A Polypeptide That Induces Flowering in Lemna paucicostata at a Very Low Concentration

A flower-inducing substance of high molecular mass, extracted from Lemna paucicostata, was purified to homogeneity. It had characteristics of a polypeptide, with an amino-terminal sequence of Leu-Val-Gly-Asn-Thr, and induced formation of flower buds of L. paucicostata 151 at a concentration of 10⁻¹⁰ molar.     

Specific Levels of DNA Methylation in Various Tissues, Cell Lines, and Cell Types of Daucus carota

The level of DNA methylation in Daucus carota was found to be tissue specific, but no simple correlation between developmental stage or age of tissue and the level of DNA methylation was found. Among three different suspension culture lines from the same variety grown under identical conditions, large differences in the level of DNA methylation were observed. The highest and lowest levels were found in two embryogenic cell lines originating from the same clone. Suspension cells from one of the embryogenic cell lines were fractionated into three morphologically defined cell types using Percoll gradient density centrifugation, and the uniformity of these fractions was evaluated by image analysis. The three cell types showed different levels of DNA methylation. The lowest level was found in the fraction containing the precursor cells of somatic embryos.     

Oxidation of spermine by an amine oxidase from lentil seedlings

Spermine is a substrate of lentil (Lens culinaris) seedling amine oxidase and the oxidation products are reversible inactivators of the enzyme. The spermine is oxidized at the terminal amino groups to a dialdehyde: 2 moles of hydrogen peroxide and 2 moles of ammonia per mole of spermine are formed. The pH optimum of the enzyme with spermine is 7.9 in TI-HCI buffer; the K_m value is 4.4·10⁻⁴ molar, similar to that found with other substrates (putrescine and spermidine).     

Stromal low temperature compartment derived from the inner membrane of the chloroplast envelope

Leaf discs of four dicotyledonous species, when incubated at temperatures of 4 to 18°C (optimum at 12°C) for 30 or 60 minutes, responded by accumulations of membranes in the chloroplast stroma in the space between the inner membrane of the envelope and the thylakoids. The accumulated membranes, here referred to as the low temperature compartment, were frequently continuous with the envelope membrane and exhibited kinetics of formation consistent with a derivation from the envelope. Results were similar for expanding leaves of garden pea (Pisum sativum), soybean (Glycine max), spinach (Spinacia oleracea), and tobacco (Nicotiana tabacum). We suggest that the stromal low temperature compartment may be analogous to the compartment induced to form between the transitional endoplasmic reticulum and the Golgi apparatus at low temperatures. The findings provide evidence for the possibility of a vesicular transfer of membrane constituents between the inner membrane of the chloroplast envelope and the thylakoids of mature chloroplasts in expanding leaves.     

Transformation of Zea mays L. Using Agrobacterium tumefaciens and the Shoot Apex

Agrobacterium tumefaciens is established as a vector for gene transfer in many dicotyledonous plants but is not accepted as a vector in monocotyledonous plants, especially in the important Gramineae. The use of Agrobacterium to transfer genes into monocot species could simplify the transformation and improvement of important crop plants. In this report we describe the use of Agrobacterium to transfer a gene into corn, the regeneration of plants, and detection of the transferred genes in the F₁ progeny. Shoot apices of Zea mays L. variety Funk's G90 were cocultivated with A. tumefaciens EHA 1, which harbored the plasmid pGUS3 containing genes for kanamycin resistance (NPT II) and β-glucuronidase (GUS). Plants developed from these explants within 4 to 6 weeks. Fluorometric GUS assays of leaves and immature seeds from the plants exhibited low GUS activity. Both NOS and GUS gene fragments were amplified by polymerase chain reaction in the DNA isolated from the F₁ generations of one of the original transformed plants. Southern analysis showed both GUS and NPT probes hybridized to DNA in several of the F₁ progeny, demonstrating the incorporation of GUS and NPT II genes into high molecular weight DNA. These data establish successful gene transfer and sexual inheritance of the genes.     

Isolation and Characterization of a UDPGlucose: Flavonol O-Glucosyltransferase from Illuminated Red Cabbage (Brassica oleracea cv Red Danish) Seedlings

A UDPGlc:flavonol O³-glucosyltransferase (EC 2.4.1.91) that catalyzes the formation of quercetin and kaempferol O³-glucosides has been purified about 1450-fold from illuminated red cabbage (Brassica oleracea cv Red Danish) seedlings with a 3.3% yield. Purification of the enzyme was achieved by (NH₄)₂SO₄-precipitation, gel-filtration, ion-exchange chromatography on DEAE-Bio-Gel and Q-Sepharose, chromatofocusing, and electrophoresis in nondenaturing polyacrylamide (10%) gels. The enzyme preparation had a pH optimum between 5.8 and 6.2, isoelectric point in the pH range 4.25 to 4.55, a M_r of 59,000, and it was composed of two similar subunits of M_r 29,500. The glucosyltransferase reached half substrate saturation at 180 micromolar (UDPGlc) and 7 micromolar (quercetin) concentrations. Kaempferol, which was glucosylated at a relative rate of 87%, had a lesser affinity for the enzyme (K_m~12 micromolar). Flavanones, flavanols, flavones, dihydroflavonols, and anthocyanidins were not readily utilized as substrates, suggesting that the enzyme is specific for flavonol glucoside biosynthesis.     

Wheat Inhibitors of Heterologous alpha-Amylases : Characterization of Major Components from the Monomeric Class

The four major components of the wheat monomeric α-amylase inhibitors (WMAI) from wheat, Triticum aestivum, endosperm have been isolated and characterized. Two of them, WMAI-1 and WMAI-2, are highly active against the α-amylase from the insect Tenebrio molitor and their N-terminal amino acid sequences indicate that they are closely related to each other (86% identical residues) and to the other members of the family (subunits of dimeric and tetrameric α-amylase inhibitors and trypsin inhibitors). WMAI-1, which is identical to the previously described 0.28 inhibitor, is encoded by a gene located in the short arm of chromosome 6D and WMAI-2 by a gene in the short arm of chromosome 6B. Components 3 and 4, which have blocked N-terminal residues, have identical internal amino acid sequences and are a separate class of proteins with respect to WMAI-1 and WMAI-2, although their amino acid composition and apparent molecular weights are quite similar. Their inhibitory activity versus α-amylases is either unstable during the purification process or due to contamination with other inhibitors.     

Purification and characterization of pea chloroplastic phosphoriboisomerase

Pea (Pisum sativum L.) chloroplastic phosphoriboisomerase (EC 5.3.1.6) can be purified to apparent homogeneity in less than 2 days time with a 53% yield. Important steps in the purification include heat treatment and pseudoaffinity chromatography on Red H-3BN Sepharose. The purified isomerase has a subunit molecular mass of 26.4 kD. The N-terminal sequence has been determined through 34 residues. pH optima are 7.8 (ribose-5-phosphate) and 7.7 (ribulose-5-phosphate); K_m values are 0.9 millimolar (ribose-5-phosphate) and 0.6 millimolar (ribulose-5-phosphate). The enzyme is inhibited by erythrose-4-phosphate, sedoheptulosebisphosphate, glyceraldehyde-3-phosphate, and 3-phosphoglycerate at concentrations close to those found in photosynthesizing chloroplasts. Countercurrent phase partitioning experiments indicate that the pea chloroplastic phosphoriboisomerase interacts physically with phosphoribulokinase.     

Xylanase and xylosidase activities in avocado fruit

The activities of xylanase and xylosidase were demonstrated in mature avocado (Persea americana Mill.) fruits from different cultivars. When monitored on the day of harvest during the season at 1-month intervals, xylanase activity decreased and xylosidase activity increased between January and February and then remained stable until May. When monitored during the ripening process (January harvest), xylanase activity was constant, and xylosidase activity reached a peak at the climax of ethylene evolution and cellulase activity. Xylanase, which originated from Trichoderma viride and was added to the medium in which avocado discs were incubated, induced ethylene evolution.