Biomedical subjects

Mark W Davey

Publications and source records attributed to Mark W Davey.

5 recordsLinked to original sources

PubMed2006

Methods for the efficient quantification of fruit provitamin A contents.

As part of a screening program to identify micronutrient-rich banana and plantain (Musa) varieties, a simple, robust, and comparatively rapid protocol for the quantification of the provitamin A carotenoids contents of fruit pulp and peel tissues by HPLC and by spectrophotometry has been developed. Major points to note include the use lyophilisation and extensive tissue disruption procedures to ensure quantitative recoveries, and the avoidance of saponification and/or concentration steps which lead to significant losses of provitamin A carotenoids. The protocol showed excellent reproducibility between replicate extractions, without the need for an internal standard. Application of the methodology demonstrated that Musa fruit pulp has a relatively simple provitamin A carotenoids content, quite different from the overlying peel, and that the proportions of alpha- and beta-carotene are characteristic for each genotype. The protocol was also used to profile the provitamin A carotenoids of several other fruits.

Alkalies↗

PubMed2006

Genetic control of fruit vitamin C contents.

An F(1) progeny derived from a cross between the apple (Malus x domestica) cultivars Telamon and Braeburn was used to identify quantitative trait loci (QTL) linked to the vitamin C (l-ascorbate [l-AA]) contents of fruit skin and flesh (cortex) tissues. We identified up to three highly significant QTLs for both the mean l-AA and the mean total l-AA contents of fruit flesh on both parental genetic linkage maps, confirming the quantitative nature of these traits. These QTLs account for up to a maximum of 60% of the total population variation observed in the progeny, and with a maximal individual contribution of 31% per QTL. QTLs common to both parents were identified on linkage groups (LGs) 6, 10, and 11 of the Malus reference map, while each parent also had additional unique QTLs on other LGs. Interestingly, one strong QTL on LG-17 of the Telamon linkage map colocalized with a highly significant QTL associated with flesh browning, and a minor QTL for dehydroascorbate content, supporting earlier work that links fruit l-AA contents with the susceptibility of hardfruit to postharvest browning. We also found significant minor QTLs for skin l-AA and total l-AA (l-AA + dehydroascorbate) contents in Telamon. Currently, little is known about the genetic determinants underlying tissue l-AA homeostasis, but the presence of major, highly significant QTL in both these apple genotypes under field conditions suggests the existence of common control mechanisms, allelic heterozygosity, and helps outline strategies and the potential for the molecular breeding of these traits.

Ascorbic Acid↗

PubMed2004

Determining the potential to breed for enhanced antioxidant status in Malus: mean inter- and intravarietal fruit vitamin C and glutathione contents at harvest and their evolution during storage.

Vitamin C (L-ascorbate, L-ascorbic acid; L-AA) and glutathione (GSH) are major hydrophilic antioxidants in plants with important roles in stress resistance and nutrition. To evaluate the potential for breeding for enhanced levels of these compounds, a comprehensive screen of the fruit from some 31 apple (Malus) cultivars has been carried out to determine the biodiversity present in the mean inter- and intracultivar concentrations of both the oxidized and reduced forms of these compounds, as well as the impact of storage on their concentrations. It is noted that despite limited variation at harvest, cultivars differed substantially in their ability to maintain L-AA levels during storage, primarily due to the loss of L-AA by "low-vitamin C" cultivars. Generally, cultivars that could maintain their L-AA and GSH pools also had better storage properties. Interestingly, there was also a correlation between fruit vitamin C contents and the harvest date, such that cultivars with the highest vitamin C contents were harvested latest in the season and the lowest contents were found among the early varieties. Correlations with other physiological parameters, however, were too weak to serve as useful predictive tools.

Antioxidants↗

PubMed2003

Ascorbic acid concentration in Cv. conference pears during fruit development and postharvest storage.

L-ascorbic acid (L-AA) concentration changes during the development of cv. Conference pears and the influence of postharvest handlings (gas condition, cooling rate, cooling duration) on L-AA breakdown were studied. L-AA concentration fluctuates in young fruits, remains stable during fruit maturation, and starts to decline 1 week before commercial harvest. The most rapid decrease in L-AA concentration was found during immediate controlled atmosphere. During short-term storage, only the gas condition was found to influence L-AA breakdown; no significant difference between gradually or immediately cooled pears was determined. Under air conditions, both cooling strategies did not differ from the L-AA breakdown in pears allowed to ripen on the tree up until 3 weeks after the optimal harvest date. During long-term storage, the cooling duration (1-3 weeks) had no effect whereas both O2 and CO2 had a significant effect on L-AA retention. After 7 months of storage, no difference was found in dehydroascorbic acid concentration; the L-AA and total L-AA concentrations, in contrast, were significantly lower in the 5% CO2 conditions.

Ascorbic Acid↗

PubMed2002

Gamma-glutamyl transpeptidase in transgenic tobacco plants. Cellular localization, processing, and biochemical properties.

gamma-Glutamyl transpeptidase (gamma-GT) is a ubiquitous enzyme that catalyzes the first step of glutathione (GSH) degradation in the gamma-glutamyl cycle in mammals. A cDNA encoding an Arabidopsis homolog for gamma-GT was overexpressed in tobacco (Nicotiana tabacum) plants. A high level of the membrane-bound gamma-GT activity was localized outside the cell in transgenic plants. The overproduced enzyme was characterized by a high affinity to GSH and was cleaved post-translationally in two unequal subunits. Thus, Arabidopsis gamma-GT is similar to the mammalian enzymes in enzymatic properties, post-translational processing, and cellular localization, suggesting analogous biological functions as a key enzyme in the catabolism of GSH.

Amino Acid Sequence↗