Estimating the rate of photorespiration in leaves

The influence of Li⁺ on the circumnutations of hypocotyls of Helianthus annuus L . cv. Californicus was investigated. LiCl at concentration levels from 0 to 40 m M (lethal) was added to intact hypocotyls grown in liquid nutrient medium. The Li⁺ concentration in the hypocotyls was measured by flame photometry. The growth of the hypocotyls was not affected by the LiCl.
Amplitude and frequency of the circumnutations were determined by correlation analysis. The oscillatory pattern of the movements became less regular at concentrations above 10 m M LiCl. The amplitude of the movements was reduced for concentrations above 7 m M LiCl. The frequency of the movements was reduced when LiCl was increased from 0 to 10 m M . Above 10 m M LiCl the frequency of the circumnutations was higher than for control plants. The results showed that circumnutations of sunflower hypocotyls can be added to the group of oscillators in biological organisms that are affected by Li⁺.     

Methode zum Nachweis der Dauersporen des Kohlhernieerregers Plasmodiophora brassicae in gärtnerischen Kultursubstraten

Populations of pathogenic Pseudomonas syringae pv. syringae were monitored on apparently healthy leaves, blossoms, and fruit from two apple orchards with known histories of blister bark and a pear orchard with a known history of blossom blast. Populations on blossoms and fruits were higher on pears than on apples. Yellow-pigmented, non-pathogenic bacteria might have suppressed or masked the presence of P. syringae pv. syringae on apple trees. Populations of P. syringae pv. syringae on apple and pear leaves fluctuated sharply but higher levels generally occurred during the 1984/85 growing season than during the drier 1983/84 season. This investigation indicates that the resident phase of P. syringae pv. syringae is probably a major source of inoculum for apple blister bark and pear blossom blast in South Africa.     

Physical fine mapping of genes underlying X-linked deafness and non fra(X)-X-linked mental retardation at Xq21

Summary Linkage studies and cytogenetically visible deletions associated with nonspecific X-linked mental retardation (XLMR) and a specific form of deafness (DFN3) have indicated that the genes responsible for these disorders are located at Xq21. Using DNA probes from this region, we have studied several overlapping deletions spanning different parts of Xq21. This has enabled us to assign the DFN3 gene and a gene for nonspecific XLMR to an interval that encompasses the locus DXS232 and that is flanked by DXS26 and DXS121.     

Effects of feminization of male F344 rats on induction of tumors and on nucleic acid alkylation by nitrosobis-(2-oxopropyl)amine

Groups of male and female F344 rats were treated twice weekly by gavage with 2.5 mg of nitrosobis-(2-oxopropyl)amine (BOP) for 35 weeks. Additional groups given the same treatment were male rats castrated at birth, male rats bearing an implant of a pellet containing estradiol and castrated male rats bearing an estradiol pellet. Most rats died with tumors related to the treatment; intact male rats survived the least well of the five groups. Most rats in all groups had alveolar/bronchiolar neoplasms of the lung. Many of the male rats also had follicular cell neoplasms of the thyroid and transitional cell neoplasms of the urinary bladder and kidney pelvis; there were no liver tumors in intact male rats. Almost all female rats and castrated male rats had liver neoplasms, including hepatocellular, cholangiocellular and hemangiosarcomatous neoplasms, but few neoplasms of the thyroid, kidney or bladder. The male rats feminized with estradiol, intact or castrated, had liver neoplasms, mainly cholangiocellular, and also neoplasms of the thyroid. Two rats of each of the five groups were treated at 20 weeks of age with [14C]BOP. As measured by respiration of 14CO2, metabolism of BOP was faster in the two groups of male rats with the estradiol implant than in the other groups. DNA and RNA of the liver were isolated 6 h after treatment. The extent of methylation of liver DNA as 7-methylguanine and O6-methylguanine was higher in the females and in the feminized males than in the intact male rats, but when normalized to the dose of nitrosamine per unit body weight there was little difference among the five groups.     

Mechanism of inactivation of rat liver microsomal cytochrome P-450c by 2-bromo-4'-nitroacetophenone

The mechanism by which 2-bromo-4'-nitroacetophenone (BrNAP) inactivates cytochrome P-450c, which involves alkylation primarily at Cys-292, is shown in the present study to involve an uncoupling of NADPH utilization and oxygen consumption from product formation. Alkylation of cytochrome P-450c with BrNAP markedly stimulated (approximately 30-fold) its rate of anaerobic reduction by NADPH-cytochrome P-450 reductase, as determined by stopped flow spectroscopy. This marked stimulation in reduction rate is highly unusual in that Cys-292 is apparently not part of the heme- or substrate-binding site, and its alkylation by BrNAP does not cause a low spin to high spin state transition in cytochrome P-450c. Under aerobic conditions the rapid oxidation of NADPH catalyzed by alkylated cytochrome P-450c was associated with rapid reduction of molecular oxygen to hydrogen peroxide via superoxide anion. The intermediacy of superoxide anion, formed by the one-electron reduction of molecular oxygen, established that alkylation of cytochrome P-450c with BrNAP uncouples the catalytic cycle prior to introduction of the second electron. The generation of superoxide anion by decomposition of the Fe2+ X O2 complex was consistent with the observations that, in contrast to native cytochrome P-450c, alkylated cytochrome P-450c failed to form a 430 nm absorbing chromophore during the metabolism of 7-ethoxycoumarin. Alkylation of cytochrome P-450c with BrNAP did not completely uncouple the catalytic cycle such that 5-20% of the catalytic activity remained for the alkylated cytochrome compared to the native protein depending on the substrate assayed. The uncoupling effect was, however, highly specific for cytochrome P-450c. Alkylation of nine other rat liver microsomal cytochrome P-450 isozymes with BrNAP caused little or no increase in hydrogen peroxide formation in the presence of NADPH-cytochrome P-450 reductase and NADPH.     

Foraging-efficiency-predation-risk trade-off in the grey squirrel

Many animals must often respond to environmental patterns that simulatneously influence both foraging efficiency and predation risk. We noted that grey squirrels (Sciurus carolinensis) sometimes immediately consume food items in areas of relatively great exposure to predators, and at other times carry food items to the safety of a tree prior to consumption. We outlined a hypothesis that the squirrels were somehow trading-off energy intake rate against predation risk. A simple model shows that maximal energetic efficiency is associated with immediate consumption, whereas (under the field conditions studied) carrying items to the safety of trees provides for minimal exposure to predation. Our analysis of the model predicts that the tendency to carry a food item should decrease with distance of food from cover (travel time) and increase with item size (handling time). To test our predictions, we presented free-roaming grey squirrels with patches containing a fixed number of identical food items. We estimated the proportion of items carried to trees before consumption for 12 different combinations of distance to the nearest tree and item size. The results support our hypothesis and indicate that a simple behavioural criterion based solely on foraging rate or time exposed to predators is insufficient to explain the variation in the data.     

Nonrandom catabolism of proteins in the formation of antigenic peptide fragments

To examine the role of protein catabolism in the formation of antigenic peptide fragments, human fibrinopeptide-immune guinea pig T cells were stimulated with the large native molecule, human fibrinogen. Two different systems were tested. In the first, we determined responses by human fibrinopeptide B (hFPB)-immune T cells, to which strain (St.) 2 guinea pigs are responders and St. 13 are nonresponders, and by human fibrinopeptide A (hFPA)-immune T cells to which St. 13 are responders and St. 2 are nonresponders. Of interest in this comparison is that both hFPA and hFPB are amino terminal peptides on the A and B chain of fibrinogen, respectively, and are readily cleaved by thrombin during fibrin formation and by other trypsin-like enzymes, leaving a carboxyl terminal Arg. Thus, if fibrinogen catabolism occurred, both antigenic peptides should be equally represented for availability in T cell responses. It was found that hFPB-immune St. 2 T cells responded to fibrinogen, but no response was observed with hPFA-immune St. 13 T cells cultured with fibrinogen. To rule out that there was a general catabolic defect in St. 13 antigen-presenting cells, fibrinogen was presented by (2 X 13)F1 macrophages to fibrinopeptide-immune parental T cells. Again it was found that F1 macrophages could present fibrinogen to hFPB-immune T cells but failed to present hFPA. In another comparison, responses with fibrinogen were also determined with des-ARg-hFPB, which lacks the carboxyl terminal Arg of hFPB, to which St. 13 are responders and St. 2 are nonresponders. The advantage of this comparison is that both antigenic determinants are contained within the same small peptide. St. 13 des-Arg-hFPB-immune T cells failed to respond in vitro by culture with human fibrinogen, suggesting that these antigenic determinants are not produced from larger peptides or proteins containing those determinants. To rule out the possibility that this was only an in vitro phenomenon, guinea pigs were immunized with the larger protein, the B chain of fibrinogen, and the immune T cells were examined for responses to fibrinopeptides derived from the B chain. Immune St. 2 T cells responded to hFPB but not to des-Arg-hFPB, whereas St. 13 T cells remained unresponsive with both peptides. These results indicate that proteolysis of larger proteins to form small antigenic peptides is not a random event and that not all potential antigenic determinants contained in a protein are produced during antigen processing.