A simple screening procedure for adenylate kinase, hexokinase and glucose-6-phosphate dehydrogenase deficiencies

A simple screening procedure for the detection of adenilate kinase (AK), hexokinase (Hx) or glucose-6-phosphate dehydrogenase (G6PD) deficiencies in blood, is described. It consists of two assays : in the first, the ATP formed by blood AK is coupled to Hx and G6PD, and in the second, the glucose-6-phosphate formed by blood Hx is coupled to G6PD. The enzyme activities are visually estimated by the reduction of NADP+ (non-fluorescent) to NADH (fluorescent). The appearance of fluorescence in the first assay indicates that the three enzyme activities are present. The absence of fluorescence could be due to the deficiency of any one of the three enzymes; in this case the second assay used in combination with the Beutler's screening test for G6PD permits the detection of the specific enzymatic deficiency.     

Water and nutrient relations of woody perennials from tropical dry forests

Abstract. Dry forests occupy a larger area in the tropics than rain forests. They grow under a wide range of rainfall conditions; the determining characteristics are the occurrence of a dry season of 2–6 months duration, and the dominance of deciduous woody perennials. The knowledge of the ecophysiological properties of woody perennials from these forests, essential for the development of forest restoration strategies, is still scanty. This paper describes the ecophysiological behaviour of 10 species of woody perennials growing in a secondary dry forest, which has been recovering since 1944 on the hills of the Botanical Garden of Caracas. Four species, Astronium graveolens, Bauhinia megalandra, Sapindus saponaria and Tabebuia chrysantha, were initially planted while the others, Bursera simaruba, Capparis flexuosa, Erythroxylon cumanense, E. densum, E. orinocense and Eugenia casearioides, reproduced from seed sources existing in forest remnants growing nearby. Specific leaf areas measured are relatively high, covering a range from 11 to 34 m²/kg. Nitrogen and phosphorus levels are also high compared to data reported from dry forests elsewhere, therefore no nutrient limitation for photosynthetic productivity is apparent. Osmotic pressure (π) of leaf sap, extracted from frozen samples taken during the growing season, is correlated with the corresponding content of soluble sugars and the ions Mg and K; Ca-ions do not play a significant role in explaining the variance of π. Most species maintained a diluted leaf sap during the rainy season, characterized by π values between 5–15 bar. The osmotic pressure increased strongly in older leaves and during the dry season. Four species showed more stable π values throughout the growing season, with C. flexuosa and B. simaruba characterized by higher and lower π values, respectively. Proline was found to be a reliable indicator of water stress in these woody species, the amount of proline measured in leaf sap being logarithmically correlated with the corresponding π value. Osmotic pressure of leaf sap and leaf xylem tension was higher during the dry season for all species, while the contrary was true for leaf conductance. Leaf conductance was better correlated with leaf-air vapour pressure deficit than with leaf xylem tension. The most drought-tolerant species were C. flexuosa, E. casearioides and the three Erythroxylon species. Drought resistance of B. simaruba, B. megalandra and A. graveolens was associated with their high sensitivity to leaf-air VPD and lower leaf conductances. The other two species occupied intermediate positions.     

Stability and transmissibility of the cryptic plasmids of Rhizobium meliloti GR4

Rhizobium meliloti strain GR4 harbours two cryptic plasmids sharing extensive regions of homology between them and with other non-symbiotic plasmids of different strains of R. meliloti. They both are very stable showing a segregation rate of less than 0.1% loss per generation. pRmeGR4a (115 MDa) is a self-transmissible plasmid at a variable frequency to other species, and it is also responsible for promoting, at low frequency, the contransfer of pRmeGR4b (140 MDa), the other cryptic plasmid of the strain. A 4.8 kb PstI fragment of pRmeGR4a, responsible for the high stability in cis of this plasmid, has been isolated and several recombinant plasmids have been constructed showing different segregation rates in the strains used in this study. Their stabilities can be considerably improved by insertion of the stabilization mrs/par region of RK2.     

Location of nif genes on large plasmids in Rhizobium strains isolated from legume tree root nodules

Abstract The presence of plasmids in Rhizobium strains isolated from legume tree root nodules has been studied. Bacteria isolated from Acacia melanoxylon, A. cyanophylla, Prosopis chilensis and Sophora microphylla harbour 2 to 5 plasmids of an M _r higher than 115 · 10⁶. Hybridization experiments have shown DNA homology between plasmid pID1 ( R. meliloti 41 nifH and D genes) and one of the plasmids in each of the bacteria studied.