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Ferulate cross-linking of lignin to arabinoxylan contributes to poor cell wall degradability of grass forages. We hypothesized that reduced ferulate ester deposition will result in formation of fewer ferulate cross links and improved degradability. Objectives were to determine if the putative seedling ferulate ester (sfe) maize (Zea mays L.) mutant, selected for reduced ferulate esters in seedling leaves, (i) exhibits reduced ferulate ethers; (ii) alters morphology, yield, and cell wall concentration and composition; and (iii) changes degradability. Four near-isogenic sfe lines and backcrosses to W23 were compared with the inbred W23 in replicated field trials. Leaf blade, sheath, and stem of immature (1-m plant height) and mature (silage) growth stages were analyzed for ferulate esters and ethers, cell wall concentration and composition, and in vitro rumen degradability. The sfe lines were taller and had greater internode cross-sectional area than W23. Plant yield was greater at silage maturity for sfe lines and backcross lines yielded more than sfe. Mature plant parts of sfe lines had lower ferulate ester concentrations than W23. At silage stage sfe lines had less ferulate ethers, small reductions in cell wall concentration, and shifts in composition. Immature samples were inconsistent for cell wall traits and backcross lines were generally intermediate, regardless of maturity. Cell wall degradability was higher for the sfe mutant as hypothesized. Reducing ferulate-mediated cross-linking of lignin to arabinoxylan in the cell walls of maize stover appears to be an effective strategy for improving cell wall degradability, and the sfe mutant may offer an opportunity to identify a gene controlling ferulate deposition in grasses. doi: 10.2135/cropsci2009.04.0191

The use of oat (Avena sativa L.) dwarfing genes in breeding programs to improve lodging resistance has been limited, mainly because of decreases in yield and grain quality in many environments. The objectives of this study were to evaluate the effects of the dominant Dw6, Dw7, and Dw8 dwarfing genes on plant height components and the gibberellic acid (GA) response of the dwarf lines. Plant height components including internode length, panicle length, and panicle exertion were measured in plants of three nondwarf and nine dwarf lines grown in the field at St. Paul in 1992 and 1993. Five experiments were performed in growth chambers to assay the response of nondwarf and dwarf oat genotypes to exogenous GA applied at the seedling stage. The Dw6 gene in line OT207 caused a 34 to 37% reduction in plant height due to the reduction in the length of the three uppermost internodes but not internode number. The 46% reduction in height caused by the Dw7 gene in line NC2469-3 resulted from decreases in both internode number and elongation. The Dw8 gene present in derivatives of seven Japanese lines shortened all internodes but did not affect internode number, reducing plant height by about 50%. The dwarf lines that carry these dwarfing loci are responsive to exogenously added G[A.sub.3], G[A.sub.1] and G[A.sub.20], and thus the mutations appear not to involve disruptions of the conversion of G[A.sub.20] to G[A.sub.1]. The results indicate that different strategies may be needed to adjust for the different plant height component effects of each of the three dwarfing genes for their use in oat cultivar development., THE DEVELOPMENT of shorter cultivars with increased resistance to lodging is of interest in oat breeding. Major dwarfing genes have been used extensively in developing semidwarf wheat (Triticum aestivum L.) [...]

Accelerator mass spectrometer 14C dated stable isotope data from Neogloboquadrina pachyerma in cores raised from the Mendeleyev Ridge and slope provide evidence for significant influx of meltwater to the western Arctic Ocean during the early part of marine oxygen isotope stage 1 (OIS 1) and during several intervals within OIS 3. The strongest OIS 3 meltwater event occurred before ca. 45 ka (conventional radiocarbon age) and was probably related to the deglaciation at the beginning of OIS 3. Major meltwater input to the western Arctic Ocean during the last deglaciation coincides closely with the maximum rate of global sea-level rise as determined from the Barbados sea-level record, demonstrating a strong link between the global record and changes in the central Arctic Ocean. OIS 2, which includes the last glacial maximum, is very condensed or absent in the cores. Abundance and [Delta]13C values for N. pachyderma in the middle part of OIS 3 are similar to modern values, indicating high productivity and seasonal ice-free areas along the Arctic margin at that time. These records indicate that the Arctic Ocean was a source of heat and moisture to the northern polar atmosphere during parts of OIS 3.

A set of oat-maize chromosome addition lines with individual maize (Zea mays L.) chromosomes present in plants with a complete oat (Avena sativa L.) chromosome complement provides a unique opportunity to analyze the organization of centromeric regions of each maize chromosome. A DNA sequence, MCS1a, described previously as a maize centromere-associated sequence, was used as a probe to isolate cosmid clones from a genomic library made of DNA purified from a maize chromosome 9 addition line. Analysis of six cosmid clones containing centromeric DNA segments revealed a complex organization. The MCS1a sequence was found to comprise a portion of the long terminal repeats of a retrotransposon-like repeated element, termed CentA. Two of the six cosmid clones contained regions composed of a newly identified family of tandem repeats, termed CentC. Copies of CentA and tandem arrays of CentC are interspersed with other repetitive elements, including the previously identified maize retroelements Huck and Prem2. Fluorescence in situ hybridization revealed that CentC and CentA elements are limited to the centromeric region of each maize chromosome. The retroelements Huck and Prem2 are dispersed along all maize chromosomes, although Huck elements are present in an increased concentration around centromeric regions. Significant variation in the size of the blocks of CentC and in the copy number of CentA elements, as well as restriction fragment length variations were detected within the centromeric region of each maize chromosome studied. The different proportions and arrangements of these elements and likely others provide each centromeric region with a unique overall structure.

A class of tandemly repeated DNA sequences (TR-1) of 350-bp unit length was isolated from the knob DNA of chromosome 9 of Zea mays L. Comparative fluorescence in situ hybridization revealed that TR-1 elements are also present in cytologically detectable knobs on other maize chromosomes in different proportions relative to the previously described 180-bp repeats. At least one knob on chromosome 4 is composed predominantly of the TR-1 repeat. In addition, several small clusters of the TR-1 and 180-bp repeats have been found in different chromosomes, some not located in obvious knob heterochromatin. Variation in restriction fragment fingerprints and copy number of the TR-1 elements was found among maize lines and among maize chromosomes. TR-1 tandem arrays up to 70 kilobases in length can be interspersed with stretches of 180-bp tandem repeat arrays. DNA sequence analysis and restriction mapping of one particular stretch of tandemly arranged TR-1 units indicate that these elements may be organized in the form of fold-back DNA segments. The TR-1 repeat shares two short segments of homology with the 180-bp repeat. The longest of these segments (31 bp; 64% identity) corresponds to the conserved region among 180-bp repeats. The polymorphism and complex structure of knob DNA suggest that, similar to the fold-back DNA-containing giant transposons in Drosophila, maize knob DNA may have some properties of transposable elements.

The recovery of maize (Zea mays L.) chromosome addition lines of oat (Avena sativa L.) from oat x maize crosses enables us to analyze the structure and composition of specific regions, such as knobs, of individual maize chromosomes. A DNA hybridization blot panel of eight individual maize chromosome addition lines revealed that 180-bp repeats found in knobs are present in each of these maize chromosomes, but the copy number varies from [approximately]100 to 25,000. Cosmid clones with knob DNA segments were isolated from a genomic library of an oat-maize chromosome 9 addition line with the help of the 180-bp knob-associated repeated DNA sequence used as a probe. Cloned knob DNA segments revealed a complex organization in which blocks of tandemly arranged 180-bp repeating units are interrupted by insertions of other repeated DNA sequences, mostly represented by individual full size copies of retrotransposable elements. There is an obvious preference for the integration of retrotransposable elements into certain sites (hot spots) of the 180-bp repeat. Sequence microheterogeneity including point mutations and duplications was found in copies of 180-bp repeats. The 180-bp repeats within an array all had the same polarity. Restriction maps constructed for 23 cloned knob DNA fragments revealed the positions of polymorphic sites and sites of integration of insertion elements. Discovery of the interspersion of retrotransposable elements among blocks of tandem repeats in maize and some other organisms suggests that this pattern may be basic to heterochromatin organization for eukaryotes.

Cores from Northwind Ridge, a high-standing continental fragment in the Chukchi borderland of the oceanic Amerasia basin, Arctic Ocean, contain representatives of every Phanerozoic system except the Silurian and Devonian systems. Cambrian and Ordovician shallow-water marine carbonates in Northwind Ridge are similar to basement rocks beneath the Sverdrup basin of the Canadian Arctic Archipelago. Upper Mississippian(?) to Permian shelf carbonate and spicularite and Triassic turbidite and shelf lutite resemble coeval strata in the Sverdrup basin and the western Arctic Alaska basin (Hanna trough). These resemblances indicate that Triassic and older strata in southern Northwind Ridge were attached to both Arctic Canada and Arctic Alaska prior to the rifting that created the Amerasia basin. Late Jurassic marine lutite in Northwind Ridge was structurally isolated from coeval strata in the Sverdrup and Arctic Alaska basins by rift shoulders and grabens, and is interpreted to be a riftogenic deposit. This lutite may be the oldest deposit in the Canada basin. A cap of late Cenomanian or Turonian rhyodacite air-fall ash that lacks terrigenous material shows that Northwind Ridge was structurally isolated from the adjacent continental margins by earliest Late Cretaceous time. Closing Amerasia basin by con joining seafloor magnetic anomalies beneath the Canada basin or by uniting the pre-Jurassic strata of Northwind Ridge with kindred sections in the Sverdrup basin and Hanna trough yield similar tectonic reconstructions. Together with the orientation and age of rift-margin structures, these data suggest that (1) prior to opening of the Amerasia basin, both northern Alaska and the continental ridges of the Chukchi borderland were part of North America, (2) the extension that created the Amerasia basin formed rift-margin grabens beginning in Early Jurassic time and new oceanic crust probably beginning in Late Jurassic or early Neocomian time. Reconstruction of the Amerasia basin on the basis of the stratigraphy of Northwind Ridge and sea-floor magnetic anomalies in the Canada basin accounts in a general way for the major crustal elements of the Amerasia basin, including the highstanding ridges of the Chukchi borderland, and supports S. W. Carey's hypothesis that the Amerasia basin is the product of anticlockwise rotational rifting of Arctic Alaska from North America.

One important goal in oat (A vena sativa L.) breeding is the development of shorter cultivars; with increased resistance to lodging. Although seven dwarfing genes have been identified in oat, only two genes, Dw6 and Dw7, are still readily available in breeding programs. New sources of dwarfing genes were recently identified in Japan from accessions of A. fatua L. and introgressed into the cultivar `Kanota'. The objectives of this study were to examine seven of these new sources with apparent dominant genes for dwarfness in oat and to determine their usefulness in oat breeding. Allelism tests using analysis of [F.sub.2] populations demonstrated that a new dominant dwarfing gene is present in the Japanese lines and that it is independent of the Dw6 and Dw7 loci. The symbol Dw8 has been assigned to the dwarfing gene found in the Japanese lines. [F.sub.2] populations derived from 17 crosses made among the seven Japanese lines did not segregate for height, indicating that the same dwarfing gene or closely linked genes were present in these lines. Based on the numbers of progenies analyzed from these crosses, we concluded that if there are distinct linked dominant dwarfing genes among the Japanese lines, there would be no more than 20% recombination among them. [F.sub.1] progenies from four Dw8 lines crossed with tall elite lines all segregated in a 3 dwarf: 1 tall ratio. The Dw8 gene, combined with other height modifier genes, may provide new opportunities for breeding for reduced plant height and improved lodging resistance in oat., Oat is an important crop grown in temperate regions of the world and is valuable in human and animal nutrition and for soil conservation (Forsberg and Shands, 1989). One of [...]

Breeding programs in major crops normally restrict the use of parents to those improved for a variety of traits. Gain from utilizing these good x good crosses appears to be high, and improvements are sufficient to encourage continued breeding within narrow gene pools even though each cycle is expected to lead to reduced genetic variability. These finely tuned programs have gradually limited the amount of new diversity introduced into the breeding gene pool. This breeding strategy has led to a genetic gap where there is a large difference in the favorable gene frequency between the improved and unimproved lines and to a narrowing of genetic diversity within elite gene pools. At the same time, evidence has accumulated in plant breeding programs and long-term selection experiments in several organisms that the genome is more plastic and amenable to selection than previously assumed. In the barley (Hordeum vulgare L.) case study reported here, incremental genetic gains were made for several traits in what appears, based on pedigree analysis, to be a narrow gene pool. Given this situation, we call for an examination of the generally held belief that the variation on which selection is based in elite gene pools is provided almost exclusively from the original parents. Classical and molecular genetic analyses have shown that many mechanisms exist to generate variation de novo, such as gene amplification and transposable elements. Accordingly, we put forward the hypothesis that newly generated variation makes an important contribution. We also hypothesize that gene interaction, epistasis, is more important than commonly viewed and that it arises from de novo generated diversity as well as the original diversity., The purposes of this paper are to highlight the importance of genetic diversity, to call attention to the need for a better understanding of genetic diversity from the standpoint of [...]

The mutual coherence function in the source-receiver plane of a reflected Gaussian beam wave from a retroreflector is calculated and analyzed for two refractive-index spectral models and compared with similar results for the case of a plane mirror. Specific expressions are calculated for the mean irradiance and spatial coherence radius based on a Gaussian model for the finite reflector. Results that we obtained here using a modified spectrum with a high wave-number rise and inner scale generally show greater amplitude enhancements in the reflected wave than predicted by the pure power-law spectrum of Kolmogorov. In contrast, a finite outer scale in the spectral model leads to a reduction in the amount of beam spreading caused by turbulence and, in the case of a retroreflector, also leads to a reduction in the peak amplitude enhancement on the optical axis. This last result is in contrast with a plane mirror reflector, in which outer scale effects tend to increase the peak amplitude enhancement on the optical axis. The theory also predicts that, except for small reflectors, the coherence radius associated with a retroreflector can be as much as 1.4 times larger than that associated with a plane mirror, and 1.2 times that of a bistatic configuration for a plane mirror. All calculations are based on weak fluctuation theory and generalized spectral representations that use complex ABCD ray matrices.

Two mathematical models can be used to describe the dynamics of mitosis and DNA endoreduplication during the development of maize endosperm. The kinetics of mitosis during endosperm development are determined using modified standard growth curves. The kinetics of DNA endoduplication are studied with a model consisting of six differential equations representing the progression of nuclei from one DNA content to another.

A study of the specific genetic changes noticed among regenerated plants and their progeny leads to better comprehension of tissue culture-induced variation. A preexisting mechanism for genomic change such as RIP acts as the effector of tissue culture-invoked mutagenesis. This mechanism explains the genomic variation due to stress, factors influencing genomic stability and different methods to inhibit tissue culture regenerant variations.

Methylation changes in 21 maize inbred strain A188 plasmids are investigated using molecular DNA probes. The hypothesis regarding the possible contribution of DNA methylation variation in tissue culture-induced variation is also tested. Chromatin structure is possibly influenced by a decline in methylation. Frequency of the pattern of DNA methylation changes in a few progeny lines is higher than the others as is evident from molecular probes. The probes used are PstI genomic clones and two cDNA clones.

Maize (Zea mays L.) kernels are nutritionally deficient in the amino acids lysine, tryptophan, and methionine. Exogenous lysine-plus-threonine (LT) synergistically inhibits root growth of germinating kernels. We tested the hypothesis that the relative growth of seedlings grown on LT-supplemented and unsupplemented media (LT response) is a function of the relative concentrations of kernel methionine and lysine. Thirty-three genotypes were evaluated for LT response and amino acid composition. The correlation between LT response and the methionine to lysine ratio (M/L) was highly significant (r = 0.59). The root-growth bioassay effectively detects kernels with altered amino acid concentrations.

DNA endoreduplication is the replication of nuclear DNA without subsequent mitosis and cell division, and is believed to be important in maize (Zea mays L.) kernel development. DNA endoreduplication has been shown to be negatively affected by high temperature treatments (HTTs) imposed during early kernel development in maize; however, the specific period of endosperm development at which the process is most sensitive to HTT has not been determined. To address this issue, HTTs (4 and 6 d at 35 ° C) were applied to in vitro-grown maize kernels starting at 4, 6, 8, 10, or 12 d after pollination (DAP). Our approach was to isolate endosperms to determine the effect of elevated temperature on endosperm fresh weight (FW), number of endosperm cells, mitotic index, and DNA endoreduplication. The 4- and 6-d HTTs imposed during the mitotic phase of the endosperm cell cycle (4, 6, and 8 DAP) reduced nuclei number and kernel FW, delayed cell division, decreased average DNA content, and reduced the percentage of nuclei in the 24, 48, and 96 C classes (C is the DNA content of a haploid nucleus in maize). In contrast, delaying the imposition of the 4- or 6-d HTTs until 10 or 12 DAP (during the endoreduplication phase of the endosperm cell cycle) did not affect nuclei number, average DNA content, and DNA endoreduplication compared to the control. Thus, HTTs are most deleterious to DNA endoreduplication, endosperm FW, and nuclei number when applied during the mitotic phase of the endosperm cell cycle. These data further show that 4 to 10 DAP is the period during maize endosperm development that is most sensitive to high temperature, and that prolonged exposure restricts entry of mitotic cells into the endoreduplication phase of the cell cycle., THE MAIZE ENDOSPERM makes 70 to 90% of kernel mass; thus, factors that mediate endosperm development to a great extent also determine grain yield of maize. Previous studies have shown [...]