Auxin bound

Okra, Hibiscus escuentus L. The immature pods of okra are popular as a vegetable and okra is also used for the ability to thicken soups and stews, and for fiber and oil. Notmuch is known about okra most workers concentrate their research on the chemical composition (26-29) of the mucilaginous materials found in the pod (30) stalk, nutritional properties (31). Research has also been conducted on the developmental properties of the okra seed (32). This paper is the first report of the chemical composition of auxin conjugates in okra pods bound to nitrocellulose membrane. 

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... 

D-galactosidase nor / -D-glucosidase plays an important role in shortterm growth promoted by auxin or acid in oat coleoptiles, Greve and Ordin245 purified, and characterized, the wall-bound a-D-mannosidase of this tissue. 

Dichlorophenpxy) acetic acid-14C is metabolized by plant tissue to inactive, water-soluble substances, some of which regenerate the parent acid on hydrolysis. The rate of metabolism differs with different species, but is usually low in comparison with the indole or naphthalene auxins. One of the earlier studies described a single major metabolite in corn, wheat, peas, and tomatoes,121 the identity of which is still uncertain. In another study of differences between species which were susceptible and those which were resistant to the herbicide, the resistant red currant metabolized 50% of the carboxyl-labeled and 20% of the methylene-labeled (2,4 dichlorophenoxy)acetic acid to 14COi in seven days, whereas the susceptible black currant altered122 only 2%. Similar effects were found with apple varieties. Strawberry and lilac decarboxylated the herbicide readily however, 16 other species, of various susceptibilities to herbicide, were unable to decarboxylate the acid to any significant extent. In both varieties of currant, 5 to 10% of the herbicide was converted into water-soluble derivatives of the parent acid, and 10 to 30% was bound in the leaf tissue in an unextractable form. 

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... 

The effects of auxin upon the growth of plants were truly remarkable. As a result of the concerted effort and interest that plant scientists devoted to this highly fashionable and exciting field of research, much of what we know of the control of plant growth and development by auxin was discovered in these highly productive years. The hormone was derived from the aromatic amino acid tryptophan and was relatively abundant in the rapidly growing meristematic parts of plants such as apical buds and root tips. Inactive bound forms existed, as in seeds, where hydroly-... 

Matthyssee and Phillips (20) isolated two nuclear proteins, from tobacco cells, that bound specifically to 2,4-D. Receptor proteins for auxins, kinetins, and GA have been found (21). Sub-cellular fractions from bean leaves were recently shown to bind abscisic acid (22). Preliminary experiments (22) indicated that maximum ABA binding activity coincides with the activities of membrane-bound Mg -dependent, K+-stimulated ATPase and glucan synthetase. Table I of Biswas and Roy (21) lists hormone receptor proteins reported in plant tissue. For a protein to qualify as a receptor molecule, it should have a high stereo-specific binding capacity (Kd 10 6 to 10 SM) for its particular hormone. In com coleoptiles, both IAA and NAA are equally effective in inducing cell elongations fractions of plasma membrane and endoplasmic reticular membrane contain receptor proteins with Kd values of 10 M to 10 M for auxins (5, 18). When one considers procedural... 

From a critical study of the metabolism of poly (A) in auxin-treated pea epicotyl, Verma and Maclachlan (73) showed that discreet classes of poly (A) (presumably part of mRNA s) are differentially associated with free and membrane-bound polysomes. The induction of specific mRNA s, the decline in the rate of synthesis of mRNA s, the polysome content per cell, and the formation of cellulase were all related to the membrane-bound polysomes. Although the rate of in vivo enzyme synthesis is... 

I. Effects of auxin on template capacity and chromatin-bound RNA polymerase. Mech. Ageing Dev., 1978, 8, 97-112. 

Guilfoyle, T. J. Hanson, J. B. Greater length of ribonucleic acid synthesized by chromatin-bound polymerase from auxin-treated soybean hypocotyls. Plant Physiol., 1974, 53,... 

The natural auxins are represented by a single compound, indole-3-acetic acid (IAA), which occurs as the free acid and in various "bound" forms, including a thioglucoside, glycosyl esters, and IAA peptides. For a recent discussion see the book chapter by Bandurski and Nonhebel (2) in Wilkins (3). 

The major breakthroughs in the biochemical identification of ethylene receptors occurred almost simultaneously. It had been assumed that the methods used in receptor studies for auxins and other hormones would be inappropriate for ethylene. Thus, the displacement assays used for auxins seemed unlikely to work in the case of ethylene, firstly because bound ethylene would dissipate before it could be measured, and secondly because only relatively low specific activity labelled ethylene is possible. This situation would be exacerbated given the likely low abundance of receptors. 

The phenylpropanoid pathway (Fig. 3.1) is responsible for the production of many natural products that are of interest in the context of plant growth and development, human health, and ecology. For example, flavonoids are necessary for pollen viability in maize and petunia, and have been suggested to play a role in directed auxin transport. Flavonoids and sinapate esters have been found to be important UV-protectants in many species, including Arabidopsis. Furthermore, wall-bound phenolics are thought to impart control over cell wall expansion, and hydroxycinnamic acids are an important structural component of the hydrophobic barrier polymer suberin. Finally, lignin is a phenylpropanoid polymer ubiquitous in higher plants, which is necessary for mechanical support and water transport. " ... 

This batch-cultured cell line apparently lacks the membrane-bound auxinbinding protein [6]. It thus provides us with a good auxin-target system to study the role of soluble auxin-binding sites in the auxin perception-transduction mechanism. Auxin-starved early-stationary phase cells respond relatively rapidly to added auxin with cell division. 

M.A. Venis and R.M. Napier Membrane-Bound Auxin Receptors... 

Since it is suggested that the signal dependent stimulation of the phosphoinosi-tidase C in animal cells is processed by the involvement of an as yet unknown G-protein [4], the effect of G-nucleotides on the in vitro lipid phosphorylation of carrot microsomal membranes was tested. Whereas only a weak release of inositol phosphates and a drastic inhibition of lipid phosphorylation could be observed in the presence of high GTP concentrations, a prominent production of p P]IP2 and [,32pjip3 caused by micromolar concentration of GTP. S (Fig. 3). That the auxin-mediated reaction was not found to be absolutely dependent on GTP can be a result either of the presence of sufficient amounts of endogenous G-nucleotides bound to a membrane protein or of the introduction of GTP as a contamination of commercially available ATP used as energy substrate in the assays. Although the... 

Fig. 5. Displacement of bound [5- H]IAA on carrot microsomal membranes by increasing amounts of unlabelled lAA. Results are given as saturable auxin binding, i.e. the residual unspecific binding at 100 /nM lAA was subtracted systematically. The insert exhibits the Scatchard analysis of the same data, but only those of the high-affinity binding...

Large yields of auxins have been obtained by prolonged extraction with ether at room temperature. Probably bound auxins are liberated during extraction. 

A problem of long standing concerns the absorption or release of indoleacetic acid from plant proteins. This is not easily studied at physiological concentrations, and there is some question whether the release of bound auxin from proteins by various means parallels in any way natural processes. Similarly, the details of the binding process are not yet known. 

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