Synthesis and Content of Polyamines in Bloodstream Trypanosoma brucei*

SYNOPSIS. The sensitive dansyl procedure was used to detect putrescine and spermidine, but not spermine and cadaverine, in pleomorphic Trypanosoma brucei. The polyamines were synthesized in vitro from [³H]ornithine, [¹⁴C]arginine and [¹⁴C]methionine. Proline, agmatine, and citrulline, but not glutamine, glutamic or pyroglutamic acids, stimulated spermidine formation from [¹⁴C]methionine. Putrescine and spermidine synthesis occurred rapidly from ornithine: putrescine synthesis peaked in 0.5 h, spermidine in 1 h. Trypanosoma brucei assimilated exogenous ¹⁴C-labeled putrescine, spermidine, and spermine; spermidine and spermine were taken up 5 times as rapidly as putrescine. Polyamine syntheses may therefore be a practical target for novel trypanocies.     

Incorporation of Radioactive Pyrimidine Nucleosides into DNA and RNA of Eimeria tenella (Coccidia) Cultured In Vitro*

Autoradiographic methods were used to study the incorporation of tritiated cytidine, thymidine, and uridine into asexual stages of Eimeria tenella cultured in embryonic chick kidney cells. Developing parasites did not incorporate ³H-thymidine either when host cells were labeled prior to infection or when the cultures were labeled for 30 min, 48–72 hr after infection. Continuous exposure of infected cultures to ³H-thymidine for up to 18 hr resulted in light labeling of cell cytoplasm and schizonts. ³H-cytidine and ³H-uridine were incorporated into parasites developing in cultures that were labeled before infection. When the cultures were labeled for 30 min, 48–72 hr postinfection and fixed immediately, schizonts were labeled lightly with ³H-cytidine but contained dense accumulations of ³H-uridine.     

The Effect of Defoliation on the Nitrogen Economy of White Clover: Regrowth and the Remobilization of Plant Organic Nitrogen

Single plants of white clover (Trifolium repens) were establishedfrom stolon cuttings rooted in acid-washed silver sand. Allplants were inoculated with Rhizobium trifolii, and receivednutrient solution containing 0·5 mg ¹⁵N as either ammoniumor nitrate weekly for 12 weeks (i.e. 6 mg ¹⁵N in total). Plantswere then leniently defoliated or left intact, and the labelledN supply was replaced with unlabelled N. Lenient defoliationremoved fully expanded leaves only, leaving immature leaveswhich accounted for 50–55% of the total; growing pointnumbers were not reduced. Nodules, leaves and growing pointswere counted over the following 21 d period, and d. wts, N contents,and ¹⁵N enrichments of individual plant organs were determined. Defoliated plants had fewer nodules, but numbers of growingpoints were unaffected by defoliation. The rates of both leafemergence and expansion were accelerated in defoliated plants;in consequence the number of young leaves remained less thanin intact plants until day 21. Total dry matter (DM) and N accumulationwere less in defoliated plants, and a greater proportion oftotal plant DM was invested in roots. About 97 % of plant totalN was derived from fixed atmospheric N, but there was incompletemixing of fixed and mineral N within the plant. Relatively moremineral N was incorporated into roots, whereas there was relativelymore fixed N in nodules. There was isotopic evidence that Nwas remobilized from root and stolon tissue for leaf regrowthafter defoliation; approximately 2 % of plant N turned overdaily in the 7-d period after defoliation, and this contributedabout 50% of the N increment in leaf tissue. White clover, Trifolium repens L. cv. SI84, lenient defoliation, N economy, regrowth, N remobilization     

Microsporogenesis in Monocotyledons

This paper critically reviews the distribution of microsporogenesistypes in relation to recent concepts in monocot systematics.Two basic types of microsporogenesis are generally recognized:successive and simultaneous, although intermediates occur. Theseare characterized by differences in tetrad morphology, generallytetragonal or tetrahedral, although other forms occur, particularlyassociated with successive division. Successive microsporogenesisis predominant in monocotyledons, although the simultaneoustype characterizes the ‘lower’ Asparagales. Simultaneousmicrosporogenesis also occurs inJaponolirion and Petrosavia(unplaced taxa), some Araceae, Aponogeton, Thalassia andTofieldia(Alismatales), Dioscorea, Stenomeris and Tacca (Dioscoreales),and some Commelinanae: Arecaceae (Arecales), and Cyperaceae,Juncaceae and Thurniaceae (Poales). Simultaneous microsporogenesisis of phylogenetic significance within some of these groups,for example, Asparagales, Dioscoreales and Poales. An intermediatetype is recorded in Stemonaceae (Pandanales), Commelinaceae(Commelinales) and in Eriocaulaceae and Flagellariaceae (Poales).There is little direct relationship between microsporogenesistype and pollen aperture type in monocots (except for trichotomosulcateand pantoporate apertures), although trichotomosulcate aperturesin monocot pollen, and equatorial tricolpate and tricolporateapertures in eudicot pollen, are all related to simultaneousmicrosporogenesis. Copyright 1999 Annals of Botany Company Microsporogenesis, monocotyledons, pollen apertures, phylogeny, tetrads, simultaneous, successive, systematics.     

Spatial and temporal changes in genetic structure of greenhouse and field populations of cabbage looper,Trichoplusia ni

Trichoplusia ni is a subtropical moth that migrates annually from southern California to southern British Columbia, Canada where it invades vegetable greenhouses and field crops. The heated greenhouse environment has altered the natural extinction–recolonization dynamics of T. ni populations, and allows year‐round persistence in some locations. In addition, the extensive use of the biopesticide, Bacillus thuringiensis subspecies kurstaki (Bt) in some greenhouses has selected for resistance. Here we investigated the genetic structure of T. ni populations in British Columbia greenhouses and in field populations in California and British Columbia using amplified fragment length polymorphisms (AFLP) as related to patterns of Bt resistance. The majority of British Columbia field populations were similar to the California field populations, the potential source of migrants. However populations in two geographic areas with high concentrations of greenhouses showed local genetic differentiation. Some of these populations experienced severe bottlenecks over‐winter and following Bt sprays. Greenhouse populations showed a pattern of isolation by distance and a strong positive relationship between genetic differentiation and levels of Bt resistance. These patterns indicate that greenhouses that sometimes support year‐round populations of T. ni and the ensuing strong bottlenecking effects following winter cleanups and Bt application cause genetic differentiation of T. ni populations. Long distance migrants to field populations contribute to genetic homogeneity of these.     

From the Crest to the Periphery: Control of Pigment Cell Migration and Lineage Segregation

Pigment cells are one of many cell types derived from the neural crest. This review focuses on the mechanisms that control the timing and pathways of migration of pigment cells into the epidermis and determinants that control the differentiation of pigment cells. Several factors may control the timing and pattern of pigment cell migration in the dorsolateral space including the loss of inhibitory molecules in the pathway, the appearance of chemotactic molecules emanating from the dispersing dermatome, and the differentiation of pigment cells, which may be the only neural crest derivative capable of utilizing the substratum found in the dorsolateral path Control of pigment cell differentiation remains controversial. A working model presented in this review suggests that multipotent neural crest cells that disperse ventrally upon separation from the neural tube preserve neurogenic ability and lose melanogenic ability, whereas those cells that are arrested at the entrance to the dorsolateral path lose neurogenic ability so that the population becomes primarily melanogenic. During the time that the latter population is arrested in migration it is speculated that the neural crest cells are exposed to an environment comprised of specific extracellular matrix molecules and/or growth factors that enhance pigment cell differentiation.