Respiration rate in maize roots is related to concentration of reduced nitrogen and proliferation of lateral roots

The relationship between specific rate of respiration (respiration rate per unit root dry weight) and concentration of reduced nitrogen was examined for maize ( Zea mays L.) roots. Plants with 2 primary nodal root axes were grown for 8 days in a split-root hydroponic system in which NO-₃ was supplied to both axes at 1.0 mol m⁻³, to one axis at 1.0 mol m⁻³ and the other axis at 0.0 mol m⁻³ or to both axes at 0.0 mol m⁻³ Respiration rates and root characteristics were measured at 2-day intervals. Specific rate of respiration was positively correlated in a nonlinear relationship with concentration of reduced nitrogen. The lowest specific rates of respiration occurred when neither axis received exogenous NO⁻³ and the concentration of reduced nitrogen in the axes was less than 9 mg g⁻¹. The greatest rates occurred in axes that were actively absorbing NO⁻³ and contained more than 35 mg g⁻¹ of reduced nitrogen. At 23 mg g⁻¹ of reduced nitrogen, below which initiation of lateral branches was decreased by 30–50%. specific rate of respiration was 17% greater for roots actively absorbing NO⁻³ than for roots not absorbing NO⁻³ Increases in specific rate of respiration associated with concentrations of reduced nitrogen greater than 23 mg g⁻¹ were concluded to be attributable primarily to proliferation of lateral branches.     

Annual changes in the nutritive state of North Sea dab

The nutritive state of dab Limanda limanda was investigated over a 2-year period at a fixed sampling site northwest of Helgoland (German Bight, North Sea), with respect to feeding habits and the accumulation of biochemical storage products. Ophiuroids formed the main weight of food organisms (50%) while polychaetes (10%), molluscs and crustaceans (<5% each) were less frequent. Feeding activity in males varied between summer and winter, while females fed more constantly. The condition factor and the hepatosomatic index showed characteristic seasonal cycles in both sexes. The glycogen content in the liver reached 40–60 mg g⁻¹ FW in summer and fell to about 10–20 mg g⁻¹ FW in late winter. Total lipids of the liver showed a distinct seasonal cycle with 400 mg g⁻¹ FW in summer and a minimum of 50–100 mg g⁻¹ FW in spring. The lipid content of the muscle ranged from 5 to 6 mg g⁻¹ FW and did not vary significantly between seasons.     

Survival of genetically modified Pseudomonas fluorescens introduced into subtropical soil microcosms

Abstract A genetically modified strain of Pseudomonas fluorescens and its parent showed grossly similar decline rates following introduction into subtropical clay and sandy soils. In unplanted clay soit at pH 6.9 and 25°C, population densities declined progressively from about 10⁸ to 10³ colony forming units (cfu) g⁻¹ dry soil over 75 days, but in unplanted sandy soil the introduced populations could not be detected after 25 days. In clay soil at pH 8.7 or 4.7, or at environmental temperature, decay rates were enhanced as compared to those at pH 6.9 and 25°C. Counts of introduced strains in clay bulk soil and in rhizosphere and rhizoplane of maize suggested that the introduced bacteria competed well with the native bacteria, and colonized the roots at about 10⁶ cfu g⁻¹ dry root at 25°C, over 20 days. However, rhizoplane colonization was lower at environmental temperature. The decay rate of both strains was slower in planted than in unplanted sandy soil. The population densities in the rhizosphere and rhizoplane in the sandy soil were significantly lower than those in the clay soil. Both introduced strains colonized the maize roots in both soils, using seeds coated with bacteria in 1% carboxymethyl cellulose. Introduced cells were localized at different sites along the roots of plants developing in clay soil, with higher densities in the original (near the seeds) and root hair zones as compared to the intermediate zones. No significant difference was observed between the extent of root colonization of the genetically modified strain and its parent.     

Changes of Respiratory Chain Activity in Mitochondrial and Synaptosomal Fractions Isolated from the Gerbil Brain After Graded Ischaemia

Abstract: In this study we have examined (1) the integrated function of the mitochondrial respiratory chain by polarographic measurements and (2) the activities of the respiratory chain complexes I, II–III, and IV as well as the ATP synthase (complex V) in free mitochondria and synaptosomes isolated from gerbil brain, after a 30-min period of graded cerebral ischaemia. These data have been correlated with cerebral blood flow (CBF) values as measured by the hydrogen clearance technique. Integrated functioning of the mitochondrial respiratory chain, using both NAD-linked and FAD-linked substrates, was initially affected at CBF values of ∼35 ml 100 g⁻¹ min⁻¹, and declined further as the CBF was reduced. The individual mitochondrial respiratory chain complexes, however, showed differences in sensitivity to graded cerebral ischaemia. Complex I activities decreased sharply at blood flows below ∼30 ml 100 g⁻¹ min⁻¹ (mitochondria and synaptosomes) and complex II–III activities decreased at blood flows below 20 ml 100 g⁻¹ min⁻¹ (mitochondria) and 35–30 ml 100 g⁻¹ min⁻¹ (synaptosomes). Activities declined further as CBF was reduced below these levels. Complex V activity was significantly affected only when the blood flow was reduced below 15–10 ml 100 g⁻¹ min⁻¹ (mitochondria and synaptosomes). In contrast, complex IV activity was unaffected by graded cerebral ischaemia, even at very low CBF levels.     

Manganese accumulation in leaves of Hakea prostrata (Proteaceae) and the significance of cluster roots for micronutrient uptake as dependent on phosphorus supply

When grown at a low P supply, Hakea prostrata R.Br. (Proteaceae) develops dense clusters of determinate branch roots, termed 'proteoid' or 'cluster' roots and accumulates Mn in its leaves. The aim of this study was to vary the production of cluster roots and assess the relationship between Mn uptake and cluster-root mass. We collected native soil from a location inhabited by H . prostrata and amended this with 'high' and 'low' amounts of insoluble or soluble P. After 14 months, we measured the impact of the treatments on cluster-root development and the [P], [Mn], [Fe], [Zn] and [Cu] in young (expanding) and mature leaves. Dry mass and leaf area increased with increasing P availability in the soil, but growth decreased at the highest soluble [P], which caused symptoms of P toxicity. The [P] in young leaves (1.3–2.7 mg g⁻¹ DM) exceeded that in older leaves (0.28–0.85 mg g⁻¹ DM), except when plants were grown with soluble P (3.2–21 mg g⁻¹ DM). Cluster-root formation was inhibited when leaf [P] increased; [P] in young leaves, rather than that in old leaves, appeared to be the factor that determined the proportion of the root mass invested in cluster roots. Old leaves of all treatments had [Mn] from 90 to 120 µg g⁻¹ DM, except for plants grown at high levels of soluble P, when [Mn] decreased below 30 µg g⁻¹ DM. The [Mn] and [Zn] in old leaves and the [Cu] in young leaves were positively correlated with the fraction of roots invested in cluster roots. These findings support our hypothesis that cluster roots play a significant role in micronutrient acquisition, and also provide an explanation for Mn accumulation in leaves of H . prostrata , and presumably Proteaceae in general.     

Energy and ration requirements of juvenile Pacific halibut (Hippoglossus stenolepis) based on energy consumption and growth rates

Growth of captive juvenile Pacific halibut was linearly related to energy consumption (J g⁻¹ day⁻¹) at 4°C by the following equation: growth (% body weight (b.w.) day⁻¹)=0–007 (consumption J g⁻¹ day⁻¹)– 0.192; r² =0.81. Weight gain was independent of size for fish between 9 and 7000 g when growth was expressed as a function of consumption in J g⁻¹ day⁻¹. Maintenance ration determined in feeding–growth experiments averaged 27.4 J g⁻¹ day⁻¹ at 4–0°C. Small halibut ate significantly more food than large fish. Single meals following 2 day fasts averaged 4.1% b.w. for halibut under 100 g, 1.72% b.w. for 1.2 kg fish and 1.1% B.W. for 6.8 kg fish. Both large and small size categories of halibut tended to evacuate their meal in about 3 days even though small fish ate relatively larger meals. Minimum estimates for daily ration to achieve growth rates observed in the Gulf of Alaska were approximately 0.5 to 2.4% b.w. day⁻¹ depending on fish size and whether northern shrimp or yellowfin sole were their prey.     

Species of Anguilla as indicators of mercury in the coastal rivers and lakes of Victoria, Australia

Mercury concentrations in the axial muscle tissue of most (243) of the 254 Anguilla australis and most (20) of the 27 A. reinhardtii collected from 30 sites in coastal rivers and lakes in Victoria, Australia, during 1975–78 were well below the Australian statutory health limit (0.5 μg g⁻¹ wet weight). For A. australis the mean mercury concentration was 0.17 μg g⁻¹ (±0.16 s.d. , range 0.01–1.60 μg g⁻¹); for A. reinhardtii the values were 0.37 ± 0.23 μg g⁻¹ (range 0.12–1.10 μg g⁻¹). Statistical analyses showed that variation in mercury concentration due to total length accounted for only 13% of the total variation in A. australis and 2% in A. reinhardtii whereas locality accounted for 54 and 68%, respectively. Both species are thus considered suitable as indicators of mercury pollution.     

The content of prostaglandins and their precursors in Mortierella and Cunninghamella species

Five strains of filamentous fungi belonging to the genera Mortierella and Cunninghamella were examined for the content of dihomo-γ-linolenic, arachidonic, eicosapentaenoic acids and prostaglandins (type E₂ and F _2α). Prostaglandins were detected using an ELISA method in mycelia of all tested strains (range 50–4800 ng g⁻¹ of PGE₂ and 6–30 ng g⁻¹ of PG F _2α). Several micro-organisms also produced prostaglandins in the culture medium (2·2–137·6 μg l⁻¹ for PGE₂ and 0·4–7·8 μg l⁻¹ for PG F _2α).     

Zinc and cadmium hyperaccumulation by Thlaspi caerulescens from metalliferous and nonmetalliferous sites in the Mediterranean area: implications for phytoremediation

Growth, tolerance and zinc and cadmium hyperaccumulation of Thlaspi caerulescens populations from three metal contaminated soils and three normal soils were compared under controlled conditions. Individuals of six populations were cultivated on five soils with increasing concentrations of zinc (50–25000 μg g⁻¹) and cadmium (1–170 μg g⁻¹). There was no mortality of normal soil populations in the four metal-contaminated soils, but plant growth was reduced to half that of populations from metal-contaminated soils. However, in noncontaminated soil, the growth of individuals from normal soils was greater than that of individuals from metal-contaminated soils. Individuals from normal soils concentrated three times more zinc in the aboveground biomass than those from metal-contaminated soils, but the latter accumulated twice as much cadmium. We conclude that populations of T. caerulescens from both normal and metal-contaminated soils are interesting material for phytoextraction of zinc and cadmium, but to optimize the process of phytoextraction it is necessary to combine the extraction potentials of both type of populations.     

Respiration and energetics of the bumblebee Bombus terrestris queen

Carbon dioxide production by the Bombus terrestris queen was measured at different temperatures (10–30°C) and during different activities of the bumblebee. During flight the CO₂ production averaged 50 ml g⁻¹ (fresh weight) h⁻¹ and was only slightly affected by temperature. During rest (with a readiness to fly) and incubation the respiration rate clearly increased with decreasing temperature (5–40 and 13–56 ml g⁻¹ h⁻¹, respectively), whilst during torpor it increased with temperature (0.1–1.7 ml g⁻¹ h⁻¹ at temperatures from 10 to 30°C).
The expenditure of energy as calculated from the continuous respiration measurements agreed well with the amount of energy obtained from food (discrepancy 6–19%). The energy budget of an incubating queen was correctly predicted using the measured respiratory functions, prevailing temperatures, and the behaviour of the queen. The number of flower visits needed to fulfil the daily energy requirements of an incubating queen is discussed.     

Methanogenesis and methanotrophy within a Sphagnum peatland

Abstract: Methane production and consumption activities were examined in a Massachusetts peatland. Peat from depths of 5–35 cm incubated under anaerobic conditions, produced an average of 2 nmol CH₄ g⁻¹ h⁻¹ with highest rates for peat fractions between 25–30 cm depth. Extracted microbial nucleic acids showed the strongest relative hybridization with a 16S rRNA oligonucleotide probe specific for Archaea with samples from the 25–30 cm depth. In aerobic laboratory incubations, the peat consumed methane with a maximum velocity of 67 nmol CH₄ g⁻¹ h⁻¹ and a K _s of 1.6 μM. Methane consumption activity was concentrated 4–9 cm below the peat surface, which corresponds to the aerobic, partially decomposed region in this peatland. Phospholipid fatty acid analysis of peat fractions demonstrated an abundance of methanotrophic bacteria within the region of methane consumption activity. Increases in temperature up to 30°C produced an increase in methane consumption rates for shallow samples, but not for samples taken from depths greater than 9 cm. Nitrogen fixation experiments were carried out using ¹⁵N₂ uptake in order to avoid problems associated with inhibition of methanotrophy. These experiments demonstrated that methane in peat samples did not stimulate nitrogen fixation activity, nor could activity be correlated with the presence of methanotrophic bacteria in peat fractions.     

Soil microbial carbon uptake characteristics in relation to soil management

Abstract The kinetics of glucose uptake by soil microbial communities in 16 different soild (7 under monocultures and 9 under crop rotations) differing in microbial biomass content, % C_org, pH and clay content were investigated at 22°C. The V _max value of microbial bimasses under monoculture, was o.27 μg C_gluc · μg⁻¹ C_mic · h⁻¹ (range 0.18–0.44), twice as high as the mean value of V _max of microbial biomasses under rotations (0.13 μg C_gluc, range 0.07–0.19). Mean values of K _m were 714 μg C_gluc and 290 μg C_gluc · g⁻¹ soil, respectively.
These differences were highly significant ( P =0.001, based on SE) and could not be relate to particle size distribution of the soils, pH or C_org. A Michaelis-Menten type uptake response was apparent over the total range of glucose concentrations used (45.4–1453.3 μg C_gluc · g⁻¹ soil) for microbial biomasses under rotation while the majority of microbial biomasses under monocultures showed a similar response only at low glucose concentrations. A different uptake mechanism appeared to be involved at higher glucose concentrations (similar to diffusion) in monoculture soils.     

Uptake kinetics of iron-phytosiderophores in two maize genotypes differing in iron efficiency

Iron inefficiency in the maize ( Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe-phytosiderophores. To characterize this defect further, the uptake kinetics of Fe-phytosiderophores in ysl was compared to the Fe-efficient maize cultivar Alice. Short-term uptake of ⁵⁹Fe-labeled Fe-deoxymugineic acid (Fe-DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe-deficient plants followed Michaelis-Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe-phytosiderophores. The saturable component had similar K_m (∼ 10 μM) in both genotypes. In contrast. V_max was 5.5 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in Alice, but only 0.6 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in _ysl. Uptake experiments with double-labeled ⁵⁹Fe-[¹⁴C]DMA suggest that in both cultivars Fe-DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high-affinity and a low-affinity uptake system mediating Fe-phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high-affected uptake and led to a decrease in activity and/or number of Fe-phytosiderophore transporters.     

Anti-bacterial activity of synthetic N-heterocyclic oxidizing compounds

Synthetic chlorochromate derivatives of pyridine and quinoline were active in vitro against type cultures of Escherichia coli (ATCC 128), Staphylococcus aureus (ATCC 14775), Pseudomonas aeruginosa (ATCC 10145) and Bacillus subtilis (NCTC 8236). The minimum inhibitory concentrations (MIC) were 125–250 μg ml⁻¹ and 250–500 μg ml⁻¹ for pyridinium chlorochromate and quinolinium chlorochromate, respectively. An established derivative of quinoline (Perfloxacin) had an MIC of 125–250 μg ml⁻¹. The extinction time for 10⁵ cfu in broth was 90 min for pyridinium chlorochromate and 120 min for quinolinium chlorochromate, except for B. subtilis which survived up to about 180 min and 360 min. A combination of the two compounds produced an antagonistic effect. The 50% lethal dose (LD₅₀ toxicity) in mice was estimated at 76 μg g⁻¹ and 33 μg g⁻¹ body weight for the quinolinium and pyridinium chlorochromates. The compounds also exhibited some potential for suppressing a simulated staphylococcal infection in mice at the dosage levels of ca 22 μg g⁻¹ for pyridinium chlorochromate and 45 μg g⁻¹ for quinolinium chlorochromate.     

Endogenous cytokinin levels and metabolism of zeatin riboside in genetic tumour tissues and non-tumourous tissues of tobacco

The cytokinin content of stem tissues, primary genetic tumours (excised from 2-month-old plants) and 3-week-old in vitro cultured genetic tumour tissues derived from Nicotiana glauca (Grah.) × langsdorffii (Weinm.) and N. suaveolens (Lehm.) × langsdorffii (Weinm.) hybrids and stem tissues derived from 2-month-old N. suaveolens and N. langsdorffii plants has been analysed by radioimmunoassay. Stem tissues of tumour-prone hybrids contain high cytokinin levels (3–3.7 nmol g⁻¹). This increase is caused mainly by increased levels of cytokinin nucleotides, particularly those of zeatin nucleotide (0.5 nmol g⁻¹) in stem tissues of parent plants and 2.4 nmol g⁻¹ in stem tissues of hybrids). All other tissues contain lower cytokinin levels (0.7–1.7 nmol g⁻¹). Cytokinin bases and ribosides are major compounds in cultured tumour tissues while the nucleotides are dominant cytokinins in all freshly excised tissues from parent plants and their hybrids. In a separate study, the metabolic fate of supplied [³Hj-zeatin riboside. which is inactivated mainly by sidechain cleavage, has been studied. The results collectively suggest that cytokinins may be involved in tumourigenesis.     

Estimation of the bioenergetic costs of fruit and other organ synthesis in apple

The specific bioenergetic cost of apple fruit ( Malus domestica Borkh. cv. Braeburn) growth was calculated from seasonal elemental analysis (for carbon, hydrogen, nitrogen, and sulphur) and ash data. Specific cost changed during fruit development and at harvest was 1.16 g glucose g⁻¹ dry weight of which 0.142 g glucose g⁻¹ dry weight was consumed in growth respiration. Comparisons of those end-of-season values with those from a range of other apple cultivars (early through late maturing, and with a range of sugar/acid ratios) showed little difference, despite variations in elemental composition. Specific costs ranged between 1.15 and 1.16 g glucose g⁻¹ dry weight, and growth respiration between 0.136 and 0.148 g glucose g⁻¹ dry weight. Specific costs were also calculated for leaves (extension and spur), wood (1 and 2 year), and trunk and roots (fine and coarse). Leaves had the greatest cost (mean 1.44 g glucose g⁻¹ dry weight), then wood and trunk (mean 1.38 g glucose g⁻¹ dry weight), and fruit had the smallest. Specific growth costs were also calculated from heats of combustion data. Little difference was observed between the two methods, but the values calculated from the elemental analysis data tended to be higher than those calculated from the heats of combustion data.     

Seasonal variation in egg production and batch fecundity of European hake Merluccius merluccius (L.) in the Bay of Biscay

Sexually mature female hake Merluccius merluccius with hydrated ovaries were sampled on a monthly basis in the Bay of Biscay, from May 1996 to October 1997 and from March to April 1998. The batch fecundity was positively related to total length. The relative batch fecundity ( F _Brel) varied significantly among months and years, but not between areas, i.e. International Council for the Exploration of the Sea Divisions VIIIa and VIIIb within the Bay of Biscay. Two levels of F _Brel were found in 1997: the highest between January and April (mean ± s . e . 167 ± 5 eggs g⁻¹) and the lowest from May to October (112 ± 3 eggs g⁻¹). Population condition factor and gonado-somatic indices ( I _G) followed the expected trend in relation to the monthly changes in F _Brel during 1997. The F _Brel variation between years was 9% for 1996–1997 and 28% for 1997–1998, and the difference of the I _G was c. 14 and 36%, respectively. Population relative egg production varied from a high value in January to March (985 eggs g⁻¹) to a low egg production between April and October 1997 (445 eggs g⁻¹).     

Thiols of Cu-treated maize plants inoculated with the arbuscular-mycorrhizal fungus Glomus intraradices

Mycorrhizal colonization of roots, fresh weight, content of cysteine, γ-glutamylcysteine (γEC). glutathione (GSH), thiol groups in Cu-binding peptides (CuBP), and the uptake of Cu were measured in roots and shoots of maize ( Zea mays L., cv. Honeycomb F-1) grown in quartz sand, with Cu at 0, 4.5, 9, 15 and 30 μg g⁻¹ added with or without inoculum of the arbuscular-mycorrhizal fungus (AMF) Glomus intraradices . In control plants (no Cu added) AMF significantly reduced shoot growth, but did not affect root growth. At an external Cu supply of 9 μg (g quartz sand)⁻¹ or higher, both mycorrhizal colonization and growth of roots and shoots of mycorrhizal and non-mycorrhizal plants were significantly reduced.
With up to 9 μg Cu g⁻¹, mycorrhizal colonization increased the content of cysteine, γEC and GSH in the roots. However, the amount of thiols in CuBPs was not increased by mycorrhizal colonization in Cu-treated plants and no differences in Cu uptake were detected between non-mycorrhizal and mycorrhizal plants. A CuBP-complex with a relative molecular mass of 7300 and a SH:Cu ratio of 1.77:1 was separated on a Sephadex G-50 column from both non-inoculated and inoculated roots of Cu-treated plants. HPLC chromatography of the CuBPs of both non-inoculated and inoculated roots resulted in a similar peak pattern, indicating that no additional CuBPs were formed by the fungus. In conclusion, our results do not support the idea that AMF protects maize from Cu-toxicity.     

Electrical signalling and cytokinins mediate effects of light and root cutting on ion uptake in intact plants

Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1–2 min) effects on net K⁺ and H⁺ transport at the root surface. H⁺ efflux decreased (from −18 to −12 nmol m⁻² s⁻¹) and K⁺ uptake (∼2 nmol m⁻² s⁻¹) reverted to efflux (∼−3 nmol m⁻² s⁻¹). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a ∼3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H⁺ efflux and stopped K⁺ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 m m NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (−50 nmol m⁻² s⁻¹). Kinetin (2–4  µ m ), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed.     

Distribution of aromatic l-amino acid decarboxylase in tissues of skipjack tuna using l-DOPA as the substrate

Aromatic L-amino acid decarboxylase activity was measured in brain, heart, intestine, kidney, liver, muscle, pyloric caeca, spleen and stomach of skipjack, using L-3,4–dihydroxyphenylalanine as the substrate. Aromatic L-amino acid decarboxylase activity was found to be present in all of the organs studied. The highest activity was found in the intestine (1774 μmol min ⁻¹ g⁻¹ wet wt of tissue). The liver showed the lowest activity (48.7 umol min ⁻¹ g ⁻¹).