Antigenic Makeup of Subcellular Fractions of Trypanosoma cruzi

Trypanosoma cruzi epimastigotes from cultures were separated into nuclear, mitochondrial, lysosomal, microsomal, and cell-sap fractions. Enzymic and ultrastructutal controls served to determine the cleanness of separation. The bulk of the DNA was in the nuclear (78%) and mitochondrial (12%) fractions. RNA was found in microsomal (74%) and cell-sap (14%) fractions. Marker enzyme distribution (succinic dehydrogenase, acid phosphatase, and glucose-6-phosphatase) was compared with their distribution in mammalian tissues. Subcellular localization of antigens by Ouchterlony tests revealed 2 specific precipitin lines in cell sap and 1 in the microsomal fraction. These antigens may prove diagnostically and immunoprotectively valuable.     

The effect of low temperatures on the phloem transport of radioactive assimilates in the stolon of Saxifraga sarmentosa L.

Abstract. The movement of naturally assimilated ¹⁴C down the stolon of Saxifraga sarmentosa under the influence of localized cold treatments (0°-10°C) applied over lengths up to 10 cm was followed by finding the distribution of tracer at the termination of the experiment. Inhibition is slight at 10°C and very considerable at 0°C. It is very dependent on the length treated, but is definite even when this is only 0.8 cm. Cooling the daughter plantlet to 0°C has a smaller inhibitory effect than might be expected. This is difficult to understand if 'unloading' is metabolic; perhaps the concentration free energy of the sucrose or other solute can be utilized in the sink terminals on the lines of the chemi-osmotic hypothesis. If so the same source of non-respiratory free energy might be available to energize an active sieve-tube mechanism in mid-path chilling experiments.     

Factors Affecting the Rate of Photophosphorylation by Isolated Chloroplasts of Euglena gracilis*

SYNOPSIS The rate of photophosphorylation by Euglena chloroplasts depends not only on the physiologic stage of cell growth but also on the stage of development of chloroplasts in these cells at the time of harvesting. Both of these processes can be markedly influenced by a number of environmental factors; they are affected neither in a parallel manner nor completely independent of each other. In addition, the rate of photophosphorylation of chloroplasts can also be greatly affected by the conditions employed for their isolation. After investigating the various environmental factors both during cell growth and chloroplast isolation, we have developed a procedure which increased the photophosphorylation rate of our chloroplast preparations more than 5-fold, giving a specific activity in the range of 100-150 μmoles ATP/mg chlorophyll/hr routinely. The procedure is simple, needs no special equipment and requires only 2 or 3 days for cell growth.     

NO signalling in cytokinin-induced programmed cell death

Cell death can be induced by cytokinin 6-benzylaminopurine (BA) at high dosage in suspension-cultured Arabidopsis cells. Herein, we provide evidence that BA induces nitric oxide (NO) synthesis in a dose-dependent manner. A reduction in cell death can be observed when the cytokinin is supplemented with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) or the nitric oxide synthase (NOS) inhibitors: 2-aminoethyl-isothiourea (AET) and N^G.-monomethyl- l -arginine ( l -NMMA), which suggests that NO is produced via a NOS and is a signalling component of this form of programmed cell death. In BA-treated cells, mitochondrial functionality is altered via inhibition of respiration. This inhibition can be prevented by addition of either cPTIO or AET implying that NO acts at the mitochondrial level.     

Diversity in Mediterranean farm ponds: trade‐offs and synergies between irrigation modernisation and biodiversity conservation

1. Agricultural intensification has caused dramatic biodiversity loss in many agricultural landscapes over the last century. Here, we investigated whether new types of farm ponds (made of artificial substrata) in intensive systems and natural‐substratum ponds in traditional farming systems differ in their value for aquatic biodiversity conservation. 2. We analysed the main patterns of environmental variation, compared α‐, β‐ and γ‐diversity of macroinvertebrates between ponds types and evaluated the role of submerged aquatic vegetation (SAV). Generalised additive models (GAM) were used to analyse the relationships of α‐ and β‐diversity with environmental predictors, and variation partitioning to separate the effect of environmental and spatial characteristics on the variation in macroinvertebrate assemblages. Moran’s eigenvector maps (MEMs) were used to define spatial variables. 3. A principal coordinate analysis (PCoA) detected a primary environmental gradient that separated nutrient‐rich ponds from those dominated by SAV; a secondary morphometric gradient distinguished natural‐substratum ponds, with large surface area and structural complexity, from artificial‐substratum ponds with steeper slopes. Natural‐substratum ponds had almost twice the α‐ and γ‐diversity of artificial‐substratum ponds, and diversity significantly increased when SAV was present, particularly in artificial‐substratum ponds. Total phosphorus (TP) strongly contributed to explain the patterns in diversity, while SAV was a significant predictor of assemblage composition and diversity. GAMs revealed optima of both α‐diversity at intermediate SAV covers and β‐diversity at intermediate–high TP concentrations. 4. These findings have important implications for conservation planning. Adaptation of artificial‐substratum ponds by adding natural substratum and smoothing the gradient of pond margins would improve their conservation value. Development of SAV with occasional harvests and certain cautionary measures to control nutrient levels may also improve both the agronomical and environmental function of ponds.