Agrobacterium and plant genetic engineering

Erratum

Agrobacterium and plant genetic engineering     

Insect fungal symbionts: A promising source of detoxifying enzymes

Summary Many species of insects cultivate, inoculate, or contain symbiotic fungi. Insects feed on plant materials that contain plant-produced defensive toxins, or are exposed to insecticides or other pesticides when they become economically important pests. Therefore, it is likely that the symbiotic fungi are also exposed to these toxins and may actually contribute to detoxification of these compounds. Fungi associated with bark beetles, ambrosia beetles, termites, leaf-cutting ants, long-horned beetles, wood wasps, and drug store beetles can variously metabolize/detoxify tannins, lignins, terpenes, esters, chlorinated hydrocarbons, and other toxins. The fungi (Attamyces) cultivated by the ants and the yeast (Symbiotaphrina) contained in the cigarette beetle gut appear to have broad-spectrum detoxifying abilities. The present limiting factor for using many of these fungi for large scale detoxification of, for example, contaminated soils or agricultural commodities is their slow growth rate, but conventional strain selection techniques or biotechnological approaches should overcome this problem.Presented at the Symposium on Fungal Detoxification at the 48th Annual Meeting of the Society for Industrial Microbiology, Philadelphia, PA, August 4–9, 1991.     

玉米未成熟胚乳愈伤组织和器官的发生及其倍性变化的初步研究

本试验在附加和不附加外源激素的MS培养基上,均得到了玉米未成熟胚乳愈伤组织。愈伤组织在附加外源激素的MS培养基上达到器官分化,获得了发育正常的和许多畸形的胚乳植株。所得到的愈伤组织细胞和植株根尖细胞染色体数目和倍性是不稳定的,二者有相同的趋向,其中有整倍体的细胞(2n=10,20,30,40,50),也有各种非整倍体的细胞(2n=5—49)。     

Structural Characteristics of the Short-Tail Fibers of T4 Bacteriophage

The characteristics of pure preparations of short-tail fibers of bacteriophage T4 have been studied in the optical and electron microscope. Three main structures were observed: 1) spheres of 8.1 nm diameter; 2) fibers 43 nm long and 3.8 nm thick; and 3) fibers 54 nm long and 3.2 nm thick. Both types of fibers exhibited a regular beaded appearance. The 43-nm fibers were the most abundant structure. During the process of purification of the short-tail fibers, the formation of aggregates was observed each time the material containing the short-tail fibers was dialyzed against saline solutions. These aggregates became increasingly fibrous (as observed in the optical microscope) as the material used was increasingly enriched in short-tail fibers. Finally, most of the aggregates were of the fibrous type when they were formed from a purified preparation of short-tail fibers. In the electron microscope, it was found that the filamentous aggregates were organized in well-defined bundles. The amino acid composition of the highly purified short-tail fibers was also determined. Among the known fibrous proteins, the ones that most resemble the amino acid composition of the short-tail fibers are actin and fibrinogen. These observations are discussed in relation to the T4 short-tail fiber structure and their localization on the hexagonal baseplate of the T4 tail structure.     

A phylogenetic analysis of the land plants

Phylogenetic systematics (cladistics) is a theory of phylogeny reconstruction and classification widely used in zoology. Taxa are grouped hierarchically by the sharing of derived (advanced) characters. The information is expressed in a cladogram, a best estimate of a phylogeny. Plant systematists generally use a phenetic system, grouping taxa on overall similarity which results in many groups being formed, at least in part, on the basis of shared primitive characters.
The methods of phylogenetic systematics are used to create a preliminary cladogram of land plants. The current classification of land plants is criticized for its inclusion of many groups which are not monophyletic.
Objections to the use of phylogenetic systematics in botany, apparent convergences within major groups and frequent hybridization, are shown to be invalid. It is concluded that cladistic analysis presents the best estimate of die natural hierarchy of organisms, and should be adopted by plant systematists in their assessment of plant interrelationships.     

Hormonal mechanisms for differentiation in plant tissue culture

Summary Cells possess extraordinary powers to organize their molecular processes not only to maintain a cell in a given steady state but also to recognize that state during differentiation. Regulation of these organizational forces appears to be under the control of chemical factors, and a hormonal concept of regulation has evolved. Hormones have been considered to act by reacting with a specific target site. This may be part of their mode of action, but I would like to suggest that a hormone enters and becomes part of a total molecular resonance system. In so doing, the entire molecular system of the cell is modified. Of the known plant hormones, the cytokinins, because of their role in experimentally induced cell division and differentiation, serve as a probe of hormonal involvement in differentiation. Cultured somatic cells of tobacco plants can be induced to undergo differentiation by addition of cytokinin and auxin to the medium. Studies of the cytokinin hormones show a series of diverse molecular involvements. The archetype cytokinin, N⁶-(Δ²-isopentenyl) adenosine (i⁶Ado), occurs in some molecular species of tRNA where it plays a vital role in the codon-anticodon interaction of tRNA and m-RNA. i⁶Ado under-goes extensive metabolism in the tobacco tissue. It is either degraded to adenosine or converted to derivatives that possess biological activity. It is perhaps, therefore, more correct to consider the hormone function as being derived from this total metabolic web. The normal somatic cells of tobacco cultures spontaneously change occasionally into an autonomous form that requires no external growth factors. This line of cells synthesizes i⁶Ado. The metabolic web of the hormone-dependent strain can be perturbed by added auxin but such is not the case in the autonomous strain. These data provide some insight into the altered state of cytokinin activity in which a cell line changes into an autonomous form. Curiously, in become independent of the requirement for exogenous cytokinin, the autonomous tissue becomes sensitive to added cytokinin. i⁶Ado also inhibits the growth of lines of mammalian cancer cells grown in culture. Presented in the formal symposium on Information Transfer in Eukaryotic Cells, at the 26th Annual Meeting of the Tissue Culture Association, Montreal, Quebec, June 2–5, 1975.     

基于源-库互反馈的温室青椒坐果时空动态模拟

基于源-库互反馈的温室青椒坐果时空动态模拟     

Cucurbit Powdery Mildew: First Insights for the Identification of the Causal Agent and Screening for Resistance of Squash Genotypes (Cucurbita moschata (Duchesne ex Lam.) Duchesne ex Poir.) in Mendoza,Argentina

The cucurbit powdery mildew (CPM) caused by different fungal species is a major concern for cucurbit crops around the world. In Argentina CPM constitutes the most common and damaging disease for cucurbits, especially for squash crops (Cucurbita moschata). The present study displays initial insights into the knowledge of the disease in western Argentina, including the determination of the prevalent species causing CPM, as well as the evaluation of the resistance of squash cultivars and breeding lines. Fungal colonies were isolated from samples collected in Mendoza province, Argentina. A field trial was also performed to assess the resistance of five squash accessions, including commercial cultivars and breeding lines. The severity of CPM was analyzed and epidemiological models were built based on empirical data. The morphological determinations and analysis with specific molecular markers confirmed Podosphaera xanthi as the prevalent causal agent of CPM in Mendoza. The results od the field trial showed differences in the resistance trait among the squash accessions. The advanced breeding line BL717/1 showed promising results as source of CPM resistance for the future development of open pollinated resistant cultivars, a crucial tool for an integrative control of the disease.