Blood vitamin D(3) metabolite concentrations of adult female bearded dragons (Pogona vitticeps) remain stable after ceasing UVb exposure.

Vitamin D deficiency can lead to several health problems collectively called metabolic bone disease (MBD). One commonly kept reptile species prone to develop MBD if managed incorrectly is the bearded dragon (Pogona vitticeps). This study aimed to determine the extent to which adult female bearded dragons fed a diet low in vitamin D can use stored vitamin D and its metabolites to maintain plasma 25(OH)D(3) and 1,25(OH)(2)D(3) concentrations after discontinuing UVb exposure. Blood samples of healthy adult female bearded dragons, exposed to UVb radiation for over 6 months were collected (day 0) after which UVb exposure was discontinued for 83 days and blood was collected. Blood plasma was analysed for concentrations of total Ca, total P, ionized Ca, uric acid, 25(OH)D(3) and 1,25(OH)(2)D(3). There was no significant change in plasma 25(OH)D(3) and 1,25(OH)(2)D(3) concentrations during the study. While total Ca and P in whole blood was found to significantly decrease over time (P < 0.0088 and 0.0016, respectively), values were within the reference range. Plasma ionized Ca tended (P = 0.0525) to decrease during the study. Adult female bearded dragons, previously exposed to UVb, are able to maintain blood vitamin D metabolite concentrations when UVb exposure is discontinued for a period of up to 83 days.

Multiple allelism as a control mechanism in metabolic pathways: GBSSI allelic composition affects the activity of granule-bound starch synthase I and starch composition in potato.

Multiple allelism in heterozygous autopolyploid species like potato not only occurs for genes that affect morphological characteristics but also for genes involved in metabolic pathways. Based on a combination of Southern and PCR analyses, at least eight alleles encoding granule-bound starch synthase I (GBSSI), which is responsible for amylose biosynthesis, have been identified in potato. These alleles were grouped into four classes, distinguishable by Southern analysis, and subdivided based on PCR. Despite the heterozygous and polyploid character of potato it was possible to assign variation in GBSSI activity to the allelic composition at the GBSSI loci within a large population of Solanum tuberosum cultivars and Solanum breeding lines. Moreover, the availability of an amf allele made it possible to reduce heterogeneity and enabled us to demonstrate an effect of GBSSI allelic composition on amylose content. The major difference between the alleles identified was the absence or presence of a 140-bp fragment at a site 0.5 kb upstream of the ATG start codon of the gene for GBSSI. The absence of this 140-bp fragment had a major effect on GBSSI activity and amylose content, while the presence of small deletions and simple sequence repeats had no obvious effect.

Amylose is synthesized in vitro by extension of and cleavage from amylopectin.

Amylose synthesis was obtained in vitro from purified Chlamydomonas reinhardtii starch granules. Labeling experiments clearly indicate that initially the major granule-bound starch synthase extends glucans available on amylopectin. Amylose synthesis occurs thereafter at rates approaching or exceeding those of net polysaccharide synthesis. Although these results suggested that amylose originates from cleavage of a pre-existing external amylopectin chain, such transfer of chains from amylopectin to amylose was directly evidenced from pulse-chase experiments. The structure of the in vitro synthesized amylose could not be distinguished from in vivo synthesized amylose by a variety of methods. Moreover high molecular mass branched amylose synthesis preceded that of the low molecular mass, suggesting that chain termination occurs consequently to glucan cleavage. Short pulses of synthesis followed by incubation in buffer with or without ADP-Glc prove that transfer requires the presence of the glucosyl-nucleotide. Taken together, these observations make a compelling case for amylopectin acting as the in vivo primer for amylose synthesis. They further prove that extension is followed by cleavage. A model is presented that can explain the major features of amylose synthesis in plants. The consequences of intensive amylose synthesis on the crystal organization of amylopectin are reported through wide angle x-ray analysis of the in vitro synthesized polysaccharides.