Water use efficiency as a function of leaf age and position within the cotton canopy

The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention in recent years. However, insufficient information exists on the coordination of transpiration and CO₂ uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration (E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO₂ mmol⁻¹ H₂O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in stomatal conductance (g_s·H₂O) since decreases in g_s·H₂O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these findings are presented in relation to light competition within the plant canopy during development.     

Immunocytochemical localization of the 27K beta-crystallin polypeptide in the mouse lens during development using a specific monoclonal antibody: implications for cataract formation in the Philly mouse

The Philly mouse develops a hereditary cataract about 5 weeks after birth. Although the causative agent is not known, data suggest that there is a correlation between cataract formation and the selective absence of a 27 kilodalton (27K) beta-crystallin lens polypeptide. The ontogeny of the 27K beta-crystallin polypeptide was examined in normal mice in order to evaluate its role in normal development and determine what impact its absence may have on the Philly mouse lens. A monoclonal antibody was used with the PAP method to immunocytochemically localize the 27K polypeptide in lenses of normal mice during development. beta-Crystallins detected with polyclonal antisera were found in differentiated fiber cells throughout the lens. In contrast, the 27K beta-crystallin polypeptide detected with a specific monoclonal antibody was not found in the fiber cells of the inner part of the lens (nucleus), but was specifically localized in the fiber cells of the outer part of the lens called the cortex. The polypeptide was found only in elongating and differentiated fiber cells and not in mitotically active epithelial cells. Although a minor component of the 2-day-old lens, the 27K polypeptide comprised a large portion of the 16-day-old lens including the anterior and posterior poles. These data show that the 27K polypeptide is a minor component of the embryonic lens, but becomes a major contributor to the postnatal lens. The 27K beta-crystallin lens polypeptide is abundant in the fiber cells of the normal postnatal mouse lens. The absence of the 27K polypeptide in the Philly mouse may contribute to the observed failure of fiber cells to differentiate in the Philly mouse after birth or may be deleterious in some other manner to normal lens development. The selective absence of the 27K beta-crystallin polypeptide, a defect which precedes cataract formation in the Philly mouse, is intriguing since it suggests a relationship between this major lens polypeptide and lens clarity.     

Elevation of the heat resistance of Salmonella typhimurium by sublethal heat shock

The survival of Salmonella typhimurium after a standard heat challenge at 55°C for 25 min increased by several orders of magnitude when cells grown at 37°C were pre-incubated at 42°, 45° or 48°C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Preincubation of cells at 48°C for 30 min increased their resistance to subsequent heating at 50°, 52°, 55°, 57° or 59°C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge.     

Pressure chamber measurements using two wheat leaves

Summary The most widely used technique of leaf water potential measurements is with the Scholander pressure chamber. Representative leaf water potential values require many determinations on individual leaves and this can be time consuming in large fields or experiments with multiple treatments. This paper describes a method of obtaining a mean value more rapidly, by using two leaves in the pressure chamber at the same time, but recording the end point of each leaf separately.     

The isolation of pig liver monoamine oxidase

Monoamine oxidase from pig liver has been isolated and purified approximately three hundred-fold. This enzyme has a molecular weight of 1,200,000, is highly polymeric, and contains subunits of molecular weight 146,000, as determined by Sephadex chromatography. The apparent K_m at 25°C is 1.28 × 10^?6 M at pH 9.0 (0.05 M glycine) and 1.74 × 10^?5 M at pH 7.2 (0.2 M phosphate) using benzylamine as a substrate. This enzyme contains approximately 8 copper(II) ions per 1,200,000 molecular weight.     

The annual variation of asthma in Brisbane: Its relation to the weather

A study has been made of the annual incidence of asthma in Brisbane for 7 years in relation to the weather. The element most closely associated with asthma was rainfall. There was a minor, independent association with temperature. The association of asthma with rain and warmth, which promote the growth of vegetation, supports the suggestion arising from the seasonal study of asthma that vegetation may be an important source of allergens.

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Zusammenfassung Die Beziehung zwischen dem Wetter und der Häufigkeit von Asthma in Brisbane während 7 Jahren wurde untersucht. Unter den meteorologischen Elementen ergab sich die engste Beziehung zwischen Asthmahäufigkeit und Niederschlägen. Eine geringere, unabhängige Beziehung bestand mit der Temperatur. Die Verbindung von Asthma mit Niederschlägen und Wärme stützt die Vermutung, dass die Vegetation eine wichtige Allergenquelle ist.

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Resume On a étudié durant 7 années la relation existant entre le temps et la fréquence des crises d'asthme à Brisbane. Parmi les éléments météorologiques examinés, celui qui donna la plus étroite relation est la précipitation.Une relation indépendante, moindre il est vrai, existe également avec la température.L'étroite relation entre les crises d'asthme d'une part, les précipitations et la chaleur d'autre part renforce l'hypothèse que la végétation est la principale source des principes allergènes.

     

Identification of the C2-1H histidine NMR resonances in chloramphenicol acetyltransferase by a 13C-1H heteronuclear multiple quantum coherence method

Chloramphenicol acetyltransferase (CAT) was used to assess the feasibility of study of specific proton resonances in an enzyme of overall molecular mass 75,000, [ring 2-13C]Histidine was selectively incorporated into the type III chloramphenicol acetyltransferase (CATIII) using a histidine auxotroph of E. coli. Heteronuclear multiple and single quantum experiments were used to select the C2 protons in the histidyl imidazole ring. One- and two-dimensional spectra revealed six signals out of a total of seven histidine residues in CATIII. pH titration, chemical modification and ligand binding were used to demonstrate that the signal from H195, the histidine at the active site, is not among those observed. Nevertheless, this work demonstrates that selective isotopic enrichment and multiple quantum coherence techniques can be used to distinguish proton resonances in a protein of high molecular mass.     

Determination of the solution structures of domains II and III of protein G from Streptococcus by 1H nuclear magnetic resonance.

We have used 1H nuclear magnetic resonance spectroscopy to determine the solution structures of two small (61 and 64 residue) immunoglobulin G (IgG)-binding domains from protein G, a cell-surface protein from Streptococcus strain G148. The two domains differ in sequence by four amino acid substitutions, and differ in their affinity for some subclasses of IgG. The structure of domain II was determined using a total of 478 distance restraints, 31 phi and 9 chi 1 dihedral angle restraints; that of domain III was determined using a total of 445 distance restraints, 31 phi and 9 chi 1 dihedral angle restraints. A protocol which involved distance geometry, simulated annealing and restrained molecular dynamics was used to determine ensembles of 40 structures consistent with these restraints. The structures are found to consist of an alpha-helix packed against a four-stranded antiparallel-parallel-antiparallel beta-sheet. The structures of the two domains are compared to each other and to the reported structure of a similar domain from a protein G from a different strain of Streptococcus. We conclude that the difference in affinity of domains II and III for IgG is due to local changes in amino acid side-chains, rather than a more extensive change in conformation, suggesting that one or more of the residues which differ between them are directly involved in interaction with IgG.