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Robert D. Slocum

Bio: Robert D. Slocum is an academic researcher from Goucher College. The author has contributed to research in topics: Complementary DNA & Pyrimidine metabolism. The author has an hindex of 19, co-authored 31 publications receiving 2176 citations. Previous affiliations of Robert D. Slocum include Yale University & Williams College.

Papers
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Journal ArticleDOI
TL;DR: The authors' entry into the polyamine field was accidental, but their attention was drawn to a report that the rapid senescence of detached leaves of this plant could be delayed substantially by the application of arginine, and this work was started on cereal leaf protoplasts.

514 citations

Book
20 Dec 1991
TL;DR: A historical perspective on research in Plant Polyamine Biology and how changes in Polyamine Metabolism in Response to Abiotic Stress contributed to its development are presented.
Abstract: INTRODUCTION An Historical Perspective On Research in Plant Polyamine Biology (Terence A. Smith). POLYAMINE METABOLISM IN PLANTS. Polyamine Biosynthesis in Plants (Robert D. Slocum). Polyamine Catabolism in Plants (Rodolfo Federico and Riccardo Angelini). Polyamines and Plant Secondary Metabolites (Hector E. Flores and Josette Martin-Tanguy). Metabolic and Physiological Relationships Between the Polyamine and Ethylene Biosynthetic Pathways (Mosbah M. Kushad and Erwin B. Dumbroff). Tissue and Subcellular Localization of Polyamines and Enzymes of Polyamine Metabolism (Robert D. Slocum). Uptake and Transport of Polyamines and Inhibitors of Polyamine Metabolism in Plants (Nello Bagni and Rosella Pistocchi). Uncommon Polyamines in Plants and Other Organisms (Gregory C. Phillips and Glenn D. Kuehn). Molecular Analyses of Polyamine Synthesis in Higher Plants (Russell L. Malmberg and Erin Bell). POLYAMINES IN PLANT GROWTH AND DEVELOPMENT. Polyamines in Cell Division, Fruit Set and Development, and Seed Germination (Marcos Egea-Cortines and Yosef Mizrahi). Cell Cycle-Dependent Changes in Plant Polyamine Metabolism (Donatella Serafini-Fracassini). Polyamines and Plant Morphogenesis (Arthur W. Galston and Hector E. Flores). Effects of Light and Plant Growth Regulators on Polyamine Metabolism in Higher Plants (Rajeev Rastogi and Peter J. Davies). Physiological and Biochemical Studies on the Antisenescence Properties of Polyamines in Plants (Ravindar Kaur-Sawhney and Arthur W. Galston). Changes in Polyamine Metabolism in Response to Abiotic Stress (Hector E. Flores). ANALYTICAL METHODS FOR POLYAMINES AND ENZYMES OF POLYAMINE METABOLISM. Chromatographic Methods for the Identification and Quantitation of Polyamines (Mary A. Smith). Assay Methods for Enzymes of Polyamine Metabolism (Helena Birecka). INDEX.

340 citations

Journal ArticleDOI
Robert D. Slocum1
TL;DR: Gene expression profiling for pathway enzymes further suggests that NAGS, NAGK, NAOGAcT and NAOD are coordinately regulated in response to changes in Arg demand during plant growth and development.

245 citations

Journal ArticleDOI
TL;DR: Synchronous changes in PA titers and in the rates of PA biosynthesis, macromolecular synthesis, and growth in the tobacco ovary suggest that PAs may play a role in the regulation of postfertilization growth and development of this reproductive organ.
Abstract: Polyamine (PA) titers and the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17), enzymes which catalyze rate-limiting steps in PA biosynthesis, were monitored during tobacco ovary maturation. In the period between anthesis and fertilization, the protein content of ovary tissues rapidly increased by about 40% and was accompanied by approximately a 3-fold increase in ODC activity, while ADC activity remained nearly constant. PA titers also remained relatively unchanged until fertilization, at which time they increased dramatically and the DNA content of ovary tissues doubled. This increase in PA biosynthesis was correlated with a further 3-fold increase in ODC activity, reaching a maximum 3 to 4 days after fertilization. During this time, ADC activity increased only slightly and accounted for approximately 1% of the total decarboxylase activity when ODC activity peaked. The postfertilization burst of biosynthetic activities slightly preceded a period of rapid ovary enlargement, presumably due to new cell division. During later stages of ovary development, DNA levels fell precipitously, while PA titers and decarboxylase activities decreased to preanthesis levels more slowly. In this period, growth producing a 300% increase in ovary fresh weight appears to be the result of cell enlargement. Synchronous changes in PA titers and in the rates of PA biosynthesis, macromolecular synthesis, and growth in the tobacco ovary suggest that PAs may play a role in the regulation of postfertilization growth and development of this reproductive organ.

135 citations

Journal ArticleDOI
TL;DR: A simple modification of the original HPLC procedure greatly improves the separation and quantitation of these amines, and further allows the simulation analysis of phenethylamine and tyramine, which are major monoamine constituents of tobacco and other plant tissues.
Abstract: The high performance liquid chromatographic (HPLC) method of Flores and Galston (1982 Plant Physiol 69: 701) for the separation and quantitation of benzoylated polyamines in plant tissues has been widely adopted by other workers. However, due to previously unrecognized problems associated with the derivatization of agmatine, this important intermediate in plant polyamine metabolism cannot be quantitated using this method. Also, two polyamines, putrescine and diaminopropane, also are not well resolved using this method. A simple modification of the original HPLC procedure greatly improves the separation and quantitation of these amines, and further allows the simulation analysis of phenethylamine and tyramine, which are major monoamine constituents of tobacco and other plant tissues. We have used this modified HPLC method to characterize amine titers in suspension cultured carrot (Daucas carota L.) cells and tobacco (Nicotiana tabacum L.) leaf tissues.

104 citations


Cited by
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Journal ArticleDOI
TL;DR: A mechanism is proposed whereby the interconversions of proline and P5C in different cell types and the associated transfer of redox potential between tissues may constitute a form of metabolic signalling within higher plants.
Abstract: In many plants, free proline accumulates in response to the imposition of a wide range of biotic and abiotic stresses. Controversy has surrounded the extent to which this shift in nitrogen metabolism benefits plants under adverse environmental conditions. Most attempts to account for the phenomenon have focused on the ability of proline to mediate osmotic adjustment, stabilise subcellular structures and scavenge free radicals. However, often the cytoplasmic pool of free proline even after the imposition of stress is insufficient size to account for pronounced biophysical effects. Alternatively, selective preservation of this stress-induced response may relate to endpoints other than simply augmenting the cellular pool of free proline. Proline accumulation may reduce stress-induced cellular acidification or prime oxidative respiration to provide energy needed for recovery. High levels of proline synthesis during stress may maintain NAD(P)+/NAD(P)H ratios at values compatible with metabolism under normal conditions. Consideration of the cofactor preference of plant Δ1-pyrroline-5-carboxylate (P5C) reductase as well as the in vivo concentrations of the two pyridine nucleotide cofactors and their respective redox ratios suggests that even a small increase in proline biosynthesis might have a large impact on the level of reduction of the cellular NADP pool. The increased NADP+/NADPH ratio mediated by proline biosynthesis is likely to enhance activity of the oxidative pentose phosphate pathway. This would provide precursors to support the demand for increased secondary metabolite production during stress as well as nucleotide synthesis accompanying the accelerated rate of cell division upon relief from stress, when oxidation of proline is likely to provide an important energy source for ADP phosphorylation. Thus, the extreme sensitivity of the metabolic processes of proline synthesis and degradation themselves may be of benefit by regulating metabolic processes adversely affected by stress. This viewpoint is supported by consideration of other physiological phenomena not directly related to stress responses, but in which proline metabolism may also play a regulatory role. A mechanism is proposed whereby the interconversions of proline and P5C in different cell types and the associated transfer of redox potential between tissues may constitute a form of metabolic signalling within higher plants. Stress-related alterations in proline metabolism may impinge on systems of redox control of plant gene expression.

1,410 citations

Journal Article
TL;DR: The genes governing the proline biosynthetic pathway, its degradation and regulation are summarized and an account on transgenics raised so far to engineer the overproduction of osmolyte proline is provided.
Abstract: Dramatic accumulation of proline due to increased synthesis and decreased degradation under a variety of stress conditions such as salt, drought and metal has been documented in many plants. Similarly, a decrease in the level of accumulated proline in the rehydrated plants is due to both down regulation of proline biosynthetic pathway enzymes and upregulation of proline degrading enzymes. But, the role of proline during plant development and the molecular basis of the effect of proline accumulation during stress and upon relief of stress are still largely obscure. Here, we summarize the genes governing the proline biosynthetic pathway, its degradation and regulation. Sequentially, we provide an account on transgenics raised so far to engineer the overproduction of osmolyte proline. Also, the identification of specific cellular pathways involved in proline biosynthesis and metabolic changes occurring in transgenic plants developed for proline enhancements are discussed. Further, emphasis is also made on an untouched area of signal transduction of proline biosynthetic pathway.

1,265 citations

Journal ArticleDOI
TL;DR: All the data support the view that putrescine and derived polyamines (spermidine, spermine, long-chained polyamides) may have several functions during environmental challenges.

1,185 citations

Journal ArticleDOI
TL;DR: This review deals with N-containing metabolites frequently preferentially synthesized under heavy metal stress such as Cd, Cu, Ni, and Zn, with special focus on proline and certain other amino acids and oligopeptides, as well as betaine, polyamines, and nicotianamine.
Abstract: Plants exposed to heavy metals accumulate an array of metabolites, some to high millimolar concentrations. This review deals with N-containing metabolites frequently preferentially synthesized under heavy metal stress such as Cd, Cu, Ni, and Zn. Special focus is given to proline, but certain other amino acids and oligopeptides, as well as betaine, polyamines, and nicotianamine are also addressed. Particularly for proline a large body of data suggests significant beneficial functions under metal stress. In general, the molecules have three major functions, namely metal binding, antioxidant defence, and signalling. Strong correlative and mechanistic experimental evidence, including work with transgenic plants and algae, has been provided that indicates the involvement of metal-induced proline in metal stress defence. Histidine, other amino acids and particularly phytochelatins and glutathione play a role in metal binding, while polyamines function as signalling molecules and antioxidants. Their accumulation needs to be considered as active response and not as consequence of metabolic dys-regulation.

1,142 citations

Journal Article
TL;DR: Salinity stress response is multigenic, as a number of processes affected, such as various compatible solutes/osmolytes, polyamines, reactive oxygen species and antioxidant defence mecha- nism, ion transport and compartmentalization of inj u- rious ions.
Abstract: ions and to some extent Cl and SO 4 2 of Mg 2+ and nutrient imbalance caused by excess of Na + and Cl ions. Salinity stress response is multigenic, as a number of processes i n- volved in the tolerance mechanism are affected, such as var ious compatible solutes/osmolytes, polyamines, reactive oxygen species and antioxidant defence mecha- nism, ion transport and compartmentalization of inj u- rious ions. Various genes/cDNAs encoding proteins involved in the above-mentioned processes have been identified and isolated. The role of genes/cDNAs e n- coding proteins involved in regulating other genes/ pro- teins, signal transduction process involving hormones like ABA, JA and polyamines, and strategies to i mprove salinity stress tolerance have also been di scussed. EXCESS amount of salt in the soil adversely affects plant growth and development. Nearly 20% of the world's cul- tivated area and nearly half of the world's i rrigated lands are affected by salinity 1

1,071 citations