Activation of chloroplast ATPase by reduced thioredoxin

Chloroplast thioredoxin that is reduced by dithiothreitol activates the ATPase that is associated with solubilized preparations of chloroplast coupling factor (CF₁).     

Formaldehyde-induced appearance of septate junctions between digestive vacuoles

Tissue biopsies from (1) some chronic inflammatory diseases, (2) a necrotic tumoral process, (3) normal human lymphatic ganglia, and (4) two congenital diseases of the adrenal cortex were selected for study. A block from each biopsy was fixed in glutaraldehyde-paraformaldehyde; a second block was fixed in 10% formaldehyde. In all cases septate junctions between digestive vacuoles did occur in phagocytic cells and some adrenal cortex cells fixed in formaldehyde. These junctions were similar to those reported recently for malakoplakia phagocytes. Consistently, they were not found to attach organelles other than lysosomes derivatives. Both phagocytes and adrenal cortex cells in the material fixed in glutaraldehyde-paraformaldehyde did not display adhesive specializations between digestive vacuoles. This suggests that the septate junctions described herein are artifactuous structures induced by formaldehyde. There is, however, a certain degree of specificity of cells having the capability of developing these septate junctions. It is assumed that the coating material of digestive organelles in phogocytes and some other cells would be responsible for both cell specificity and organelle specificity of the formaldehyde-induced septate junctions.     

Inhibition of the Na+/K+ cotransport system by cyclic AMP and intracellular Ca2+ in human red cells

Human erythrocytes are able to incorporate cyclic AMP (cAMP) in amounts larger than those required to saturate cAMP-dependent protein kinase. In contrast to previous observations in avian red blood cells in which cAMP stimulates the Na⁺/K⁺ cotransport system, we demonstrate that cAMP inhibits this system in human erythrocytes. The cotransport inhibition is enhanced by addition of phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine to the incubation medium. The cAMP concentration giving half-maximal cotransport inhibition showed a wide variation among different individuals (from 0.1 to 5 mM external cAMP concentration). In contrast to cAMP, cyclic GMP showed little effect on the cotransport system. Ca²⁺ introduced into the cell interior was an inhibitor of the Na⁺/K⁺ cotransport system. These results suggest that in human cells in which endogeneous levels of cAMP and Ca²⁺ are modulated by hormones, the Na⁺/K⁺ cotransport system may be under hormonal regulation.     

Fructose 1,6-bisphosphatase: Dissociation of AMP cooperativity and AMP inhibition by carbamylation

Selective treatment of pig kidney fructose 1,6-bisphosphatase with potassium cyanate leads to the formation of an active carbamylated enzyme that has lost the cooperative interactions among AMP sites, but retains sensitivity to inhibition of catalytic activity by the regulator AMP. Incorporation data on [¹⁴C]KNCO indicate that the loss of enzyme cooperativity at the AMP sites is related to selective carbamylation of four lysine residues per mole of tetrameric enzyme. Exhaustive carbamylation suggests that a second lysine residue per subunit is essential for AMP inhibition.     

INFLORESCENCE SIZE AND FRUIT DISTRIBUTION AMONG INDIVIDUALS IN THREE ORCHID SPECIES

Fruit distribution among individuals in populations of three orchid species was analyzed. Fruit set was low in the three species. The distribution of fruits in the non-autogamous species was skewed to the right, with high variance: mean ratios, and a moderate to high proportion of fruitless plants. Larger inflorescence size did not necessarily result in an increase in percent fruit set but tended to increase the probability to produce at least one fruit. Pollinator-mediated selection on inflorescence size through fruit production may be limited by the low overall level of visitation and the resulting uncertainty of pollination at the individual level.     

Vegetation responses to past volcanic disturbances at the Araucaria araucana forest‐steppe ecotone in northern Patagonia

Volcanic eruptions play an important role in vegetation dynamics and its historical range of variability. However, large events are infrequent and eruptions with a significant imprint in today''s vegetation occurred far in the past, limiting our understanding of ecological processes. Volcanoes in southern Andes have been active during the last 10 ka and support unique ecosystems such as the Araucaria–Nothofagus forest. Araucaria is an endangered species, with a fragmented distribution and well‐adapted to fire and volcanic disturbances. Yet, it was suggested that volcanism might have increased the fragmentation. Through the use of pollen and tephra analysis from a sedimentary record, this paleoecological study aims to provide an insight into the vegetation responses to past volcanic disturbances, to assess the role of volcanic disturbance on the vegetation dynamics and to determine if the current fragmentation has been caused by volcanism. Results show that during the last 9 kyr, 39 tephra falls buried the vegetation around Lake Relem, more frequently between 4 and 2 ka. The pollen percentage indicates that the vegetation changed after small tephra fall but seldom caused significant changes. However, the large eruption of Sollipulli volcano (~3 ka) changed the environmental conditions affecting severely the vegetation. Ephedra dominated the early successional stage, perhaps facilitating Nothofagus recovering after ~500 years. Slight increase of Araucaria and Nothofagus obliqua‐type pollen percentages suggests that forest resisted without permanent changes and recovered relatively fast after the large eruption, perhaps because of sparse biological legacies distributed in the landscape. In the study area, the relative stability of Araucaria pollen after several tephra fall suggests no change in its past distribution at the current forest‐steppe ecotone, thus not affecting its current conservation status. Perhaps, random factors, the colonization patterns of the high elevations in the Andes after deglaciation and topography might play a more important role than previously thought.