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Some species of the genusEchinochloaare troublesome weeds in rice fields. The taxonomy of this genus leads to confusion in many cases due to its great morphological diversity. Because of the differential sensitivity to the herbicide quinclorac shown byEchinochloaspp., it was necessary to assess the botanical and molecular characterization of this weed.Echinochloa colonum, E. oryzoides, andE. oryzicolawere very susceptible to quinclorac treatment; by contrast,E. crus-galliandE. hispidulashowed some degree of natural tolerance. Physiological and molecular results agreed with the botanical classification of the genusEchinochloain Flora Europea. The importance of these results is due to yield losses produced by the infestation ofEchinochloaand the need for a strategy forEchinochloamanagement depending on the distribution of theEchinochloaspecies.

Flow cytometry was used to provide a rapid and accurate assessment of electroporation-induced uptake of macromolecules into plant protoplasts. Rice protoplasts were electroporated in the presence of fluorescein isothiocyanate-conjugated dextran (FITC-dextran). After washing, the protoplasts were resuspended in a solution containing propidium iodide which intercalates with DNA, but which is excluded by an intact plasma membrane. Electroporation in the presence of FITC-dextran gave rise to populations of protoplasts that fluoresced green or yellow due to the presence of non-conjugated FITC. Non-viable protoplasts fluoresced red because of their inability to exclude propidium iodide molecules. Flow cytometry was used to resolve and quantify these protoplast populations and thus identify optimal conditions for macromolecule uptake. A direct relationship was observed between FITC-dextran uptake and transient gene expression following plasmid uptake. Thus, simultaneous electroporation of protoplasts with foreign DNA and FITC-dextran followed by fluorescence activated cell sorting may permit partial selection of transformed cells and so reduce the need for a selectable marker.

Design details for a high-speed digital cross correlator for the Owens Valley Millimeter Array are presented. The correlator uses ECL gate arrays operating at a 256-MHz clock rate to compute the real cross-correlation function for up to four independent frequency bands with bandwidths in the range of 2-128 MHz. For each baseline in the array the correlator provides 512 lags, giving a spectral resolution of 2 MHz at the maximum bandwidth. Two-bit digitization is used, and this results in a sensitivity of 0.88 relative to a perfect analog correlator. >

Restriction analysis of mitochondrial (mt) DNA from 3-month-old callus cultures of the cytoplasmic male sterile rice, V41A, which contains S2 or "wild abortive" cytoplasm, and its fertile maintainer, V41B, showed the same BamHI restriction profiles as mtDNA from the corresponding leaf material. Similarly, mtDNA of rice (var. Taipei 309) from leaves, a 2-month-old cell suspension (T3MS2/A), a totipotent suspension (T3MS) and a 19-month-old suspension, which had lost its protoplast regeneration ability (LB3), showed indistinguishable BamHI restriction profiles. However, clear differences in mtDNA restriction profiles were observed between LB3 and a 30-month-old suspension culture of Taipei 309 (LB1), which appeared to reflect substantial changes in the relative abundance of specific DNA sequences. Hybridisation of a maizecoxII gene probe to blots of restricted mtDNA confirmed that, while the relative abundance of certain mtDNA sequences was preserved during long-term tissue culture of rice, major changes in abundance were observed with other sequences.

Echinochloa spp. are weeds of maize and rice that cause serious yield losses and require to be controlled. Two main herbicides used in these crops are atrazine and quinclorac. Triazine herbicides inhibit photosystem II and quinclorac enhances ethylene production in susceptible plants (Devine et al., 1993; Grossmann and Kwiatkowski, 1993). Development of resistance to atrazine in weeds is well documented (Gronwald, 1994), but quinclorac resistance has not been reported in Echinochloa spp. We describe the characterisation of atrazine and quinclorac resistance in Echinochloa spp. Classification and identification of Echinochloa spp. is notoriously difficult but establishing the identity of herbicide susceptible/wild biotypes of Echinochloa is essential when undertaking comparative mode of action studies with putative herbicide-resistant biotypes of the same species. Accordingly, we employed molecular techniques to make genetic comparisons of test biotypes of Echinochloa, free from the vaguaries of morphological variation and subjective assessment (Carretero, 1981).

It is worth attempting a definition of molecular ecology. At the outset we may consider molecular ecology to be the application of molecular techniques to solve problems in ecology. Still, this definition is rather narrow and it may be more satisfactory to consider molecular ecology as a new discipline which supports the interests of plant ecologists, population biologists, geneticists, physiologists, biochemists and molecular biologists. It is via a multidisciplinary approach to problem solving in plant biology that molecular ecology is likely to continue to expand its activities and achievements. Presently, in molecular ecology, molecular approaches are undertaking studies on biodiversity, taxonomic identities, interspecific gene flow, assessment of kinship relationships, analysis of mixed genome samples and the production of specific diagnostic probes. The object of this review is to describe the latest molecular techniques with examples of their use for studies on herbicide resistance.

Straightforward explanations of the theory and methods associated with the now widely used molecular/recombinant technologies are not easy to find in the literature. Current research articles in the field rarely explain the theory behind the techniques utilized, or quote the original publication, and this makes life difficult for the student or researcher who is new to the subject. In this chapter, an attempt is made to explain, in relatively simple terms, how nucleic acids can be isolated, analysed and utilized for the genetic manipulation of plants. This serves to provide explanations of the terminology used in the following chapters and the reader is encouraged to refer back to this chapter as necessary. Only a few key papers relating to specific techniques are quoted in Chapter 1, and these citations, along with the suggestions for further reading, are for readers who require more than what is, essentially, an outline and overview of the more widely used tools and techniques.

Wild species within the genus Oryza and other related graminaceous species offer sources of important genes conferring traits such as salinity tolerance and resistance to pests and diseases (Swaminathan 1986). Since many of the wild species in question are sexually isolated from rice, protoplast fusion offers a unique opportunity to develop previously unobtainable hybrids and cybrids. Furthermore, direct interactions of protoplasts with recombinant plasmids can lead to the incorporation and expression of specific-gene constructs.

The Caltech Millimeter Array has numerous sensors built into it to detect when components fail to go out of tolerance. A fault handling scheme has been developed for the array that allows complete tracking of system faults and control of the effect that faults have on the data. The fault handling strategy is designed around the inter-dependent nature of the components in the array and uses that information to isolate faults. It is flexible enough to function effectively under the many telescope configurations that are used during normal observing. This paper discusses the need for such a fault handling system and the design and implementation of the one used in the Caltech Millimeter Array.

The telescopes and signal processing systems of the Owens Valley Millimeter Array are considered, and improvements in the sensitivity and stability of the instrument are characterized. The instrument can be applied to map sources in the 85 to 115 GHz and 218 to 265 GHz bands with a resolution of about 1 arcsec in the higher frequency band. The operation of the array is fully automated. The current scientific programs for the array encompass high-resolution imaging of protoplanetary/protostellar disk structures, observations of molecular cloud complexes associated with spiral structure in nearby galaxies, and observations of molecular structures in the nuclei of spiral and luminous IRAS galaxies.