Performance of recombinant inbred lines in Brussels sprouts (Brassica oleracea var. gemmifera)

Summary Performance of a random array of recombinant inbred lines derived by single seed descent from five different source populations of Brussels sprouts (Brassica oleracea var. gemmifera) is presented. A total of 2,356 lines were tested in trials during 1985 and 1986. Three of the source populations were derived from double crosses between F₁ hybrids. These hybrids show a considerable heterotic advantage over their inbred parents for the most important agronomic traits. The recombinant inbred lines performed, on average, less well than the parental inbred material, indicating that additive x additive genie interactions may make a significant contribution to the performance of current inbred material. Nevertheless, the very large variation among the recombinant inbred lines permitted many lines to be identified which outperformed the best parental inbred for all traits. Two lines outperformed the reference F₁ hybrid, Gower, for an index that included marketable yield and quality. Consideration was also given to the dangers of misinterpreting phenotypically based proportions. Accordingly, response equations were used to ascertain the real genetic progress that was made. Advance seemed small when compared with the large heterotic effect, which is consistent with the segregation of a large number of loci. The distribution of the recombinant inbred lines was compared to predictions made from early generation trials. There was broad agreement but significant discrepancies existed which, it is suggested, may arise from the effects of genotype-environment interactions.     

Role of Auxin in Maize Endosperm Development (Timing of Nuclear DNA Endoreduplication,Zein Expression,and Cytokinin)

The timing of developmental events and regulatory roles of auxin were examined in maize (Zea mays L.) endosperms. Zeatin, zeatin riboside, and indole-3-acetic acid (IAA) levels were determined by enzyme-linked immunosorbent (ELISA). Zeatin and zeatin riboside increased to maximal concentrations at an early stage (9 d after pollination [DAP]), corresponding to the stage when cell division rate was maximal. In contrast, IAA concentration was low at 9 DAP and abruptly increased from 9 to 11 DAP, thus creating a sharp decline in the cytokinin to auxin ratio. Coincident with the increase in IAA was an increase in DNA content per nucleus, attributed to postmitotic DNA replication via endoreduplication. Exogenous application of 2,4-dichlorophenoxyacetic acid (2,4-D) at 5 or 7 DAP hastened the time course of DNA accumulation per nucleus and increased the average nuclear diameter, whereas 2-(para-chlorophenoxy)isobutyric acid delayed such development. Exogenously applied 2,4-D hastened the accumulation of the zein polypeptides of apparent molecular masses of 12, 14, and 16 kD and the expression of mRNA hybridizing with a zein DNA probe. We conclude that an abrupt increase in auxin induces cellular differentiation events in endosperm, including endoredupliction and expression of particular zein storage proteins.     

Reserve carbohydrate in maize stem : [C]glucose and [C]sucrose uptake characteristics

Maize (Zea mays L.) stem is thought to function alternately as a net importing and net exporting organ during ontogeny, depending on whole plant photosynthetic source and sink status. The [¹⁴C]sucrose and [¹⁴C]glucose uptake capacity of stem tissues was investigated to increase our understanding of the transport factors which may influence sink status.     

Abscisic Acid Translocation and Metabolism in Soybeans following Depodding and Petiole Girdling Treatments

It was found earlier that depodding and girdling treatments which obstruct translocation, result in increased leaf AbA levels and partial stomatal closure. In the present work (±) [2-¹⁴C]abscisic acid (AbA) was introduced into leaves and the mass, and radioactivity of AbA and AbA-metabolites were analyzed following translocation obstruction to determine whether the increased AbA was due to higher rates of synthesis, or lower rates of catabolism or export. The (±) [2-¹⁴C]AbA was introduced into soybean (Merr.) leaves by injection into the petiole region. AbA and AbA-metabolites (phaseic acid [PA], dihydrophaseic acid [DPA], AbA-conjugate, and an unknown metabolite) were separated with preparative high performance liquid chromatography. Methyl esters of AbA (free and that released after hydrolysis of AbA-conjugate), PA and DPA were determined with gas chromatography using electron capture detection.     

Phe-Gly-Leu-amide allatostatin in the termite Reticulitermes flavipes: content in brain and corpus allatum and effect on juvenile hormone synthesis

In the subterranean termite Reticulitermes flavipes, allatostatins (ASTs) with the C-terminus Phe-Gly Leu-amide were localized by immunocytochemistry with antibody against a cockroach AST, Dippu AST-7. AST-immunoreactivity occurred in the corpus cardiacum and corpus allatum and in the lateral and medial neurosecretory cells of the brain that innervate these organs as well as in many other nerve cells of the brain. This was observed in workers, nymphs, soldiers and secondary reproductives. A radioimmunoassay, using anti-Dippu AST-11, demonstrated about 40 fmole equivalents of AST in brains of soldiers and secondary reproductives. The product of the corpora allata in this species was determined to be juvenile hormone III. Its synthesis by corpora allata of secondary reproductives, determined by in vitro radiochemical assay, was inhibited in a dose-dependent fashion by two cockroach allatostatins, Dippu AST-7 and Dippu AST-11. Thus, as in cockroaches and crickets, allatostatin-containing nerves innervate the corpora allata of this termite species and their production of juvenile hormone is inhibited by these neuropeptides.     

Sweeps in time: leveraging the joint distribution of branch lengths

Current methods of identifying positively selected regions in the genome are limited in two key ways: the underlying models cannot account for the timing of adaptive events and the comparison between models of selective sweeps and sequence data is generally made via simple summaries of genetic diversity. Here, we develop a tractable method of describing the effect of positive selection on the genealogical histories in the surrounding genome, explicitly modeling both the timing and context of an adaptive event. In addition, our framework allows us to go beyond analyzing polymorphism data via the site frequency spectrum or summaries thereof and instead leverage information contained in patterns of linked variants. Tests on both simulations and a human data example, as well as a comparison to SweepFinder2, show that even with very small sample sizes, our analytic framework has higher power to identify old selective sweeps and to correctly infer both the time and strength of selection. Finally, we derived the marginal distribution of genealogical branch lengths at a locus affected by selection acting at a linked site. This provides a much-needed link between our analytic understanding of the effects of sweeps on sequence variation and recent advances in simulation and heuristic inference procedures that allow researchers to examine the sequence of genealogical histories along the genome.     

Impact of defoliation by the biocontrol agentZygogramma bicolorataon the weed Partheniumhysterophorus in Australia

The leaf-feeding beetle Zygogrammabicolorata Pallister was introduced from Mexico intoAustralia in 1980 as a biocontrol agent for the weedParthenium hysterophorus L. (Asteraceae). Z. bicolorata became abundant in 1990, and since 1992there has been regular outbreaks resulting in thedefoliation of the weed in central Queensland. In thisstudy we evaluated the impact of defoliation by Z. bicolorata on P. hysterophorus from 1996 to1998. Z. bicolorata caused 91–100% defoliationresulting in reductions in weed density by 32–93%,plant height by 18–65%, plant biomass by 55–89%,flower production by 75–100%, soil seed-bank by13–86% and seedling emergence in the following seasonby 73–90%. At sites with continued outbreaks ofZ. bicolorata, it is expected that the existing soilseed-bank will be minimised, resulting in reduceddensity of parthenium in 6 to 7 years.     

Quantitation of cytokine-stimulated migration of endothelium and epithelium by a new assay using microcarrier beads

Recent studies have identified a group of cytokines which appear to be cell-specific regulators of mobility in nonleukocytic mammalian cells. One example is scatter factor (SF), a soluble protein(s) produced by cultured fibroblasts and vascular smooth muscle cells which causes spreading and separation ("scattering") of tight, cohesive colonies of epithelial cells. Studies of SF action have been limited because the degree of scattering is difficult to quantitate and because scattering assays cannot be used to study potential target cells that do not form tight, cohesive colonies. We developed a simple, quantitative assay of SF-stimulated mobility based on migration of target cells off microcarrier beads onto plastic culture surfaces in 24-well plates. We showed that crude and partially purified SF derived from ras-transformed 3T3 cells stimulates migration of both epithelial and vascular endothelial cells but not of producer or nonproducer fibroblasts. Scatter and migration-stimulating activities copurified on cation exchange chromatography; and the degree of stimulation was closely correlated with scattering titer regardless of SF purity. Migration of endothelial cells from beads, while extremely sensitive to SF, was not affected by serum concentration (1 to 10%), various purified growth factors, or fibronectin. Both scattering and migration from beads were blocked by cycloheximide (0.1 microgram/ml) during assay incubation, suggesting that these processes require protein synthesis. The microcarrier bead assay may be a useful quantitative tool to study the biochemical mechanisms of SF-stimulated cell migration.