California Agriculture, August 1982
Volume 36, Number 8
Special Issue: Genetic Engineering of Plants
peer-reviewed research articles
1. Genetic engineering: The new techniques and their potential
by Carole P. Meredith
Not available – first paragraph follows: In one sense, genetic engineering of plants is really nothing new. Since the beginnings of agriculture, when crop species were first domesticated, people have modified plants to suit their needs. In saving seed from only their best plants, ancient farmers practiced genetic selection. Systematic and scientific plant breeding began about 200 years ago and has evolved into a powerful technology. Crop plants are now deliberately improved through controlled pollinations to achieve defined objectives. But although genetic engineering is in a way as old as agriculture itself, in current usage the term refers collectively to a number of very new techniques for changing plants genetically- techniques that do not rely on pollination, but instead involve genetic manipulations at the cellular and molecular levels. This technology promises to be a powerful adjunct to modern plant breeding.
2. Plant breeding: Successes and limitations
by Paulden F. Knowles
Not available – first paragraph follows: Since its beginning, the University of California has been actively involved, directly or indirectly, in traditional plant breeding programs, including germplasm collection and evaluation, development of genetic stocks for use in plant breeding programs, development of finished varieties, new crop development, and training of plant breeders. Such plant breeding is actually a form of genetic engineering. It involves management of genes and their carriers, the chromosomes.
3. Plant genes: Understanding mechanisms of gene expression
by William E. Timberlake, Robert B. Goldberg
if and hup genes/valentine; Maize anaerobic genes/Freeling; Leaf protein synthesis/Taylor et al.; Storage protein genes/Breidenbach, Goldberg, Taylor
‘Nif’ and ‘hup’ genes
by Raymond C. Valentine
Not available – first paragraph follows: All crops need nitrogen for growth. Nitrogen fixation—the enzymatic conversion of atmospheric nitrogen gas into a form available to the plant—is a trait that only some bacteria have evolved.
Maize anaerobic genes
by Michael Freeling
Not available – first paragraph follows: A higher plant has between one and ten million genes, each of which holds information that specifies the structure of a product RNA and, often, a protein. In addition, each has nucleotide sequences involved in recognizing on-off signals. Using recombinant DNA technology, pieces of DNA carrying one or a few genes can now be removed from practically any organism, replicated in microorganisms, and then studied at the level of nucleotide sequence and sequence arrangement. A few genes from higher plants are now being analyzed at this level, and alcohol dehy-drogenase-1 (Adhl) in maize, the gene studied most intensively in my laboratory, is one of them.
Leaf protein synthesis
by William C. Taylor, Timothy Nelson, Mark Harpster, Lino Fragoso, Belinda Martineau, Steven Mayfield, Judy Yamaguchi
Not available – first paragraph follows: The most abundant proteins in the leaves of higher plants perform specialized functions in photosynthesis. Many of these proteins are located within the chloroplast. Some are encoded by the chloroplast genome, and some by the nuclear genome. The synthesis of several of these proteins has been shown to be controlled by light.
Storage protein genes
by R. William Breidenbach, Robert B. Goldberg, Scott E. Taylor
Not available – first paragraph follows: Interest in the developmental and molecular biology of the proteins that accumulate as reserves in seeds has become keen in recent years. Although most plant cells contain large numbers of different proteins, each present only in small quantities, food chemists, using criteria of size and solubility, long ago found that most of the protein in seeds of the soybean and other legumes appears to be composed of only a few different kinds. In the late 1960s we recognized that, if this were true, it was likely that a correspondingly small number of different kinds of messenger RNA (mRNA) molecules encoded to direct the synthesis of the storage proteins would also be present in higher concentrations in seed tissue cells. Higher concentrations of specific mRNA's would make it much easier to learn how these intermediaries between genes and their protein products are modulated and, in turn, how they control the rates of protein production.
4. Gene vectors: Crossing natural barriers to genetic manipulations
by Clarence I. Kado
Not available – first paragraph follows: The potential application of genetic engineering to agriculture has been predicted to be limitless. Such enthusiasm, however, should be expressed judiciously, because much information is needed before we can apply the methods to the agricultural industry. The potentials of this technology are apparent, but several important natural barriers need to be crossed before progress can be achieved. A primary limitation is the need to find an efficient means of introducing foreign genes (or DNA) into plant cells. Since 1978, U.C., Davis, scientists have devised several ways by which this can be accomplished. Foreign genes may be introduced as purified DNA directly into plant cells through the use of protoplasts (plant cells freed of their rigid cell wall material). Or these genes can be spliced to another DNA molecule, which serves as a vector. These gene vectors may be plant DNA viruses, bacterial and yeast plasmids, plant organelle DNA, and transposition elements from lower and higher cells.
The Ti plasmid
by John W. Einset
Not available – first paragraph follows: Crown gall, a bacterial disease of dicots and gymnosperms, is characterized by tu-morous overgrowths on infected plants. Because the disease involves gene transfer from a bacterium to a plant cell and subsequent expression of new characteristics, crown gall has tremendous potential as a vector for genetic manipulation of important agricultural crops.
DNA plant viruses
by Robert J. Shepherd, Stephen D. Daubert, Richard C. Gardner
Not available – first paragraph follows: A remarkably simple genetic system for study of DNA multiplication and gene expression in plants is provided by DNA plant viruses. These viruses have only a half-dozen or so genes that are believed to be regulated in the same way as other plant genes. The DNA replicates in nuclei and may be associated with nuclear proteins (histones) in the same way as plant genetic material. Thus, the virus provides a small-scale, readily manipulated model for gene expression.
5. Somatic cell genetics: Manipulating plants through single-cell techniques
by Z. Renee Sung, Ian J. Furner
Protoplast regeneration/Engler, Grogan; Regeneration of plants/Murashige; Somaclonal variation/Orton; Cell mutagens/G. E. Jones
by Dean E. Engler, Raymond G. Grogan
Not available – first paragraph follows: Plant cells without walls (protoplasts) can be isolated from leaves by a process of enzy-matically digesting away the middle lamellae between cells and the cell walls. Tremendously large numbers of protoplasts can be isolated from a single leaf; yields are typically two to four million protoplasts per gram of leaf tissue. Development of techniques and procedures causing isolated protoplasts to reform their walls, proliferate, and regenerate into whole plants is essential for the utilization of the new genetic technology.
Regeneration of plants
by Toshio Murashige
Not available – first paragraph follows: Reporting his pioneering experiments on plant cell culture to the German Academy of Science in 1902, G. Haberlandt predicted that someday “in this way one could successfully cultivate embryos from vegetative cells.” Had IAA and kinetin been at his disposal, Haberlandt might have realized his prediction, and there is no telling how much further plant cell culture might be today.
by Thomas J. Orton
Not available – first paragraph follows: Successful application of in vitro cell and tissue culture technology to crop improvement hinges on the ability to regenerate plants of known genetic constitution. For example, when using cell or tissue culture as a means of cloning, or amplifying numbers of plants for field or seed production, it is essential that regenerated “copy” plants be genetically similar or identical to the original. Alternatively, when using this approach to develop a new improved variety, a selection scheme would be devised that would theoretically find only cells with altered genotypes at loci whose function bears on a desired character, but which were genetically identical to the original tissue donor in all other respects. However, some of the earliest research papers in this area have documented the existence of spontaneous genetic variability in both cultured cells and corresponding regenerated plants. A useful label, “somaclonal” variation, has recently been advanced for this phenomenon—“soma,” occurring in somatic tissues as opposed to sexual progeny, and “clonal,” expressed as differences among and within clones.
by Gary E. Jones
Not available – first paragraph follows: Realizing the full potential of plant somatic cell genetic techniques will depend on development of methods for isolating a wide variety of cultured cell strains with characteristics different from those of cells in the original cultures. To isolate such variant cell strains, techniques well known in microbial studies will have to be applied to cultured plant cell systems.
6. Innovations in plant breeding: New concepts in whole-plant genetics
by Thomas J. Orton
Wheat-barley hybrids/Jan, Qualset, Dvorak; Induced chromosome pairing/Irvine, McGuire; Hybridization in Strawberries/Bringhurst, Voth; Pollen selection/R. A. Jones; Embryo callus hybrids/Thomas, Pratt; Isozymes in plant breeding/Rick
by Chao-Chien Jan, Calvin O. Qualset, Jan Dvorak
Not available – first paragraph follows: Some crop plants have simple inherited characters that would be desirable if transferred to another crop. Our current work on transfer of resistance to the barley yellow dwarf virus (BYDV) from barley to wheat is an example of a simple modification to the embryo culture method that produced hybrid plants from two difficult-to-hybridize species.
Induced chromosome pairing
by Jonathan Irvine, Patrick McGuire
Not available – first paragraph follows: Success in hybridizing wild with cultivated species ultimately depends on the ability of the alien chromosomes to pair and recombine with the chromosomes of the crop species at meiosis. In bread wheat, pairing and thus recombination normally occur only between identical or homologous chromosomes and not, unfortunately, between a wheat chromosome and an alien chromosome. However, increasing knowledge of the components of the genetic system controlling pairing has made it possible to manipulate them to achieve pairing between nonhomologous chromosomes. A major advantage of such induced pairing is that it usually occurs between closely related but not homologous chromosomes—termed homoeologues. Recombination of genetic material between homoeologues is likely to result in genetically more balanced chromosomes than if recombination were between unrelated chromosomes.
Hybridization in strawberries
by Royce S. Bringhurst, Victor Voth
Not available – first paragraph follows: Polyploidy is important in strawberries, because only in the end products found in nature (octoploids Fragaria chiloensis and F virginiana) were the necessary genes found, organized, and conserved in such a way as to make possible the relatively rapid breeding of the modern large-fruited strawberry cultivare. Lower ploidy levels are of interest, because they tend to be highly specialized to specific environments, and many of the traits they carry as a result may be useful in the cultivare of the future, if they can be introduced into the octoploids.
by Richard A. Jones
Not available – first paragraph follows: Conventional plant breeding has steadily improved food production efficiency, but in the process, crops have been selected for genetic uniformity and adaptation to relatively optimal environments. Environmental stresses at particularly vulnerable stages during crop development may severely diminish productivity. Adaptation of crops by genetic means to suboptimal temperatures is among the neglected areas of potentially useful research and development. Sensitivity to chilling in many important crop plants limits their climatic distribution for economic production. Even in areas normally suited to these crops, this sensitivity causes losses through injury suffered from sporadic low temperatures.
Embryo callus hybrids
by Bruce R. Thomas, David Pratt
Not available – first paragraph follows: Hybridization between cultivated species and related wild species has been of great value for cultivar improvement. Genes that enhance the survival of the wild species by providing disease or insect resistance, salt tolerance, cold tolerance, and the like, often confer the same trait on the cultivar to which they are transferred. Fertility barriers restrict the number of wild species that can contribute genes to any particular cultivated species through normal sexual crosses, but these fertility barriers can often be overcome through the use of special procedures.
Isozymes in plant breeding
by Charles M. Rick
Not available – first paragraph follows: Isozymes are multiple molecular forms of an enzyme derived from a tissue of an organism. They are usually separated when an electric charge causes their migration through a gel, and they are visualized when the gel is placed in a solution of the proper substrate for the enzyme and the end product of the reaction is stained. This procedure results in discrete bands, whose positions in the gel are determined by the charge and molecular weight of the isozymes. The preparation is usually a simple extract, sometimes just the unmodified juice obtained by crushing the plant sample.
7. Agricultural applications: Integrating conventional and molecular genetics
by Calvin O. Qualset
Developing salt tolerance/Rains; Genetic disease resistance/Gilchrist, Keen; Enhancing nitrogen fixation/Phillips, Williams; Herbicide tolerance/Thomas, Pratt; Improving woody crops/Durzan; Cloning coast redwoods/Libby; Genetic alteration of yeast/Snow
Developing salt tolerance
by D. William Rains
Not available – first paragraph follows: Salinity and its potential influence on plant productivity can be managed either by physically manipulating the environment in which the plant grows or by biologically manipulating the plant to reduce the harmful effects of excess salt. The concept of biological manipulation is based on the observation that salt tolerance appears to be genetically controlled and that plants vary widely in their sensitivity to high levels of salt.
Genetic disease resistance
by David G. Gilchrist, Noel T. Keen
Not available – first paragraph follows: The most widely used plant disease control method has been the incorporation of single, usually dominant, genes for disease resistance into cultivated plants. In some cases, disease control also has been accomplished by withdrawal from plants of certain dominant alleles conferring vulnerability to attack by pathogens that produce specific toxins. By either approach, genetic resistance affords the only practical control strategy in most major crops.
Enhancing nitrogen fixation
by Donald A. Phillips, Larry E. Williams
Not available – first paragraph follows: Production of ammonia from atmospheric nitrogen by the Rhizobium-legume symbiosis offers opportunities for genetic improvement of both Rhizobium bacteria and host legume. Root nodules formed by rhizobia are the organs responsible for nitrogen fixation. California crops that might benefit most directly from such improvements are alfalfa, clover, common beans, lima beans, garbanzos, and blackeye peas. Additional nitrogen fixed, but not used, by those plants would be bound in an organic form that could carry over to benefit subsequent crops.
by Bruce R. Thomas, David Pratt
Not available – first paragraph follows: Isolation of mutants tolerant or resistant to herbicides may become a valuable application of cell culture techniques. Every herbicide is restricted in use by the number of crops it damages or kills. Tolerant mutants of various plant species could broaden the usefulness of currently available herbicides. The advantages of searching for this kind of mutant using cell cultures are (1) accuracy and uniformity of herbicide exposure in culture, (2) the ease with which billions of cultured cells may be screened for ability to grow in the presence of the herbicide, and (3) the potential (as yet unrealized for most crop species) for easy isolation of recessive mutants using haploid cell cultures.
Improving woody crops
by Don J. Durzan
Not available – first paragraph follows: Genetic engineering and cell and tissue culture have already begun to influence the breeding and vegetative propagation of superior rootstocks and woody perennial trees for efficient forestry systems and urban plantings. In our laboratory, hard-to-root biomass species such as Douglas-fir, white sprace, and jack pine have been cloned through micropropagation. The American elm has been propagated from cell suspension cultures. With similar methods being used for fruit and nut trees, valuable root-stocks of Prunus and Pistacia species are at the point of being cloned and modified to capture the maximum genetic variation available. Currently, a considerably smaller proportion is obtained through conventional selection and breeding.
Cloning coast redwoods
by William J. Libby
Not available – first paragraph follows: In a redwood breeding program, time is a problem. Between germination (or planting) and harvest as a renewable source of wood, a redwood must survive and grow in a minimally managed environment for three to eight decades. Trees in park and amenity plantings may be expected to grow for centuries, or even millenia. Redwood foresters thus, and properly, tend to be conservative.
Genetic alteration of yeast
by Richard Snow
Not available – first paragraph follows: Yeast is one of the major industrial microorganisms, used in the brewing, baking, and wine industries. Most improvements in wine making have resulted from better grape varieties (such as Ruby Cabernet developed at University of California, Davis) or from improvements in fermentation practices. Not much attention has been given to planned improvement of the other organism on which the wine industry is based, the wine yeast. Yeast has many favorable characteristics making it one of the best organisms to use for basic genetics research, and as a result, our genetic understanding of it has reached an extremely high level.
editorial, news, letters & science briefs
California agriculture and genetic engineering
by Lowell N. Lewis
The role of the university in genetic engineering
by James M. Lyons, Charles E. Hess
Not available – first paragraph follows:From a cursory glance at university and industry responsibilities, it would appear that the roles are clearly different, easily distinguished from one another. Unfortunately, this is not so. In fact, some argue there should not be a clear distinction between the two, citing the current strength of the Japanese economy as resulting from close association of academic and industry research. At the other extreme, some voice concern over alleged or potential domination of research priorities by the private sector, fearing that free and open exchange of scientific ideas will be stifled because of the focus on proprietary needs in a competitive market.