Redundant roles of photoreceptors and cytokinins in regulating photosynthetic acclimation to canopy density.

The regulation of photosynthetic acclimation to canopy density was investigated in tobacco canopies and in tobacco and Arabidopsis plants with part of their foliage experimentally shaded. Both species acclimated to canopy light gradients and partial shading by allocating photosynthetic capacity to leaves in high light and adjusting chloroplast organization to the local light conditions. An investigation was carried out to determine whether signalling mediated by photoreceptors, sugars, cytokinin, and nitrate is involved in and necessary for proper photosynthetic acclimation. No evidence was found for a role for sugars, or for nitrate. The distribution of cytokinins in tobacco stands of contrasting density could be explained in part by irradiance-dependent delivery of cytokinins through the transpiration stream. Functional studies using a comprehensive selection of Arabidopsis mutants and transgenics showed that normal wild-type responses to partial shading were retained when signalling mediated by photoreceptors or cytokinins was disrupted. This indicates that these pathways probably operate in a redundant manner. However, the reduction of the chlorophyll a/b ratio in response to local shade was completely absent in the Arabidopsis Ws-2 accession mutated in PHYTOCHROME D and in the triple phyAphyCphyD mutant. Moreover, cytokinin receptor mutants also showed a reduced response, suggesting a previously unrecognized function of phyD and cytokinins.

A novel disorder of N-glycosylation due to phosphomannose isomerase deficiency.

Three siblings suffered from an unusual disorder of cyclic vomiting and congenital hepatic fibrosis. Serum transferrin isoelectric focusing showed increased asialo- and disialotransferrin isoforms as seen in the carbohydrate-deficient glycoprotein (CDG) syndrome type I. Phosphomannomutase, which is deficient in most patients with type I CDG syndrome, was found to be normal in all three patients. Structural analysis of serum transferrin revealed nonglycosylated, hypoglycosylated, and normoglycosylated transferrin molecules. These findings suggested a defect in the early glycosylation pathway. Phosphomannose isomerase was found to be deficient and the defect was present in leucocytes, fibroblasts, and liver tissue. Phosphomannose isomerase deficiency appears to be a novel glycosylation disorder, which is biochemically indistinguishable from CDG syndrome type I. However, the clinical presentation is entirely different.

Rapid isolation of muscle and heart mitochondria, the lability of oxidative phosphorylation and attempts to stabilize the process in vitro by taurine, carnitine and other compounds.

We modified the isolation procedure of muscle and heart mitochondria. In human muscle, this resulted in a 3.4 fold higher yield of better coupled mitochondria in half the isolation time. In a preparation from rat muscle we studied factors that affected the stability of oxidative phosphorylation (oxphos) and found that it decreased by shaking the preparation on a Vortex machine, by exposure to light and by an increase in storage temperature. The decay was found to be different for each substrate tested. The oxidation of ascorbate was most stable and less sensitive to the treatments. When mitochondria were stored in the dark and the cold, the decrease in oxidative phosphorylation followed first order kinetics. In individual preparations of muscle and heart mitochondria, protection of oxidative phosphorylation was found by adding candidate stabilizers, such as desferrioxamine, lazaroids, taurine, carnitine, phosphocreatine, N-acetylcysteine. Trolox-C and ruthenium red, implying a role for reactive oxygen species and calcium-ions in the in vitro damage at low temperature to oxidative phosphorylation. In heart mitochondria oxphos with pyruvate and palmitoylcarnitine was most labile followed by glutamate, succinate and ascorbate. We studied the effect of taurine, hypotaurine, carnitine, and desferrioxamine on the decay of oxphos with these substrates. 1 mM taurine (n = 6) caused a significant protection of oxphos with pyruvate, glutamate and palmitoylcarnitine, but not with the other substrates. 5 mM L-carnitine (n = 6), 1 mM hypotaurine (n = 3) and 0.1 mM desferrioxamine (n = 3) did not protect oxphos with any of the substrates at a significant level. These experiments were undertaken in the hope that the in vitro stabilizers can be used in future treatment of patients with defects in oxidative phosphorylation.

Differential stimulation by oxygen-free-radical-altered immunoglobulin G of the production of superoxide and hydrogen peroxide by human polymorphonuclear leucocytes.

1. The effect of free-radical-altered IgG (monomer and polymer u.v.-irradiated IgG), compared with that of native and heat-aggregated IgG, on the production rate of superoxide anion and hydrogen peroxide by granulocytes (polymorphonuclear leucocytes) from normal blood and granulocytes obtained from the blood and synovial fluid of patients with rheumatoid arthritis was studied. 2. Similar rates of superoxide production by granulocytes from normal blood at rest and in the presence of any form of IgG were found. In contrast, the rate of hydrogen peroxide production could be stimulated in a dose-dependent fashion by monomer or polymer u.v.-irradiated IgG. 3. The stimulatory effect of free-radical-altered IgG on the rate of hydrogen peroxide production did not occur in the presence of 2-deoxyglucose, which deprives the NADPH:O2 oxidoreductase of its substrate NADPH by inhibition of glycolysis and the pentose phosphate pathway. This points to a stimulatory effect on the direct divalent reduction of oxygen without intermediate superoxide production by this enzyme complex. 4. Granulocytes obtained from the blood and synovial fluid of patients with rheumatoid arthritis reacted differently to polymer u.v.-irradiated IgG. In the presence of this stimulus the rate of release of both superoxide and hydrogen peroxide was increased. Furthermore, these granulocytes synthesized superoxide and hydrogen peroxide at a higher rate than did granulocytes from normal blood in the presence of serum-treated zymosan but not in the presence of phorbol myristate acetate. 5. Taken together, these results indicate that the rate of superoxide and hydrogen peroxide production by the granulocyte NADPH:O2 oxidoreductase depends on the pathological condition of the donor and the type of stimulus used.

Nonselective squeeze-out of dioleoylphosphatidylcholine and dioleoylphosphatidylglycerol from binary mixed monolayers with dipalmitoylphosphatidylcholine.

In order to enable the possible use of dipalmitoylphosphatidylcholine as an artificial lung surfactant, the addition of dioleoylphosphatidylcholine or dioleoylphosphatidylglycerol has been suggested. A preferential loss of molecules of the second component during compression of the interfacial layer was proposed. In this study two types of measurement were carried out in order to verify such a preferential squeeze-out. In the first type, electron micrographs of a pure dipalmitoylphosphatidylcholine monolayer and of mixed monolayers of dipalmitoylphosphatidylcholine and egg phosphatidylglycerol were taken in order to study the nature of the structures formed during compression of the monolayer. The electron microscopy photos show horizontally stacked layers in the collapse phase of dipalmitoylphosphatidylcholine, and long vertical ridges in the mixed monolayers up to 20% second component. At higher concentrations of the second component no such structures can be detected. The second type involved monolayer studies with binary mixtures of dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine or dioleoylphosphatidylglycerol, one of the pair being always radioactively labelled. Counting the radioactivities in bulk phase and monolayer after compression revealed nonselective squeeze-out of either component.

Lack of change in the composition of fetal lamb lung surfactant during gestation.

Fetal surfactant from lamb lung fluids collected daily from day 114 to day 146 of gestation, was isolated by centrifugation (pellet material) and further purified by sucrose density gradient centrifugation. The concentration of the pellet material from lung fluid (crude surfactant) increased from day 125 till day 135 and fluctuated strongly from that period onwards, whereas lung fluid secretion increased linearly until a few days before parturition. The pellet phospholipid composition changed with gestational age, suggesting biochemical maturation of the surfactant-producing system. The purified surfactant fraction, of which approximately 85% was phosphatidylcholine, did not change however from day 122 onwards except for a small increase in the percentage of phosphatidylglycerol. Alveolar wash surfactant or the lamellar body material, isolated from fetal lungs at different gestational ages had the same composition as surfactant from lung fluids. Only the composition of lamellar bodies of '125 day' lungs differed slightly from that of the lung fluid surfactant. The similar characteristics of all purified surfactant fractions throughout gestation indicate that, in the fetal lamb, lung maturation is associated with an increase in surfactant production no significant changes in phospholipid composition.