Geza Hrazdina

Bio: Geza Hrazdina is an academic researcher from Cornell University. The author has contributed to research in topics: Anthocyanin & Chalcone synthase. The author has an hindex of 32, co-authored 83 publications receiving 3327 citations. Previous affiliations of Geza Hrazdina include ETH Zurich & Trent University.

Spatial Organization of Enzymes in Plant Metabolic Pathways

Abstract: INTRODUCTION ...... .. . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......... . . . . . . . . . . . . . . . . . . . . 241 COMPARTMENTATION OF PATHWAYS IN ORGANELLES . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Role of Isozymes in Metabolic Compartmentation . . . . . .. . . .. . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . 243 METABOLIC ORGANIZATION IN THE DIVERSE PATHWAyS 245 Role of Isozymes in Cellular Metabolism . . . . . . . . . . ...... . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 Carbohydrate Metabolism . . . . .. . .. . . . .. . . ...... . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .... . . . . . . 245 Pyruvate and Citric Acid Cycle.... . . . . . . . .... ... . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . 247 Biochemical Inteiface B etween Carbohydrate Metabolism and Aromatic A mino Acid Biosynthesis . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 Aromatic Amino Acid Biosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . ... ". . . . . . . . . . . . . 249 Phen ylpropanoid and Flavonoid Pathways . . .. . . . . . . . .. . . . . . ... . ... .. .. . . . . . . . . . . . . . . . . . . . . . 253 Cyanogenic Glycosides . . . . . . . . . . . . . . . ... ......... .... . . . . . . . . . . . . . . . . . . . . . . . . ..... ... . . .. . . . . . . . 256 Isochorismate Derivatives . . . . ......... . . . . . . . . . . .. . . . . . . . . .... . . . . . .. . . . . ....... 256 Other Specialized Pathways . . . . . . . . . . . . . . . . . . . ... . . ... . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 257 Other A mino Acid Pathways . . . . . . . . . . . . . . . . . . . . .. . ...... . . . . . . . . . . . . ... . . . . . . . . .... 259 PERSPECTIVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

Interaction of Nitrogen Availability During Bloom and Light Intensity During Veraison. II. Effects on Anthocyanin and Phenolic Development During Grape Ripening

Abstract: Grape ripening is affected by a number of environmental factors, and of these light and nitrogen (N) are of particular importance. Using pot-grown Cabernet Sauvignon ( Vitis vinifera L.) vines, we studied the effects of N availability at bloom (0.34, 1.7, or 3.4 g N per plant as NH 4 NO 3 ) and light intensity at veraison (3 weeks at 100%, 20%, or 2% sunlight, using shade cloth) on the accumulation of total phenols, anthocyanins and flavonols in ripening grapes. Total soluble solids in the pulp were closely correlated with total phenols (r 2 = 0.91 *** ), total anthocyanins (r 2 = 0.90 *** ) and total flavonols (r 2 = 0.52 *** ) in the skin in all treatments. High rates of N supply delayed the accumulation of phenolic compounds, particularly flavonols, in the grape skin at veraison. However, the differences between N treatments generally decreased towards fruit maturity. Low light intensity at veraison restricted phenolics accumulation even more than did heavy N supply and the effects of low light were most severe in vines with high N status. However, ripening was not stopped entirely by light intensities as low as the light compensation point of photosynthesis. Moreover, removal of the shade cloth partly restored the rate of phenolics accumulation in the berry skin. All five anthocyanins started accumulating concurrently at the inception of ripening. However, while peonidin-, malvidin-, and cyanidin-3-glucosides were the major pigments at veraison, malvidin- and delphinidin-3-glucosides became most abundant towards maturity. The accumulation of cyanidin-3-glucoside was most strongly influenced by prevailing environmental conditions, while malvidin-3-glucoside was the least affected. Thus, the proportions of individual anthocyanins were most equal at low N status and high light intensity, whereas the percentage of malvidin-3-glucoside increased with high rates of N fertilization and became predominant under low light intensity. This is important for red winemaking, because the grape skins9 anthocyanin profile determines the color potential of the resulting wine. Excessive N fertilization can decrease wine quality, particularly when light conditions during grape ripening are poor.

Physiological and biochemical events during development and maturation of grape berries.

Abstract: Some of the most important physiological and biochemical processes that occur during the development and maturation of de Chaunac grape berries have been investigated. The studies included monitoring changes in the pH, in total and individual major acids, cations, sugars, anthocyanins and their biosynthetic enzymes. Brix, pH, K+, sugars and anthocyanins showed a sharp rise during and immediately after veraison. There was a concomitant rise in the activity of anthocyanin biosynthetic enzymes. Total acidity and malic acid content increased during the first four weeks and declined thereafter, reaching a steady level approximately five weeks later. The concentration of phosphoric acid showed a rise during the maturation process, while tartaric acid levels declined continuously. On the per gram basis, the levels of Na+ showed no consistent changes, while Ca++, Cu++, Mg++, and Mn++ showed sharp declines during the expansion period of the berries and steady, low levels during the maturation process. The data suggest that the majority of metabolic events in the berries come to a steady state approximately eight weeks after veraison under the climatic conditions of the northeastern United States.

Stress responses in alfalfa (Medicago sativa L.) 11. Molecular cloning and expression of alfalfa isoflavone reductase, a key enzyme of isoflavonoid phytoalexin biosynthesis.

Abstract: The major phytoalexin in alfalfa is the isoflavonoid (−)-medicarpin (or 6aR, 11aR)-medicarpin. Isoflavone reductase (IFR), the penultimate enzyme in medicarpin biosynthesis, is responsible for introducing one of two chiral centers in (−)-medicarpin. We have isolated a 1.18 kb alfalfa cDNA (pIFRalf1) which, when expressed in Escherichia coli, converts 2′-hydroxyformononetin stereospecifically to (3R)-vestitone, as would be predicted for IFR from alfalfa. The calculated molecular weight of the polypeptide (35400) derived from the 954 bp open reading frame compares favorably to estimated Mrs determined for IFR proteins purified from other legumes. The transcript (1.4 kb) is highly induced in elicited alfalfa cell cultures. The kinetics of induction are consistent with the appearance of IFR activity, the accumulation of medicarpin, and the observed induction of other enzymes in the pathway. Low levels of IFR transcripts were found in healthy plant parts (roots and nodules) which accumulate low levels of a medicarpin glucoside. IFR appears to be encoded by a single gene in alfalfa. The cloning of IFR opens up the possibility of genetic manipulation of phytoalexin biosynthesis in alfalfa by altering isoflavonoid stereochemistry.

The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer

Abstract: Flavonoids are nearly ubiquitous in plants and are recognized as the pigments responsible for the colors of leaves, especially in autumn. They are rich in seeds, citrus fruits, olive oil, tea, and red wine. They are low molecular weight compounds composed of a three-ring structure with various substitutions. This basic structure is shared by tocopherols (vitamin E). Flavonoids can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3, or a hydroxyl group in position 3 of the C (middle) ring. These characteristics appear to also be required for best activity, especially antioxidant and antiproliferative, in the systems studied. The particular hydroxylation pattern of the B ring of the flavonoles increases their activities, especially in inhibition of mast cell secretion. Certain plants and spices containing flavonoids have been used for thousands of years in traditional Eastern medicine. In spite of the voluminous literature available, however, Western medicine has not yet used flavonoids therapeutically, even though their safety record is exceptional. Suggestions are made where such possibilities may be worth pursuing.

Stress-Induced Phenylpropanoid Metabolism.

Abstract: Phenylpropanoid compounds encompass a wide range of structural classes and biological functions. Limiting discussion to stress-induced phenylpropanoids eliminates few of the structural classes, because many compounds thst are constitutive in one plant species or tissue can be induced by various stresses in another species or in another tissue of the same plant (Beggs et al., 1987; Christie et al., 1994).

The oxidative burst in plant disease resistance

Abstract: Rapid generation of superoxide and accumulation of H2O2 is a characteristic early feature of the hypersensitive response following perception of pathogen avirulence signals. Emerging data indicate that the oxidative burst reflects activation of a membrane-bound NADPH oxidase closely resembling that operating in activated neutrophils. The oxidants are not only direct protective agents, but H2O2 also functions as a substrate for oxidative cross-linking in the cell wall, as a threshold trigger for hypersensitive cell death, and as a diffusible signal for induction of cellular protectant genes in surrounding cells. Activation of the oxidative burst is a central component of a highly amplified and integrated signal system, also involving salicylic acid and perturbations of cytosolic Ca2+, which underlies the expression of disease-resistance mechanisms.

Flavonoid Biosynthesis. A Colorful Model for Genetics, Biochemistry, Cell Biology, and Biotechnology

Abstract: The role of flavonoids as the major red, blue, and purple pigments in plants has gained these secondary products a great deal of attention over the years. From the first description of acid and base effects on plant pigments by Robert Boyle in 1664 to the characterization of structural and