Importance of 2,4-DAPG in the biological control of brown patch by Pseudomonas fluorescens HP72 and newly identified genes involved in 2,4-DAPG biosynthesis

The Pseudomonas fluorescens strain HP72 used as biocontrol agent was isolated from the roots of creeping bentgrass on brown patch-suppressive soil. This strain can suppress brown patch disease caused by Rhizoctonia solani. The analysis of secondary metabolites from strain HP72 revealed that it produced known antifungal compounds, 2,4-diacetylphloroglucinol (2,4-DA-PG), HCN, and a fluorescent siderophore. In the present study, the Tn5inserted mutants of strain HP72, which did not show any antifungal activity, were selected. None of the mutants produced 2,4-DA-PG but they produced a fluorescent siderophore, while some strains produced HCN. Therefore, it is suggested that 2,4-DA-PG plays a major role in the biological control of brown patch disease caused by R. solani. In the genomic region where Tn5 was inserted, two open reading frames (ORFs A and B), which are not included in the 2,4-DAPG gene cluster of HP72, were detected. It was demonstrated that ORFs A and flare involved in the regulation of 2,4-DAPG biosynthesis.     

Accumulation mechanism of γ-aminobutyric acid in tomatoes (Solanum lycopersicum L.) under low O2 with and without CO2

The storage of ripe tomatoes in low-O(2) conditions with and without CO(2) promotes γ-aminobutyric acid (GABA) accumulation. The activities of glutamate decarboxylase (GAD) and α-ketoglutarate-dependent GABA transaminase (GABA-TK) were higher and lower, respectively, following storage under hypoxic (2.4 or 3.5% O(2)) or adjusted aerobic (11% O(2)) conditions compared to the activities in air for 7 days at 25 °C. GAD activity was consistent with the expression level of mRNA for GAD. The GABA concentration in tomatoes stored under hypoxic conditions and adjusted aerobic conditions was 60-90% higher than that when they are stored in air on the same day. These results demonstrate that upregulation of GAD activity and downregulation of GABA-TK activity cause GABA accumulation in tomatoes stored under low-O(2) conditions. Meanwhile, the effect of CO(2) on GABA accumulation is probably minimal.     

Oxygenation of bisphenol A to quinones by polyphenol oxidase in vegetables

To understand conversion of bisphenol A and its related compounds under some chemical and biological environments, oxidation of these compounds was performed. Bisphenol A was oxidized to monoquinone and bisquinone derivatives by Fremy's salt, a radical oxidant; but salcomine and alkali did not catalyze the oxidation by molecular oxygen. Bisphenol A, bisphenol B, and 3,4'-(1-methylethylidene)bisphenol were converted to their monoquinone derivatives in the presence of oxygen and polyphenol oxidase from mushroom at 25 degrees C at pH 6.5. Among crude enzyme solutions of fruits and vegetables, potato, mushroom, eggplant, edible burdock, and yacon showed remarkable oxidative activity on bisphenol A. The highest activity was observed in potato, and the main product obtained by the enzymatic oxygenation was the monoquinone derivative of bisphenol A, accompanied by a small amount of the bisquinone derivative. The oxidation reactions found here will be useful for developing techniques for elimination of phenolic endocrine disrupters from the environment.     

Nutritional Study of Silicon in Graminaceous Crops (Part 1)

Silicon in crop plants has been studied in various ways, for example, in elucidating its effects on phosphorus and nitrogen uptake by roots, or increase of resistance to diseases and insect pests, Graminaceous crops generally contain much more silicon in them than other families of plants, Remarkable effects of silicon application to plants On their growth appear especially in case they have contained about 5 to 10% of silicon before-hand. When silicon content in plants, on the other hand, is quite low, such as less than 0.5% for dry matter, plants show retardation of their grOwth at both vegetative and reproductive stages. It may be deduced that silicon applied to plants might play a role in different ways in cases where they have already had either considerable or quite small amounts of silicon. While the former case has been studied very much, extreme deficiency of silicon in plants has been investigated very little^1)-8). Experiments reported here were designed for elucidating roles of silicon in its defiCient plants and getting information about the essentiality of silicon for them.     

A supernodulating mutant isolated from soybean cultivar enrei

Abstract

Symbiotic nitrogen fixation in nodules of legumes depends on the complex interaction between the legume plant and (Brady)Rhizobium bacteria. Nodule formation and nitrogen fixation are closely regulated by both the host plant and the microsymbiont. Plant mutants with altered symbiotic performance are considered to be useful to gain a better understanding of the plant—microbe interactions in the legume—(Brady)Rhizobium symbiosis (Jacobsen 1984; Carroll et al 1985a, b; Park and Buttery 1988; Duc and Messager 1989; Gremaud and Harper 1989). Recently, Carroll et al. (1985a, b) have isolated the supernodulating mutants of the soybean cv. “Bragg,” which display a very large number of nodules and “nitrate-tolerant-symbiotic” (nts) characteristics. More recently, Gremaud and Harper (1989) have also isolated similar mutants from the soybean cv. “Williams.” These mutants not only provide materials that are useful for investigatings on the interaction in the nodule formation processes but also for agricultural practice. In particular, the nitrate-tolerance of these supernodulating mutants (Carroll et al. 1985b; Gremaud and Harper 1989) is useful for their cultivation in Japan where the level of soil nitrogen in fields is generally high. However, the cultivars previously used for the isolation of these mutants cannot adapt easily in Japanese climate due to different Maturity Group. Therefore, we attempted to isolate mutants with altered symbiotic phenotypes from the soybean cultivar “Enrei,” one of the most common cultivars in Japan.     

Isolation of transposon Tn5-induced hydrophobic mutants of a Bradyrhizohium japonicum strain with improved competitive nodulation abilities

Abstract

Hydrophobic mutants of the Bradyrhizohium japonicum strain 138NR were obtained by transposon Tn5 mutagenesis followed by replica-plating on polystyrene plates. Fifteen mutants were isolated at a frequency of 10⁶. Gel-filtration analysis of the exopolysaccharides revealed that the hydrophobic mutants produced a significantly smaller amount of low-molecular-weight polysaccharides than the parent. Four of the isolated mutants formed a larger number of nodules on soybean (Glycine max L. Merr. cv. Tamahomare) than the parent, two were superior in symbiotic nitrogen fixation, and two were symbiotically defective on soybean. Competitive nodulation abilities of the mutants were examined by inoculating them to soybean with B. japonicum strain 123ET as a competitor and determining the nodule occupancy based on the antibiotic resistance. All the mutants tested except for the symbiotically defective ones were superior in their competitive nodulation ability to the parent strain. When inoculated 24 h before the inoculation with 123ET, the mutants exhibited an increased nodule occupancy (44–93% compared to 9% by the parent).     

Inhibition of malonaldehyde formation in oxidized calf thymus DNA with synthetic and natural antioxidants

Calf thymus DNA was oxidized by Fenton's reagent with or without synthetic antioxidants (Trolox and DMPO) and natural antioxidants-quercetin, apigenin, 2'-O-glycosylisovitexin (2'-O-GIV), (+)-catechin, cyanidin, pelargonidin, keracyanin, and callistephin. Malonaldehyde (MA) formed in oxidized DNA was analyzed using gas chromatography. MA formed from oxidized DNA without antioxidants was 4.0 +/- 0.53 nmol/mg of DNA in buffer solution, 3.7 +/- 0.34 nmol/mg of DNA in NaOH solution, and 4.6 +/- 0.19 nmol/mg of DNA in HCl solution. MA formed from DNA with antioxidants (at the level of 0.1 micromol/mL) ranged from 1.90 +/- 0.18 (catechin) to 4.10 +/- 0.18 nmol/mg of DNA (cyanidin). Trolox and DMPO inhibited MA formation from DNA by 41.2% and 18.6%, respectively, at the level of 0.1 micromol/mL. Trolox (water-soluble vitamin E) exhibited dose-dependent inhibition. The decreasing order of inhibitory effect by flavonoids at the level of 0.1 micromol/mL was catechin (48.5%) > quercetin (47.1%) > 2'-O-GIV (40.5%) > apigenin (29.9%) and by the anthocyanins at the level of 0.1 micromol/mL was callistephin (45%) > keracyanin (33.2%) > pelargonidin (25.1%) > cyanidin (10.2%).     

Statistical Analysis of Metal Concentrations in a Sediment Core to Reveal Influences of Human Activities on Atmospheric Environment for 200 Years

Metal concentrations in a sediment core from a moat outside Osaka Castle in Japan were measured by ICP-MS following a microwave extraction method. Concentrations of metals in the sediment core samples peaked around 1945 when the World War II ended. This is in part due to great air raids on Osaka. In cluster analysis using metal concentrations, the fractions of sediment core samples were classified into two groups, representing natural sources (1795–1915) and anthropogenic sources (1922–1976), respectively. Results of lead isotope ratios also showed the anthropogenic influences from 1915 by changing the ratio values compared to those of natural sources. In addition, several components contributing to metal concentrations were identified by principal component analysis. The main component was controlled by natural sources and a decrease of the component score corresponded to an increased influence from anthropogenic sources. The largest impact of anthropogenic sources was shown around 1945.