fusicoccin and indoleacetic-acid

• Pondweed (Potamogeton distinctus) turions can elongate in the absence of O(2). Alcoholic fermentation serves to produce energy for anoxic elongation via the breakdown of starch stored in cells. However, the mechanism of cell growth during anoxic elongation is not fully understood. • Changes in pH, H(+) equivalent and lactate content of the incubation medium were measured during anoxic elongation. The effects of fusicoccin (FC), indole-3-acetic acid (IAA), vanadate, erythrosine B and K(+) channel blockers on anoxic elongation were examined. Cytoplasmic pH and vacuolar pH were measured by (31)P nuclear magnetic resonance (NMR) spectroscopy. • Acidification of the incubation medium occurred during anoxic elongation. The contribution of CO(2) and lactic acid was not sufficient to explain the acidification. FC and IAA enhanced the elongation of stem segments. Vanadate and erythrosine B inhibited anoxic elongation. Acid growth of notched segments was observed. The activity of plasma membrane H(+)-ATPase extracted from pondweed turions was increased slightly in anoxic conditions, but that from pea epicotyls sensitive to anoxic conditions was decreased by incubation in anoxic conditions. Both the cytoplasmic pH and vacuolar pH of pondweed turion cells chased by (32)P NMR spectroscopy were stabilized during a short period < 3 h after anoxic conditions. • We propose that the enhancement of H(+) extrusion by anoxic conditions induces acidification in the apoplast and may contribute to the stabilization of pH in the cytoplasm.

Topics: Anaerobiosis; Buffers; Cell Membrane; Culture Media; Glycosides; Hydrogen-Ion Concentration; Indoleacetic Acids; Microsomes; Plant Stems; Potamogetonaceae; Potassium Channels; Proton-Translocating ATPases; Protons; Time Factors; Vacuoles

Among the Agrobacterium T-DNA genes, rolB, rolC, orf13, orf8, lso, 6b and several other genes encode weakly homologous proteins with remarkable effects on plant growth. The 6b oncogene induces tumors and enations. In order to study its properties we have used transgenic tobacco plants that carry a dexamethasone-inducible 6b gene, dex-T-6b. Upon induction, dex-T-6b plants develop a large array of morphological modifications, some of which involve abnormal cell expansion. In the present investigation, dex-T-6b-induced expansion was studied in intact leaves and an in vitro leaf disc system. Although T-6b and indole-3-acetic acid (IAA) both induced expansion and were non-additive, T-6b expression did not increase IAA levels, nor did it induce an IAA-responsive gene. Fusicoccin (FC) is known to stimulate expansion by increasing cell wall plasticity. T-6b- and FC-induced expansion were additive at saturating FC concentrations, indicating that T-6b does not act by a similar mechanism to FC. T-6b expression led to higher leaf osmolality values, in contrast to FC, suggesting that the T-6b gene induces expansion by increasing osmolyte concentrations. Metabolite profiling showed that glucose and fructose played a major role in this increase. We infer that T-6b disrupts the osmoregulatory controls that govern cell expansion during development and wound healing.

Topics: Bacterial Proteins; Cell Enlargement; Dexamethasone; DNA, Bacterial; Fructose; Glucose; Glycosides; Indoleacetic Acids; Nicotiana; Oncogene Proteins; Plant Growth Regulators; Plant Leaves; Plants, Genetically Modified; Potassium; Rhizobium

A study was made of the influence of two activators of plasma membrane proton pump [indole-3-acetic acid (IAA) and fusicoccin (EC)] and of the blocker of potassium channels of outward direction [tetraethylammonium chloride (TEA)] on exogenous [U-14C]glucose incorporation into cellulose fraction of cell wall, and on the value of plasmalemma membrane potential. It has been shown that IAA and FC exert different influences on the intensity of [U-14C]glucose incorporation into cellulose fraction: IAA activates, while FC inhibits incorporation intensity. A conclusion is made that differences in affects of IAA and FC on the intensity of cellulose synthesis at the plasma membrane level may be due to the fact that the activating effect of IAA on plasma membrane proton pump involves activation of the inward direction potassium channels, whereas that of FC, on the contrary, is associated with their blocking. Under the action of TEA, the intensity of incorporation of radioactively labeled glucose was increased. Apparently, the role of plasma membrane in regulation of the intensity of cellulose synthesis may be associated with not only the activity of proton pump on plasma membrane, but also the functional condition of potassium channels of this membrane.

Topics: Cell Membrane; Cells, Cultured; Cellulose; Glycosides; Indoleacetic Acids; Membrane Potentials; Plant Growth Regulators; Plant Roots; Potassium Channel Blockers; Potassium Channels; Proton Pumps; Seedlings; Tetraethylammonium; Triticum

To gain insight into the functional diversity of the XTH (xyloglucan endotransglucosylase/hydrolase) gene family, we analyzed the expression profiles of two azuki bean genes, VaXTH1 and VaXTH2, which share a striking resemblance in their amino acid sequences. The two XTH genes exhibit essentially similar tissue-specific expression profiles, in that both mRNAs are found predominantly in the phloem fibers of growing internodes. However, their expression profiles are not identical. Whereas VaXTH1 is expressed in xylem cells in the basal part of the internode, little or no expression of VaXTH2 is found in the xylem. Furthermore, they exhibit spatially divergent RNA distribution profiles along the internode, VaXTH1 being expressed nearer to the top of the internode than VaXTH2. This indicates their temporally divergent expression profiles during development of the phloem fiber. Indole-3-acetic acid (IAA) up-regulates both of the mRNA levels. However, this effect of IAA on the VaXTH1 gene is nullified in 0.25 M mannitol, which prevents cell expansion without affecting auxin action per se. In contrast, the IAA-induced up-regulation of the VaXTH2 gene is not affected by mannitol. Furthermore, fusicoccin, which promotes acidification and growth, up-regulates VaXTH1 expression, but not VaXTH2 expression. Thus, the two XTH genes are committed to different steps of the cell wall dynamics in the same cell type at different stages of phloem fiber development, and are regulated by IAA in different ways.

Topics: Fabaceae; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Glycosides; Glycosyltransferases; Indoleacetic Acids; Isoenzymes; Mannitol; Molecular Sequence Data; Multigene Family; Phylogeny; Plant Proteins; RNA, Messenger

The dependence of growth induced by the fungal toxin fusicoccin (FC) on the K+ content of the incubation medium was investigated in abraded maize coleoptiles. If the divalent ion Ca2+ was included in the bathing medium, no FC-induced growth occurred in the absence of K+, whereas a strong response was detected in presence of K+. The optimal K+ concentration was in the range of 1-10 mM. With the exception of Rb+, none of the other alkali ions (Na+, Li+, Cs+) could replace for K+ in sustaining FC-induced growth. The potassium channel blocker tetraethylammonium (TEA) reversibly inhibited FC-induced growth. As shown earlier for auxin-induced growth, no strict potassium dependence of FC-triggered elongation was observed in Ca2+ -free media. However, TEA abolished this apparently K+ independent FC-induced growth. It is concluded that FC-induced growth, like auxin-induced growth, requires K+ uptake through K+ channels.

Topics: Calcium; Cotyledon; Glycosides; Indoleacetic Acids; Ion Transport; Mycotoxins; Plant Growth Regulators; Potassium; Potassium Channel Blockers; Potassium Channels; Rubidium; Tetraethylammonium; Zea mays

Endogenous extractable factors associated with auxin action in plant tissues were investigated, especially their effects on elongation of 1-mm coleoptile segments of maize (Zea mays L.), in the presence of saturating 10 microM indole-3-acetic acid (IAA). The relative growth response, to auxin alone, was much smaller in segments shorter than 2-3 mm compared to 10-mm segments. Fusicoccin-induced elongation, however, was less affected by shortening the segments. A reduced auxin response may result from the depletion through cut surfaces of a substance required for IAA-mediated growth. Sucrose, phenolics like flavonoids, and vitamins were ruled out as the causal factors. A partially purified methanol extract of maize coleoptiles supported longterm, auxin-controlled elongation. The active material was also found among substances bleeding from scrubbed maize coleoptiles. The active factor from maize was further purified by HPLC and characterised by the UV spectrum and its pH shift. This factor was identified as 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) by mass spectroscopy. Activity tests confirmed that pure DIMBOA from other sources sustained auxin-induced elongation of short maize coleoptile segments. However, DIMBOA only partially restored the activity lost from short segments. This indicates that an additional factor, other than DIMBOA, is required. Extracts from Avena or Cucurbita did not contain the factor DIMBOA; it was active on maize elongation, but not on Avena coleoptiles or Cucurbita hypocotyls. This narrow specificity and the lack of DIMBOA action in short-term tests with maize indicate that DIMBOA is not the general auxin cofactor but may specifically "spare" the co-auxin in maize.

Topics: Benzoxazines; Cell Division; Cotyledon; Glycosides; Indoleacetic Acids; Oxazines; Plant Growth Regulators; Zea mays

Leaves originate from the shoot apical meristem, a small mound of undifferentiated tissue at the tip of the stem. Leaf formation begins with the selection of a group of founder cells in the so-called peripheral zone at the flank of the meristem, followed by the initiation of local growth and finally morphogenesis of the resulting bulge into a differentiated leaf. Whereas the mechanisms controlling the switch between meristem propagation and leaf initiation are being identified by genetic and molecular analyses, the radial positioning of leaves, known as phyllotaxis, remains poorly understood. Hormones, especially auxin and gibberellin, are known to influence phyllotaxis, but their specific role in the determination of organ position is not clear. We show that inhibition of polar auxin transport blocks leaf formation at the vegetative tomato meristem, resulting in pinlike naked stems with an intact meristem at the tip. Microapplication of the natural auxin indole-3-acetic acid (IAA) to the apex of such pins restores leaf formation. Similarly, exogenous IAA induces flower formation on Arabidopsis pin-formed1-1 inflorescence apices, which are blocked in flower formation because of a mutation in a putative auxin transport protein. Our results show that auxin is required for and sufficient to induce organogenesis both in the vegetative tomato meristem and in the Arabidopsis inflorescence meristem. In this study, organogenesis always strictly coincided with the site of IAA application in the radial dimension, whereas in the apical-basal dimension, organ formation always occurred at a fixed distance from the summit of the meristem. We propose that auxin determines the radial position and the size of lateral organs but not the apical-basal position or the identity of the induced structures.

Topics: Adenine; Arabidopsis; Arabidopsis Proteins; Biological Transport; Brassinosteroids; Cell Division; Cholestanols; Culture Techniques; Gibberellins; Glycosides; Indoleacetic Acids; Kinetin; Membrane Proteins; Membrane Transport Proteins; Meristem; Morphogenesis; Mutation; Phenotype; Phthalimides; Plant Leaves; Plant Structures; Solanum lycopersicum; Steroids, Heterocyclic

When auxin stimulates rapid cell elongation growth of cereal coleoptiles, it causes a degradation of 1,3:1,4-beta-glucan in hemicellulosic polysaccharides. We examined gene expressions of endo-1,3:1,4-beta-glucanase (EI) and exo-beta-glucanase (ExoII), of which optimum pH are about 5, and molecular distribution of hemicellulosic polysaccharides in barley (Hordeum vulgare L.) coleoptile segments treated with or without IAA. IAA (10(-5) M) stimulated the gene expression of EI, while it did not affect that of ExoII. IAA induced gene expression of EI after 4 h and increased wall-bound glucanase activity after 8 h. The molecular weight distribution of hemicellulosic polysaccharides from coleoptile cell walls was shifted to lower molecular weight region by 2 h of IAA treatment. Fusicoccin (10(-6) M) mimicked IAA-induced elongation growth and the decrease in molecular weight of hemicellulosic 1,3:1,4-beta-glucan of coleoptiles in the first 4 h, but it did not promote elongation growth thereafter. These facts suggest that acidification of barley cell walls by IAA action enhances pre-existing cell wall-bound glucanase activity in the early first phase of IAA-induced growth and the late second phase involves the gene expression of EI by IAA.

Topics: beta-Glucosidase; Blotting, Northern; Cell Wall; Cellulase; Cotyledon; Dose-Response Relationship, Drug; Gene Expression Regulation, Developmental; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Glucan 1,3-beta-Glucosidase; Glucose; Glycosides; Hordeum; Indoleacetic Acids; Molecular Weight; Plant Growth Regulators; Polysaccharides; RNA, Plant; Time Factors

Segments can be cut from the peduncular-1 internode of oat (Avena sativa L.) shoots so as to contain the graviresponsive leaf-sheath pulvinus and gibberellin-sensitive internodal tissue. Incorporation of [14C]glucose was used to monitor cell wall synthesis in these two tissues as affected by gravistimulus, indoleacetic acid (IAA), gibberellic acid (GA3), and fusicoccin (FC). Pulvinar cell wall synthesis was promoted by IAA and FC (both within about 1 h), as well as by gravistimulus (starting between 3 and 6 h), whereas GA3 had no effect on nongravistimulated pulvini. In contrast, GA3 and FC promoted internodal cell wall synthesis (initiated between 1 and 2 h), whereas IAA and gravistimulus caused a decrease in internodal uptake. FC preferentially promoted incorporation into the matrix component of the wall in both tissues. Gravistimulus failed to increase responsiveness of pulvinar tissue to IAA, whereas GA3 partially overcame gravistimulus-promoted incorporation into pulvinar cell wall, probably because of preferential movement of label into the rapidly elongating internode. The results demonstrate that these eight stimulus/tissue combinations can be examined easily in an isolated 10-mm stem segment, providing new opportunities for the comparative study of tissue- and stimulus-specific events in gene regulation and signal transduction in agronomically important cereals.

Topics: Avena; Carbon Radioisotopes; Cell Wall; Gibberellins; Glucose; Glycosides; Gravitation; Gravitropism; Indoleacetic Acids; Plant Growth Regulators; Plant Shoots; Pulvinus

A study has been made of the prolonged growth of Avena coleoptile sections in response to fusicoccin (FC), a phytotoxin that promotes apoplastic acidification. The final amount of FC-induced growth is a function of the FC concentration. Removal of the epidermis speeds up the initial rate of elongation and shortens the duration of the response, without affecting the total amount of extension. A suboptimal FC concentration (7 x 10(-8) M) which induces the same rate of proton excretion as does optimal indoleacetic acid (IAA) (1 x 10(-5) M), causes elongation which is 60-75% of that induced by IAA in 4 h or 50-65% in 7 h. This suggests that acid-induced extension could make a major contribution to auxin-induced growth for at least 7 h.

Topics: Avena; Cotyledon; Culture Media; Glycosides; Hydrogen-Ion Concentration; Indoleacetic Acids; Plant Epidermis; Plant Growth Regulators; Potassium Chloride; Protons; Sucrose; Time Factors

Galactose inhibits auxin-induced growth of Avena coleoptiles by at least two mechanisms. First, it inhibits auxin-induced H(+)-excretion needed for the initiation of rapid elongation. Galactose cannot be doing so by directly interfering with the ATPase since fusicoccin-induced H(+)-excretion is not affected. Secondly, galactose inhibits long-term auxin-induced growth, even in an acidic (pH 4.5) solution. This may be due to an inhibition of cell wall synthesis. However, galactose does not reduce the capacity of walls to be loosened by H+, given exogenously or excreted in response to fusicoccin.

Topics: Avena; Cotyledon; Drug Interactions; Galactose; Glycosides; Hydrogen-Ion Concentration; Indoleacetic Acids; Plant Growth Regulators; Protons; Time Factors

Seven day old etiolated pea epicotyls were loaded symmetrically with 3H-indole 3-acetic acid (IAA) or 45Ca2+, then subjected to 1.5 hours of 1g gravistimulation. Epidermal peels taken from top and bottom surfaces after 90 minutes showed an increase in IAA on the lower side and of Ca2+ on the upper side. Inhibitors of IAA movement (TIBA, 9-hydroxyfluorene carboxylic acid) block the development of both IAA and Ca2+ asymmetries, but substances known to interfere with normal Ca2+ transport (nitrendipine, nisoldipine, Bay K 8644, A 23187) do not significantly alter either IAA or Ca2+ asymmetries. These substances, however, are active in modifying both Ca2+ uptake and efflux through oat and pea leaf protoplast membranes. We conclude that the 45Ca2+ fed to pea epicotyls occurs largely in the cell wall, and that auxin movement is primary and Ca2+ movement secondary in gravitropism. We hypothesize that apoplastic Ca2+ changes during graviresponse because it is displaced by H+ secreted through auxin-induced proton release. This proposed mechanism is supported by localized pH experiments, in which filter paper soaked in various buffers was applied to one side of a carborundum-abraded epicotyls. Buffer at pH 3 increases calcium loss from the side to which it is applied, whereas pH 7 buffer decreases it. Moreover, 10 micromolar IAA and 1 micromolar fusicoccin, which promote H+ efflux, increase Ca2+ release from pea epicotyl segments, whereas cycloheximide, which inhibits H+ efflux, has the reverse effect. We suggest that Ca2+ does not redistribute actively during gravitropism: the asymmetry arises because of its release from the wall adjacent to the region of high IAA concentration, proton secretion, and growth. Thus, the asymmetric distribution of Ca2+ appears to be a consequence of growth stimulation, not a critical step in the early phase of the graviresponse.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Biological Transport; Calcimycin; Calcium; Calcium Channel Agonists; Calcium Channel Blockers; Cycloheximide; Glycosides; Gravitation; Gravitropism; Hydrogen-Ion Concentration; Indoleacetic Acids; Ionophores; Nisoldipine; Nitrendipine; Pisum sativum; Plant Growth Regulators; Plant Shoots; Protein Synthesis Inhibitors; Protoplasts

According to the chemiosmotic polar diffusion hypothesis, auxin pulse velocity and basal secretion should increase with decreasing cell wall pH. Experiments were designed to test this prediction. Avena coleoptile sections were preincubated in either fusicoccin (FC), cycloheximide, pH 4.0, or pH 8.0 buffer and subsequently their polar transport capacities were determined. Relative to controls, FC enhanced auxin (IAA) uptake while CHI and pH 8.0 buffer reduced IAA uptake. Nevertheless, FC reduced IAA pulse velocity while cycloheximide increased velocity. Additional experiments showed that delivery of auxin to receivers is enhanced by increased receiver pH. This phenomenon was overcome by a pretreatment of the tissue with IAA. Our data suggest that while acidic wall pH values facilitate cellular IAA uptake, they do not enhance pulse velocity or basal secretion. These findings are inconsistent with the chemiosmotic hypothesis for auxin transport.

Topics: Avena; Biological Transport; Cell Wall; Cotyledon; Cycloheximide; Glycosides; Hydrogen-Ion Concentration; Indoleacetic Acids; Plant Growth Regulators; Protein Synthesis Inhibitors

Theory predicts that, for growing plant cells isolated from a supply of water, stress relaxation of the cell wall should decrease cell turgor pressure (P) until the yield threshold for cell explanation is reached. This prediction was tested by direct P measurements of pea (Pisum sativum L.) stem cortical cells before and after excision of the growing region and isolation of the growing tissue from an external water supply. Cell P was measured with the micro-pressure probe under conditions which eliminated transpiration. Psychrometric measurements of water potential confirmed the pressure-probe measurements. Following excision, P of the growing cells decreased in 1 h by an average of 1.8 bar to a mean plateau value of 2.8 bar, and remained constant thereafter. Treatment with 10(-5) M indole-3-acetic acid or 10(-5) M fusicoccin (known growth stimulants) accelerated the rate of P relaxation, whereas various treatments which inhibit growth slowed down or completely stopped P relaxation in apical segments. In contrast, P of basal (nongrowing) segments gradually increased because of absorption of solutes from the cell-wall free space of the tissue. Such solute absorption also occurred in apical segments, but wall relaxation held P at the yield threshold in those segments which were isolated from an external water supply. These results provide a new and rapid method for measuring the yield threshold and they show that P in intact growing pea stems exceeds the yield threshold by about 2 bar. Wall relaxation is shown here to affect the water potential and turgor pressure of excised growing segments. In addition, solute release and absorption upon excision may influence the water potential and turgor pressure of nongrowing excised plant tissues.

Topics: Biomass; Cell Wall; Elasticity; Glycosides; Indoleacetic Acids; Osmotic Pressure; Pisum sativum; Pressure; Stress, Mechanical

The ability of several auxins to induce C2H4 production was examined. There is an ability scale among the various products in which IAA is the more efficient compound while 2,4-D seems to be the less efficient one. As well as other general phenomena, e.g. enlargement or weight increase, even in this case a biphasic action seems to exist, with an activation at the lower concentrations and an inhibition at the higher ones. The dose corresponding to the critical point, in which one can observe the inversion of the response, seems to be common to all the substances and to be 1 X 10(-4)M. Subsequently we verified the FC influence on the C2H4 production in the presence of the optimal dose of different auxins. The inhibiting action exerted by the toxine is a function of the concentration and does not depend on the inducing substance. The FC determines a drastic reduction in C2H4 production, nearly 60%, for the entire range of the concentrations studied. The described data give evidence of a strong FC interference on ethilene production of etiolated pea internodes.

Topics: 2,4-Dichlorophenoxyacetic Acid; Ethylenes; Glycosides; Indoleacetic Acids; Naphthaleneacetic Acids; Plants; Thiazoles