Interactions among leaf toughness, chemistry, and harvesting by attine ants

Abstract. 1. Young and mature leaves of a tropical legume, Inga edulis var. minutula Schery, are strikingly different in secondary chemistry, especially condensed tannins, and leaf toughness.
2. Bioassays with the two different leaf types indicate that leaf cutter ants, Atta cephalotes (L.), always find mature leaves relatively more acceptable than young leaves when selection was based on chemical cues.
3. Since extracts of young leaves show greziter inhibition of fungal pectinases we suggest that leaf-cutter ants are capable of distinguishing which leaf types are most suitable for the growth of their symbiotic fungus.
4. However, mature leaves are 3 times tougher than young leaves and this prevents leaf-cutter ants from harvesting the more suitable mature leaves.
5. Consequently, bioassays which require cutting before leaf removal indicate that some colonies actually harvest more from the less suitable young leaves.
6. We suggest that the quality of a colony's habitat may indicate whether a colony will harvest more of the less suitable young leaves. Colonies which are harvesting from highly suitable host plants avoid the tropical legume I.edulis while those in poorer habitats accept I.edulis but, because of leaf toughness, mostly harvest the less suitable young leaves.     

Mechanism of O-acetylserine sulfhydrylase fromSalmonella typhimurium LT-2

Summary O-Acetylserine sulfhydrylase is a pyridoxal 5-phosphate (PLP) dependent enzyme that catalyzes the final step of L-cysteine biosynthesis inSalmonella, viz. the conversion of O-acetyl-L-serine (OAS) and sulfide to L-cysteine and acetate. A spectrophotometric assay is available using 5-thio(2-nitrobenzoate) (TNB) as an analog of sulfide and monitoring the disappearance of absorbance at 412 nm. The enzyme catalyzes a ping pong mechanism with-aminoacrylate in Schiff base with the active site PLP as a covalent intermediate. Using data obtained from the pH dependence of kinetic parameters, the acid-base chemical mechanism and the optimum protonation state of enzyme and substrate functional groups necessary for binding has been determined. The Schiff base and the-amine of the substrate OAS are unprotonated for binding. There also appears to be a requirement for one active site general base to accept a proton from the-amine and to donate a proton to form cysteine. The enzyme also catalyzes an OAS hydrolase activity, and the pH dependence of this reaction suggests that the active site lysine that participated in the Schiff base linkage is protonated to start the second half reaction, and has a pK of about 8.2. The stereochemistry of³H-borohydride reduction of the Schiff base in free enzyme has been determined by degradation of the resulting pyridoxyllysine to pyridoxamine and measuring³H-release with apo-aspartate aminotransferase. The sequence around the active site lysine is AsnProSerPheSerValLysCysArg.     

A Comparison of the Free Radical Properties of Several Anthracycline Anti-Tumour Drugs and Some of Their Analogues

NADPH consumption and esr spectroscopy have been used to study the rate of formation and signal intensity of free radicals produced by various anthracycline anti-tumour drugs in rat liver microsomal extract. The drugs investigated were Adriamycin, 4'Deoxyadriamycin, Daunorubicin, 4 Demethoxydaun-orubicin and Carminomycin. Pulse radiolysis was also used to determine the ease of reduction of each of the analogues to its semiquinone radical and some kinetic properties of the radicals produced. It is believed that the Occurrence of reactions other than dismutation could be responsible for the shortened lifetimes of the semiquinone radicals observed in biological systems.     

Diversity among nemertean egg predators of decapod crustaceans

The chemistry of water in fields at two Bangladesh deepwater rice locations is compared. Although Manikganj lies in the Jamuna (-Brahmaputra) floodplain and Sonargaon in the old Meghna floodplain, their chemistries during the flood season are similar, apart from higher Mg % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\]: 3.57 v.1.8 mg 1^–1), Ca (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\]: 13.1 v.4.5 mg l^–1 ), pH and total alkalinity at the former.Diel changes in oxygen and sometimes also pH were evident 10 cm below the surface in deepwater rice fields, but such changes were typically much greater in fallow fields. Measurements made between 1400 and 1600 h in a range of habitats showed a trend for high pH values to be associated with high O₂ values. Water in Eichhornia beds had the lowest values, deepwater rice fields were intermediate and fallow fields and other open areas typically had the highest values. O₂ concentrations in excess of 15 mg l^–1 and pH values of about 10.0 sometimes occurred in fallow fields with dense masses of submerged plants and loosely associated algal flocs.There was an increasing tendency for the water to become anoxic towards the end of the season and water 10 cm above the bottom was almost or entirely anoxic in deepwater rice fields at both locations over the whole 24-h period of 4/5 October, at a time when the depth of the water was starting to drop. Nitrite increased and sulphate decreased at both locations towards the end of the season.     

Conifer growth on residual organic soils: A greenhouse study

The effects of the addition of compost, prepared from vegetable market refuse and stomach contents of slaughtered cattle, were studied in a sandy soil contained, in pots and kept in a greenhouse environment. Comparison was made between: i) a treatment involving pots containing compost mixed with 5% soil, ii) four treatments in which increasing quantities of compost homogeneously taken from the same lot (0, 10000, 20000, 30000 kg ha⁻¹) were integrated with NPK mineral fertilizer to equalize available nutrients; iii) an untreated control. At 3, 4, and 5 years from the date of treatment, after various other crops, sunflower was planted. The yield obtained, though it fell off from year to year, was approximately double in the case of 95% compost. The other four treatments also resulted in production increases compared with the untreated control. Production was found to rise progressively with increasing quantities of compost. The improvement in soil chemistry and microbiology, as shown by analyses performed 5 years after treatment with compost, suggests that the rise in crop production may be attributed to an overall improvement in all components involved in the fertility of the soil used, in our experimental conditions.     

Isolation and fluorescence studies on a lipophorin from the weevil diaprepes abbreviatus

Lipophorin was isolated from larvae of a root weevil, Diaprepes abbreviatus (Coleoptera: Curculionidae), using density gradient ultracentrifugation. D. abbreviatus lipophorin contained two apoproteins, apolipophorin-I (M_r = 226,000) and apolipophorin-II (M_r = 72,100) and had a density of 1.08. Relative to other larval lipophorins, D. abbreviatus lipophorin contained little cysteine (determined as cysteic acid) and methionine. Fluorescence spectroscopy of intrinsic tyrosine and tryptophan residues excited at 290 nm revealed a single broad emission peak at 330 nm. Upon denaturing and delipidating lipophorin in guanidine HCl, this peak resolved into two peaks with maxima at 305 and 350 nm. Excitation spectra suggested that the two peaks were due to tyrosine and tryptophan, respectively. Fluorescence quenching agents, iodide and acrylamide, were used to determine accessibility of tyrosine and tryptophan residues to the aqueous environment. Iodide, a polar quenching agent, did not quench fluorescent emission from native lipophorin; quenching by iodide increased to moderate levels when lipophorin was denatured in guanidine HCl. Acrylamide quenched the fluorescence of native lipophorin moderately and very efficiently quenched fluorescence of denatured lipophorin. No difference was observed between fluorescence quenching of denatured vs. denatured and delipidated lipophorin by either iodide or acrylamide.     

Crystals and their taxonomic significance in some Verbenaceae

MATHEW, L. & SHAH, G. L., 1984. Crystals and their taxonomic significance in some Verbenaceae. The morphology, plant distribution and chemical composition of crystals in 35 tropical species in the family Verbenaceae have been investigated using light microscopy, SEM and an energy dispersive X-ray analyser.
Crystals may be solitary, aggregated or as conglomerates and crystal sand. Eleven kinds of solitary crystals and five aggregate or conglomerate forms have been observed. Their occurrence varies from species to species and sometimes from organ to organ in the same plant, suggesting that there might be taxonomic significance of crystal form and distribution.
Most of the crystals are compounds of a range of elements, silicon, calcium, potassium, iron, magnesium, aluminium, sulphur sodium and titanium in varying proportions. Calcium is the major component of solitary acicular crystals and silicon of other kinds of crystals.     

The sensitivity of Afromontane tarns in the Maloti-Drakensberg region of South Africa and Lesotho to acidic deposition

Despite their remoteness from sources of atmospheric pollutant emissions, the Afromontane tarns in the Maloti-Drakensberg region are perfect candidates to study the negative effects of acidifying atmospheric pollution, because mountain lakes are widely recognised as sentinel ecosystems, unimpacted by direct human disturbance within their catchments. Thirty-four tarns were sampled in the Maloti-Drakensberg region and most were found to be extremely sensitive to acidic deposition, as indicated by their low acid neutralising capacity. There are very few studies of freshwater critical loads for any region within South Africa. The steady-state water chemistry model (SSWC) was adapted and used to determine critical loads, whereas exceedance was estimated relative to modelled regional deposition data, in order to understand the risk of harmful effects to aquatic ecosystems. Seventy-six percent of sampled sites across the Maloti-Drakensberg would exceed critical loads even at the lowest modelled deposition levels, but there are no current measured deposition data for the region. The sensitivity of the Maloti-Drakensberg tarns needs to be considered in future policy formulation regarding acceptable levels of acidifying atmospheric pollution from South Africa’s energy sector and indicates the need for assessing aquatic ecosystem impacts in other regions of South Africa.     

Development of a new procedure for the determination of captopril in pharmaceutical formulations employing chemiluminescence and a multicommuted flow analysis approach

This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t‐test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0–150.0 µmol/L (r = 0.997), a limit of detection (3σ) of 2.0 µmol/L, a sample throughput of 164 determinations per hour, reagent consumption of 9 µg luminol and 42 µg hypochlorite per determination and generation of 0.63 mL of waste. A relative standard deviation of 1% (n = 6) for a standard solution containing 80 µmol/L captopril was also obtained. Copyright © 2015 John Wiley & Sons, Ltd.