The rate of nitrite reduction in leaves as indicated by O2 and CO2 exchange during photosynthesis.

Light response (at 300 ppm CO(2) and 10-50 ppm O(2) in N(2)) and CO(2) response curves [at absorbed photon fluence rate (PAD) of 550 µmol m(-2) s(-1)] of O(2) evolution and CO(2) uptake were measured in tobacco (Nicotiana tabacum L.) leaves grown on either NO(3)(-) or NH(4)(+) as N source and in potato (Solanum tuberosum L.), sorghum (Sorghum bicolor L. Moench), and amaranth (Amaranthus cruentus L.) leaves grown on NH(4)NO(3). Photosynthetic O(2) evolution in excess of CO(2) uptake was measured with a stabilized zirconia O(2) electrode and an infrared CO(2) analyser, respectively, and the difference assumed to represent the rate of electron flow to acceptors alternative to CO(2), mainly NO(2)(-), SO(4)(2-), and oxaloacetate. In NO(3)(-)-grown tobacco, as well as in sorghum, amaranth, and young potato, the photosynthetic O(2)-CO(2) flux difference rapidly increased to about 1 µmol m(-2) s(-1) at very low PADs and the process was saturated at 50 µmol quanta m(-2) s(-1). At higher PADs the O(2)-CO(2) flux difference continued to increase proportionally with the photosynthetic rate to a maximum of about 2 µmol m(-2) s(-1). In NH(4)(+)-grown tobacco, as well as in potato during tuber filling, the low-PAD component of surplus O(2) evolution was virtually absent. The low-PAD phase was ascribed to photoreduction of NO(2)(-) which successfully competes with CO(2) reduction and saturates at a rate of about 1 µmol O(2) m(-2) s(-1) (9% of the maximum O(2) evolution rate). The high-PAD component of about 1 µmol O(2) m(-2) s(-1), superimposed on NO(2)(-) reduction, may represent oxaloacetate reduction. The roles of NO(2)(-), oxaloacetate, and O(2) reduction in the regulation of ATP/NADPH balance are discussed.

Cytotoxic Lesion of the Corpus Callosum in an Adolescent with Multisystem Inflammatory Syndrome and SARS-CoV-2 Infection.

Multisystem inflammatory syndrome in children is a recently described complication in the late phase of Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) infection involving systemic hyperinflammation and multiorgan dysfunction. The extent of its clinical picture is actively evolving and has yet to be fully elucidated. While neurologic manifestations of SARS-CoV-2 are well-described in the adult population, reports of neurologic complications in pediatric patients with SARS-CoV-2 infection are limited. We present a pediatric patient with SARS-CoV-2 infection with development of multisystem inflammatory syndrome and acute encephalopathy causing delirium who was found to have a cytotoxic lesion of the corpus callosum on neuroimaging. Cytotoxic lesions of the corpus callosum are a well-known, typically reversible entity that can occur in a wide range of conditions, including infection, seizure, toxins, nutritional deficiencies, and Kawasaki disease. We hypothesized that the cytotoxic lesion of the corpus callosum, in the index case, was secondary to the systemic inflammation from SARS-CoV-2 infection, resulting in multisystem inflammatory syndrome in children.

Energy transfer from phycobiliproteins to photosystem I in vegetative cells and heterocysts of Anabaena variabilis.

The presence of phycobilins in heterocysts of Anabaena variabilis is established on the basis of absorption and fluorescence spectroscopy. At 77 K heterocysts exhibit fluorescence emission bands at 645 and 661 nm indicative of phycocyanin and allophycocyanin, respectively. Both allophycocyanin levels and fluorescence emission at 695 nm were low in heterocysts relative to whole filaments. In situ fluorescence microscopy confirmed the presence of phycobilins in individual heterocysts, but the pigment levels varied considerably among cells. Heterocysts exhibited Photosystem I activity, as evidenced by photooxidation of P-700, but no Photosystem II activity. The quantum efficiency of phycobilins in sensitizing P-700 photooxidation was 50-70% that of chlorophyll a. Phycoibins were also effective in promoting light-dependent reduction of acetylene to ethylene. The results are discussed in terms of the role of the heterocyst in nitrogen fixation and of the significance of energy transfer from phycobilins to Photosystem I in heterocysts.

Modes of reduction of nitrogen in heterocysts isolated from Anabaena species.

N2 fixation (acetylene reduction) has been studied with heterocysts isolated from Anabaena cylindrica and Anabaena 7120. In the presence of ATP and at very low concentrations of sodium dithionite, reducing equivalents for activity of nitrogenase in these cells can be derived from several compounds. In the dark, D-glucose 6-phosphate, 6-phosphogluconate and DL-isocitrate support acetylene reduction via NADPH. In the light, reductant can be generated by Photosystem I.

Regulation of Electron Transport in Photosystems I and II in C3, C3-C4, and C4 Species of Panicum in Response to Changing Irradiance and O2 Levels.

Regulation of the quantum yields of linear electron transport and photosystem II photochemistry ([phi]II) with changing irradiance and gas-phase O2 concentration was studied in leaf tissue from Panicum bisulcatum (C3), Panicum milioides (C3-C4), and Panicum antidotale (C4) at 200 [mu]bars of CO2 and 25[deg]C using infrared gas analysis and chlorophyll fluorescence yield measurements. When the O2 level was increased from 14 to 213 mbars at high irradiance, [phi]II increased by as much as 115% in P. bisulcatum but by no more than 17% in P. antidotale. Under the same conditions [phi]II increased to an intermediate degree in P. milioides. Measurements of accumulation of the photooxidized form of the photosystem I reaction center (P700+) based on the light-dependent in vivo absorbance change at 830 nm indicate that the steady-state concentration of P700+ varied in an antiparallel manner with [phi]II when either the irradiance or O2 concentration was changed. Hence, O2-dependent changes in [phi]II were indicative of variations in linear photosynthetic electron transport. These experiments revealed, however, that a significant capacity was retained for in vivo regulation of the apparent quantum yield of photosystem I ([phi]I) independently of [phi]II+ Coordinate regulation of quantum yields of photosystems I and II (expressed as [phi]I:[phi]II in response to changing irradiance and O2 level differed markedly for the C3 and C4 species, and the response for the C3-C4 species most closely resembled that observed for the C4 species. The fraction of total linear electron transport supporting photorespiration at 213 mbars of O2 was negligible in the C4 species and was 13% lower in the C3-C4 species relative to the C3 species as calculated from fluorescence and gas-exchange determinations. At high photon-flux rates and high O2 concentration, the potential benefit to light use for net CO2 uptake arising from lower photorespiration in P. milioides was offset by a reduced capacity for total CO2- and O2-dependent noncyclic electron transport in this species compared with P. bisulcatum.

Chlorophyll Fluorescence Induction in Leaves of Phaseolus vulgaris Infected with Bean Rust (Uromyces appendiculatus).

To our knowledge, this report describes the first application of video imaging of Chl fluorescence to the study of light utilization in photosystem II of attached leaves of Phaseolus vulgaris infected with the obligate biotrophic fungus Uromyces appendiculatus (race 38). The video-based detection system produced a spatially resolved, quantifiable signal that was highly specific for chlorophyll fluorescence. Video images of spatial variation in the initial stage of the fluorescence induction (dark-light) transient revealed discreet regions of intense emission coinciding with centers of subsequent lesion development and accompanying chlorosis. Incipient lesions were visible by this procedure 3 d following inoculation, fully 3 to 4 d prior to visible symptoms. Fluorescence emission patterns in infected areas during the induction transient were heterogeneous with radial distance from the point of invasion and varied with the length of the time delay between re-illumination and image capture. During later ([greater than or equal to]1 min) stages of the induction transient, fluorescence emission in incipient lesions was quenched compared to surrounding tissue. These essential features of the induction transient observed in video images were also noted when individual lesions were examined using pulse modulation fluorimetry.

Chlorophyll fluorescence at 680 and 730 nm and leaf photosynthesis.

Chlorophyll fluorescence constitutes a simple, rapid, and non-invasive means to assess light utilization in Photosystem II (PS II). This study examines aspects relating to the accuracy and applicability of fluorescence for measurement of PS II photochemical quantum yield in intact leaves. A known source of error is fluorescence emission at 730 nm that arises from Photosystem I (PS I). We measured this PS I offset using a dual channel detection system that allows measurement of fluorescence yield in the red (660 nm < F < 710 nm) or far red (F > 710 nm) region of the fluorescence emission spectrum. The magnitude of the PS I offset was equivalent to 30% and 48% of the dark level fluorescence F(0) in the far red region for Helianthus annuus and Sorghum bicolor, respectively. The PS I offset was therefore subtracted from fluorescence yields measured in the far red spectral window prior to calculation of PS II quantum yield. Resulting values of PS II quantum yield were consistently higher than corresponding values based on emission in the red region. The basis for this discrepancy lies in the finite optical thickness of the leaf that leads to selective reabsorption by chlorophyll of red fluorescence emission originating in deeper cell layers. Consequently, red fluorescence measurements preferentially sense emission from chloroplasts in the uppermost layer of the leaf where levels of photoprotective nonphotochemical quenching are higher due to increased photon density. It is suggested that far red fluorescence, corrected for the PS I offset, provides the most reliable quantitative basis for calculation of PS II quantum yield because of reduced sensitivity of these measurements to gradients in leaf transmittance and quenching capacity.

Temperature-sensitive gel for virus concentration from urine.

Cross-linked, partially hydrolyzed polyacrylamide gels (temperature-sensitive gels) with the property to swell at 4 degrees C and collapse at higher temperatures (greater than 19 degrees C) were used to concentrate bacteriophage T-2 from urine. Samples of urine, 50 ml, seeded with bacteriophage T-2 were reduced to approximately 5 ml, with an average virus recovery of 53%. Subsequent experiments with feline cell-associated herpes virus resulted in a 6-fold decrease in volume with 54% virus recovery. The gel could be used repeatedly without any loss in efficiency.

Method for the concentration of infectious pancreatic necrosis virus from hatchery water.

A method was developed for concentrating infectious pancreatic necrosis virus from hatchery water using positively charged 1-MDS filters. The method consists of passing large volumes (Ca. 1001) of hatchery water through 1-MDS microporous filter followed by the elution of the adsorbed virus using a high pH buffer. The virus adsorbed efficiently to 1-MDS filters when the pH of the water was 5.5 and was eluted optimally with 3% beef extract solution (pH 10). This procedure permitted the processing of 100 1 of hatchery water which resulted in a 300-fold reduction in the volume of water and greater than 90% recovery of the seeded virus.

Propagation and quantitation of animal herpesviruses in eight cell culture systems.

A comparative study was carried out to determine the relative sensitivities of eight different cell culture systems to six different herpesviruses of animals. The cells used were: OFL (ovine fetal lung), ML (mink lung), FK (ferret kidney), PTK-2 (potoroo kidney), TEK (turkey embryo kidney), ED (equine dermal), BT (bovine turbinate), and PK15 (porcine kidney). The viruses tested were: PRV (pseudorabies) of swine, CPHV (caprine herpesvirus), IBRV (infectious bovine rhinotracheitis virus), DN-599 strain of bovine herpesvirus type 4, EHV-1 (equine herpesvirus), and CHV (canine herpesvirus). On the basis of virus titers obtained and the time of appearance of CPE (cytopathic effects), ML cells were found to be the most useful because of their sensitivity to all six viruses tested. BT and OFL cells were also found to be highly sensitive to all viruses with the exception of CHV.

Quantitation of the O(2)-Dependent, CO(2)-Reversible Component of the Postillumination CO(2) Exchange Transient in Tobacco and Maize Leaves.

The postillumination transient of CO(2) exchange and its relation to photorespiration has been examined in leaf discs from tobacco (Nicotiana tabacum) and maize (Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O(2) in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO(2) exchange equivalents (i.e. nanomoles CO(2)) versus time were derived from the analyzer responses of individual transients. In tobacco (C(3)), subtraction of the time course of cumulative CO(2) exchange under photorespiratory conditions (21 or 43% O(2)) from that obtained under nonphotorespiratory conditions (1% O(2)) revealed the presence of an O(2)-dependent and CO(2)-reversible component within the first 60 seconds following darkening. This component was absent in maize (C(4)) and at low external O(2):CO(2) ratios (i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O(2). This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO(2) evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration.

Partitioning of Noncyclic Photosynthetic Electron Transport to O(2)-Dependent Dissipative Processes as Probed by Fluorescence and CO(2) Exchange.

The partitioning of noncyclic photosynthetic electron transport between net fixation of CO(2) and collective O(2)-dependent, dissipative processes such as photorespiration has been examined in intact leaf tissue from Nicotiana tabacum. The method involves simultaneous application of CO(2) exchange and pulse modulated fluorescence measurements. As either irradiance or CO(2) concentration is varied at 1% O(2) (i.e. absence of significant O(2)-dependent electron flow), the quantum efficiency of PSII electron transport (phi(se)) with CO(2) as the terminal acceptor is a linear function of the ratio of photochemical:nonphotochemical fluorescence quenching coefficients (i.e. q(Q):q(NP)). When the ambient O(2) concentration is raised to 20.5% or 42% the q(Q):q(NP) is assumed to predict the quantum efficiency of total noncyclic electron transport (phi'(se)). A factor which represents the proportion of electron flow diverted to the aforementioned dissipative processes is calculated as (phi'(se) - phi(se))/phi'(se) where phi(se) is now the observed quantum efficiency of electron transport in support of net fixation of CO(2). Examination of changes in electron allocation with CO(2) and O(2) concentration and irradiance at 25 degrees C provides a test of the applicability of the Rubisco model to photosynthesis in vivo.

Enhanced Incorporation of Tritium into Glycolate during Photosynthesis by Tobacco Leaf Tissue in the Presence of Tritiated Water.

Tobacco (Nicotiana tabacum var. Havana Seed) leaf discs were allowed to photosynthesize for 3 to 20 minutes in the presence of (14)CO(2) and (3)H(2)O. Several metabolites of the Calvin cycle and photorespiratory pathway were isolated and purified and the (3)H:(14)C values measured. Glycolate had a 5- to 10-fold higher (3)H:(14)C than the Calvin cycle intermediate 3-phosphoglyceric acid, or its end product sucrose. The glycolate oxidase inhibitor alpha-hydroxy-2-pyridinemethanesulfonic acid caused glycolate to accumulate in the tissue and lowered the (3)H:(14)C in glycolate to a value similar to that in 3-phosphoglyceric acid. Phosphoglycolate, a possible precursor of glycolate arising from the Calvin cycle, exhibited a (3)H:(14)C value similar to 3-phosphoglyceric acid under all conditions. The finding of a (3)H enrichment in glycolate suggests that another source of glycolate, possibly the reduction of glyoxylate, exists in leaf tissue. Analyses of incorporation of (3)H into the pro-2R and pro-2S hydrogens of glycolate, in the presence and absence of alpha-hydroxy-2-pyridinemethanesulfonic acid, suggest an alternative source of glycolate. Biochemical mechanisms to account for (3)H enrichment into glycolate are evaluated.

Regulation of Glycine Decarboxylase and l-Serine Hydroxymethyltransferase Activities by Glyoxylate in Tobacco Leaf Mitochondrial Preparations.

Glyoxylate at a concentration of 10 millimolar caused 50% inhibition of decarboxylation of 20 millimolar [1-(14)C]glycine and accompanying synthesis of serine in a mitochondria-enriched preparation from tobacco (Nicotiana tabacum var. John Williams Broadleaf) leaves. None of the other compounds tested including formate, acetate, oxalate, aspartate, and glutamate appreciably affected activity. Occasional inhibition produced by glycolate may have resulted from residual glycolate oxidase in these preparations. Added glyoxylate was not converted to glycine in these preparations and about 98% of it could be recovered at the end of the reaction. Hence, the observed inhibition by glyoxylate did not result from dilution of radioactivity in the substrate.Glyoxylate also regulated synthesis of HCHO from l-serine catalyzed by l-serine hydroxymethyltransferase in mitochondrial preparations. Control of this enzyme activity by glyoxylate was complex and was characterized by enhancement of activity at low glyoxylate concentrations (less than 10 millimolar) and inhibition by concentrations generally above 10 millimolar. These results define potential sites of biochemical regulation of important steps in the pathway of photorespiratory carbon flow and are considered in the light of other observations of effects of exogenous glyoxylate on photorespiration in leaf tissue.

Effects of water vapor pressure deficit on photochemical and fluorescence yields in tobacco leaf tissue.

The relationship between photochemical quantum yield (phi(s)) and fluorescence yield have been investigated in leaf tissue from Nicotiana tabacum using CO(2) exchange and a modulated fluorescence measuring system. The quantum yield of CO(2) fixation at 1.6% (v/v) O(2) and limiting irradiance was reduced 20% by increasing the mean H(2)O vapor pressure deficit (VPD) from 9.2 to 18.6 mbars. As [CO(2)] and irradiance were varied, the intrinsic quantum yield of open photosystem II units (phi(s)/q(Q) where q(Q) is the photochemical fluorescence quenching coefficient) declined linearly with the degree of nonphotochemical fluorescence quenching. The slope and y-intercept values for this function were significantly reduced when the mean VPD was 18.4 millibars relative to 8.9 millibars. Susceptibility of the leaf tissue to photoinhibition was unaffected by VPD. Elevated O(2) concentrations (20.5% v/v) reduced the intrinsic quantum yield of net CO(2) uptake due to the occurrence of O(2)-reducing processes. However, the relative effect of high VPD compared to low VPD on intrinsic quantum yield was not dependent on the O(2) level. This suggests that the Mehler reaction does not mediate the response of quantum yield to elevated VPD. The results are discussed with regard to the possible role of transpiration stress in regulating dissipation of excitation by electron transport pathways other than noncyclic electron flow supporting reduction of CO(2) and/or O(2).

Effects of Irradiance on the in Vivo CO(2):O(2) Specificity Factor in Tobacco Using Simultaneous Gas Exchange and Fluorescence Techniques.

The effects of gas phase O(2) concentration (1%, 20.5%, and 42.0%, v/v) on the quantum yield of net CO(2) fixation and fluorescence yield of chlorophyll a are examined in leaf tissue from Nicotiana tabacum at normal levels of CO(2) and 25 to 30 degrees C. Detectable decreases in nonphotochemical quenching of absorbed excitation occurred at the higher O(2) levels relative to 1% O(2) when irradiance was nearly or fully saturating for photosynthesis. Photochemical quenching was increased by high O(2) levels only at saturating irradiance. Simultaneous measurements of CO(2) and H(2)O exchange and fluorescence yield permit estimation of partitioning of linear photosynthetic electron transport between net CO(2) fixation and O(2)-dependent, dissipative processes such as photorespiration as a function of leaf internal CO(2) concentration. Changes in the in vivo CO(2):O(2) ;specificity factor' (K(sp)) with increasing irradiance are examined. The magnitude K(sp) was found to decline from a value of 85 at moderate irradiance to 68 at very low light, and to 72 at saturating photon flux rates. The results are discussed in terms of the applicability of the ribulose bisphosphate carboxylase/oxygenase enzyme model to photosynthesis in vivo.

Analysis of changes in minimal and maximal fluorescence yields with irradiance and o(2) level in tobacco leaf tissue.

The responses of minimal and maximal fluorescence yields of chlorophyll a to irradiance of actinic white light were determined by pulse modulated fluorimetry in leaf discs from tobacco, Nicotiana tabacum, at 1.6, 20.5, and 42.0% (v/v) O(2). Steady-state maximal fluorescence yield (F(m)', measured during a saturating light pulse) declined with increasing irradiance at all O(2) levels. In contrast, the steady-state minimal fluorescence yield (F(o)', measured during a brief dark interval) increased with irradiance relative to that recorded for the fully dark-adapted leaf (F(o)) or that observed after 5 minutes of darkness (F(o) (*)). The relative magnitude of this increase was somewhat greater and extended to higher irradiances at the elevated O(2) levels compared with 1.6% O(2). Suppression of F(o)' was only observed consistently at saturating irradiance. The results are interpreted in terms of the occurrence of photosystem II units possessing exceedingly slow turnover times (i.e. "inactive" units). Inactive units play an important role, along with thermal deactivation of excited chlorophyll, in determining the response of in vivo fluorescence yield to changes in irradiance. Also, a significant interactive effect of O(2) concentration and the presence or absence of far red light on oxidation of photosystem II acceptors in the dark was noted.

Effects of O(2) and CO(2) Concentrations on Quantum Yields of Photosystems I and II in Tobacco Leaf Tissue.

The interactive effects of irradiance and O(2) and CO(2) levels on the quantum yields of photosystems I and II have been studied under steady-state conditions at 25 degrees C in leaf tissue of tobacco (Nicotiana tabacum). Assessment of radiant energy utilization in photosystem II was based on changes in chlorophyll fluorescence yield excited by a weak measuring beam of modulated red light. Independent estimates of photosystem I quantum yield were based on the light-dark in vivo absorbance change at 830 nanometers, the absorption band of P700(+). Normal (i.e. 20.5%, v/v) levels of O(2) generally enhanced photosystem II quantum yield relative to that measured under 1.6% O(2) as the irradiance approached saturation. Photorespiration is suspected to mediate such positive effects of O(2) through increases in the availability of CO(2) and recycling of orthophosphate. Conversely, at low intercellular CO(2) concentrations, 41.2% O(2) was associated with lower photosystem II quantum yield compared with that observed at 20.5% O(2). Inhibitory effects of 41.2% O(2) may occur in response to negative feedback on photosystem II arising from a build-up in the thylakoid proton gradient during electron transport to O(2). Covariation between quantum yields of photosystems I and II was not affected by concentrations of either O(2) or CO(2). The dependence of quantum yield of electron transport to CO(2) measured by gas exchange upon photosystem II quantum yield as determined by fluorescence was unaffected by CO(2) concentration.

Estimation of Photorespiration Based on the Initial Rate of Postillumination CO(2) Release: I. A Nonsteady State Model for Measurement of CO(2) Exchange Transients.

Although open systems have been used for the study of transients in leaf CO(2) exchange such as the postillumination burst, these systems frequently do not permit reliable estimates of transient rates due to their nonsteady state nature. A nonsteady state mathematical approach is described which predicts changes in CO(2) concentration in the leaf chamber and infrared gas analyzer measuring cell as a function of leaf CO(2) exchange rate in Nicotiana tabacum vars John Williams Broadleaf and Havana Seed. With the aid of a computer, a numerical formula simulates the mixing and dilution which occurs as CO(2) passes through the finite volume of the measuring cell of the analyzer. The method is presented with special relevance to photorespiration as manifested by the postillumination burst of CO(2). The latter is suggested to decline with the first order kinetics following darkening of a C(3) leaf. This approach provides a basis for reliable estimation of the initial and, hence, maximal rate of CO(2) evolution during the postillumination burst under a variety of environmental conditions.