Tandem constructs: preventing the rise of superweeds.

Transgenic crops may interbreed with nearby weeds, increasing their competitiveness, and may themselves become a 'volunteer' weed in the following crop. The desired transgene can be coupled in tandem with genes that would render hybrid offspring or volunteer weeds less able to compete with crops, weeds and wild species. Genes that prevent seed shatter or secondary dormancy, or that dwarf the recipient could all be useful for mitigation and may have value to the crop. Many such genes have been isolated in the past few years.     

Low intraspecific competitive fitness in a triazine-resistant,nearly nuclear-isogenic line of Brassica napus

The maternally-inherited triazine-resistant biotypes that have appeared usually have had a much reduced competitive fitness. As such studies did not use nuclear isogenic material, we tested rapeseed cv. Regent that had had triazine resistance introduced from Brassica campestris and was then extensively backcrossed to cv. Regent. Seeds of each biotype were alternated at 5-cm spacing to ascertain competitive fitness and various growth parameters were followed. The fresh weight, dry weight, number and weights of siliques (seed pods) and yield of seed of the interplanted triazine-resistant biotype were all less than one-third of the susceptible biotype.     

Metabolism of lignin related aromatic compounds by Aspergillus japonicus

Archives of Microbiology - Aspergillus japonicus metabolizes a wide variety of aromatic compounds, some of them resulting from lignin degradation. The efficient conversion of such compounds is...     

Elevated riboflavin requirement for postphotoinductive events in sporulation of a trichoderma auxotroph

A riboflavin auxotroph of Trichoderma required more riboflavin for blue-light-induced conidiation than for growth. Colonies transferred after illumination from 0.2 micromolar (limiting conidiation, not growth) to 3.5 micromolar riboflavin (nonlimiting), responded the same as those grown at 3.5 micromolar. The additional riboflavin is therefore not required as a photoreceptor. The data do not rule out the hypothesis that cryptochrome(s) is/are flavin(s).     

Synthesis and processing of RNA in Lemna: Characterization by gel electrophoresis

The synthesis and processing of rapidly labelled RNAs from Lemnaperpusilla 6746 was followed by polyacrylamide electrophoresis,as the first step in a study of the changes which occur withenvironmental changes. Two RNAs with high apparent molecularweights of 2.8 M and 2.3 M were detected. Time-course studyresults were consistent with the idea that the 2.8 M was cleavedto form 2.3 M RNA and "excess" RNA with a molecular weight of0.5 M. The latter had a far lower turnover than the 2.3 M RNA.Another rapidly labelled RNA which has not been described beforein plants, had an apparent weight of 1.2 M. This was followedby labelling the 1.4 M component, then the light rRNA (0.7 M),and finally the heavy rRNA (1.3 M). A relatively large amountof high molecular weight, polydisperse RNA was synthesized understeadystate conditions. Incubation of plants on distilled water reduced synthesis of1.2 M RNA, while other components were less affected. The processingof rRNA precursors was also slowed. (Received December 11, 1972; )     

Somatic hybridization of an atrazine resistant biotype of Solanum nigrum with Solanum tuberosum

Summary Representative regenerated clonal plants from protoplast fusion of Solanum tuberosum L. and an atrazine resistant biotype of S. nigrum L. were studied to ascertain which plastomes each clone contained. DNA was isolated from fractionated chloroplasts, restricted with DNAases XHO-1, BGL-1, PVU-2 and BAM-H1, and the fragments separated by agarose gel electrophoresis for comparison. No difference could be found between resistant and susceptible biotypes of S. nigrum with all four enzymes. XHO-1, BGL-1, BAM-H1 differentiated between S. nigrum and S. tuberosum. All atrazine resistant regenerants, despite plant morphology, had the plastid DNA pattern of S. nigrum while all sensitive ones resembled S. tuberosum, even the subclone 38S having a S. nigrum morphology and chromosome number.     

Removal of pectins from methylated rRNA and precursors by LiCl

The methyl group of radioactive methylmethionine is incorporated preferentially into pectin, a methylated polysaccharide, which massively contaminates RNA preparations. This makes it difficult to discern the methylated RNA species of growing tissues of higher plants. A method for the extraction of pectic substances from RNA preparations of plants is described. Ethanol precipitates containing RNA are suspended in 2m lithium chloride (LiCl) and the pectin is removed with the supernatant after centrifugation. LiCl purification of RNA from Vicia faba root meristems allows the direct identification on polyacrylamide gels of methylated RNA species labeled with [³H]methyl methionine. Presumpive precursors of rRNA which fall into the range of apparent molecular weights of 2.7–2.9, 2.2–2.4, 1.4–1.5, and 0.72–0.75 × 10⁶ are shown to be methylated, in addition to the methylation of the fully processed rRNAs of MW 1.3 and 0.7 × 10⁶.     

Engineering hypervirulence in a mycoherbicidal fungus for efficient weed control

Agents proposed for biocontrol of major weeds in arable row-crop agriculture have not met expectations because an evolutionary balance has developed between microorganism and weed, even when the mycoherbicide is used inundatively at very high levels (>10(4)spores/cm<(2)). Sufficient virulence can be achieved by transferring genes to the microorganism, tipping the evolutionary balance. Virulence was increased ninefold and was more rapidly effected; furthermore, the requirement for a long duration at high humidity was decreased by introducing NEP1 encoding a phytotoxic protein, to an Abutilon theophrasti-specific, weakly mycoherbicidal strain of Colletotrichum coccodes. The parent strain was at best infective on juvenile cotyledons of this intransigent weed. The transgenic strain was lethal through the three-leaf stage, a sufficient time window to control this asynchronously germinating weed. Strategies of coupling virulence genes with fail-safe mechanisms to prevent spread (due to broadened host range) and to mitigate transgene introgression into crop pathogens could be very useful in the biocontrol of major weeds in row crops.     

The paucity of plants evolving genetic resistance to herbicides: Possible reasons and implications

Resistances to antibiotics and pesticides except herbicides rapidly developed following their introduction. Despite repeated use of herbicides only a few cases of acquired genetic resistance have been reported. By extrapolation from analogous situations, it is suggested that this is due to a combination of low selection pressure of most herbicides, lower fitness of resistant weed strains in the absence of herbicide, the ability of herbicide thinned strands of susceptible weeds to produce relatively more seeds, as well as to the large soil reservoir of susceptible weed seeds. The few reported cases of resistance are to persistent, high selection pressure herbicides supporting our contentions.