Photosynthesis in ozone-exposed duckweed (Lemna gibba)

The photosynthetic light saturation curve in duckweed was lowered by 20–25% after ozone exposure (300 nmol mol⁻¹, 1 h). The light flux and oxygen concentration during ozone-exposure had no effect on reduction of net photosynthesis. Net photosynthesis and photorespiration were both depressed by about 40% after exposure for 1 h to 360 nmol mol⁻¹ ozone. We could not find any change in dark respiration after ozone exposure below 300 nmol mol⁻¹. When the concentration of ozone was doubled from 150 nmol mol⁻¹ to 300 nmol mol⁻¹, the uptake of ozone in duckweed changed from 100 nmol m⁻² s⁻¹ to 170 nmol m⁻² s⁻¹. We found no differences in fluorescence (pattern) between ozone treated plants and the control plants during a period of 150 min after ozone treatment, but there was an increase in synthesis of the Dl-protein and a significant reduction in degradation after ozone treatment (300 nmol mol⁻¹, 1 h). These results, together with fluorescence measurements, indicate that photochemical electron transport was not responsible for the ozone-induced reduction in net photosynthesis.     

The hygienic efficiency of conventional and inverted lamb dressing systems

R.G. BELL AND S.C. HATHAWAY. 1996. Aerobic plate counts (APC 37°C and APC 25°C) and Escherichia coli enumerations (Petrifilm) were used to determine sources of bacterial contamination during sheep dressing, determine the hygienic efficacy of hand wash and knife 'sterilization'procedures and compare the hygiene efficiency of conventional and inverted sheep dressing systems. The major slaughterline sources of microbial contamination were: fleece > workers' hands > faecal pellets > knife blades. Aerobic plate counts (APC 37°C) exceeding log 4.4 cfu cm^-2 were considered indicative of direct fleece contact, whereas E. coli numbers exceeding log 3.3 cfu cm^-2 were considered indicative of direct faecal contact. A 44°C water hand rinse removed 90% of the microbial contamination from workers' hands, but rinsed hands, particularly those contacting the fleece, still carried a microbial population exceeding log 4.0 cfu cm^-2. A 44°C rinse followed by an 82°C water dip reduced the contamination on knife blades to less than log 3.0 cfu cm^-2. Inverted dressing systems produced carcasses with a lower contamination level than conventional systems. With both systems little increase in contamination occurred after pelt removal. The areas of highest contamination were the forequarter region with inverted dressing and the hindquarter with conventional dressing. In both cases these regions are the sites where cuts are made through the skin. With both systems contamination around these cuts was entirely consistent with direct fleece contact resulting from 'rollback'.     

A community of epiphytic diatoms living on low irradiances

22 samples of the benthic plant Nitella flexilis collected fortnightly in Grane Langsø from July 1959 to June 1960 were examined for epiphytic diatoms. The relative abundance of every taxon was determined by counting 400 valves from each of the Nitella samples. The species composition of the diatom assemblages seemed unchanged throughout the year. A clear seasonal periodicity in relative abundance could not be proved for any of the diatoms in spite of a variation in the irradiance from about 8–10 cal.cm^-2 day^-1 in June-July to 0.1–0.2 cal.cm^-2 day^-1 in February. The diatoms were living on a yearly PAR-irradiance of only 1000 cal.cm^-2 year^-1, which is 2.2% of that at the lake surface. The seasonal fluctuations in C0₂ and pH in 11.25 m subsurface depth are shown by diagrams. Diatom inferred pH is compared with measured pH.     

Characterization of prolamellar bodies, from dark-grown seedlings of Scots pine, containing light- and NADPH-dependent protochlorophyllide oxidoreductase

Cotyledons of conifers have a light-independent pathway for chlorophyll biosynthesis. To investigate whether the prolamellar body of Scots pine ( Pinus sylveslris L.) is similar to the better known prolamellar body of wheat, etioplast membrane fractions were isolated from cotyledons of dark-grown Scots pine. Dark-grown cotyledons contained both chlorophyll and protochlorophyllide, 158 and 10 nmol (g fresh weight)'respectively, and had a chlorophyll a to b ratio of 4.2. The content of glyco- and phospholipids was 7.1 μmol (g fresh weight)¹. About 40 mol % of these lipids were the specific plastid lipids – monogalactosyl diacylglycerol. digalactosyl diacylglycerol and sulfoquinovosyl diacylglycerol in the relative amounts 50, 35 and 7 mol %. The mol ratio of monogalactosyl diacylglycerol to digalactosyl diacylglycerol was 1.7. Low temperature fluorescence emission spectra of intact cotyledons and homogenate showed maxima at 633, 657, 686, 696 nm and a broad peak at 725–735 nm. The maxima at 633 and 657 nm represented different forms of protochlorophyllide and the other emission maxima represented chlorophyll protein complexes. The 657 nm form of protochlorophyllide was phototransformable both in vivo and in the isolated membranes. The phototransformable protochlorophyllide was substantially enriched in the prolamellar body fraction.
The specific activity of light dependent protochlorophyllide oxidoreductase in the prolamellar body fraction was found to be 2 nmol chlorophyllide formed [(mg protein)⁻¹ min⁻¹]. The molecular weight of the enzyme polypeptide was determined as 38 000 dalton with sodium dodecylsulphate-polyacrylamide gel electrophoresis.     

Biomass Production and Carbohydrate Content of Arabidopsis thaliana at Atmospheric CO2 Concentrations from 390 to 1680 μl l-1

Abstract: The concentration dependency of the impact of elevated atmospheric CO₂ concentrations on Arabidopsis thaliana L. was studied. Plants were exposed to nearly ambient (390), 560, 810, 1240 and 1680 μl I^-1 CO₂ during the vegetative growth phase for 8 days. Shoot biomass production and dry matter content were increased upon exposure to elevated CO₂. Maximal increase in shoot fresh and dry weight was obtained at 560 μl I^-1 CU₂, which was due to a transient stimulation of the relative growth rate for up to 3 days. The shoot starch content increased with increasing CO₂ concentrations up to two-fold at 1680 μl I^-1 CO₂, whereas the contents of soluble sugars and phenolic compounds were hardly affected by elevated CO₂. The chlorophyll and carotenoid contents were not substantially affected at elevated CO₂ and the chlorophyll a/b ratio remained unaltered. There was no acclimation of photosynthesis at elevated CO₂; the photosynthetic capacity of leaves, which had completely developed at elevated CO₂ was similar to that of leaves developed in ambient air. The possible consequences of an elevated atmospheric CO₂ concentration to Arabidopsis thaliana in its natural habitat is discussed.     

Induction of nitrate reductase in needles of Scots pine seedlings by NOX and NO3−

The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine ( Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO₃⁻, no such increase could be detected in the needles. Detached seedlings placed in NO₃⁻ solution showed increasing NR activities with increasing NO₃⁻ concentrations. Exposure of seedlings to NO_x (70–80 ppb NO₂ and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO₂⁻ (g fresh weight)⁻¹ h⁻¹ to about 400 nmol NO₂⁻ (g fresh weight)⁻¹ h⁻¹. This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO₂⁻ (g fresh weight)⁻¹ h⁻¹. Analyses of free amino acids showed low concentrations of arginine and glutamine in NO_x-fumigated seedlings compared to corresponding controls.     

Endogenous light-dependent rhythm of zonation in Penicillium claviforme

In darkness, sporalation of Penicillium claviforme Bainier CBS strain 126–23 was uniform. A single 10 J m⁻² blue light pulse (in the range 360 to 520 nm) was sufficient to elicit an endogenous zonation rhythm (coremia formation); the higher the fluence, the longer the rhythm expression. The period was 30 to 36 h as long as sufficient fluence rate (3 μW m⁻² for broad band blue light and 18.1 nmol m⁻² s⁻¹ for wavelengths 433, 457 or 465 nm) was continuously maintained; this rhythm became desynchronized in about a week. The period increased rapidly and reached 72 to 120 h as soon as the fluence rate was too low or dark was established. The 445,479 and 495 nm radiations evoked the rhythm in pulse experiments, whereas the rhythm was immediately desynchronized in continuous light. The participation of two photosensitive reactions in the rhythm regulation of P. claviforme is postulated.     

Effects of monovalent cations on light energy distribution between two pigment systems of photosynthesis in isolated spinach chloroplasts

The effects of monovalent cations on the light energy distribution between two pigment systems of photosynthesis were studied in isolated spinach chloroplasts by measuring chlorophyll a fluorescence and photochemical reactions.

The addition of NaCl to the chloroplast suspension produced a 40–80% increase in fluorescence yield measured at 684 nm at room temperature. The fluorescence increase was completed about 5 min after the addition. The effect saturated at 100 mM NaCl. Low-temperature fluorescence spectra showed that NaCl increased the yields of two fluorescence bands of pigment system II at 684 and 695 nm but decreased that of pigment system I at 735 nm. Similar effects on chlorophyll a fluorescence at room and at low temperatures were obtained with NaBr, NaNO₃, Na₂SO₄, LiCl, KCl, RbCl, CsCl, NH₄Cl and CH₃NH₃Cl.

NaCl suppressed the quantum efficiency of NADP⁺ reduction supported by the ascorbate-2,6-dichlorophenolindophenol (DCIP) couple as an electron donor system in the presence of 3-(3′,4′-chlorophenyl)-1,1-dimethylurea (DCMU). On the other hand, NaCl only slightly enhanced the quantum yield of photoreaction II measured by the Hill reaction with DCIP.

It is concluded that the monovalent cations tested suppressed the excitation transfer from pigment system II to pigment system I; the effects were the same as those of alkaline earth metals and Mn²⁺ (refs. 1, 2).     

Effects of cadmium on growth of Helianthus annuus seedlings: physiological aspects

Sunflower seedlings ( Helianthus annuus hybrid Select) were grown in a complete nutrient solution in the absence or presence of Cd²⁺ (10 and 20 μM). Analyses were performed to establish whether there was a differential effect of Cd²⁺ on mature and young leaves. After 7 d the growth parameters as well as the leaf area had decreased in both mature and young leaves. Accumulation of Cd²⁺ in the roots exceeded that in the shoots. Seedlings treated with Cd²⁺ exhibited reduced contents of chlorophyll and CO₂ assimilation rate, with a greater decrease in young leaves. The photochemical efficiency of photosystem II (PSII) was not altered by Cd²⁺ treatment in either mature or young leaves, although during steady-state photosynthesis in young leaves there was a significant alteration in the following parameters: quantum yield of electron transport by PSII (Φ_PSII), photochemical quenching ( q _P), non-photochemical quenching ( q _NP), and excitation capture efficiency of PSII (Φ_exc).     

Spectrophotometric quantitation of protochlorophyll(ide): Specific absorption and molar extinction coefficients reconsidered

To allay doubt about how to calculate molar extinction eoeffieients from the specific absorption coefficients of protoehlorophyll(ide), dark-grown leaf segments and saponin protochlorophyll(ide) holochrome subunits frotn barley ( Hordeum vulgare L.) and cotyledons of cucumber ( Cucumis sativus L.) were extracted with acetone without or following prior, brief illumination. Absorbance data and eoeffieients of chlorophyll a were used to derive extinetion eoeffieients of protoehlorophyll(ide); 626 nm (range: 30 to 35 1 mmol^-1 cm^-1) without recourse to published coefficients c protochlorophyll(ide). These results combined with evaluation of how the origin; coefficients were obtained, argue for using the molecular weight of protochlorophy rather than protochlorophyllide to calculate molar extinction eoeffieients from th specific absorption coefficients.     

Heat-induced electrical signals affect cytoplasmic and apoplastic pH as well as photosynthesis during propagation through the maize leaf

Combining measurements of electric potential and pH with such of chlorophyll fluorescence and leaf gas exchange showed heat stimulation to evoke an electrical signal (propagation speed: 3–5 mm s⁻¹) that travelled through the leaf while reducing the net CO₂ uptake rate and the photochemical quantum yield of both photosystems (PS). Two-dimensional imaging analysis of the chlorophyll fluorescence signal of PS II revealed that the yield reduction spread basipetally via the veins through the leaf at a speed of 1.6 ± 0.3 mm s⁻¹ while the propagation speed in the intervein region was c. 50 times slower. Propagation of the signal through the veins was confirmed because PS I, which is present in the bundle sheath cells around the leaf vessels, was affected first. Hence, spreading of the signal along the veins represents a path with higher travelling speed than within the intervein region of the leaf lamina. Upon the electrical signal, cytoplasmic pH decreased transiently from 7.0 to 6.4, while apoplastic pH increased transiently from 4.5 to 5.2. Moreover, photochemical quantum yield of isolated chloroplasts was strongly affected by pH changes in the surrounding medium, indicating a putative direct influence of electrical signalling via changes of cytosolic pH on leaf photosynthesis.     

Limnochemical and phytoplankton studies on Nyumba ya Mungu reservoir, Tanzania

This publication reports on the chemical and phytoplankton aspects of a three month biological survey of Nyumba ya Mungu reservoir, Tanzania.
The lake had a total salt concentration of about 8 meq dm^-3 and specific conductivity of 900 μS cm^-1. The main salt in solution was sodium bicarbonate, and when the lake level fell it sometimes formed a crust on the exposed shore. The concentrations of major nutrient ions were probably not limiting to algal growth and good nutrient replenishment was provided by the two inflow rivers.
Nyumba ya Mungu supports a rich phytoplanton dominated by Melosira and blue-green algae. Acetone extractions gave chlorophyll 'a' concentrations ranging from 20–40 mgm^-3 in the vertical profiles, and light and dark bottle experiments indicated a maximum gross photosynthesis of about 800 mg O₂ m^-3h^-1. There was evidence of chemical stratification in the open water and diurnal stratification in the sheltered bays, but discontinuities were short-lived and the Trade Winds ensured regular mixing of the water. The lake appeared to have a higher primary production than the larger Rift Valley lakes and it was considered that this level of production would continue.     

Effect of manganese ions on benzyladenine-induced growth and chlorophyll synthesis in excised cucumber cotyledons

The behaviour of endogenous Mn²⁺ was studied by electron spin resonance spectro-scopy during benzyladenine-induced growth of excised cucumber ( Cucumis sativis L. cv. Long green) cotyledons. The level of endogenous Mn²⁺ was decreased by ben-zyladenine treatment, most pronounced after 96 h. MnCl₂ applied alone promoted chlorophyll synthesis at relatively low concentrations but in the presence of ben-zyladenine higher concentrations of MnCl₂ were required for stimulation of chlorophyll synthesis. A pronounced increase in growth was observed when Mn²⁺ was applied with benzyladenine at 96 h, when the decline in the endogenous level of paramagnetic Mn²⁺ was maximal.     

Fibronectin and proteolytic fragments of fibronectin interfere with the adhesion of Staphylococcus epidermidis to plastic

W.M. DUNNE AND E.M. BURD. 1993. The adhesion of five strains of slime-positive Staphylococcus epidermidis to plastic microwells was significantly diminished ( P < 0.005) in a concentration-dependent fashion when wells were previously coated with increasing concentrations (1.6–13.1 μg cm^-2) of human fibronectin (FN). The adhesion of four of five strains was significantly reduced when wells were coated with 3.2 μg cm^-2 of FN and at concentrations ≥6.5 μg cm^-2 the adhesion of all slime-positive strains was significantly reduced. The coating of microwells with chymotryptic fragments of FN containing the heparin-binding, gelatin-binding, or cell-binding domains also reduced bacterial adhesion but none of the fragments exceeded the anti-adhesive activity of intact FN. A comparison of FN-coated or albumin-coated microwells showed that both proteins caused a significant reduction in the adhesion of test strains to plastic but that the anti-adhesive activity of FN was greater than albumin at all concentrations tested. The adhesion of the slime-negative phase variant of one of the test strains to plastic was neither enhanced nor reduced by FN coating indicating that the production of an exopolysaccharide by Staph. epidermidis influences interactions with protein-coated surfaces. These results support the contention that FN does not mediate the adhesion of all strains of Staph. epidermidis to plastic surfaces.     

The periphyton communities of Nyumba ya Mungu reservoir, Tanzania

The periphyton communities established in Nyumba ya Mungu were investigated between July and September 1974.
One hundred and ninety-two taxa were identified. One hundred and fifteen taxa were collected in the southern end of the lake, where 97 taxa were non-selectively distributed in the littorine epiphytic, epilithic, and epixylic environments. The offshore epixylon supported only 53 taxa. The epipelon and epipsammon were poorly developed at the southern end of the lake but were well developed in the northern inflow regions.
Diatoms and cyanophytes were the dominant phyla which contributed over 80% of the algal numbers. Chlorophytes were not common. Taxonomic compositions of periphyton on artificial and natural surfaces were similar, but artificial substrata accumulated greater proportional representations of diatoms.
The mean net production rates of periphyton on artificial substrata located at depths from 0-0.65 m for 28 days ranged from 140 mg organic dry weight m^-2 day^-1 on shoots in the macrophyte zone to 820 mg organic dry weight m^-2 day^-1 on glass surfaces on a rocky shore. The epiphytic environments produced the least standing crops of less than 250, 000 individuals cm^-2, but maximum densities of over 2,000,000 individuals cm^-2 were recorded in the epilithon.     

Properties of lucerne transient streak virus, and evidence of its affinity to southern bean mosaic virus

A virus obtained from naturally infected lucerne ( Medicago sativa ) in New Zealand reacted with antiserum to an Australian isolate of lucerne transient streak virus (LTSV). Some plants infected with New Zealand isolates showed yellow flecks along lateral veins of leaves; symptoms were transient in some lucerne plants but persistent in others. A New Zealand isolate (LTSV-NZ) infected 14 of 39 plant species tested by mechanical inoculation, but was not transmitted by five aphid species. In sap of Nicotiana clevelandii , LTSV-NZ was infective after storage for 4 wk at 20 ^oC, diluting to 10^-5, or heating for 10 min at 70 ^oC. Purified virus preparations contained a single electrophoretic component and a single sedimenting component (s_20w= 112 S ) which formed a single buoyant density component in CsCl (1.37 g cm^-3) but two density components in Cs₂SO₄ (1.26 and 1.32 g cm^-3). LTSV-NZ particles were stable in 10 ITIM EDTA at pH 5, but not at pH 8, being degraded into two sedimenting components of 105 S and 92 S. Particles contained c. 18% RNA in the form of one single-stranded RNA molecule of mol. wt 1–4 times 10⁶, and a polypeptide of mol. wt c. 32 400. LTSV-NZ was serologically unrelated to 24 other isometric plant viruses. However, its properties are similar to those of southern bean mosaic virus and allied viruses. The present cryptogram of LTSV is R/l: 1–4/(18):S/S:S/*.     

Light-dependent changes of the Mg concentration in the stroma in relation to the Mg dependency of CO2 fixation in intact chloroplasts

(1) Light-dependent changes of the Mg²⁺ content of thylakoid membranes were measured at pH 8.0 and compared with earlier measurements at pH 6.6. In a NaCl and KCl medium, the light-dependent decrease in the Mg²⁺ content of the thylakoid membranes at pH 8.0 is found to be 23 nmol Mg²⁺ per mg chlorophyll, whereas in a sorbitol medium it is 83 nmol Mg₂₊ per mg chlorophyll.

(2) A light dependent increase in the Mg²⁺ content of the stroma was detected when chloroplasts were subjected to osmotic shock, amounting to 26 nmol/mg chlorophyll. Furthermore, a rapid and reversible light-dependent efflux of Mg²⁺ has been observed in intact chloroplasts when the divalent cation ionophore A 23 187 was added, indicating a light-dependent transfer of about 60 nmol of Mg²⁺ per mg chlorophyll from the thylakoid membranes to the stroma.

(3) CO₂ fixation, but not phosphoglycerate reduction, could be completely inhibited when A 23 187 was added to intact chloroplasts in the absence of external Mg²⁺. If Mg²⁺ was then added to the medium, CO₂ fixation was restored. Half of the maximal restoration was achieved with about 0.2 mM Mg²⁺, which is calculated to reflect a Mg²⁺ concentration in the stroma of 1.2 mM. The further addition of Ca²⁺ strongly inhibits CO₂ fixation.

(4) The results suggest that illumination of intact chloroplasts causes an increase in the Mg²⁺ concentration of 1–3 mM in the stroma. Compared to the total Mg²⁺ content of chloroplasts, this increase is very low, but it appears to be high enough to have a possible function in the light regulation of CO₂ fixation.     

Effect of competition and leaf age on visible and infrared reflectance in pine foliage

Abstract. The effect of plant competition on spectral reflectance in the 400–2500 nm wavelength region was determined for 3-month-old and 15-month-old leaves of loblolly pine ( Pinus taeda L.). Strong competition decreased water potentials and Mg concentrations, and increased K in young and old leaves. Also, competition decreased Ca and total chlorophyll in young leaves. As measured with a scanning radiometer, reflectance in young leaves at 551 nm decreased from 20 to 14% as water potentials increased from -2.2 to -0.9 MPa (r²= 0.82). For young and old leaves reflectance at 551 nm decreased from 20 to 10% with increasing total chlorophyll (r²= 0.64). Reflectance decreased slightly with increasing K in young leaves (401 nm, r²= 0.55), and with increasing Mg in old leaves (470 nm, r²= 0.57). Increased visible reflectance under strong competition may have resulted primarily from decreased water potentials. Reflectances were much greater in young versus old leaves in the 750–1300 nm range, and were greater in old rather than young leaves from 1400–2500 nm. Infrared reflectances were not, however, significantly affected by competition.     

Neuroprotective Effect of the Iron Chelator Desferrioxamine Against MPP+ Toxicity on Striatal Dopaminergic Terminals

Abstract: Microdialysis was used to evaluate the effect of desferrioxamine (DES) against 1-methyl-4-phenylpyridinium (MPP⁺) toxicity. The presence of DES (40 fmol-40 nmol/15 min for a total of 90 min) in the Ringer solution, coperfused with MPP⁺ (40 nmol/15 min) on day 1, produced on day 2 a higher extracellular dopamine output after perfusion of MPP⁺ than in control MPP⁺ perfusion experiments, in which no DES was administered on day 1. Both Ringer perfusion alone (control Ringer) and coperfusion of 40 nmol DES with 40 nmol MPP⁺ on day 1 produced on day 2 similar increases in extracellular dopamine output after a second MPP⁺ perfusion. In the control Ringer experiment, note that the MPP⁺ on day 2 is the first MPP⁺ perfusion. Perfusion of 800 fmol FeCl₃/15 min along with 40 nmol MPP⁺ and 400 fmol DES on day 1 completely abolished on day 2 the neuroprotective effect found with 40 nmol MPP⁺ and 400 fmol DES; 800 fmol FeCl₃ did not increase the neurotoxic effect of 40 nmol MPP⁺ perfusion. The ability of DES to protect against MPP⁺ toxicity may indicate a therapeutic strategy in the treatment of diseases when iron is implicated.     

Influence of red light on the activity of phosphofructokinase in Chlorella kessleri

In crude extracts of the unicellular green alga Chlorella kessleri Fott et Novákóva grown in red light the activity of the glycolytic enzyme phosphofructokinase (PFK, EC 2.7.1.11) is about 40% higher compared to white light conditions giving the same dry matter production. Application of cycloheximide and density labelling with D₂O indicate that this increase depends on the de novo synthesis of the enzyme: Twelve h of illumination at a fluence rate of 7 × 10¹⁸ quanta m⁻² s⁻¹ (11.6 μmol m⁻² s⁻¹) suffice to saturate the effect. In autotrophically grown algae maximal increase in enzyme saturate the effect. In autotrophically grown algae maximal increase in enzyme activity is reached in light of 680 nm, while in 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU)-poisoned, glucose-fed cells, light of wavelengths around 727 nm is most effective. Involvement of a phytochrome-like photoreceptor is discussed.