Restriction fragment polymorphisms as probes for plant diversity and their development as tools for applied plant breeding

Summary Maize and tomato cDNA clones have been hybridized in Southern blotting experiments to plant genomic DNA prepared from different lines to detect restriction fragment polymorphisms (RFPs). In maize we have found that a high degree of genetic variability is present, even among domestic inbred lines. Most randomly chosen maize cDNA clones can be used to detect elements of this variability. Similar levels of polymorphism are observed when genomic DNA is digested with any of a number of different restriction enzymes and probed with individual clones. When a clone is hybridized to genomic DNAs prepared from several different maize lines, a number of different alleles are often detected at a single locus. At the same time one clone can often detect more than one independently segregating locus by cross hybridization to related sequences at other loci. As expected these markers are inherited as simple codominant Mendelian alleles from one generation to the next and colinkage of these markers can be demonstrated in the progeny from a heterozygous parent. In similar studies with tomato, remarkably different results were found. Few RFPs were demonstrable among domestic Lycopersicon esculentum lines although a higher level of variability could be detected when comparing esculentum with its wild Lycopersicon relatives. These results are discussed in relation to the applied uses of RFPs in plant breeding as well as the inherent variability of different plant genomes.This work was supported in part by funds from Sandoz Ltd. (Basel, Switzerland) and its subsidiary company, Northrup King Co. (Minneapolis, Minn., U.S.A.) as well as by NSF SBIR grant #BSR-8360870.     

In vitro development of the hamster and chick secondary palate

A series of experiments were undertaken to compare the in vitro behaviour of the medial edge epithelium (MEE) of hamster, in which palatal shelves normally fuse, and chick, in which they do not fuse. Homotypic pairs of hamster and chick embryo palatal processes, single palatal processes, and heterotypic palatal shelves of both animals were grown in vitro. The results indicated that contact between palatal shelves may not be crucial for MEE differentiation in mammals. The ability to acquire pre-fusion characteristics may be present in mammalian palatal tissue from their early development and may be expressed by cessation of DNA synthesis in the MEE, elevation of cAMP, and MEE cell death. Isolated chick palatal shelf cultured under identical conditions did not express these mammalian pre-fusion characteristics. When MEE of hamster and chick palatal shelves were placed in contact with one another, the intervening epithelia underwent cytolysis. This could be due to either the destruction of chick MEE by lysosomal enzymes liberated from adjacent degenerating hamster MEE cells, or by induction of cell death in chick MEE by hamster mesenchyme. Heterotypic palatal tissue combinations also suggest that release of lysosomal enzymes in the hamster MEE, which leads to its dissolution, may be the terminal event in epithelial differentiation prior to the establishment of mesenchymal continuity. It is suggested that an inverse relationship exists between DNA synthesis and cAMP levels during palatogenesis: when palate closes (as in mammals) the MEE is eliminated by increasing cAMP levels, whereas when palate remains open (as in birds) low level of cAMP preserve the integrity of MEE by supporting DNA synthesis.     

Concordant variation in thermal tolerance and allozymes of the red shiner,Notropis lutrensis,inhabiting tailwater sections of the Brazos River,Texas

Synopsis Critical thermal maxima (CTM) and genetic variation were compared for red shiners, Notropis lutrensis, from regulated and unregulated sites on the Brazos River in northcentral Texas. Tailwater fish acclimated to 25°C had significantly lower CTM's than those from a site upstream from the dam and unregulated downstream sites. Significantly different intrasite variances were observed, with two- and four-fold larger CTM variances in fish from within 1 km and 30 km of the dam. Genetic variation was determined from electrophoretic comparisons at 21 structural gene loci. Mean heterozygosity was greatest at regulated sites. Tests for locus heterogeneity at five variable loci indicated that regulated and unregulated populations are not homogeneous. Fish under regulation were genetically more similar to each other than they were to those not affected by regulation. The proportions of the gene variance attributable to habitat alteration were partitioned, and fully one-third of the gene variation was attributed to stream regulation. Patterns of variation in thermal tolerance and metabolic enzymes in the red shiner correlated closely with temperature regimes associated with hypolimnion release from the dam. These adaptive responses have occurred in less than 40 years.     

A high incidence of parasitism ofHeliothis SPP. [Lep.: Noctuidae] larvae in cotton in Southeastern Arkansas

During 1981 and 1982, bollworm,Heliothis zea (Boddie), and tobacco budworm,H. virescens (F.), larvae (n=3,666) were collected from 41 cotton fields near Portland, Arkansas (USA) to assess the occurrence of parasitism. Three strategies were employed to controlHeliothis spp. in these fields: (1) release ofTrichogramma pretiosum Riley; (2) insecticidal control; or (3) inaction (check). Insecticide use in nonchemical control fields was reduced, but not eliminated.Heliothis spp. larvae collected in cotton had higher parasitism rates in 1981 (30.9%) and 1982 (50.1%) than had been reported for cotton since the advent of organochlorine insecticide usage. Four species of larval parasites and 1 species of larval-pupal parasite were recorded. The larval parasiteMicroplitis croceipes (Cresson) comprised 90.6% and 94.5% of all parasitic insects reared from field collectedHeliothis spp. in 1981 and 1982, respectively. No difference (P>0.05) in level of parasitism existed betweenH. zea andH. virescens. Differences between treatments occurred only in 1982 whenH. zea larvae were parasitized at a greater (P<0.05) rate in check fields (68.3%) than in insecticidal control fields (44.3%). Higher levels of larval parasitism in cotton fields may be a consequence of reduced insecticide usage and changes in materials applied, particularly the pyrethroids. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Dept. of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Polymyalgia rheumatica/giant cell arteritis in a Cambridge general practice.

The aim of this study was to establish the incidence and prevalence of polymyalgia rheumatica/giant cell arteritis in general practice. Patients with this disorder, whether previously diagnosed or not, were ascertained by using a questionnaire administered by interview, and all received full clinical and laboratory assessment. A total of 579 patients aged 65 and over was seen, and 19 (33/1000) had been diagnosed or developed symptoms within the previous eight years. Thus the calculated annual incidence in those aged 65 and over was about 4/1000. The figures from this first large scale study of polymyalgia rheumatica/giant cell arteritis in general practice are much higher than those from studies carried out in hospital. The questionnaire was effective in both identifying known cases of polymyalgia rheumatica/giant cell arteritis and detecting new cases. As this is a treatable disorder, it is important that doctors become aware of how common it is in elderly people.     

Temperature dependence of the electron spin-lattice relaxation rate from pulsed EPR of CUA and heme a in cytochrome c oxidase

This work shows the feasibility of using pulsed, saturation recovery EPR to study directly the magnetic relaxation properties of metal centers in cytochrome c oxidase in the 1.5-20 K range. Heme a and CuA both showed remarkably similar Tn temperature dependences in their spin-lattice relaxation rates. Either both are in environments with very similar protein backbone configurations (Stapleton, H.J., J.P. Allen, C.P. Flynn, D.G. Stinson, and S.R. Kurtz, 1980, Phys. Rev. Lett., 45:1456-1459; Allen, J.P., J.T. Colvin, D.G. Stinson, C.P. Flynn, and H.J. Stapleton, 1982, Biophys. J., 38:299-310), or the CuA is relaxed by nearby heme a. Spin-lattice relaxation of the nitrosylferrocytochrome a3 center in mixed valence oxidase showed enhancement of relaxation by a nearby paramagnetic center, most likely heme a.     

Amoeboid locomotion of Acanthamoeba castellanii with special reference to cell-substratum interactions

The amoeboid locomotion of Acanthamoeba castellanii has been studied by observation of individual cells moving on a planar glass substratum. Cell-substratum interactions involved in traction have been observed by reflexion interference microscopy. A variable part of the ventral surface of A. castellanii formed a protean platform, the 'associated contact', from which filopodia were subtended; these established stable, focal adhesions (approximately 0.4 micron diameter) on the substratum beneath. Surprisingly, acanthopodia, a prominent feature of this protozoon, did not play an obvious role in traction. The dimensions of the cell-substratum gap in the associated contact could be modulated by the concentration of ambient electrolyte. Dilution of electrolyte from 50 mM-KC1 to 2mM resulted in (i) an increase in the cell-substratum gap, (ii) a marked decrease in cell motility, (iii) reduced cell adhesion to glass.     

Steps in the stabilization of newly packaged DNA during phage P22 morphogenesis

The protein products of three adjacent P22 genes, 4, 10 and 26, are required for the stabilization of DNA newly packaged into P22 phage capsids. We have isolated unstable DNA containing capsids from cells infected with mutants defective in these genes. All three classes could be converted into mature phage in vitro, confirming that they represent intermediates in particle maturation. The first of the three proteins to add to the newly filled capsids is gp4, followed by gp10 and gp26. The active form of gp4 sediments at 3 S, while the active forms of both gp10 and gp26 sediment at 5 S. These soluble subunits appear to polymerize onto the newly filled capsids to form the neck of the mature phage, the channel for DNA injection. Since gp4 is the first protein to act after DNA packaging, the unstable DNA containing capsids from 4- -infected cells must represent the direct product of the packaging of DNA into procapsids. The major fraction of these capsids lost activity with a half-life of 1.1 minutes at 23 degrees C, though they were much more stable at 0 degree C. Electron microscopic observations indicated that the loss of activity was due to the DNA exiting from the incomplete capsids. The marginal stability of the condensed DNA molecules within capsids is consistent with models of ATP-driven condensation and spontaneous DNA ejection. The basis of the stability of these highly condensed molecules remains to be determined.     

O2 delivery to contracting muscle during hypoxic or CO hypoxia

The consequences of a decreased O2 supply to a contracting canine gastrocnemius muscle preparation were investigated during two forms of hypoxia: hypoxic hypoxia (HH) (n = 6) and CO hypoxia (COH) (n = 6). Muscle O2 uptake, blood flow, O2 extraction, and developed tension were measured at rest and at 1 twitch/s isometric contractions in normoxia and in hypoxia. No differences were observed between the two groups at rest. During contractions and hypoxia, however, O2 uptake decreased from the normoxic level in the COH group but not in the HH group. Blood flow increased in both groups during hypoxia, but more so in the COH group. O2 extraction increased further with hypoxia (P less than 0.05) during concentrations in the HH group but actually fell (P less than 0.05) in the COH group. The O2 uptake limitation during COH and contractions was associated with a lesser O2 extraction. The leftward shift in the oxyhemoglobin dissociation curve during COH may have impeded tissue O2 extraction. Other factors, however, such as decreased myoglobin function or perfusion heterogeneity must have contributed to the inability to utilize the O2 reserve more fully.