Photosynthetic responses of seven tropical seagrasses to elevated seawater temperature

This study uses chlorophyll a fluorescence to examine the effect of environmentally relevant (1-4 h) exposures of thermal stress (35-45 [deg]C) on seagrass photosynthetic yield in seven tropical species of seagrasses. Acute response of each tropical seagrass species to thermal stress was characterised, and the capacity of each species to tolerate and recover from thermal stress was assessed. Two fundamental characteristics of heat stress were observed. The first effect was a decrease in photosynthetic yield (Fv / Fm) characterised by reductions in F and Fm'. The dramatic decline in Fv / Fm ratio, due to chronic inhibition of photosynthesis, indicates an intolerance of Halophila ovalis, Zostera capricorni and Syringodium isoetifolium to ecologically relevant exposures of thermal stress and structural alterations to the PhotoSystem II (PSII) reaction centres. The decline in Fm' represents heat-induced photoinhibition related to closure of PSII reaction centres and chloroplast dysfunction. The key finding was that Cymodocea rotundata, Cymodocea serrulata, Halodule uninervis and Thalassia hemprichii were more tolerant to thermal stress than H. ovalis, Z. capricorni and S. isoetifolium. After 3 days of 4 h temperature treatments ranging from 25 to 40 [deg]C, C. rotundata, C. serrulata and H. uninervis demonstrated a wide tolerance to temperature with no detrimental effect on Fv / Fm' qN or qP responses. These three species are restricted to subtropical and tropical waters and their tolerance to seawater temperatures up to 40 [deg]C is likely to be an adaptive response to high temperatures commonly occurring at low tides and peak solar irradiance. The results of temperature experiments suggest that the photosynthetic condition of all seagrass species tested are likely to suffer irreparable effects from short-term or episodic changes in seawater temperatures as high as 40-45 [deg]C. Acute stress responses of seagrasses to elevated seawater temperatures are consistent with observed reductions in above-ground biomass during a recent El Nino event.

Bull sperm plasma and acrosomal membranes: Fluorescence studies of lipid phase fluidity

Bull sperm plasma and outer acrosomal membranes have been isolated by discontinuous sucrose density gradient centrifugation and Ca2+-ATPase activity has been determined for both the membranes. Pyrene excimer fluorescence and diphenylhexatriene fluorescence polarization studies show that the lipid phase of the sperm plasma membranes is more fluid than the lipids of the outer acrosomal membranes. Approximately, a three fold increase in the cholesterol content has been found in the outer acrosomal membranes as compared to that in the plasma membranes.

Leaf chlorophyll concentration relates to transpiration efficiency in peanut

Two pot experiments were conducted in two different seasons at the University of Agricultural Science, Bangalore, India, to study (a) the relationship between chlorophyll concentration (by measuring the leaf light-transmittance characteristics using a SPAD metre) and transpiration efficiency (TE) and (b) the effect of leaf N on chlorophyll and TE relationship in peanut. In Experiment (Expt) I, six peanut genotypes with wide genetic variation for the specific leaf area (SLA) were used. In Expt II, three non-nodulating isogenic lines were used to study the effect of N levels on leaf chlorophyll concentration–TE relationship without potential confounding effects in biological nitrogen fixation. Leaf N was manipulated by applying N fertiliser in Expt II. Chlorophyll concentration, TE (g dry matter kg−1 of H2O transpired, measured using gravimetric method), specific leaf nitrogen (g N m−2, SLN), SLA (cm2 g−1), carbon isotope composition (Δ13C) were determined in the leaves sampled during the treatment period (35–55 days after sowing) in the two experiments. Results showed that the leaf chlorophyll concentration expressed as soil plant analytical development (SPAD) chlorophyll metre reading (SCMR) varied significantly among genotypes in Expt I and as a result of N application in Expt II. Changes in leaf N levels were strongly associated with changes in SCMR, TE and Δ13C. In both the experiments, a significant positive relationship between SCMR and TE with similar slopes but differing intercepts was noticed. However, correction of TE for seasonal differences in vapour pressure deficit (VPD) between the two experiments resulted in a single and stronger relationship between SCMR and TE. There was a significant inverse relationship between SCMR and Δ13C, suggesting a close linkage between chlorophyll concentration and Δ13C in peanut. This study provides the first evidence for a significant positive relationship between TE and leaf chlorophyll concentration in peanut. The study also describes the effect of growing environment on the relationships among SLA, SLN and SCMR.

Fluorescence in situ hybridization analysis of hindgut bacteria associated with the development of equine laminitis

In the article 'Fluorescence in situ hybridization analysis of hindgut bacteria associated with the development of equine laminitis' (Milinovich et al., 2007), it is found that with reference to Horse 1, the histological signs of laminitis were first observed at 12 h post-oligofructose administration, and not 30 h as was indicated in the Results section under the subheading 'Induction of Laminitis' and in Fig. 1.

Studies on tryptophan residues of Abrus agglutinin Stopped-flow kinetics of modification and fluorescence-quenching studies

The presence of two essential tryptophan residues/molecule was implicated in the binding site of Abrus agglutinin [Patanjali, Swamy, Anantharam, Khan & Surolia (1984) Biochem. J. 217, 773-781]. A detailed study of the stopped-flow kinetics of the oxidation of tryptophan residues revealed three classes of tryptophan residues in the native protein. A discrete reorganization of tryptophan residues into two phases was observed upon ligand binding. The heterogeneity of tryptophan exposure was substantiated by quenching studies with acrylamide, succinimide and Cs+. Our study revealed the microenvironment of tryptophan residues to be hydrophobic, and also the presence of acidic amino acid residues in the vicinity of surface-localized tryptophan residues.

Measuring and predicting canopy nitrogen nutrition in wheat using a spectral index—The canopy chlorophyll content index (CCCI).

Varying the spatial distribution of applied nitrogen (N) fertilizer to match demand in crops has been shown to increase profits in Australia. Better matching the timing of N inputs to plant requirements has been shown to improve nitrogen use efficiency and crop yields and could reduce nitrous oxide emissions from broad acre grains. Farmers in the wheat production area of south eastern Australia are increasingly splitting N application with the second timing applied at stem elongation (Zadoks 30). Spectral indices have shown the ability to detect crop canopy N status but a robust method using a consistent calibration that functions across seasons has been lacking. One spectral index, the canopy chlorophyll content index (CCCI) designed to detect canopy N using three wavebands along the "red edge" of the spectrum was combined with the canopy nitrogen index (CNI), which was developed to normalize for crop biomass and correct for the N dilution effect of crop canopies. The CCCI-CNI index approach was applied to a 3-year study to develop a single calibration derived from a wheat crop sown in research plots near Horsham, Victoria, Australia. The index was able to predict canopy N (g m-2) from Zadoks 14-37 with an r2 of 0.97 and RMSE of 0.65 g N m-2 when dry weight biomass by area was also considered. We suggest that measures of N estimated from remote methods use N per unit area as the metric and that reference directly to canopy %N is not an appropriate method for estimating plant concentration without first accounting for the N dilution effect. This approach provides a link to crop development rather than creating a purely numerical relationship. The sole biophysical input, biomass, is challenging to quantify robustly via spectral methods. Combining remote sensing with crop modelling could provide a robust method for estimating biomass and therefore a method to estimate canopy N remotely. Future research will explore this and the use of active and passive sensor technologies for use in precision farming for targeted N management.

Bilirubin binding to polypeptides and chiral amines. Induced circular dichroism and fluorescence studies

Induced Cotton effects have been observed in the visible region on interaction of bilirubin with chiral mono- and diamines and poly-l-lysine. At alkaline pH distinct CD spectra are observed for bilirubin bound to the α-helical and β-sheet conformation of poly-l-lysine, which differ from that observed for the pigment bound to human serum albumin. The CD pattern observed on binding to N-acetyl-Lys-N1-methylamide in CH2Cl2 and dioxane is different from that observed in the presence of l-Ala-NH-(CH2)6-NH-l-Ala in dioxane. The latter case resembles the spectrum observed in the presence of human serum albumin. Binding to the helical polypeptide melittin and the antiparallel β-sheet peptide, gramicidin S, in aqueous solutions results in opposite signs of the bilirubin CD bands. The quenching of tryptophan fluorescence in melittin, in aqueous solution and enhancement of bilirubin fluorescence in dioxane on binding to gramicidin S have been used to monitor pigment-peptide interactions. The results suggest the utility of bilirubin as a conformational probe.

Interaction of rat testis protein, TP, with nucleic acids in vitro. Fluorescence quenching, UV absorption, and thermal denaturation studies

The nucleic acid binding properties of the testis protein, TP, were studied with the help of physical techniques, namely, fluorescence quenching, UV difference absorption spectroscopy, and thermal melting. Results of quenching of tyrosine fluorescence of TP upon its binding to double-stranded and denatured rat liver nucleosome core DNA and poly(rA) suggest that the tyrosine residues of TP interact/intercalate with the bases of these nucleic acids. From the fluorescence quenching data, obtained at 50 mM NaCl concentration, the apparent association constants for binding of TP to native and denatured DNA and poly(rA) were calculated to be 4.4 X 10(3) M-1, 2.86 X 10(4) M-1, and 8.5 X 10(4) M-1, respectively. UV difference absorption spectra upon TP binding to poly(rA) and rat liver core DNA showed a TP-induced hyperchromicity at 260 nm which is suggestive of local melting of poly(rA) and DNA. The results from thermal melting studies of binding of TP to calf thymus DNA at 1 mM NaCl as well as 50 mM NaCl showed that although at 1 mM NaCl TP brings about a slight stabilization of the DNA against thermal melting, a destabilization of the DNA was observed at 50 mM NaCl. From these results it is concluded that TP, having a higher affinity for single-stranded nucleic acids, destabilizes double- stranded DNA, thus behaving like a DNA-melting protein.

Binding of N-dansylgalactosamine to winged-bean tuber lectin: studies by fluorescence quenching titrations

The winged-bean tuber lectin binds to N-dansyl(5-dimethylaminonaphthalene-1-sulphonic acid)galactosamine, leading to a 12.5-fold increase in dansyl fluorescence with a concomitant 25 nm blue-shift in the emission maximum. The enhancement of fluorescence intensity was completely reversed by the addition of methyl α-galactopyranoside. The lectin has two binding sites per molecule for this fluorescent sugar and an association constant of 2.59 · 105 M−1 at 25° C. The binding of N-dansylgalactosamine to the lectin shows that it can accommodate a large hydrophobic substituent on the C-2 carbon of d-galactose. Studies with other sugars indicate that a hydrophobic substituent with α-conformation at the anomeric position increases the affinity of binding. The C-4 and C-6 hydroxyl groups are also critical for sugar binding to this lectin.

Fluorescence And Nmr-Studies Of The Binding Of Cholinergic Fluorescent-Probes To Horse Serum-Cholinesterase

The interaction of the cholinergic fluorescent probes, 1-(5-dimethyl-aminoaphthalene-1-sulfonamido) ethane-2-trimethylammonium perchlorate, 1-(5-dimethylaminonaphthalene-1-sulfonamido) pentane-5-trimethylammonium tartarate and 1-(5-dimethylaminonaphthalene-1-sulfonamido) decane-10- trimethylammonium tartarate with horse serum cholinesterase has been examined by fluorescence and n.m.r. methods. Fluorescence titrations show binding of the decane derivative to two sites on the protein whereas the lower homologs bind largely to one site. Active site inhibitors like curbamylcholine and decamethonium abolish binding of the decane derivative to the high affinity site. The inhibitors are largely without effect on the binding of the lower homologs. N.m.r. studies clearly establish immobilization of both ends of the molecule on binding in the case of the decane derivative, whereas in the lower homologs the dimethylamino group on the naphthalene ring is significantly more affected in the presence of enzyme. The probes are effective inhibitors of the enzyme with the decane derivative being two orders of magnitude more effective than its lower homologs. Based on the n.m.r., fluorescence and inhibition studies, a model for probe binding to the enzyme is advanced. It appears that the decane derivative binds with high affinity to the catalytic anionic site while the lower affinity site is assigned to a peripheral anionic site. The lower homologs probe only the peripheral site. A comparison of fluorescence, n.m.r. and inhibition studies with acetylcholinesterases from electric eel and bovine erythrocytes is presented.

7-Alkoxy coumarins as fluorescence probes for microenvironments

7-Alkoxy and 4-methyl-7-alkoxy coumarins show solvent-dependent fluorescence emission. The monomeric fluorescence emission of these alkoxy coumarins was exploited as a probe to measure the surface polarity of the micelles formed by ionic (sodium dodecylsulphate and cetyltrimethyl-ammonium bromide) and non-ionic (Triton X-100) detergents. By comparing the solvent-dependent fluorescence of these alkoxy coumarins in various homogeneous solvents, the polarity of the micelles was determined qualitatively. All three micelles are more polar than hydrocarbon solvents but are less polar than water.

Ionophore-mediated transmembrane movement of divalent cations in small unilamellar liposomes: An evaluation of the chlortetracycline fluorescence technique and correlations with black lipid membrane studies

Conceptual advances in the field of membrane transport have, in the main, utilized artificial membranes, both planar and vesicular. Systems of biological interest,viz., cells and organelles, resemble vesicles in size and geometry. Methods are, therefore, required to extend the results obtained with planar membranes to liposome systems. In this report we present an analysis of a fluorescence technique, using the divalent cation probe chlortetracycline, in small, unilamellar vesicles, for the study of divalent cation fluxes. An ion carrier (X537 A) and a pore former (alamethicin) have been studied. The rate of rise of fluorescence signal and the transmembrane ion gradient have been related to transmembrane current and potential, respectively. A second power dependence of ion conduction-including the electrically silent portion thereof — on X537 A concentration, has been observed. An exponential dependence of ldquocurrentrdquo on ldquotransmembrane potentialrdquo in the case of alamethicin is also confirmed. Possible errors in the technique are discussed.

Immuno-fluorescence staining patterns of leukocyte subsets in the skin of taurine and indicine cattle

The immuno-staining patterns of skin leukocytes were investigated in three breeds of cattle: Holstein–Friesian, Brahman and Santa Gertrudis of similar age before and after tick infestation. The antibodies specific for CD45 and CD45RO reacted with cells in the skin of all Holstein–Friesian cattle but did not react with cells in the skin of any Brahman cattle. The same antibodies reacted with cells from the skin of four (CD45) and seven (CD45RO) of twelve Santa Gertrudis cattle. The antibodies specific for T cells and γδ subset of T cells recognized cells from all three breeds of cattle. The antibody specific for MHC class II molecules labelled cells of mostly irregular shape, presumably dermal dendritic cells and/or macrophages and Langerhans cells. The antibody specific for granulocytes (mAb CH138) reacted with cells only in sections cut from skin with lesions. The antibody specific for CD25+ cells labelled regularly shaped cells that showed a wide range of intensities of staining.