Avocado Extract Research Articles

In vitro activity of extracts of Persea americana leaves on acyclovir-resistant and phosphonoacetic resistant Herpes simplex virus

The lyophilized aqueous crude extract (LACE) from leaves of Persea americana (Lauraceae) species showed a strong inhibitory effect on acyclovir (ACG(r)4 and dlsp TK mutants) and PAA-resistant (PAA(r)5 mutant) herpes simplex virus. After exhaustive washing of LACE using methanol, the soluble fraction was chromatographed on a reverse-phase column giving 11 fractions that were revealed by thin-layer chromatography. Analysis of the antiviral effect of the fractions showed the extract contained compounds that were able to inhibit extracellular virus and the replication of resistant acyclovir HSV. The virucidal effect was concentrated from fraction 4 up to 8. Fraction 7 mainly contains the flavonoid isoquercitrin, and fraction 8 the flavonoid quercitrin. The flavonoid afzelin that is the major substance present in the fraction 9 showed virustatic effect with no virucidal effect. These results show P. americana is a potential plant extract for treatment of herpes simplex virus infections either alone or associated with acyclovir.

Avocado hypersensitivity.

The avocado (Av) is a fruit that belongs to the Lauraceae family. We report 17 patients with immediate hypersensitivity to avocado. Clinical manifestations in relation to avocado ingestion were as follows: systemic anaphylaxis in seven patients, angioedema/urticaria in six, vomiting in two, bronchial asthma in one, and rhinoconjunctivitis in one. Skin prick test (SPT) with fresh avocado was positive in all patients with the Strong avocado variety (SAv) and in 14 patients with the Hass avocado variety (HAv). Our patient-associated sensitizations were as follows: 10 to latex, eight to chestnut, eight to banana, four to kiwi, and four to walnut. Avocado-sensitized patients with latex allergy were typically middle-aged women, professionally exposed to latex, who also exhibited frequent associated sensitizations to chestnut, banana, and other fruits. Specific IgE against avocado was demonstrated in 11 of our patients, by both commercial CAP and RAST with avocado extract coupled to nitrocellulose disks. Despite its lower protein content, SAv seems to be more allergenic than HAv, both in vivo and in vitro. On incubating a pool of sera from our patients with avocado, latex, chestnut, and banana extracts, a progressive RAST inhibition was obtained, with SAv- and chestnut-marked disks. This suggests the existence of common antigenic determinants among these allergens.

Metabolism of 5-Methylthioribose to Methionine

During ethylene biosynthesis, the H(3)CS- group of S-adenosylmethionine is released as 5'-methylthioadenosine, which is recycled to methionine via 5-methylthioribose (MTR). In mungbean hypocotyls and cell-free extracts of avocado, [(14)C]MTR was converted into labeled methionine via 2-keto-4-methylthiobutyric acid (KMB) and 2-hydroxy-4-methylthiobutyric acid (HMB), as intermediates. Incubation of [ribose-U-(14)C]MTR with avocado extract resulted in the production of [(14)C]formate, indicating the conversion of MTR to KMB involves a loss of formate, presumably from C-1 of MTR. Tracer studies showed that KMB was converted readily in vivo and in vitro to methionine, while HMB was converted much more slowly. The conversion of KMB to methionine by dialyzed avocado extract requires an amino donor. Among several potential donors examined, l-glutamine was the most efficient. Anaerobiosis inhibited only partially the oxidation of MTR to formate, KMB/HMB, and methionine by avocado extract. The role of O(2) in the conversion of MTR to methionine is discussed.

Inhibition of the methionine cycle enzymes

Inhibition of the enzymes involved in the production of 1-aminocyclopropane-1-carboxylic acid (ACC) and the subsequent salvage of methionine from 5′-methylthioadenosine (MTA) was studied. Possible product inhibition of ACC synthase, which converts S-adenosylmethionine (SAM) to ACC and MTA, and MTA nucleosidase, which hydrolyses MTA to 5-methylthioribose (MTR) and adenine, was investigated. ACC synthase was weakly inhibited by MTA ( K i = 0.2mM). MTA nucleosidase was inhibited by adenine competitively ( K i = 40μM), but not by MTR. Some analogues of the enzymes' substrates were inhibitory. ACC synthase was strongly and competitively inhibited by sinefungin, a SAM analogue ( K i = 2μM); MTA nucleosidase was inhibited by various MTA analogues, including 5′-chloroformycin, 5′-chloroadenosine, and 5′-ethylthioadenosine. The conversion of MTR to methionine in avocado extract was inhibited by the MTR analogues 5-chlororibose and 5-ethylthioribose, which exert their inhibitory effects by inhibiting MTR kinase. The capacity to convert MTR to methionine in ripening apple tissue appears to be ample; thus, this conversion does not appear to be a limiting factor of ethylene production.

Evidence for the presence of a native, non-auxinic rooting promoter in avocado (Persea americana Mill.)

The presence of a rooting promoter in paratially purified extracts of avocado (Persea amricana Mill.) organs has been demonstrated using the mung bean rooting bioassay. Extraction with 80% methanol was followed by partition into diethyl ether, paper chromatography (PC) and 3 steps of thin layer chromatography (TLC). The number of roots induced by the rooting promoter in the absence of exogenous auxin was 5 to 7 times higher than that of the water control and 50% higher than by 4-(indol-3-yl) butyric acid (IBA) at its reported optimum concentration. Rooting of tomato, Coleus and young avocado cuttings was also enhanced by the rooting promoter. The rooting promoter was inhibitory in the wheat coleoptile section elongation bioassay for auxins and had slight inhibitory activity in the split pea stem curvature test.

Adherence of oral streptococci: evidence for nonspecific adsorption to saliva-coated hydroxylapatite surfaces

It is proposed that binding of oral streptococci to saliva-coated hydroxylapatite (SHA) surfaces is a multifactorial process involving both specific and nonspecific receptors. In this context, specific binding is described as a high-affinity, saturable interaction between the cell and binding surface. Conversely, nonspecific binding is considered to be a nonsaturable, generalized, low-affinity reaction. Experimental differentiation of specific binding from nonspecific binding was achieved with a competition assay which utilized a large excess of nonradiolabeled bacteria to compete with the 3H-labeled cells for attachment to receptors on 1.5 mg of SHA crystals. Competition assays of Streptococcus sanguis and Streptococcus mitis adhesion clearly demonstrated that the total binding isotherm was composed of a saturable specific binding reaction and a minor nonspecific binding component. This was further substantiated by analysis of nonlinear Scatchard plots of the total binding data. The competition data for Streptococcus mutans binding indicated that ca. 50% of the S. mutans binding appeared to be specific, although saturation of the SHA surfaces with bacterial cells could not be demonstrated. Experiments measuring desorption of radiolabeled cells from SHA crystals into buffer showed that ca. 50% of the bound S. mutans cells were removed after 4 h, whereas less than 5% of the S. sanguis cells were eluted from the SHA surfaces. The kinetics of attachment were studied by using an extract of Persea americana as a noncompetitive inhibitor of adherence. The total cell binding data for these experiments suggested a very rapid binding reaction followed by a slower rate of attachment. It was concluded from these three different experimental approaches that adherence of selected oral streptococci to SHA surfaces involves specific, high-affinity and nonspecific, low-affinity binding reactions. The concept is developed that in vitro streptococcal attachment to SHA can be described as a two-reaction process in which the low-affinity interaction of the cell with the SHA surface precedes the establishment of the stronger, specific bonds needed for the maintenance of streptococci in the oral cavity.

Rapid indexing of the sunblotch disease of avocados using a complementary DNA probe to avocado sunblotch viroid

SUMMARYA routine procedure has been established for the sensitive and specific detection of avocado sunblotch viroid in partially purified nucleic acid extracts of avocado leaves by hybridisation analysis with 32P‐complementary DNA prepared against the purified viroid. Avocado sunblotch viroid was shown to be present in 12 avocado trees that had indexed positive in a biological test for sunblotch disease but was absent from 10 trees that indexed negative. The complete correlation between sunblotch disease and the presence of viroid indicates that the complementary DNA hybridisation assay procedure can be used for the indexing of sunblotch disease. The overall procedure of leaf extraction and hybridisation analysis can be completed in 5 days and is to be compared with up to 2 yr required for indexing by biological methods.The level of avocado sunblotch viroid in partially purified nucleic acid extracts of a number of different sources of sunblotch infected avocado leaves was found to vary 10 000‐fold from 0.2% to 2 × 10‐5% by weight. The lower limit of detectability of the viroid by the hybridisation assay is considered to be about 10‐5% by weight; this is at least 103 times more sensitive than the detection of the viroid by polyacrylamide gel electrophoresis of the leaf nucleic acid extracts followed by staining.

Superoxide Dismutase in Ripening Fruits

The levels of superoxide dismutase (SOD) activity in extracts of preclimacteric apple, banana, avocado, and tomato fruits were not greatly different than in extracts of postclimacteric fruits. The results indicate that no major quantitative change in SOD occurs in fruits with or preceding the onset of senescence. Tomato fruit SOD was studied in more detail, and was found largely in the soluble fraction, and to a lesser extent in the mitochondrial and plastid fractions. The soluble fraction was purified by ammonium sulfate fractionation, column chromatography, and isoelectric focusing. Isoelectric focusing separated SOD from contaminating peroxidases. The purified tomato SOD showed an apparent molecular weight of 31,500 determined by gel filtration. Polyacrylamide gel electrophoresis of this preparation indicated two SOD components corresponding to two protein bands, one of which stained more intensely than the other. The purified tomato enzyme was inhibited 90% by 1 mm KCN.

Occurrence of Methyl (+)-Abscisate as an Artefact of Extraction

Alkaline methanolic extracts of avocado (Persea gratissima) fruit contain large amounts of methyl (+)-abscisate but little or no (+)-ABA is liberated by alkaline hydrolysis of the aqueous solution left after extraction of ether-soluble acidic and neutral compounds. No methyl (-t-)-abscisate is detectable in acetone or acidic methanol extracts but (+)-ABA can be released by alkaline hydrolysis of the aqueous solution in these experiments. It is concluded that methyl (-f)-abscisate is an artefact of extraction caused by the methanolysis of a conjugate in neutral or basic conditions. Reports of neutral inhibitors in plant extracts require re-examination because some of the inhibitory activity may be attributable to methyl (+)-abscisate formed during methanol extraction. (+)-ABA biosynthesised from (+)-[3'-14C]mevalonolactone by avocados had a higher specific activity than had the bound (+)-ABA; this suggests that free (+)-ABA is formed first and the conjugate is derived from this, rather than the reverse.

Fat Metabolism in Higher Plants

Stearyl-acyl carrier protein desaturase (EC 1.14.99.6), present in the stroma fraction of spinach (Spinacia oleracea) chloroplasts, rapidly desaturated enzymatically prepared stearyl-acyl carrier protein to oleic acid. No other substrates were desaturated. In addition to stearyl-acyl carrier protein, reduced ferredoxin was an essential component of the system. The electron donor systems were either ascorbate, dichlorophenolindophenol, photosystem I and light, or NADPH and ferredoxin-NADP reductase. The desaturase was more active in extracts prepared from chloroplasts obtained from immature spinach leaves than from mature leaves. Stearyl-acyl carrier protein desaturase also occurs in soluble extracts of avocado (Persea americana Mill.) mesocarp and of developing safflower (Carthamus tinctorius) seeds.