Ascorbate Biosynthesis during Early Fruit Development Is the Main Reason for Its Accumulation in Kiwi

Background: Ascorbic acid (AsA) is a unique antioxidant as well as an enzyme cofactor. Although it has multiple roles in plants, it is unclear how its accumulation is controlled at the expression level, especially in sink tissues. Kiwifruit (Actinidia) is well-known for its high ascorbate content. Our objective was to determine whether AsA accumulates in the fruits primarily through biosynthesis or because it is imported from the foliage. Methodology/Principal Findings: We systematically investigated AsA levels, biosynthetic capacity, and mRNA expression of genes involved in AsA biosynthesis in kiwi (A. deliciosa cv. Qinmei). Recycling and AsA localization were also monitored during fruit development and among different tissue types. Over time, the amount of AsA, with its capacity for higher biosynthesis and lower recycling, peaked at 30 days after anthesis (DAA), and then decreased markedly up to 60 DAA before declining more slowly. Expression of key genes showed similar patterns of change, except for L-galactono-1,4-lactone dehydrogenase and L-galactose-1-phosphate phosphatase (GPP). However, GPP had good correlation with the rate of AsA accumulation. The expression of these genes could be detected in phloem of stem as well as petiole of leaf and fruit. Additionally, fruit petioles had greater ascorbate amounts, although that was the site of lowest expression by most genes. Fruit microtubule tissues also had higher AsA. However, exogenous applications of AsA to those petioles did not lead to its transport into fruits, and distribution of ascorbate was cell-specific in the fruits, with more accumulation occurring in large

Ступінь приверженості до лікування та його ефективність у пацієнтів з гіпертонічною хворобою залежно від способу життя

Vitamin C is a widely used vitamin. Here we review the occurrence and properties of aldonolactone oxidoreductases, an important group of flavoenzymes responsible for the ultimate production of vitamin C and its analogs in animals, plants, and single-cell organisms

Metabolite fingerprinting: detecting biological features by independent component analysis

features by independent component analysi

The missing step of the l-galactose pathway of ascorbate biosynthesis in plants, an l-galactose guanyltransferase, increases leaf ascorbate content

The gene for one postulated enzyme that converts GDP-l-galactose to l-galactose-1-phosphate is unknown in the l-galactose pathway of ascorbic acid biosynthesis and a possible candidate identified through map-based cloning is the uncharacterized gene At4g26850. We identified a putative function for At4g26850 using PSI-Blast and motif searching to show it was a member of the histidine triad superfamily, which includes d-galactose uridyltransferase. We cloned and expressed this Arabidopsis gene and the homologous gene from Actinidia chinensis in Escherichia coli and assayed the expressed protein for activities related to converting GDP-l-galactose to l-galactose-1-P. The expressed protein is best described as a GDP-l-galactose-hexose-1-phosphate guanyltransferase (EC 2.7.7.), catalyzing the transfer of GMP from GDP-l-galactose to a hexose-1-P, most likely d-mannose-1-phosphate in vivo. Transient expression of this A. chinensis gene in tobacco leaves resulted in a >3-fold increase in leaf ascorbate as well as a 50-fold increase in GDP-l-galactose-d-mannose-1-phosphate guanyltransferase activity

Ozone affects ascorbate and glutathione biosynthesis as well as amino acid contents in three Euramerican poplar genotypes

Ozone is an air pollutant that causes oxidative stress by generation of reactive oxygen species (ROS) within the leaf. The capacity to detoxify ROS and repair ROS-induced damage may contribute to ozone tolerance. Ascorbate and glutathione are known to be key players in detoxification. Ozone effects on their biosynthesis and on amino acid metabolism were investigated in three Euramerican poplar genotypes (Populus deltoides Bartr. x Populus nigra L.) differing in ozone sensitivity. Total ascorbate and glutathione contents were increased in response to ozone in all genotypes, with the most resistant genotype (Carpaccio) showing an increase of up to 70%. Reduced ascorbate (ASA) concentration at least doubled in the two most resistant genotypes (Carpaccio and Cima), whereas the most sensitive genotype (Robusta) seemed unable to regenerate ASA from oxidized ascorbate (DHA), leading to an increase of 80% of the oxidized form. Increased ascorbate (ASA + DHA) content correlated with the increase in gene expression in its biosynthetic pathway, especially the putative gene of GDP-L-galactose phosphorylase VTC2. Increased cysteine availability combined with increased expression of gamma-glutamylcysteine synthetase (GSH1) and glutathione synthetase (GSH2) genes allows higher glutathione biosynthesis in response to ozone, particularly in Carpaccio. In addition, ozone caused a remobilization of amino acids with a decreased pool of total amino acids and an increase of Cys and putrescine, especially in Carpaccio. In addition, the expression of genes encoding threonine aldolase was strongly induced only in the most tolerant genotype, Carpaccio. Reduced ascorbate levels could partly explain the sensitivity to ozone for Robusta but not for Cima. Reduced ascorbate level alone is not sufficient to account for ozone tolerance in poplar, and it is necessary to consider several other factors including glutathione content