Douglas O. Adams

1-Aminocyclopropanecarboxylate synthase, a key enzyme in ethylene biosynthesis.

Abstract 1-Aminocyclopropanecarboxylate (ACC) synthase, which catalyzes the conversion of S -adenosylmethionine (SAM) to ACC and methylthioadenosine, was demonstrated in tomato extract. Methylthioadenosine was then rapidly hydrolyzed to methylthioribose by a nucleosidase present in the extract. ACC synthase had an optimum pH of 8.5, and a K m of 20 μ m with respect to SAM. S -Adenosylethionine also served as a substrate for ACC synthase, but at a lower efficiency than that of SAM. Since S -adenosylethionine had a higher affinity for the enzyme than SAM, it inhibited the reaction of SAM when both were present. S -Adenosylhomocysteine was, however, an inactive substrate. The enzyme was activated by pyridoxal phosphate at a concentration of 0.1 μ m or higher, and competitively inhibited by aminoethoxyvinylglycine and aminooxyacetic acid, which are known to inhibit pyridoxal phosphate-mediated enzymic reactions. These results support the view that ACC synthase is a pyridoxal enzyme. The biochemical role of pyridoxal phosphate is catalyzing the formation of ACC by α,γ-elimination of SAM is discussed.

Ethylene the gaseous plant hormone: mechanism and regulation of biosynthesis

Abstract Ethylene is a natural regulator of plant growth and development and has been used, wittingly or unwittingly, as a fruit ripening agent for many years. Its path of synthesis has recently been elucidated and there is now some understanding of how ethylene production is regulated.

Influence of geographic origin on the sensory characteristics and wine composition of Vitis vinifera cv. Cabernet Sauvignon wines from Australia

The current study explores the relationship between sensory characteristics and wine composition of Cabernet Sauvignon wines in relation to Australian geographical indications (GIs). Descriptive sensory analysis was conducted to characterize the sensory attributes of commercially produced Cabernet Sauvignon wines from the Barossa Valley, Clare Valley, Coonawarra, Frankland River, Langhorne Creek, Mount Barker, Margaret River, McLaren Vale, Padthaway, and Wrattonbully GIs. Canonical variate analysis using the significant sensory attributes demonstrated that each GI could be distinguished from the others. A recently developed analytical method was used to analyze over 350 volatile compounds in the wines assessed, and measures of the major nonvolatile components were also determined. Compositional results were analyzed using partial least squares discriminant analysis to identify candidate components that were unique to certain GIs, including 2-isobutyl-3-methoxypyrazine, menthone, isomenthone, carvacrol, δ-octalactone, p-methylacetophenone, m-dimethoxybenzene, protein-precipitable tannin, and monomeric anthocyanins. Results demonstrate that Australian Cabernet Sauvignon wines have common sensory attributes related to geographic origin. The work also identifies a number of candidate components that are related to individual GIs which warrant further investigation. The study is the first to explore the concept of regionality in Cabernet Sauvignon wines from Australia.

Tracing phenolic biosynthesis in Vitis vinifera via in situ C-13 labeling and liquid chromatography–diode-array detector–mass spectrometer/mass spectrometer detection

Phenolic compounds in Vitis vinifera contribute important flavor, functionality, and health qualities to both table and wine grapes. The plant phenolic metabolic pathway has been well characterized, however many important questions remain regarding the influence of environmental conditions on pathway regulation. As a diagnostic for this pathways regulation, we present a technique to incorporate a stable-isotopic tracer, L-phenyl-(13)C(6)-alanine (Phe(13)), into grape berries in situ and the accompanying high throughput analytical method based on LC-DAD-MS/MS to quantify and track the label into phenylalanine metabolites. Clusters of V. vinifera cv. Cabernet Sauvignon, either near the onset of ripening or 4 weeks later, were exposed to Phe(13) in the vineyard. Phe(13) was present in berries 9 days afterwards as well as labeled flavonols and anthocyanins, all of which possessed a molecular ion shift of 6 amu. However, nearly all the label was found in anthocyanins, indicating tight regulation of phenolic biosynthesis at this stage of maturity. This method provides a framework for examining the regulation of phenolic metabolism at different stages of maturity or under different environmental conditions. Additionally, this technique could serve as a tool to further probe the metabolism/catabolism of grape phenolics.

Nitrogen Status and Fermentation Dynamics for Merlot on Two Rootstocks

Adequate yeast assimilable nitrogen (YAN) levels in grape juice are necessary for yeast cells to complete fermentation to dryness. Nitrogen (N) uptake by grapevine roots varies seasonally; therefore, environmental conditions and cultural practices can affect grapevine N status. In addition, genetic differences between rootstock cultivars can influence root dynamics and, subsequently, N uptake, canopy biomass, and fruit composition. Two rootstock cultivars, 1103P and 101-14 Mgt, were fertilized with nitrogen during spring or fall or received no treatment. Vine biomass, leaf N concentration, fruit composition, juice amino-N levels, and fermentation kinetics were measured. The rootstock 1103 Paulsen (Vitis berlandieri × V. rupestris cv. 1103P) has a root system that tends to produce large canopies and high shoot growth. The rootstock 101-14 Millardet et de Grasset (V. riparia × V. rupestris cv. 101-14 Mgt) has a root system associated with smaller canopies and moderate shoot growth. The scion Merlot (V. vinifera L. cv. Merlot clone 1) was grafted onto the two rootstocks in an experimental block in Oakville, California. Merlot on 1103P had higher YAN levels and completed fermentation faster compared to Merlot on 101-14 Mgt. Differences in fermentation kinetics were observed within rootstock N treatments that were not explained by YAN levels, indicating that other factors related to N metabolism may play important roles in fermentation dynamics. Results indicated that Merlot grown on 1103P in the Napa Valley may require little to no N supplementation while Merlot on 101-14 Mgt may require N supplementation to avoid slow fermentations.

Tracing phenolic metabolism in Vitis vinifera berries with 13C6-phenylalanine: implication of an unidentified intermediate reservoir.

Understanding the regulation of phenolic compounds in agricultural products has been a topic of great interest. In V. vinifera berries, phenolics are responsible for important sensory and functional characteristics. To elucidate the ripening profile of phenolic compounds in Cabernet Sauvignon berries, the stable-isotope tracer l-phenyl-(13)C6-alanine (Phe(13)) was incorporated in situ, and the development of labeled and unlabeled phenolics was tracked in the vineyard at different stages of maturity over two vintages. Phenolic profiles during ripening were consistent with previous research. However, individual anthocyanins accumulated with different profiles during ripening; malvidin species continually climbed in concentration, whereas other anthocyanins tended to plateau or drop near the end of the growing season. The isotopic label was predominantly incorporated into anthocyanins, presumably because of their dominant accumulation during ripening. Notably, the incorporation of label continued long after levels of Phe(13) had dropped to below 1 nmol/berry, preventing an accurate assessment of the hypothesized turnover of anthocyanins. Although our tracer did not perform exactly as we had expected, the results of this study suggest the presence of a previously unreported pool of substrate in the phenolic pathway.

Aviglycine and propargylglycine inhibit conidial germination and mycelial growth of Fusarium oxysporumf. sp. luffae.

Two inhibitors, aviglycine and propargylglycine, were tested for their ability to suppress methionine synthesis thus inhibit conidial germination and mycelial growth of Czapek-Dox liquid medium grown Fusarium oxysporum f. sp. luffaeμM. The linear inhibition range for mycelial growth was about 7.6–762.9 μM. Although aviglycine did not completely inhibit both conidial germination and mycelial growth, it showed significant inhibitory effect at 1.5 μM. The inhibition range for propargylglycine against conidial germination and mycelial growth were from 0.08 to 8841 μM and from 0.8 to 884.1 μM, respectively. Propargylglycine inhibited conidial germination and mycelial growth at a concentration of 8841 μM. The EC50 values of aviglycine were 1 μM for conidial growth and 122 μM for mycelial growth, and the EC50 values of propargylglycine were 47.7 μM for conidial growth and 55.6 μM for mycelial growth. Supplement of methionine released inhibition of aviglycine or propargylglycine to conidial germination. In addition, a mixture of aviglycine (1.5 μM) and propargylglycine (8841 μM) showed additive inhibitive effect than applied alone on 10 isolates. From these results, both aviglycine and propargylglycine exhibited inhibitory activity, and suggest that they can provide potential tools to design novel fungicide against fungal pathogens.