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K J Scott

Publications and source records attributed to K J Scott.

45 records · Page 3Linked to original sources
PubMed1969

Nicotinate, quinolinate and nicotinamide as precursors in the biosynthesis of nicotinamide-adenine dinucleotide in barley.

1. The relative efficiencies of nicotinate, quinolinate and nicotinamide as precursors of NAD(+) were measured in the first leaf of barley seedlings. 2. In small amounts, both [(14)C]nicotinate and [(14)C]quinolinate were quickly and efficiently incorporated into NAD(+) and some evidence is presented suggesting that NAD(+) is formed from each via nicotinic acid mononucleotide and deamido-NAD. 3. [(14)C]Nicotinamide served equally well as a precursor of NAD(+) and although significant amounts of [(14)C]NMN were detected, most of the [(14)C]NAD(+) was derived from nicotinate intermediates formed by deamination of [(14)C]nicotinamide. 4. Radioactive NMN was also a product of the metabolism of [(14)C]nicotinate and [(14)C]quinolinate but most probably it arose from the breakdown of [(14)C]NAD(+). 5. In barley leaves where the concentration of NAD(+) is markedly increased by infection with Erysiphe graminis, the pathways of NAD(+) biosynthesis did not appear to be altered after infection. A comparison of the rates of [(14)C]NAD(+) formation in infected and non-infected leaves indicated that the increase in NAD(+) content was not due to an increased rate of synthesis.

Ascomycota↗
PubMed1968

Metabolic Regulation in Diseased Leaves II. Changes in Nicotinamide Nucleotide Coenzymes in Barley Leaves Infected With Powdery Mildew.

Nicotinamide nucleotide coenzymes were estimated spectrophotometrically in noninfected barley leaves and leaves infected with Erysiphe graminis var hordei (powdery mildew). Amounts of NADH, NADP(+) and NADPH were not altered by infection. In contrast, the NAD(+) content rose sharply and at 144 hours was 100% greater than in noninfected leaves. The respiratory rate was increased in infected leaves and the pattern of this increase was similar to that of NAD(+).The effect of infection on the intracellular distribution of NADP(+) was examined by fractionating lyophilized leaves in a nonaqueous medium. In noninfected leaves almost all of the NADP(+) was localized in the chloroplasts. In infected leaves where some chloroplast breakdown occurs, about 60% of the NADP(+) was detected in the nonchloroplast part of the cell. This intracellular redistribution of NADP(+) is discussed in relation to the increased pentose-P pathway activity occuring after infection.

Journal Article↗
PubMed1966

Metabolic regulation in diseased leaves. I. The respiratory rise in barley leaves infected with powdery mildew.

Photosynthetic and respiratory activities have been measured in leaves of Hordeum vulgare L. var. Manchuria (barley) after infection with Erysiphe graminis var. hordei (powdery mildew). Two isogenic lines, one resistant to infection and the other highly susceptible, were examined.These isogenic lines showed very different physiological responses following infection. Photosynthesis and the chlorophyll content of resistant leaves was unaffected by infection. Respiration increased slightly and this was accompanied by small increases in activities of enzymes of glycolysis, the pentose-P pathway and the tricarboxylic acid cycle.The infection of susceptible leaves resulted in a slight increase in photosynthesis 48 hours after inoculation, but subsequently there was a progressive decrease in the photosynthesis of these leaves compared with that of noninfected leaves. The capacity of infected leaves for partial reactions of photosynthesis such as the Hill reaction and the photoreduction of nicotinamide adenine dinucleotide phosphate (NADP(1)) decreased during the later stages of infection. The levels of chlorophyll, NADPH-diaphorase and aldolase also declined. There was no detectable difference in the respiration of infected and noninfected leaves until 48 hours after inoculation. After this time, the infected leaves showed a higher respiration, the maximum difference occurring about 144 hours after inoculation. The respiratory increase was not accompanied by significant changes in the levels of enzymes of glycolysis and the tricarboxylic acid cycle with the exception of malate dehydrogenase which was lower in infected leaves. In contrast, the activities of glucose-6-P dehydrogenase and 6-P-gluconate dehydrogenase showed changes similar to that observed for respiration.The respiration and the activities of glucose-6-P dehydrogenase and 6-P-gluconate dehydrogenase did not increase in infected leaves of etiolated plants, even when excellent growth of the fungus was established by growing the plants in White's basal medium supplemented with sucrose. The respiration of a susceptible mutant barley (the yellow-green virescent mutant of the variety Himalaya) when grown in the light at 11 degrees was not changed by infection although the characteristic respiratory rise occurred in plants grown at 15 degrees . At the lower temperature chloroplasts fail to develop in this mutant, although development is normal at 15 degrees .It is suggested that the pathogen is not directly responsible for the increase in respiration in green leaves, rather that this is a response in the host cells to a loss of photosynthetic capacity.

Journal Article↗