant cell cultures has been extensively studied (for reviews, see refs. 7,8,11,317). In general, the conclusion is that auxins inhibit the alkaloid production 2,4-... 

Caspar et al. (1972) suggested that the inhibition of root elongation by lAA may be caused by a metabolite of lAA, most probably 3-methyleneoxindole (3-MO). However, it has since been shown that purified 3-MO does not inhibit root elongation (Evans 1976c). These data in conjunction with the rapidity (15-20 min) with which intact root growth is inhibited by low concentrations of lAA, indicate that auxin inhibition of root cell elongation is a direct effect. 

Mayak S, Halevy AH (1972) Interrelationships of ethylene and abscisic acid in the control of rose petal senescence. Plant Physiol 50 341-346 McBride R, Evans ML (1977) Auxin inhibition of acid- and fusicoccin-induced elongation in lentil roots. Planta 136 97-102... 

The mode of action is by inhibiting 5-enolpymvyl-shikimate-3-phosphate synthase. Roundup shuts down the production of the aromatic amino acids phenylalanine, tyrosine, and tryptophane (30). Whereas all these amino acids are essential to the survival of the plant, tryptophane is especially important because it is the progenitor for indole-3-acetic acid, or auxin, which plays an important role in growth and development, and controls cell extension and organogenesis. 

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

Inhibition of tomato and barley plants growing in soils infested with Centaurea repens (knapweed) was reported by Fletcher and Renney (38). A toxic component was isolated in highest concentration from the foliage of knapweed. The inhibitor was considered to be an indole alkaloid or auxin precursor because of its ultraviolet absorption spectrum and the positive reactions obtained with Salkowski and Ehrlich reagents. The presence of the inhibitor was considered to explain partially the rapid establishment of Centaura spp. in almost pure stands. 

Next to the amount of P, the chemical form of this nutrient (Lambers et al. 2002 Shu et al. 2005 Shane et al. 2008) and the availability of other nutrients, especially nitrogen, potassium, and iron (Shane and Lambers 2005) affects the formation of cluster roots. It seems to be regulated by several plant hormones. Thus, application of auxin led to the production of cluster roots in white lupin at P concentrations that normally suppress cluster roots (Gilbert etal. 2000 Neumann et al. 2000). Cytokinines might also play a role, as kinetin applied to the growth medium of P-deficient white lupin inhibited the formation of cluster roots (Neumann et al. 2000). 

Dicamba (3,6-dichloro-2-methoxybenzoic acid) is primarily used as a postemergence broadleaf herbicide, which interferes with normal plant auxin function, subsequently causing uncontrolled growth and the inhibition of the phototropic and geotropic function. Cumulative response results in plant death. The success of auxinic analogues such as Dicamba and 2,4-dichloropheno-xyacetic acid in weed control has led to widespread manufacturing and use. Estimated U.S. production for Dicamba was 5 million kg in 1990 [391]. 

In the presence of adenine and kinetin, orotic acid or thymine can enhance the production of flower buds in vitro in stem segments of Plumbago indica [ 187]. The production of buds is often inhibited by auxins and gibbereUns [ 188]. 

The information obtained at Los Tuxtlas shows that the studied species from the secondary vegetation produce one or more allelopathic substances, mainly in leaves or through the decomposition of their organic matter, that can inhibit growth or have deleterious effects on plants and may cause parallel effects that are related to the role of auxins and to tropisms and other metabolic processes. 

Phenolic compounds naturally occurring in plants have induced many physiological responses that duplicate those reported for ozone and/or peroxyacetylnitrate (PAN). Chlorogenic acid is a competitive inhibitor of lAA-oxidase (35) and plant growth is adversely affected by increased concentrations of auxins (36). Concentrations of chlorogenic acid are increased in tobacco tissue exposed to ozone ( ) Phenols inhibit ATP synthesis (37), oxidative phosphorylation ( ) and SH enzyme activity (27) they increase respiration (38), reduce CO2 fixation (22), modify both membrane permeability (40) and oxidation rate of reduced NADH... 

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