Expression of a mouse selenocysteine lyase in Brassica juncea chloroplasts affects selenium tolerance and accumulation

Selenium is an essential nutrient for many organisms, as part of certain selenoproteins. However, selenium is toxic at high levels, which is thought to be due to non-specific replacement of cysteine by selenocysteine leading to disruption of protein function. In an attempt to prevent non-specific incorporation of selenocysteine into proteins and to possibly enhance plant selenium tolerance and accumulation, a mouse selenocysteine lyase was expressed in Brassica juncea (Indian mustard) chloroplasts, the site of selenocysteine synthesis. This selenocysteine lyase specifically breaks down selenocysteine into elemental selenium and alanine. The transgenic cpSL plants showed normal growth under standard conditions. Selenocysteine lyase activity in the cpSL transgenics was up to 6-fold higher than in wild-type plants. The cpSL transgenics contained up to 40% less selenium in protein compared to wild-type plants, indicating that Se flow in the plant was successfully redirected. Surprisingly, the selenium tolerance of the transgenic cpSL plants was reduced, perhaps due to interference of produced elemental selenium with chloroplastic sulphur metabolism. Shoot selenium levels were enhanced up to 50% in the cpSL transgenics, but only during the seedling stage.     

Degradation of Bermuda and Orchard Grass by Species of Ruminal Bacteria

Fiber degradation in Bermuda grass and orchard grass was evaluated gravimetrically and by scanning and transmission electron microscopy after incubation with pure cultures of rumen bacteria. Lachnospira multiparus D-32 was unable to degrade plant cell wall components. Butyrivibrio fibrisolvens 49 degraded 6 and 14.9% of the fiber components in Bermuda grass and orchard grass, respectively, and Ruminococcus albus 7 degraded 11.4% orchard grass fiber but none in Bermuda grass. Both B. fibrisolvens and R. albus lacked capsules, did not adhere to fiber, and degraded only portions of the more easily available plant cell walls. R. flavefaciens FD-1 was the most active fiber digester, degrading 8.2 and 55.3% of Bermuda and orchard grass fiber, respectively. The microbe had a distinct capsule and adhered to fiber, especially that which is slowly degraded, but was able to cause erosion and disorganization of the more easily digested cell walls, apparently by extracellular enzymes. Results indicated that more digestible cell walls could be partially degraded by enzymes disassociated from cellulolytic and noncellulolytic bacteria, and data were consistent with the hypothesis that the more slowly degraded plant walls required attachment. Microbial species as well as the cell wall architecture influenced the physical association with and digestion of plant fiber.     

Effect of phenolic monomers on the growth and beta-glucosidase activity of Bacteroides ruminicola and on the carboxymethylcellulase, beta-glucosidase, and xylanase activities of Bacteroides succinogenes

trans-p-Coumaric acid inhibited the growth of Bacteroides ruminicola on both cellobiose and glucose, while trans-ferulic acid and vanillin retarded growth. The phenolic monomers varied in their potential to inhibit the Bacteroides succinogenes beta-glucosidase, carboxymethylcellulase, and xylanase, with p-coumaric acid being the most inhibitory. The B. ruminicola beta-glucosidase was inhibited less than 10% by all three compounds.     

Recurrence of the unfit

Domination among strategies in an evolutionary game implies that the geometric mean of the frequencies of certain strategies—the unfit—approaches zero. However, as we show by example no one strategy need be eliminated in the limit.     

Processing of a newly identified intermediate of human myeloperoxidase in isolated granules occurs at neutral pH

Myeloperoxidase is a major component of specialized lysosomes known as azurophil granules in polymorphonuclear leukocytes or neutrophils. The processing of myeloperoxidase in human HL-60 promyelocytic leukemia cells was studied by pulse-labeling cells in culture with [35S]methionine followed by immunoprecipitation and identification of myeloperoxidase polypeptides from cell fractions after various chase intervals. These studies revealed the presence of a previously unidentified intermediate with Mr 74,000 which kinetically followed the appearance of a larger Mr 81,000 intermediate. Using an in vitro lysosomal preparation the newly identified Mr 74,000 intermediate was directly converted within protected granules to mature forms of myeloperoxidase (Mr 63,000 and 60,000). This conversion occurred optimally at pH 7.5 and was not inhibited by lysosomotropic agents (chloroquine, NH4Cl) or protonophores (monensin, carbonyl cyanide p-trifluoromethoxyphenylhydrazone). Furthermore, the uptake of radiolabeled amines indicated a neutral intragranular environment (pH 7.35-7.67) which remained unchanged in the presence and absence of 1 mM ATP or 2.5 microM carbonyl cyanide p-trifluoromethoxyphenylhydrazone. We conclude that, in contrast to other lysosomal pathways, the final proteolytic cleavage of myeloperoxidase does not require an acidic environment.     

Diversity of plants in cocoa agroforests in the humid forest zone of Southern Cameroon

In the humid forest zone of Southern Cameroon, farmers generally associate cocoa with native and exotic trees in complex agroforestry systems. Despite the socio-economic and ecological importance of these systems, few studies have investigated their plant composition. We investigated tree composition of cocoa agroforests along a gradient of market access, population density and resource use intensity in the humid forest zone of southern Cameroon, comprising (i) the sub-region of Yaoundé, (ii) the sub-region of Mbalmayo, and (iii) the sub-region of Ebolowa. Market access, population density and resource use intensity all decreased from the first to the third sub-region. We quantified the diversity of tree species associated with cocoa within individual agroforests, among agroforests in the same region, and among the three sub-regions, and classified the tree species according to their main uses. A total of 9.1 ha belonging to 60 cocoa agroforests were inventoried in 12 villages. We encountered a total of 206 tree species with an average of 21 tree species per agroforest. In the more urbanized area around Yaoundé, agroforests were less diverse than in the other sub-regions. In all of the agroforests, food producing tree species tended to be more frequent than other species. Two thirds of the food trees were native forest species and one third was introduced. From Ebolowa to Yaoundé, the density of food producing trees doubled and the density of exotic food-producing species increased relative to native species. Some local species producing high-value non-timber forest products were found in the agroforests, but their density was far lower than that of exotic tree species. The agroforests also provide medicine, charcoal and other products for household consumption and sale. We conclude that unless there are specific efforts to promote local forest tree species in cocoa agroforests, these will progressively lose importance with increasing market access, population pressure and land use intensity.