Functional analysis of isoforms of NADPH: protochlorophyllide oxidoreductase (POR), PORB and PORC, in Arabidopsis thaliana

NADPH:protochlorophyllide oxidoreductase (POR) catalyzes the light-dependent reduction of protochlorophyllide. To elucidate the physiological function of three differentially regulated POR isoforms (PORA, PORB and PORC) in Arabidopsis thaliana, we isolated T-DNA tagged null mutants of porB and porC. The mature seedlings of the mutants had normal photosynthetic competencies, showing that PORB and PORC are interchangeable and functionally redundant in developed plants. In etiolated seedlings, only porB showed a reduction in the photoactive protochlorophyllide and the size of prolamellar bodies (PLBs), indicating that PORB, as well as PORA, functioned in PLB assembly and photoactive protochlorophyllide formation in etiolated seedlings. When illuminated, the etiolated porB seedling was able to green to a similar extent as the wild type, whereas the greening was significantly reduced under low light conditions. During greening, high light irradiation increased the level of PORC protein, and the greening of porC was repressed under high light conditions. The porB, but not porC, etiolated seedling was more sensitive to the far-red block of greening than the wild type, which is caused by depletion of endogenous POR proteins resulting in photo-oxidative damage. These results suggest that, at the onset of greening, PLBs are important for efficient capture of light energy for photoconversion under various light conditions, and PORC, which is induced by high light irradiation, contributes to photoprotection during greening of the etiolated seedlings.     

Cleavage Maps of Dehalogenation Plasmid pUOl and Its Deletion Derivative Harbored in Moraxella sp.

Inhibitory effects of lactic acid bacteria for dairy use on the mutagenicities of some volatile nitrosamines were investigated in vitro using a Salmonella typhimurium TA 98 streptomycin-dependent strain (SD 510) as an indicator bacterium. Among 40 strains examined, Leuconostoc paramesenteroides R-62, R-8, Streptococcus lactis subsp. diacetylactis R-63, and St. cremoris R-48 strongly inhibited the mutagenicity of N-nitroso-diethylamine (NDEA) and moderately N-nitroso-dimethylamine (NDMA), but not N-nitroso-piperidine (NPIP) or N-nitroso-pyrrolidine (NPYR). In addition, the filtrates obtained from cell suspensions of the lactic acid bacteria examined inhibited the mutagenicity of NDEA.     

Decomposition of Organic Mercurial Compounds by Mercury-resistant Bacteria

Isopentyl isovalerate and anisic acid were first isolated and identified from the Japanese peppermint oil. The former compound possesses characteristic apple-like oder. α-Bourbonene, menthofurolactone, and β-caryophyllene epoxide were also isolated and identified from the oil of Shubi, a newly registered Japanese peppermint.     

Enhancing effects of NaCl and Na phosphate on human gustatory responses to amino acids

The effects of salts on sweet taste of amino acids (glycine,alanine and serine) were examined by the psychophysical method.There was no difference in quality of sweetness between theamino acids alone and the amino acids in the presence of saltssince low concentrations of NaCl and Na phosphate having nosalty taste were used. The sweetness of the amino acids wasgreatly increased with an increase of NaCl concentration. Thesweetness of 100 mM amino acids in the presence of 30 mM NaClwas equivalent to that of 500–600 mM amino acids containingno salt. On the other hand, Na phosphate little affected sweetnessof the amino acids. Significance of the present results in foodscience was discussed.     

Inhibitory Effects of 2-Deoxy-D-glucose on Methanol Metabolism in Torulopsis sp.

Inhibitory effects of 2-deoxy-D-glucose (2dG) on methanol metabolism in Torulopsis A–12 were investigated. The remarkable inhibition was observed on growth in the presence of 50 μg/ml of 2dG when methanol was used as a carbon source. At the earlier time of incubation with 2dG, the incorporation of ¹⁴C-methanol into hexose-phosphate by intact cells was inhibited by 2dG, and this led to the reduction of the intracellular concentration of hexose-phosphates. In the later period of incubation the specific activity of alcohol oxidase reduced, and formate accumulated extracellularly.     

Increased Resistance to Acriflavine by Amplification of the acrA Gene of Escherichia coli K-12

The wild-type acrA⁺ gene of Escherichia coli K-12, cloned intoplasmid pAF1, was expressed as resistance to acriflavine (AF)in AF-sensitive acrA mutant cells (N43). When acrA⁺ genes wereamplified by treatment of cultures with chloramphenicol (50µg/ml), cells expressed much higher resistance to AF thanthat of the wild-type strain (N90). (Received November 22, 1989; Accepted July 7, 1990)     

Attempt to simultaneously generate three chiral centers in 4-hydroxyisoleucine with microbial carbonyl reductases

A panel of microorganisms was screened for selective reduction ability towards a racemic mixture of prochiral 2-amino-3-methyl-4-ketopentanoate (rac-AMKP). Several of the microorganisms tested produced greater than 0.5 mM 4-hydroxyisoleucine (HIL) from rac-AMKP, and the stereoselectivity of HIL formation was found to depend on the taxonomic category to which the microorganism belonged. The enzymes responsible for the AMKP-reducing activity, ApAR and FsAR, were identified from two of these microorganisms, Aureobasidium pullulans NBRC 4466 and Fusarium solani TG-2, respectively. Three AMKP reducing enzymes, ApAR, FsAR, and the previously reported BtHILDH, were reacted with rac-AMKP, and each enzyme selectively produced a specific composition of HIL stereoisomers. The enzymes appeared to have different characteristics in recognition of the stereostructure of the substrate AMKP and in control of the 4-hydroxyl group configuration in the HIL product.     

Use of haloacetate dehalogenase genes as selection markers forEscherichia coli andPseudomonas vectors

The haloacetate dehalogenase gene,dehH2, cloned fromMoraxella sp. strain B could be used as a selection marker gene for vectors inEscherichia coli andPseudomonas putida. Haloacetates, especially iodoacetate, inhibit the growth of some microorganisms. ThedehH2 gene introduced into the cells conferred iodoacetate resistance on them. Therefore,E. coli andP. putida transformed with vectors marked withdehH2 could be easily selected on plates containing iodoacetate.     

Variation in leaf and soil δ<Superscript>15</Superscript>N in diverse tree species in a lowland dipterocarp rainforest,Malaysia

Key message

Large variations in leaf δ ¹⁵ N in Bornean tropical rainforest trees may indicate that various tropical species have species-specific strategy for nitrogen uptake under low soil nutrient conditions, including root symbiotic microorganisms such as ectomycorrhiza.

Abstract

Lowland tropical rainforests in Southeast Asia are characterized by high species diversity despite limited soil nutrient conditions. The plant nitrogen isotope ratio (δ¹⁵N) reflects plant uptake of soil nitrogen. We analyzed δ¹⁵N values and nitrogen content (N %) in leaves and roots of 108 woody species with different types of symbiotic microorganisms, of different life forms (emergent, canopy, sub-canopy, understory, and canopy gap species), and from different families in a Bornean lowland dipterocarp forest to gain more insight into the diversity of nitrogen uptake strategy in the rhizosphere. Leaf δ¹⁵N values in the species studied varied largely from ?7.2 to 5.0 ‰, which is comparable to the values of known Asian trees including temperate, sub-tropical, and tropical mountain forests. Leaf δ¹⁵N also varied significantly among both life forms and families, though the phylogenetically independent contrast (PIC) relationships were not statistically significant among life form, family, and symbiotic types. Some families showed specific leaf δ¹⁵N values; Dipterocarpaceae, the dominant family in the canopy layer with symbiotic ectomycorrhiza in Southeast Asia, had small intraspecific variation and higher leaf δ¹⁵N values (0.03 ‰) compared with species exhibiting arbuscular mycorrhiza, whereas several families such as Burseraceae, Euphorbiaceae, and Myrtaceae showed large interspecific variation in leaf δ¹⁵N (e.g., from ?7.2 to 5.0 ‰ in Euphorbiaceae). These variations suggest that tropical species may have family- or species-specific strategy, such as root symbiotic microorganisms, for nitrogen uptake under low-nutrient conditions in tropical rainforests in Southeast Asia.