摘要:

Synthesis of the nonprotein amino acid γ-aminobutyric acid is stimulated within minutes by diverse environmental factors. Synthesis (L-Glu + H+– γ-aminobutyric acid + CO2) is catalysed byL-Glu decarboxylase, a cytosolic enzyme having an acidic pH optimum. This study uses isolatedAsparagus sprengeri(Regel) mesophyll cells to investigate the possible role of Ca2+in stimulated γ-aminobutyric acid synthesis. Abrupt cold shock (20 °C to 1 °C) stimulated γ-aminobutyric acid levels from 2.7 to 5.6 nmol/106cells within 15 min. This 100% increase was reduced to 28% in the presence of the Ca2+channel blocker lanthanum, and was significantly reduced by incubation with 1 mM of the calmodulin antagonistN-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide. Incubation at 20 °C with 25 μM calcimycin, a Ca2+ionophore, increased levels by 61% within 15 min. A fluorescent Ca2+indicator demonstrated that cytosolic Ca2+increased within 2 s of cold shock, followed by a return to initial levels within 25 s. In contrast, comparable experiments indicate a rapid and prolonged decrease in cytosolic H+.L-Glu decarboxylase isolated from asparagus cladophylls was stimulated 100% by addition of 500 μM Ca2+and 200 nM calmodulin. This activity was reduced to control values by the calmodulin antagonist. Collectively, the data indicate that cold shock initiates a signal transduction pathway in which increased cytosolic Ca2+stimulates calmodulin-dependentL-Glu decarboxylase activity and γ-aminobutyric acid synthesis. This mechanism appears independent of increased H+.Key words: cold shock, GABA, Ca2+, H+.

ISSN:0008-4026    

DOI:10.1139/b97-040

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The host range ofFusarium oxysporumf.sp.asparagi(Foa) was studied in inoculation experiments with 21 plant species. Typical root rot symptoms were incited only in asparagus, in all experiments; lupin and pea were susceptible under in vitro conditions but showed only mild symptoms occasionally when tested in soil; none of the other species showed external disease symptoms. Root colonization by Foa was studied for 14 plant species. The pathogen was detected in externally disinfested roots of all species except leek and onion, with asparagus the most extensively colonized species. Asparagus was not susceptible to isolates ofF.oxysporumf.sp.pisi,lupini,cepae,lilii, andgladioliandFusarium saccharivar.elongatum. Naturally infested field soil was planted twice for 11 – 13 weeks with 11 plant species, including asparagus and several symptomless hosts, and subsequently with asparagus as a biotest plant. Of these crops, only asparagus greatly increased the severity of Foa root rot. It was concluded that Foa has a narrow host range as a pathogen but a broad host range as a parasite. The consequences of the latter for the epidemiology of Foa are discussed. Twenty-four Foa isolates were assigned to 18 different vegetative compatibility groups (VCGs); three additionalF.oxysporumisolates, which were not pathogenic on asparagus, each belonged to a unique VCG. These findings indicate that the Dutch Foa population is very diverse genetically, as was found previously for the Foa population in the United States.Key words: asparagus,Fusarium oxysporumf.sp.asparagi, host range, lupin, pea, symptomless hosts, vegetative compatibility.

ISSN:0008-4026    

DOI:10.1139/b97-041

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

It is well established that various strains ofSynechococcus, a genus of unicellular cyanobacteria, can photoreduce O2, at high rates even during concomitant photosynthetic CO2fixation. This photoreduction probably involves photosystem I (PS1) and the so-called Mehler reaction. Although all photosynthetic organisms carry out this reaction to some extent, the mechanistic details remain unclear. Good candidates for the study of this reaction should be the various cyanobacteria that exhibit high rates of O2photoreduction. Unfortunately, the strains ofSynechococcusthat have been examined so far in this context are obligate photoautotrophs, which precludes the dissection of the photoreduction process by mutational analysis of PS1. In the present study, we show thatSynechocystisPCC 6803, a species capable of growth on glucose can photoreduce O2at high rates. When grown photoautotrophically, the cells exhibited an O2-dependent quenching of chlorophyllafluorescence that was 50–70% that of CO2-dependent quenching. The magnitude of this O2-dependent photochemical quenching could be related to the rate of linear photosynthetic electron flow. For cells grown at a photosynthetic photon flux density of 50 μmolm−2 ∙ s−1, the rate of O2, photoreduction was saturated at about 200 μmolm−2 ∙ s−1. UnlikeSynechococcusUTEX 625 and PCC 7942, the rate of photoreduction of O2was high even at the CO2compensation point, when there would be very little active accumulation of inorganic carbon (Ci). The O2concentration, or Km(O2), that supported the half-maximal rate of O2photoreduction was in the order of 6 μM. This low value for the Km(O2) and also the ability of the cells to photoreduce O2in the presence of glycolaldehyde, which inhibits ribulose bisphosphate (RuBP) regeneration, ruled out the involvement of RuBP oxygenase. Cells grown photomixotrophically, on Ciand glucose, were also capable of high rates of O2photoreduction as manifest by high rates of O2-dependent quenching of chlorophyll fluorescence. The response to O2of these cells was very similar to that observed withSynechococcusUTEX 625 and PCC 7942, in that O2photoreduction was greatly stimulated by the accumulation of Ciby the active CO2and HCO3−transport systems. The demonstration that the facultatively heterotrophicSynechocystisPCC 6803 photoreduces O2at high rates opens up the possibility of using targeted genetic inactivation of PS1 to study the Mehler reaction.Key words: O2photoreduction, cyanobacteria, chlorophyllafluoresce

ISSN:0008-4026    

DOI:10.1139/b97-042

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

It has been hypothesized that substances that accumulate during the mushroom cropping period are responsible for decreased yields as a mushroom crop ages. The objective of this study was to determine whether chelators added to compost substrate at spawning would affect the later break yield ofAgaricus bisporus. Different types of chelators were used to determine if specific ions were involved. Supplemented compost receiving hypnum peat, IR120 (sodium saturated) cation exchange resin, ethyleneglycol tetra-acetic, and citric acid significantly increased later break yield. However, IR120 (hydrogen saturated) cation exchange resin, ethylenediamine tetra-acetic and sphagnum peat moss added to supplemented compost at spawning did not significantly increase yield in later breaks. These results suggest the accumulation of calcium or another cation may inhibit later break yields.Key words:Agaricus bisporus, hypnum peat, ion exchange resins, chelation, citric acid.

ISSN:0008-4026    

DOI:10.1139/b97-043

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Cladistic analysis of molecular data (plastidrbcL sequences) supports the interpretation of simultaneous microsporogenesis as an apomorphy for Asparagales (Lilianae), with a reversal in the most derived 'higher' asparagoid clade, which is entirely successive. 'Lower' asparagoids are mainly simultaneous, with occasional reversals to the successive state, such as inXanthorrhoea, Hypoxidaceae, and a few Orchidaceae and Iridaceae (includingGeosiris). Trichotomosulcate pollen, a characteristic feature of one of the lower asparagoid clades, is associated with simultaneous microsporogenesis. Some lower asparagoids, such asDoryanthesand a few Iridaceae, are recorded as having both successive and simultaneous microsporogenesis. Irregular tetrads occur frequently in Asphodelaceae and sometimes in higher asparagoids, although not in the group with trichotomosulcate pollen. We relate the distributions of these characters to the positions of the same taxa in therbcL tree, expanded to include more taxa sampled for pollen characters. The pollen data are highly congruent with therbcL tree, although when viewed from the perspective of all previous classifications, trichotomosulcate pollen would be interpreted to have evolved several times. We interpret distribution of both simultaneous microsporogenesis and trichotomosulcate pollen with the DNA tree to be an indication of the reliability of both for taxonomic revision of family limits.Key words: tetrads, trichotomosulcate pollen, Phormiaceae.

ISSN:0008-4026    

DOI:10.1139/b97-044

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Accelerator mass spectrometry dated pollen, plant-macrofossil, and charcoal records from Sutherland Pond (41°23′29″N, 74°02′16″W), located in the Black Rock Forest, provide a detailed account of forest history during the late-glacial – Holocene transition in the Hudson Highlands, lower Hudson Valley, southeastern New York. Pollen assemblages dating more than 12 600 radiocarbon years before present (years BP) are dominated by herbaceous and shrub types (Salix,Betula,Alnus, Ericaceae, Cyperaceae, Gramineae, and Tubuliflorae), with some arboreal types (PinusandPicea), apparently representing an open landscape possibly with scattered trees. At 12 600 years BP increased organic deposition and pollen influx and the first occurrence of macrofossils indicate dramatic environmental change. Mixed assemblages of boreal and temperate taxa (Picea,Abies,Betula papyrifera,Quercus,Ostrya–Carpinus, andFraxinus) are evident from 12 600 to 11 200 years BP. Low charcoal influx suggests that fire was a minor component of early woodland development beginning around 12 600 years BP. APicea–Abies–Alnusassemblage, suggesting a cool climatic episode, dominates between 11 200 and 10 120 years BP, with rapid onset and termination each occurring within 150 years. Fire activity is also low during this colder interval. Warmer conditions, reestablished by 10 120 years BP, are inferred from expansion ofPinus strobusand increasingQuercusandOstrya–Carpinus, followed by replacement ofB.papyriferabyBetula populifoliaand increased charcoal influx.Key words: late glacial, pollen, plant macrofossils, fire, accelerator mass spectrometry radiocarbon dating, New York.

ISSN:0008-4026    

DOI:10.1139/b97-045

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The use of proteins as a nutrient source byAchlya ambisexualiswas investigated, using media containing defined and undefined sources of carbon, nitrogen, and (or) sulfur. Release of extracellular proteases occurred during growth on all proteins and protein hydrolysates tested, but not during growth on yeast extract or in defined medium. In gelatin-containing media, three major bands of extracellular protease activity were detected by electrophoresis, with estimated molecular mass of 26, 48, and 58 kDa. Growth on gelatin was stimulated to a much greater degree by the addition of glucose to the medium than by additions of glutamic acid or methionine. This and the release of ammonia during growth indicate that gelatin is less effective in meeting metabolic needs for carbon than it is in meeting the needs for nitrogen and sulfur. Protease secretion is only partially regulated by glucose, whereas glucose, methionine, and glutamic acid in combination cause almost complete repression. The pattern of regulation indicated by these results is most consistent with one of induction + derepression.Key words: oomycetes, proteinases, regulation, secreted enzymes.

ISSN:0008-4026    

DOI:10.1139/b97-046

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Experiments were carried out, in a controlled environment during a 4-h incubation period, to examine the effects of phenolic acids on uptake by soybean (Glycine max(L.) Merr cv. Maple Bell) roots of phosphate and methionine and their incorporation into nucleic acids and proteins, respectively. Benzoic,p-hydroxy benzoic, vanillic, cinnamic,p-coumaric, and ferulic acids were used in the study. Nucleic acid and protein synthesis were assayed by the incorporation of32P and35S-methionine into soybean root. The uptake of32P was reduced by benzoic, cinnamic, vanillic, and ferulic acids, whilep-hydroxybenzoic andp-coumaric acids increased slightly its absorption. At 250 μM, all allelochemicals tested reduced the incorporation of32P into DNA and RNA. Benzoic, cinnamic, ferulic, and vanillic acids reduced the uptake of32S-methionine, whereasp-hydroxybenzoic andp-coumaric acids increased its uptake. The methionine incorporation into proteins was reduced by all phenolic acids, except forp-coumaric acid and vanillic acid at 125 μM. These results suggest that interference with nucleic acid and protein metabolism by the phenolic acids is one of the main mechanisms by which they influence plant growth.Key words: Allelochemicals, mechanism of action, phenolic acids, phosphorus, proteins, methionine, ion uptake.

ISSN:0008-4026    

DOI:10.1139/b97-047

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The seed banks of six Lake Ontario shoreline marshes were investigated to assess the potential for natural regeneration of sparse submerged macrophyte populations in marshes subjected to anthropogenic disturbance. Twenty-six core samples were taken in each of three disturbed marshes with sparse submerged vegetation, and the number of seeds was compared with samples from three reference marshes containing abundant submerged vegetation. Six cores from each of six marshes were examined to determine whether there was a difference between disturbed and reference marshes in seed density or seed distribution, and germination assays were used to assess differences in seed viability. Seeds of five submerged macrophyte taxa were identified in substrate samples of the six marshes. Mean seed density was significantly higher in the three reference marshes (4082 – 47 623 seeds/m2) than in the three disturbed marshes (0–2041 seeds/m2). The density of seedlings of submerged macrophytes germinating in reference marsh samples ranged from 333 to 2406 seedlings/m2, whereas no seedlings germinated from disturbed marsh samples. The deeper sediments (7–14 cm sediment depth) in the reference marshes had comparable seed densities to those in the shallower sediments, whereas seeds were found in only the deeper sediments of the disturbed marshes. These data suggest that regeneration from buried seeds is unlikely in the disturbed marshes, even if improvements occur in the environmental conditions that have historically inhibited the growth of submerged macrophytes.Key words: submerged macrophytes, anthropogenic disturbance, Lake Ontario, seed banks, natural regeneration.

ISSN:0008-4026    

DOI:10.1139/b97-048

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The levels of abortion at three stages (ovule, seed, and flower–fruit) and biomass allocation to flowers, seeds, and fruits were determined in 231 species from five Venezuelan plant communities. These values were analyzed as a function of the sexual systems of the plants and the presence of dichogamy. In this study, the only significant difference between sexual systems was in the level of ovule abortion, which was greater in dioecious and hermaphroditic species than in monoecious and andromonoecious species. Species with protandrous or protogynous flowers had higher seed set and lower levels of aborted ovules and aborted flowers and fruits than species with adichogamous flowers. These results indicate that hermaphroditic plants do not compensate for their inability to independently control the number of male and female flowers by producing an excess of flowers that function mainly as pollen donors. On the other hand, the temporal separation of male and female functions in hermaphroditic and monoecious species may contribute to increased seed and fruit set by enhancing reallocation of assimilates from floral organs or flowers to fruit formation in time, and by reducing pollen–stigma interference within plants.Key words: fruit abortion, ovule abortion, dichogamy, sexuality, biomass allocation.

ISSN:0008-4026    

DOI:10.1139/b97-049

出版商:NRC Research Press    

年代:1997

数据来源: NRC