Auxins enzyme activation

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... 

Many of the same conclusions may be drawn from results with synthetic auxins as from indole-3-acetic acid water intake increased, there was a lessening of the downward translocation of photosynthate with temporary increases of soluble carbohydrates in the leaves, and alterations appeared in the metabolic ratq and direction and in enzyme activity. However, the direct site of action is not known, and many of the effects are puzzling. n-Fructose oligosaccharides in artichoke and chicory storage-tissue were diminished by 70% (calculated on the content of dry matter) in 6 days... 

Alexander"2 has tried to assess the effect of indole-3-acetic acid, (2,4-dichlorophenoxy) acetic acid, and maleic hydrazide on the soluble carbohydrates and enzyme systems in sugarcane leaves. All of the chemical treatments increased sucrose, total reducing value, D-fructose, and D-glucose in leaves (compared with the controls), with a maximum at nine days after applying about two g. per plant. The indole auxin increased sucrose most, followed by the phenoxy compound and the hydrazide D-glucose increased in the reverse order. Poor translocation from the leaves may have caused the temporary increase in leaf photosynthate. Alterations in the enzyme activities as a result of the chemical treatment are difficult to interpret, partly since so little is known about their relative importance, and partly because the activity in the controls varied by as much as 100% from one sampling period to the next. 

The variety of aldehyde oxidases discovered in other plants have similarities to the maize enzyme, but also have some very important differences. Enzymes contained in a cell wall fraction from barley seedlings were able to oxidize IAAld to form IAA at a pH optimum of 7 and Km of 5 pmol 1 1, which was very similar to the enzyme found in maize.113 Two aldehyde oxidases from potato have also been identified 101 they had a similar pH optimum (between 7 and 8), but preferred aliphatic aldehydes to aromatic aldehydes. Although oat and cucumber aldehyde oxidases have been shown to oxidize IAAld to produce IAA,102 114 the oat enzyme had a lower pH optimum and higher Km than the maize enzyme, and the cucumber enzyme was inhibited by synthetic auxin and activated by 2-mercaptoethanol, which was not true for the maize enzyme. The difference in the enzymes makes it difficult to envision a common evolutionary origin for the IAAld pathway in plants if these particular enzymes are involved in each case. 

Grabowski, L., Heim, S., and Wagner, K.G., 1991, Rapid changes in the enzyme activities and metabolites of the phosphatidylinositol-cycle upon induction by growth substrates of auxin-starved suspension cultured Catharanthus roseus cells. Plant Sci. 75 33-38. 

Cell-wall-bound glycosidases present in these coleoptiles include / -d-galactosidase, / -D-glucosidase, / -D-xylosidase, / -L-fucosidase, and Ct-D-mannosidase the enzymes were reported to be activated by auxin and by hydrogen ions, and, therefore, they may be involved in cell growth.243 A contrary claim has been made by Evans244 that neither cell-wall-bound... 

Figure 1. Elution profiles of cellulase activity from Sephadex G-100 gel chromatographs of crude extracts of auxin-treated pea apices. BS cellulose activity has an elution volume corresponding to a molecular weight of 20,000. BI cellulase activity dissolves in 1M NaCl and elutes with a molecular weight of 70,000. These values correspond to those observed for purified cellulases (3), indicating that the enzymes were not altered in molecular weight during purification, and could be effectively separated by differential extraction.

Intracellular Distribution and Development. When pea segments are homogenized and centrifuged to separate fractions containing wall material from particulate material and soluble supernatant, most of BS cellulase is found in the supernatant fraction while most BI cellulase is adsorbed to the wall (Table III). A minor part of both enzymes is particulate, i.e., retained in intact cell organelles and microsomes derived by vesiculation from cell membranes. In time-course studies of the distribution between cell fractions of total cellulase following auxin treatment (23), the activity appears first in the microsomes, and only... 

If the pea cellulases are related as an inactive intracellular precursor (BS) to an active wall-bound enzyme (BI), a delay would be expected between the appearance of BS after auxin induction and its secretion as BI. Such a delay has been observed repeatedly in tests of the relative rates of development of the two enzymes following auxin treatment of decapitated or intact tissue (Figure 3). During the first day after treatment, BS cellulase activity increases up to 18-fold over controls, while BI cellulase activity barely changes. By 2 days, although the BS cellulase activity level has increased further, BI cellulase activity surpasses it. The ascendancy of BI continues for several days, i.e., until effects of the hormone subside and levels of both cellulases begin to decline. Similar... 

Leyser, O.H.M., Lincoln, C.A., Timpte, C., Lammer, D., Turner, J., Estelle, M. (1993). Arabidopsis auxin-resistance gene AXR1 encodes a protein related to ubiquitin-activating enzyme El. Nature (London) 364, 161-164. 

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