不同品种小豆光合作用和生长发育对弱光的响应

为确定小豆作为林果行间套种作物的适宜性,通过田间试验和盆栽试验,测定全光和弱光处理(全光的48%)下3个小豆品种(阜南绿小豆、早熟黑小豆、晚熟黑小豆)在初花期的叶片光合特征参数、光合色素含量和RuBPCase活性,研究小豆生长发育对弱光的响应.结果表明: 弱光使3个品种小豆叶片的最大净光合速率、光饱和点、光补偿点等光合参数不同程度地向耐荫的方向变化,净光合速率、水分利用效率和RuBPCase活性也显著下降;遮阴后,阜南绿小豆的叶绿素a和b含量显著增加,Chl a/b和类胡萝卜素含量显著降低,其他小豆的叶绿素和类胡萝卜素含量无明显变化;弱光使3个品种小豆的生物量和干物质积累效率降低,根冠比降低,根瘤量减少,叶片数和叶面积指数减小;弱光胁迫下,阜南绿小豆提前开花、提前成熟,早熟黑小豆推迟开花、延迟成熟,而晚熟黑小豆只开花不结实.从遮阴后小豆的光合特性变化和生长发育差异等方面综合考虑,3个小豆品种的耐阴能力大小为:阜南绿小豆>早熟黑小豆>晚熟黑小豆.     

Effects of silicon supply on apoplastic manganese concentrations in leaves and their relation to manganese tolerance in cowpea (Vigna unguiculata (L.) Walp.)

The effects of silicon (Si) supply on manganese (Mn) toxicity symptoms and Mn and Si concentrations in the leaf apoplast in a Mn-sensitive cowpea cultivar (Vigna unguiculata (L.) Walp. cv. TVu 91) were investigated in solution culture experiments. When 1.44 mM Si was supplied concurrently with 50 M Mn, the Mn toxicity symptoms were clearly avoided without decreasing the total Mn concentration. On the other hand, the symptoms were not completely alleviated when the plants were pretreated with 1.44 mM Si and then exposed to 50 M Mn without concurrent Si supply. Plants of both of these treatments exhibited lower Mn concentrations in the apoplastic washing fluids but higher amounts of adsorbed Mn on the cell walls than the plants treated with 50 M Mn without Si supply. However, the difference in Mn concentration between plants with continuous and interrupted Si supply was not significant. Moreover, the Mn concentration in the apoplastic washing fluids of the plants with continuous supply of 1.44 mM Si and 50 M Mn and not showing Mn toxicity symptoms was higher than that of the plants grown at 10 M Mn without Si supply which showed distinct Mn toxicity symptoms. These results show that Si supply alleviates Mn toxicity not only by decreasing the concentration of soluble apoplastic Mn through the enhanced adsorption of Mn on the cell walls. A role of the soluble Si in the apoplast in the detoxicification of apoplastic Mn is indicated.     

Inhibition of auxin-induced elongation and xyloglucan breakdown in azuki bean epicotyl segments by fucose-binding lectins

Auxin-induced elongation of epicotyl segments of azuki bean ( Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by fucose-binding lectins from Tetragonolobus purpureus Moench and Ulex europaeus L. These lectins also inhibited auxin-induced cell wall loosening (decrease in the minimum stress-relaxation time of the cell walls) of segments. Auxin caused a decrease in molecular mass of xyloglucans extracted with 24% KOH from the cell walls. The lectins inhibited auxin-induced changes in molecular mass of the xyloglucans. The autolytic release of xylose-containing products from the pectinase-treated cell walls was also suppressed by the lectins. Fucose-binding lectins pretreated with fucose exhibited little or no inhibitory effect on auxin-induced elongation, cell wall loosning, or breakdown of xyloglucans. These results support the view that the breakdown of xyloglucans is involved in the cell wall loosening responsible for auxin-induced elongation in dicotyledons.     

Comparative molecular mapping in Ceratotropis species using an interspecific cross between azuki bean (Vigna angularis) and rice bean (V. umbellata)

A genetic linkage map was developed with 86 F₂ plants derived from an interspecific cross between azuki bean (Vigna angularis, 2n=2x=22) and rice bean (V. umbellata, 2n=2x=22). In total, 14 linkage groups, each containing more than 4 markers, were constructed with one phenotypic, 114 RFLP and 74 RAPD markers. The total map size was 1702 cM, and the average distance between markers was 9.7 cM. The loci showing significant deviation from the expected ratio clustered in several linkage groups. Most of the skewed loci were due to the predominance of rice bean alleles. The azuki-rice bean linkage map was compared with other available maps of Vigna species in subgenus Ceratotropis. Based on the lineage of the common mapped markers, 7 and 16 conserved linkage blocks were found in the interspecific map of azuki bean ×V. nakashimae and mungbean map, respectively. Although the present map is not fully saturated, it may facilitate gene tagging, QTL mapping and further useful gene transfer for azuki bean breeding. Received: 20 March 1999 / Accepted: 29 April 1999     

Roles of auxin and gibberellic acid in growth and maturation of epicotyls of Vigna angularis: Cell wall changes

The effects of auxin and gibberellic acid on cell wall composition in various regions of epicotyls of azuki bean ( Vigna angularis Ohwi and Ohashi cv. Takara) were investigated with the following results. (1) Young segments excised from apical regions of the epicotyl elongated in response to added 10⁻⁴ M indole-3-acetic acid (IAA). When the segments were supplied with 50 m M sucrose, the IAA-induced segment growth was accompanied by enhanced overall synthesis of cell wall polysaccharides, such as xyloglucans, polyuronides and cellulose. This IAA effect on the cell wall synthesis is a consequence of extension growth induced by IAA. Gibberellic acid (GA) at 10⁻⁴ M synergistically enhanced the IAA-induced cell wall synthesis as well as IAA-induced extension growth, although GA by itself neither stimulated the cell wall synthesis nor extension growth. In the absence of sucrose, cell wall synthesis was not induced by IAA or GA. (2) In mature segments excised from basal regions of the epicotyl, no extension growth was induced by IAA or GA. GA enhanced the synthesis of xylans and cellulose when the segments were supplied with 50 m M sucrose. IAA had no effect on the cell wall synthesis. These findings indicate that synthesis of polyuronides, xyloglucans and cellulose, which occurs during extension growth of the apical region of the epicotyl, is regulated chiefly by auxin whereas synthesis of xylans and cellulose during cell maturation in the basal region of the epicotyl is regulated by GA.     

Resolution of dl-hydantoins by d-hydantoinase from Vigna angularis: Production of highly enantioenriched N-carbamoyl-d-phenylglycine at 100% conversion

Summary. d-Hydantoinase from Vigna angularis hydrolyzed rac-5-monosubstituted-hydantoins with polar and aromatic side chains and dihydrothymine but rac-5,5-disubstituted-hydantoins were not substrates of this enzyme. 5-Phenylhydantoin was the best substrate. By using this substrate, N-carbamoyl-d-phenylglycine was obtained in quantitative yield and over 98% ee. Received February 17, 2000; Accepted April 4, 2000     

Role of xyloglucan breakdown in epidermal cell walls for auxininduced elongation of azuki bean epicotyl segments

Auxin-induced elongation of epicotyl segments of azuki bean ( Vigna angularis Ohwi et Ohashi cv. Takara) was suppressed by a fucose-binding lectin from Tetragonolobus purpureas Moench and by polyclonal antibodies raised against xyloglucan heptasaccharide (Xyl₃Glc₄) when the cuticle present in the outer surface of epicotyls was abraded. In contrast, elongation of non-abraded segments was not influenced by the lectin or the antibodies. Epicotyl segments, from which the epidermal and the outer cortical cells had been removed, elongated rapidly for 2 h and than only slowly. Auxin slightly stimulated elongation of the inner tissue segments in the phase of slow growth. Neither in the presence nor in the absence of auxin did the lectin or the antibodies affect elongation of the inner tissue segments. The split portions of outer surface-abraded epicotyl segments incubated in buffer extended outward, and auxininhibited this outward bending. The lectin and the antibodies reversed the effect of auxin on bending. The fucose-binding lectin pretreated with fucose or the immunoglobulin fraction obtained from preimmune serum exhibited little or no inhibitory effect on auxin-induced elongation of abraded or split segments. These results support the view that a breakdown of xyloglucans in the epidermal cell walls plays an essential role in auxin-induced elongation in dicotyledons.     

In vitro synthesis of alpha-carboxyl-linked folylpolyglutamates by an enzyme preparation from Escherichia coli

Extracts of Escherichia coli contained an enzymatic activity which catalyzed the addition of L-glutamate to the alpha-carboxyl of various polyglutamate substrates, including folylpolyglutamates. Much of the enzyme activity was separated by DE52 chromatography and gel filtration from the enzyme which adds the first three glutamates in the biosynthesis of folylpolyglutamates, dihydrofolate synthetase-folylpolyglutamate synthetase. The two enzyme activities differed in many properties. Whereas dihydrofolate synthetase-folylpolyglutamate synthetase preferred pteroate or pteroylmonoglutamate substrates, the folylpoly-alpha-glutamate synthetase preparations effectively utilized tetrahydropteroylpolyglutamates, pteroylpolyglutamates, p-aminobenzoylpolyglutamates (pAB(Glu)n), and even a polyglutamate tripeptide. Several di- and triglutamyl peptides were inhibitory to folylpoly-alpha-glutamate synthetase activity, but not to dihydrofolate synthetase-folylpolyglutamate synthetase. Conversely, dihydropteroate noncompetitively inhibits the folylpolyglutamate synthetase reaction of the dihydrofolate synthetase-folylpolyglutamate synthetase protein, but did not inhibit the folylpoly-alpha-glutamate synthetase reaction. Potassium chloride was inhibitory to folylpoly-alpha-glutamate synthetase activity (as were other salts and several polyanions), in contrast to the absolute requirement of dihydrofolate synthetase-folylpolyglutamate synthetase activity for a monovalent cation such as K+. Incubation of a folylpoly-alpha-glutamate synthetase preparation with (6S)-tetrahydropteroyltri(gamma)glutamate generated products which after chemical cleavage to pAB(Glu)n were identical to those from growing E. coli, in high performance liquid chromatography retention times and in pattern of digestion by alpha-COOH bond-specific carboxypeptidase Y. High performance liquid chromatography and mass spectral analysis of the products of the in vitro reactions of folylpoly-alpha-glutamate synthetase with several substrates also demonstrated the addition of glutamate residues via alpha-COOH linkages. Thus, there appear to be two folylpolyglutamate synthetase activities in E. coli, dihydrofolate synthetase-folylpolyglutamate synthetase which adds the first three glutamate residues by gamma-COOH linkages and the folylpoly-alpha-glutamate synthetase activity which extends the folylpolyglutamate chain via gamma-COOH peptide bonds.     

Hot-Water Extracts from Adzuki Beans (Vigna angularis) Stimulate Not Only Melanogenesis in Cultured Mouse B16 Melanoma Cells but Also Pigmentation of Hair Color in C3H Mice

A hot-water extract of adzuki was obtained by boiling beans of adzuki (Vigna angularis). This hot-water extract was fractionated using HP-20 column chromatography. Its distilled water fraction (WEx) was found to stimulate tyrosinase activity in cultured mouse B16 melanoma cells and hair color pigmentation in C3H mice. At concentrations of 1–3 mg/ml, WEx stimulated melanogenesis without inhibiting cell growth. During this effect, WEx activated tyrosinase-inducing activity in the cells, but did not activate tyrosinase, which exists at an intracellular level. In this study, WEx increased cyclic adenosine-3′,5′-monophospate (cAMP) content in the cells and protein kinase A (PKA) activity, and stimulated translocation of cytosolic protein kinase C (PKC) to the membrane-bound PKC. These results suggest that the addition of WEx activates the adenylcyclase and protein kinase pathways and, as a result, stimulates melanogenesis. WEx was found to have pigmentation activity on hair color in C3H mice. It might be useful in anti-graying, protecting human skin from irradiation.     

Accumulation of an apoplastic solute in the guard-cell wall is sufficient to exert a significant effect on transpiration in Vicia faba leaflets

Accumulation of recently photosynthesized sucrose in the guard‐cell wall is the empirical foundation for a hypothesis that links the rates of photosynthesis, translocation, and transpiration (Plant Physiology 114, 109–118). Critical assumptions of this hypothesis were tested by use of Vicia faba, an apoplastic phloem loader. Following measurements of the leaflet‐apoplastic‐water volume (by P–V isotherm analysis) and the guard‐cell wall volume (by 3‐D analysis), intact leaflets were fed dilute solutions of mannitol, an impermeant non‐toxic osmolyte. Even at bulk‐leaflet mannitol concentrations that would have only a negligible osmotic effect on stomata, transpiration at constant temperature, water‐vapour pressure, air movement and irradiance was diminished up to 25%, compared with controls. This effect on transpiration, a manifestation of smaller stomatal aperture size, was explained by accumulation of mannitol, up to 350 mol m ^{? 3}, in the estimated aqueous volume of the guard‐cell wall. The conclusion is that mannitol, a xenobiotic with structural similarity to sucrose, can move throughout the apoplast of a transpiring leaflet and accumulate in an osmotically significant concentration in the guard‐cell wall. These data therefore provide support for a new role for sucrose as a signal metabolite that integrates essential functions of the whole leaf. In addition, the results raise questions about the physiological or experimental accumulation of other guard‐cell‐targeted apoplastic solutes such as plant growth regulators, particularly abscisic acid, and ions.     

Auxin-induced changes in the cell wall structure: Changes in the sugar compositions, intrinsic viscosity and molecular weight distributions of matrix polysaccharides of the epicotyl cell wall of Vigna angularis

Rapid effects of indole-3-acetic acid (IAA) on the mechanical properties of cell wall, and sugar compositions, intrinsic viscosity and molecular weight distribution of cell wall polysaccharides were investigated with excised epicotyl segments of Vigna angularis Ohwi et Ohashi cv. Takara.

• 1 IAA caused cell wall loosening as studied by stress-relaxation analysis within 15 min after the IAA application.
• 2 IAA stimulated the decrease in the content of arabinose and galactose in the hemicellulose 1 h after its application. The amounts of other component sugars in the cell wall polysaccharides remained constant during the IAA-induced segment growth.
• 3 The intrinsic viscocity of the pectin increased as early as 30 min after the IAA application. This effect was not prevented when elongation growth of the segment was osmotically suppressed by 0.15 M mannitol.
• 4 Gel permeation chromatography of the pectin on a Sepharose 4 B column demonstrated that IAA caused increase in the mass-average molecular weight of the pectin. Analysis of the sugar compositions of the pectin eluted from the Sepharose 4 B column indicated that IAA increased the molecular weight of the polysaccharides composed of uronic acid, galactose, rhamnose and arabinose. This effect became apparent within 30 min after the IAA application. Furthermore, IAA increased the molecular weight of the pectin when elongation growth of the epicotyl segments was osmotically suppressed by 0.15 M mannitol.
• 5 Hemicellulose of the cell wall chromatographed on a Sepharose CL-4 B column. Analysis of the neutral sugar compositions and the iodine staining property (specific for xyloglucans) of the polysaccharide solution eluted from the column indicated that the hemicellulose consisted of xyloglucans, arabinogalactans and polysaccharides composed of xylose and/or mannose. IAA caused a decrease in the arabinogalactan content and depolymerization of xyloglucans. These IAA effects became apparent within 30 min after the IAA application. These changes occurred even when elongation growth of the epicotyl segments was osmotically suppressed by 0.15 M mannitol.

Polymerization of the pectin, degradation of arabinogalactans and depolymerization of xyloglucans appear to be involved in the mechanism by which IAA induces cell wall loosening and therefore extension growth of cells.     

Modification of chemical properties of cell wall polysaccharides in the inner tissues by white light in relation to the decrease in tissue tension in Pisum sativum epicotyls

When white light irradiation inhibits shoot growth in derooted pea ( Pisum sativum L. cv. Alaska) cuttings, it decreases tissue tension, a driving force for shoot growth, by making the cell wall of the inner tissues mechanically rigid. To elucidate the mechanism by which light affects the mechanical properties of the cell wall in the inner tissues, its effect on the chemical properties of the cell walls was studied by analyzing qualitatively and quantitatively cell wall polysaccharides in the epdidermis and inner tissue of pea epicotyls grown in both dark and light. The amount of polysaccharides per subhook in the cell walls of both tissues increased during a 4-h dark incubation. Light suppressed the increase in hemicellulosic (HC)-II and cellulosic polysaccharides in the inner tissues, while it did not affect the increase in other wall fractions in either the epidermal or subepidermal tissues. No light effect was observed on the neutral sugar compositions of pectin, HC-I or HC-II fractions in either of the tissues. Light increased the mass-average molecular mass of xyloglucan and rhamnoarabinogalactan in HC-II fractions in the inner tissues, while such an effect was not observed in the epidermis. These facts suggest that the light-induced decrease in the tissue tension in pea epicotyls is caused by an increase in the molecular size of xyloglucan, rhamnoarabinogalactan in the HC-II fraction and/or the suppression of the synthesis of HC-II and cellulosic polysaccharides in the inner tissues.     

Quantifying determinants of ozone detoxification by apoplastic ascorbate in peach (Prunus persica) leaves using a model of ozone transport and reaction

Ascorbate in leaf apoplast (ASC_apo) reacts with ozone (O₃) and thereby reduces O₃ flux reaching plasmalemma (F_pl). Some studies have shown significant protection of cells from O₃ by ASC_apo, while others have questioned its efficacy. Hypothesizing that the protection by ASC_apo depends on other variables, we quantified determinants of O₃ detoxification with a model of O₃ transport and reaction in apoplast. The model determines ascorbic acid concentration in apoplast (AA_apo) using measured values of O₃ concentration (c_o), leaf tissue ascorbic acid concentration (AA_leaf), cell wall thickness (L₃), apoplastic pH (pH_apo), and stomatal conductance (G_sw). We compared the measured and model‐estimated AA_apo in leaves of peach (Prunus persica) grown in open‐top chambers under non‐filtered air (NF) and elevated (EO₃: NF + 80 ppb) O₃ concentrations. The estimated AA_apo in individual leaves agreed well with the measured values (R² = .91). Analyses of the simulation results yielded the following findings: (a) The efficacy of O₃ reduction with ASC_apo as quantified by fractional reduction (?₃) of O₃ flux at the surface of plasmalemma (F_pl) was lowered from 70% in NF to 40% in EO₃ due to the reduction of L₃. The EO₃ reduced AA_apo, but the lower G_sw and L₃ in EO₃ increased AA_apo resulting in no significant change in AA_apo due to EO₃. ?₃ can be calculated with measured values of AA_apo and L₃, and F_pl can be estimated with the measurement‐based ?₃. (b) When c₀ is increased, F_pl increased curvilinearly with the increase of F_st: nominal O₃ flux via stomatal diffusion, exhibiting apparent threshold on F_st. The deviation of F_pl from F_st became greater when L₃, pH_apo, and AA_leaf were increased. The quantification of ?₃ and F_pl using leaf traits shall facilitate the understanding of the mechanisms of differential plant sensitivity to O₃ and improve quantification of the O₃ impacts on plants.     

Acid-induced changes in the in vivo wall-yielding properties of hypocotyl sections of Vigna unguiculata

Elongation growth of hypocotyl sections of Vigna unguiculata under xylem perfusion was significantly enhanced when acid was applied by acid-aerosol to an abraded hypocotyl surface in the air. The in vivo wall extensibility (φ) and the effective turgor (Pⁱ– Y), both of which were determined by the pressure-jump method, increased during acid-induced growth as observed in IAA-induced growth. The intracellular pressure (Pⁱ), however, decreased significantly at the beginning of acid-induced growth whereas Pⁱ scarcely changed in IAA-induced growth. This result indicates that protons increase the effective turgor by decreasing the yield threshold as IAA does. There seems to be no essential difference between proton and auxin in the effects on the in vivo mechanical properties of the surface cell wall.     

The pH-dependent yield threshold of the cell wall in a glycerinated hollow cylinder (in vitro system) of cowpea hypocotyl

In order to determine whether the pH-dependent yield threshold of the cell wall still exists in an in vitro system, an extensometer was devised to enable the perfusion of any experimental solution through the hollow cylinder of a hypocotyl segment excised from a cowpea seedling. Stress-strain experiments on glycerinated hollow cylinders revealed the existence of a definite yield threshold (y) of the cell wall in this in vitro system. The y value decreased reversibly with acidification (pH 4) to the same extent as the decrease of the yield threshold obtained in vivo (Y) with auxin-induced growth acceleration of hypocotyl segments. Heat treatment of the glycerinated hollow cylinder completely inhibited the decrease in y with acidification. The increase in the extensibility of the cell wall with acidification was inhibited significantly but not completely by heat treatment. These results support strongly the ‘acid growth’ theory and provide evidence that the acid-induced decrement of the yield threshold is mediated by an enzymatic reaction of a wall-binding protein. The combination of in vitro and in vivo studies presented here provides a basis for the establishment of a molecular theory on the nature of the growth parameters Y and Ф which control the yielding of the cell wall.     

An oat coleoptile wall protein that induces wall extension in vitro and that is antigenically related to a similar protein from cucumber hypocotyls

Plant cell walls expand considerably during cell enlargement, but the biochemical reactions leading to wall expansion are unknown. McQueen-Mason et al. (1992, Plant Cell 4, 1425) recently identified two proteins from cucumber (Cucumis sativus L.) that induced extension in walls isolated from dicotyledons, but were relatively ineffective on grass coleoptile walls. Here we report the identification and partial characterization of an oat (Avena sativa L.) coleoptile wall protein with similar properties. The oat protein has an apparent molecular mass of 29 kDa as revealed by sodium dodecyl sulfate-polyacrylamide gel eletrophoresis. Activity was optimal between pH 4.5 and 5.0, which makes it a suitable candidate for acid growth responses of plant cell walls. The oat protein induced extension in walls from oat coleoptiles, cucumber hypocotyls and pea (Pisum sativum L.) epicotyls and was specifically recognized by an antibody raised against the 29-kDa wall-extension-inducing protein from cucumber hypocotyls. Contrary to the situation in cucumber walls, the acid-extension response in heat-inactivated oat walls was only partially restored by oat or cucumber wall-extension proteins. Our results show that an antigenically conserved protein in the walls of cucumber and oat seedlings is able to mediate a form of acid-induced wall extension. This implies that dicotyledons and grasses share a common biochemical mechanism for at least part of acid-induced wall extensions, despite the significant differences in wall composition between these two classes of plants.Abbreviations ConA concanavalin A - CM carboxymethyl - DEAE diethylaminoethyl - DTT dithiothreitol - Ex29 29-kDa expansin     

Expression and low pH increase the activity of an apoplastic acid phosphatase in growing tissues from Zea mays

Auxin‐induced secretion of an acid phosphatase (EC 3.1.3.2) leads to the hypothesis that this enzyme may be involved in plant cell elongation growth (W. Pfeiffer. 1996. Physiol. Plant. 98: 773–779). Elongation growth can be characterized by the effects of pH, phosphate and citrate, and the correlation with a particular region of the root: the elongation region. Therefore, it was investigated whether these parameters may reveal further correlations between acid phosphatase and elongation growth. The following results were obtained. (1) An extracellular acid phosphatase with high substrate affinity was characterized (Michaelis‐Menten constant, 0.03 m M for 4‐methylumbelliferyl phosphate; pH optimum, 3.0). The pH dependence of the enzyme was similar to that of elongation growth of coleoptile segments after pretreatment with phosphate (U. Kutschera and P. Schopfer. 1985. Planta 163: 483–493). (2) Phosphate inhibited both the acid phosphatase and coleoptile growth. Phosphate was a competitive inhibitor of the acid phosphatase (inhibitor constant, 2.5 m M ). (3) Citrate inhibited coleoptile growth and the acid phosphatase in a similar way (inhibitor constant, 21 mM). (4) The elongation region of maize roots contained more apoplastic acid phosphatase than adjacent regions (170%). The pH dependence of the enzyme suggests that the low pH reported for the elongation region would result in an additional increase of the enzymatic activity (pH optimum at 3.0).     

In vivo evidence for the involvement of phospholipase A and protein kinase in the signal transduction pathway for auxin-induced corn coleoptile elongation

Auxin-induced elongation of com coleoptiles is accompanied by cell wall acidification, which depends upon H⁺-pump activity. We tested the hypothesis that phospholipase A and a protein kinase are involved in the pathway of auxin signal transduction leading to H⁺ secretion, and elongation of corn coleoptiles. Initially, the pH of the bath solution at 50–100 μm from the surface of a coleoptile segment (pH_o) ranged between 4.8 and 6.6 when measured with an H⁺-sensitive microelectrode. Twenty or 50 μM lysophosphatidylcholine, 50 μM linolenic acid or 50 μM arachidonic acid induced a decline in pH_o by 0.3 to 2.1 units. The effect was blocked by 1 mM vanadate, suggesting that lysophosphatidylcholine or linolenic acid induced acidification of the apoplast by activating the H⁺-pump. Lysophosphatidylcholine and linolenic acid also accelerated the elongation rate of the coleoptiles. While linolenic acid and arachidonic acid, highly unsaturated fatty acids, promoted pH_o decrease and coleoptile elongation, linoleic acid, oleic acid, and stearic acid, fatty acids with a lesser extent of unsaturation, had no such effects. The effects of lysophosphatidylcholine, linolenic acid, and arachidonic acid on H⁺ secretion were not additive to that of indoleacetic acid (IAA), suggesting that lysophospholipids, fatty acids and auxin use similar pathways for the activation of the H⁺-pump. The phospholipase A₂ inhibitors, aristolochic acid and manoalide, inhibited the IAA-induced pH_o decrease and coleoptile elongation. The general protein kinase inhibitors, H-7 or staurosporine, blocked the IAA- or lysophosphatidylcholine-induced decrease in pH_o. H-7 also inhibited the coleoptile elongation induced by IAA or lysophosphatidylcholine. These results support the hypothesis that phospholipase A is activated by auxin, and that the products of the enzyme, lysophospholipids and fatty acids, induce acidification of the apoplast by activating the H⁺-pump through a mechanism involving a protein kinase, which in turn promotes com coleoptile elongation.     

In vitro synthesis of thyroxine in a low molecular weight polypeptide fragment from human thyroglobulin

A peptide fragment of Mr 16 K was purified from the cyanogen bromide digest of human thyroglobulin either normally iodinated in vivo (0.21 % I) or highly iodinated in vitro (1.40 % I). This peptide segment represents in the native molecule a zone in which tyrosine residues are not or poorly accessible to iodination and consequently do not produce thyroxine. In contrast, after isolation from thyroglobulin and iodination in vitro, the peptide is capable of synthesizing thyroxine with a high efficiency. It is concluded that the peptide described which probably represents a potential hormone forming site in the whole thyroglobulin molecule should constitute a valuable model to study the mechanism of thyroxine formation in vitro.     

Light-induced increase in the contents of ferulic and diferulic acids in cell walls of Avena coleoptiles: its relationship to growth inhibition by light

White fluorescent light (5 W m⁻²) inhibited Avena coleoptile growth. Light caused in increase in minimum stress relaxation time and a decrease in extensibility (strain/load) of coleoptile cell walls. Light increased the contents of ferulic acid (FA) and diferulic acid (DFA) ester-linked to the hemicellulose I in cell walls. These changes in the phenolic contents correlated with those of the mechanical properties of cell walls, suggesting that light stimulates the formation of DFA in hemicellulose I, making cell walls rigid, and thus results in growth inhibition. The ratio of DFA to FA was almost constant in the dark, but decreased in light, although it was almost constant in Oryza coleoptiles either in the dark or in light (Tan et al. 1992). From this fact, it is speculated that in the light condition, the formation of DFA in cell walls is limited in the step of the peroxidase catalyzed coupling reaction to produce DFA, while in the dark it is limited in the step of the feruloylation of hemicellulose I.