Showing papers in "Basic life sciences in 1973"

Potential genetic resources in tomato species: clues from observations in native habitats.

Abstract: Interspecific hybridization is playing an increasingly important role in the breeding of improved cultivars of higher plants. Lycopersicon is a good example of a genus in which the cultivated species (L. esculentum Mill.) is being improved in this fashion. The advantages offered by the tomato species for this purpose are: a. All species can be readily grown for experimental purposes, and L. esculentum is widely cultivated under a wide range of environmental conditions. b. Excellent sources of germ plasm now exist in the wild species as well as in modern and primitive cultivars of L. esculentum. c. All of the wild species can be hybridized with L. esculentumn, albeit requiring special aids in certain combinations; fertility and viability of the hybrid generations permit the intended gene transfers. All species have 12 pairs of chromosomes, which are essentially homologous. d. The cultivated species is well known genetically; its chromosomes have been mapped cytologically and genetically; it behaves as a basic diploid (27, 28).

Hormonal regulation of ovalbumin synthesis in chick oviduct.

Abstract: Estrogens and progesterone regulate the differentiation and function of chick oviduct (1–4). Our attention has been focused on hormonal regulation of ovalbumin synthesis, since this single polypeptide comprises 50–60% of the protein synthesized in the fully differentiated oviduct. This feature allows potentially for isolation of the molecular elements involved in specific protein synthesis, including specific polysomes, mRNA, and genes, and an analysis of various regulatory steps between transcription and translation of specific mRNAs, as affected by developmental and hormonal variables.

Factors favoring the formation of androgenetic embryos in anther culture.

Abstract: Guha and Maheshwari in 1966 (4) were the first to obtain haploid embryos in vitro by culturing anthers of Datura. Realizing the wide potential of these interesting results, Dr. J. P. Nitsch started to pursue the work by regenerating whole haploid plants. He obtained haploid Nicotiana in 1967 (3). Such plants, in his view, could be of great interest for plant breeding and genetic studies.

Potential of Cell and Tissue Culture Techniques as Aids in Economic Plant Improvement

Abstract: There are many ways to increase the genetic base of a population for effective selection. Sexual reproduction is nature’s own way of broadening this base. It is the most effective way, but not the only tool available to the breeder. There are ways of bypassing sex. Among these are the use of induced mutations and manipulations at the cellular level. At least six ways are being studied for potential use in manipulating plant systems at the cellular level in order to use them in “asexual plant improvement.” These six approaches are (a) variation in cell and tissue culture, polyploidy, aneuploidy, and chromosomal mosaics; (b) induced mutations; (c) induced polyploidy; (d) haploid plants from pollen; (e) fusion of vegetative cells (intraspecific, interspecific, intergeneric, interfamilial); and (f) transformation. Although the potential of cell and tissue culture for crop improvement could be enormous, caution in being too optimistic prematurely is stressed.

Genetic Regulatory Mechanisms in the Fungi

Abstract: There are at least two interdependent signals controlling the production, by three unlinked structural genes, of the three leucine biosynthetic enzymes of Neurospora (1). Leucine represses the first enzyme, α-isopropylmalate synthetase (the synthetase), the product of the leu-4 cistron. The synthetase catalyzes the production of α-isopropylmalate (α-IPM), which is the second signal—an obligate inducer for the synthesis of α-IPM isomerase (the isomerase) and β-IPM dehydrogenase (the dehydrogenase), specified, respectively, by the leu-2 and leu-1 cistrons. Endogenous α-IPM concentrations respond inversely to endogenous leucine concentration, not only because leucine represses synthetase formation but more importantly because leucine feedback inhibits the catalytic activity of the synthetase (1, 2).

Geographical distribution of cultivated cottons relative to probable centers of domestication in the New World.

Abstract: Most cotton geneticists would agree that the cottons cultivated in the New World separate clearly into two well-defined species, Gossypium hirsutum L. and G. barbadense L. If modern annual forms are excluded from consideration, most forms of G. hirsutum occur in Central America and southern Mexico and most forms of G. barbadense in tropical and subtropical South America. The two species are widely sympatric in the Caribbean area, from northern coastal Colombia through Venezuela and extending through the Lesser and Greater Antilles.

Messenger RNA: its origin and fate in mammalian cells.

Abstract: One of the central problems of eukaryotic cell biology concerns the elucidation of the origin and fate of messenger RNA (mRNA). The mRNAs, which function in the cytoplasm as templates for protein synthesis, are synthesized in the nucleus as part of a heterogeneous population of molecules, the so-called heterogeneous nuclear RNAs (HnRNAs). The HnRNAs range in size from about 5 × 105 daltons to more than 107 daltons, whereas the mRNAs range from about 105 to 2 × 106 daltons. Only a relatively small fraction of the HnRNA (less than 20% in terms of total nucleotide) can actually be accounted for as cytoplasmic mRNA; the remainder appears to be degraded within the nucleus at a relatively rapid rate [for references, see review by Darnell (1)].

Factors Affecting Flowering of Coffee

Abstract: Two distinct processes should be considered when studying the relation between environmental factors and the flowering of coffee: flower-bud initiation and flower opening or anthesis. These two processes are controlled by different environmental factors. With most coffee varieties, it has been experimentally demonstrated that flower-bud initiation is a typical response to short days (10,19), one exception being the variety semperflorens which produces flower buds under any photoperiodic condition (22). Anthesis, on the other hand, depends primarily on rainfall distribution and appears to be a response to rain following a period of moisture stress (3). This chapter will review the present knowledge concerning the external and internal factors controlling flower opening, or the transition from dormancy to bud break.

Synthesis of mitochondrial proteins.

Abstract: The recent discovery that the ubiquitous energy-transducing organelle of eukaryotic cells, the mitochondrion, contains its own DNA, distinct from that of the nucleus (for recent reviews, see 1-4), has generated intensive investigations in a number of related areas. They have made accessible possible answers to such fundamental questions as the nature and extent of the genetic and biogenetic autonomy of the organelle; the origin, mode of transmission, and significance of extrachromosomal, non-Mendelian hereditary determinants; and the whole chain of events that must intervene in the course of the expression of the mitochondrial genome. Central to this area is the problem of mitochondrial protein synthesis, both in vivo and in vitro; known now for some 13 years (5,6), it has been raised from its former status of relative obscurity as a laboratory curiosity to one of the fashionable fields of inquiry of contemporary biochemistry and molecular biology. Since the topic has been the subject of several recent and comprehensive reviews (7ߝ11), I shall restrict my presentation, in the main, to our own investigations with the unicellular eukaryote Saccharomyces cerevisiae or baker’s yeast.

Increasing the Effectiveness, Efficiency, and Specificity of Mutation Induction in Flowering Plants

Abstract: Numerous agents are now available for inducing mutations and chromosome aberrations for a variety of investigations in plant genetics, development, and evolution and in plant breeding (mutation breeding). These include the widely used physical mutagens X-rays, γ-rays, neutrons, and β-rays; the potent alkylating compounds ethyl methanesulfonate (EMS), diethyl sulfate (dES), and ethyleneimine (EI); and nitroso compounds, nitroso ethylurethane (NEH), nitroso methylurethane (NMU), ethyl nitrosourea (ENH), and methyl nitrosourea (MNH). Much of the recent research on induced mutation in plants has been reviewed by Auerbach and Kilbey (4). Thus information in this chapter will be largely confined to experiments with flowering plants.

Visualization of genetic transcription.

Abstract: Transcription of structural genes by RNA polymerase to produce messenger RNAs (mRNAs) and the translation of such messengers by polyribosomes to produce proteins are intimately coupled processes in bacterial cells (1). In fact, it is possible to reconstruct coupled transcription and translation systems in vitro from separated bacterial components (2,3). Using techniques developed by Miller and Beatty (4) to prepare the nuclear contents of amphibian oocytes for electron microscopy, we can now directly visualize genetically active bacterial chromosomes. In these studies, we have identified both structural genes and ribosomal RNA (rRNA) genes (5,6).

Feedback-resistant mutants of histidine biosynthesis in yeast.

Abstract: Mutants resistant to the histidine analog 1, 2, 4-triazole-3-alanine have been isolated and characterized. All members of one group, TRA1, map in the gene encoding the first enzyme of histidine biosynthesis, have a feedback-resistant first enzyme, and are dominant in diploids. As a consequence of the altered feedback properties, some TRA1 mutants have an internal histidine pool 12–15 times higher than that of wild type. In addition to their inability to control the size of their histidine pool, these mutants are unable to derepress normally. Some implications of these results for the study of feedback-resistant strains of higher plants are discussed.

Rhynchosciara angelae Salivary Gland DNA: Kinetic Complexity and Transcription of Repetitive Sequences

Abstract: Flies of the genus Rhynchosciara, in common with other Diptera, have polytene chromosomes of large size and clearly defined morphology in cells of many tissues. Because the larvae originating from a clutch of eggs develop synchronously, it is possible to obtain material in large enough quantities for biochemical experimentation, even from specialized tissues such as the salivary glands. This makes it possible to correlate biochemical and morphological events taking place in defined tissues. In this organism, we also have the “DNA puffs,” which develop in the salivary gland chromosomes. It is this aspect of Rhynchosciara that makes it an especially interesting system for the study of gene action in higher organisms.

Defined mutants in higher plants.

Abstract: This chapter briefly reviews work on mutant selection using somatic cells of higher plants and then describes experiments designed to recover agriculturally useful variants. Mutants of Nicotiana tabacum were recovered which were resistant to an analog of methionine. These plants were found to be much less susceptible to damage by the pathogen Pseudomonas tabaci, which produces a toxin that is an analog of methionine. Several mutants show a specific increase in the level of free methionine.

Population genetics in the American Tropics. IX. Rhythmic genetic changes that prove the adaptive nature of the detrimental load in Drosophila melanogaster from Caracolisito, Colombia.

Abstract: Our comparative genetic study with the second chromosome of Drosophila melanogaster from Hungary and Colombia (25) produced a quantitative appraisal of the detrimental, normal, subvital, and supervital loads. Results such as these lend support to the theory that the genetic characteristics of a gene pool reflect the ecological situation of the population. The most prominent and significant data in this direction were reported for populations of D. pseudoobscura on Mount San Jacinto in California (6,9,16), and of D. pseudoobscura and D. persimilis in Yosemite Park, California (7,8). These pioneering works and our present one detected changes in time. However, while Dobzhansky’s shifts were described in terms of the relative frequencies of various karyotypes for which they were found to be polymorphic, our present report deals with genetic modifications in viability similar to those found in Fusagasuga (26). The profound changes in the organization of the genetic architecture found in Fusagasuga were caused by recurrent cycles of rainfall-bound seasons in the area. Our analysis revealed surprising shifts in the mean viability of homozygotes. Furthermore, a suggestive correlation appeared between rain cycles and the genetic load observed. If maximum and minimum temperatures had been used to describe the climatogical situation, as was done in the past, we would not have detected anything consistent with the cyclic shifts in lethals and semilethals. Other work (27) revealed that even within 7 months significant shifts in the sterility content in the second chromosome of D. melanogaster from Fusagasuga could be effected by the cyclic rainfall-bound seasons. Testing for heterogeneity among homozygotes of the different temporal populations showed the coexistence of a high- and a low-sterility group. Further partitioning of X 2 in contingency tables revealed that through female sterility in the dry season and male sterility in the wet season the local demographic unit is altered. Still other works (21,22) have shown how even reforestation can produce profound genetic changes within a single area.

Structural and Functional Studies on Mammalian Nuclear DNA-Dependent RNA Polymerases

Abstract: Although DNA-dependent RNA polymerase was first identified in rat liver nuclei (1), this enzyme has only recently been solubilized and purified from eukaryotic cells, due to difficulties in separating the enzyme from nuclear chromatin, the relatively small amounts of enzyme in animal cells, and its marked instability when separated from chromatin. One of the most interesting findings was the existence of multiple nuclear DNA-dependent RNA polymerases [for references, see (2)], which suggested that gene expression in animal cells could be regulated, at least in part, by distinct RNA polymerases with different template specificities. Three lines of evidence supported the existence of multiple RNA polymerases. Several peaks of enzyme activity were obtained by chromatography on substituted cellulose columns (3,4,7), and these activities appeared to have distinctive intranuclear localizations (4–6). Furthermore, two classes of enzyme were distinguished, according to the inhibitory effect of α-amanitin (7,15), a toxin of the toadstool Amanita phalloides. More recently, complete purification and structural analysis of some of the RNA polymerase activities have firmly established the multiplicity of RNA polymerases in animal tissues (8,9). This led us to propose a terminology for animal DNA-dependent RNA polymerase based both on the inhibitory effect of amanitin and the subunit structure of the enzyme (8) (Table I).

On the Regulation of RNA Synthesis in Escherichia coli

Abstract: The accumulation of the stable RNA species, ribosomal RNA (rRNA) and transfer RNA (tRNA), in bacteria is regulated in accordance with the physiological state of the cell. (This subject is extensively reviewed in refs. 1–4.) Thus at high growth rates ribosomal RNA is accumulated rapidly, the synthesis of ribosomal RNA accounting for up to 40% of the instantaneous rate of RNA synthesis (5,6), although the cistrons coding for these RNA species comprise less than 0.5% of the bacterial genome (7,8). However, at low growth rates, when, for example, the carbon source is restricted, the accumulation of rRNA may proceed at less than 20% of the rate approached during maximal exponential growth. This type of regulation occurring during balanced growth of the bacterium may be regarded as a “fine tuning” (9).

Environmental and Hormonal Control in Seedlings

Abstract: The ever increasing urge for intensive and highly productive agriculture demands from biological research the answers to numerous new or scarcely investigated questions. Besides the more spectacular problems of genetic research, the use of foliar fertilizers, the intensive application of herbicides and insecticides, etc., there are many other unresolved problems. The work on such problems may not provoke another “green revolution” but may help our understanding of the physiology of development, a field of considerable practical importance.

Chromosome knob patterns in Latin American maize.

Abstract: Although much has been written about the history of maize, important unanswered questions still remain. Some highly speculative studies have motivated new and intensive research, which has developed important information. Most of such studies are based on archeology, botany, genetics, geography, and history. Nevertheless, cytological data have been used, mainly those referring to the chromosome knobs.

Cytokinins in Regulation of Plant Growth

Abstract: The extension of principles governing gene-controlled protein biosynthesis in prokaryotes as a basic regulatory mechanism common to all growth and developmental processes in eukaryotes, also, is now generally accepted. The question, then, is, what factors are involved in modulating the expression of genetic potentials in cells with an identical genome so as to permit development of functional, multicellular organisms? In the case of plants, it is clear that environmental factors, temperature, light, and inorganic nutrients influence differentiation and development in striking, specific ways, but, as in animals, it is recognized that endogenous growth factors, or hormones, mediate these effects and more generally serve to regulate the expression of genetic potentials. Furthermore, in plants as in animals, several categories of such substances exist, and changing balances in activity between them may modulate metabolism and bring about morphogenesis and functional changes characteristic of normal ontogeny. In this context, I wish to discuss the group of substances referred to as cytokinins.

What do we know about protein synthesis

Abstract: Of the three polymerizations that produce the tapes for the replication of genetic information, the framework of the biosynthetic process for protein synthesis is probably the one best understood. And yet close inspection shows our understanding to be still rather superficial. I will attempt here to summarize briefly what we know and to single out a few phases where we now hope to gain a deeper knowledge.

The effect of sodium fluoride, edeine, and cycloheximide on peptide synthesis with reticulocyte ribosomes.

Abstract: Our purpose in studying antibiotics and other inhibitors of protein synthesis has been to use these compounds to elucidate and characterize reaction mechanisms. The followng discussion is limited to three compounds, sodium fluoride, edeine, and cycloheximide, that have related but dissimilar effects on peptide initiation. Portions of the material presented were published previously (1, 2, 5).

Reconstitution of 50S ribosomal subunits and the role of 5S RNA.

Abstract: Bacterial 30S ribosomal subunits can be reconstituted from 16S ribosomal RNA and about 21 30S ribosomal proteins (1,2). The reconstituted 30S subunits have physical properties, protein composition, and functional capability almost identical to those of the original 30S subunits. This indicates that the information for the correct assembly of 30S ribosomal subunits is contained in the structure of their molecular components and not in some other nonribosomal factors.

"Enzymatic" and "nonenzymatic" translation.

Abstract: According to modern concepts, the translating ribosome is a cyclically working molecular machine. Each elementary working cycle of the ribosome in the process of translation (elongation) results in the reading out of one template triplet and the formation of one peptide bond. It is now known that in addition to the ribosome, the bound template, the bound peptidyl-tRNA, and the aminoacyl-tRNA, the participants of each cycle include the soluble proteins T and G (or TF1 and TF2 in the case of animal ribosomes), acting as enzymatic factors, and GTP,* which is cleaved into GDP and orthophosphate in the course of translation.

Some molecular aspects of mitochondrial complementation and heterosis.

Abstract: Studies of heterosis in plants and animals generally emphasize one of four aspects of the phenomenon: yield of final product, the genetic basis of heterosis, the gene product and its function, or the biochemical systems involved in the accomplishment of heterotic phenotype. The latter two, together with information on the rate of formation of the final product, should be a guide for more meaningful studies of heterosis. The ultimate aim of such studies is to remove the mystique of heterosis. This aim can be achieved through operational devices whereby an experimentally induced biochemical event resembling heterosis in inbred individuals can be manipulated at will in the laboratory. It is a great honor to have been asked by the Organizing Committee of this Symposium to discuss some of the work and reasoning that my students and I have done over the past few years that may contribute to the eventual attainment of the ultimate aim.

Conformational States of Transfer Ribonucleic Acids

Abstract: The occurrence of different conformations of tRNAs is described or postulated in many recent publications. No review of the topic is attempted here, but rather a discussion of a few selected experiments. Although the figures are taken from our work, the main body of this article will include discussion of publications from various laboratories. For more general information, the reader may turn to one or the other of the numerous review articles on tRNA (e.g., refs. 1–5).

Host Proteins in the Replication of Bacteriophage RNA

Abstract: In recent years, the bacteriophage Qβ RNA polymerase reaction has become a highly characterized system for studying the synthesis of genetic material. An outstanding feature of this reaction is the actual replication of infectious bacteriophage RNA, as first shown by Spiegelman et al. (1). All of the reaction components have now been isolated as discrete species: (a) The enzyme, containing four proteins. (b) A host RNA binding factor, composed of a single protein. (c) A basic protein factor, of which there are many active species. (d) Qβ RNA. (e) Q β RNA complementary strand.

Genetic manipulation of plant protein quality and its value in human nutrition.

Abstract: The “green revolution” is causing an increase in production of major cereal crops in the developing tropics and in some cases may contribute to a reduction in quality of the consumer’s diet due to better availability of cereal grains and fewer legumes and other crops. This may be aggravated as well by changes in the relative prices of alternative food sources as a result of increased cereal production and diversion of land and resources from the more protein-rich legume species. A new “quality revolution” is the next frontier for improving cereal grain crops.

Plant-Rhizobium interaction and its importance to agriculture.

Abstract: Rhizobia gain entry to leguminous roots, form nodules, and fix atmospheric nitrogen through a complex process, many stages of which may be influenced by host-bacteria interaction. The most common mechanism for nodule formation is described briefly here, and some of the interactions affecting both nodule formation and N2 fixation are discussed. a. Nodulation begins when a suitable strain of Rhizobium encounters a leguminous root system. The Rhizobium multiplies, in the process producing substantial amounts of IAA and other as yet unidentified but specific substances. These substances cause deformation and curling of the plant root hairs (Fig. 1). b. The root hair invaginates at the apical portion, and some rhizobia pass into the invaginated section. This reaction is very localized and in many plants is also acid sensitive (Fig. 2). c. A fungus-like infection thread is formed by the plant, and the rhizobia are contained within this thread even as they move down the root hair and into the cortex of the plant (Figs. 3 and 4). d. When the infection thread penetrates a tetraploid cell, it begins to break up, and the rhizobia, still surrounded by a coating of plant mucilage, are released into the plant cell cytoplasm (Fig. 5). They begin to multiply, and the IAA produced causes multiplication of the tetraploid and surrounding diploid cells. This multiplication leads to the structure we call a “nodule.” When released into the plant cell, the rhizobia are still bacillary in shape. They quickly lose this cylindrical appearance, becoming “bacteroids,” and in this form begin N2 fixation. e. During active fixation, there are usually four distinct nodular zones (Fig. 6): an outer cortical tissue uninfected by bacteria, an inner zone where the cells are infected but the rhizobia are still in the bacillary form, the central tissue containing N2-fixing but generally nonviable Rhizobium “bacteroids,” and an area of degenerating nodule tissue.