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  • Knowing that kiwifruit were very rich in vitamin C1, researchers at Plant & Food Research were prompted in 2002 to find out why. Initial investigations revealed that a biosynthetic pathway for vitamin2 C production in plants was not well understood, so they set about confirming a pathway first proposed by British scientists Glen Wheeler and Nickolas Smirnoff in 1998.

    Rights: Plant & Food Research Ltd

    Kiwifruit varieties

    Plant & Food Research has worked alongside the New Zealand kiwifruit industry for over 30 years breeding new varieties of kiwifruit from the genetic diversity housed in their germplasm collection. The most well known of these is 'Hort16A', known to the world as ZESPRI®GOLD Kiwifruit.

    The pathway consists of a number of steps, each one catalysed by a unique enzyme3. Several of these enzymes4 had been postulated but not identified. Using kiwifruit as an enzyme source, in 2004, the team were able to confirm the existence of an enzyme capable of converting L-galactose-1-phosphate into L-galactose, which was one of the steps in the process.

    Further research followed, and working with various kiwifruit varieties, coupled with the world’s largest kiwifruit DNA5 database, the team isolated the last undiscovered enzyme in the vitamin C production pathway. This enzyme is an important control6 point of vitamin C production in plants catalysing the step GDP-galactose to L-galactose-1-phosphate. This discovery in 2007 gained worldwide recognition and completed a scientific quest that began in Europe in the 1930s.

    Current research

    Plant & Food Research scientists have now turned their attention to the numerous varieties of kiwifruit and why it is that vitamin C levels vary markedly from one variety to another. Work is under way to try to identify the genes7 controlling the production of vitamin C in these different varieties.

    Dr Sean Bulley is a member of the team of scientists working on this project. He has identified a number of candidate genes from the kiwifruit database and is conducting experiments to validate8 their involvement.

    Rights: The University of Waikato Te Whare Wānanga o Waikato

    Dr Sean Bulley

    Dr Sean Bulley was one of the scientists responsible for Plant & Food Research’s breakthrough discovery of the missing link in our understanding of how plants produce vitamin C.

    Once this has been done, a plant breeding programme can be initiated that utilises these genes in such a way that the plant vitamin C production process is switched on to a higher than normal level. The knowledge gained from this work with kiwifruit can then be used to develop cultivars of other plants, such as apples, that will produce fruit with higher levels of vitamin C. Work is also being done to identify molecular markers9 that will enable the quick recognition of seedlings capable of high levels of vitamin C biosynthesis10. The fruit produced from these seedlings, on maturity, can be used by plant breeders to develop new varieties with high vitamin C content.

    Ultimately the aim is to help breeders identify good parents – breeders then make the cross. Seeds from the cross are collected and planted out, and seedlings are screened for the presence of correct marker11, greatly cutting down the numbers of seedlings to grow up to see what kind of fruit they bear, saving time and space. A limited number of selections are taken forward to advanced trials resulting in a new variety with desirable characteristics including high vitamin C. The new selections have to meet a range of criteria as only the best fruit will do.

    Importance of vitamin C

    Rights: University of Waikato

    Vitamin C – the antiscorbutic

    Dr Sean Bulley outlines some of the history surrounding the discovery of vitamin C and explains why its chemical name is ascorbic acid. He outlines its main function in the body. He explains why humans, unlike most other mammals, have lost the ability to synthesise their own vitamin C.

    Vitamin C is a crucial component in the human diet and although only small amounts are required on a daily basis (45mg per day) its long-term absence can result in death. Most of our daily requirement of vitamin C is obtained through the consumption of fresh fruit and vegetables. The outcomes of Plant & Food’s research programme could well be a fruit variety such as an apple or kiwifruit with a recommended daily dose12 of vitamin C in one piece of fruit.

    1. vitamin C: An antioxidant found in fruits and vegetables, such as oranges, kiwifruit, berries, tomatoes and leafy greens.
    2. vitamin: An organic compound required as a nutrient in tiny amounts by an organism.
    3. enzyme: A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
    4. enzyme: A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
    5. DNA: Deoxyribonucleic acid (DNA) is a molecule that contains the instructions needed for an organism to develop and function. These instructions are stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T).
    6. control: 1. Part of a scientific experiment in which no treatment has been applied in order to see whether there are any detectable differences to the experiment that did receive a treatment. 2. To hold in check or to curb.
    7. genes: A segment of a DNA molecule that carries the information needed to make a specific protein. Genes determine the traits (phenotype) of the individual.
    8. validate: To prove something is accurate. With remote sensing, it is a comparison of data obtained via satellite or other imaging with data collected by conventional means.
    9. marker: A short sequence of DNA within a genome that can be readily detected. Markers are usually associated with a known gene and provide information about which allele(s) of the gene an individual is likely to carry.
    10. biosynthesis: The production of a new molecule by a living organism.
    11. marker: A short sequence of DNA within a genome that can be readily detected. Markers are usually associated with a known gene and provide information about which allele(s) of the gene an individual is likely to carry.
    12. dose: The amount of a substance that comes into contact with a living organism or some part of a living organism.
    Published 18 March 2011 Referencing Hub articles
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        vitamin C

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      2. An antioxidant found in fruits and vegetables, such as oranges, kiwifruit, berries, tomatoes and leafy greens.

        DNA

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      4. Deoxyribonucleic acid (DNA) is a molecule that contains the instructions needed for an organism to develop and function. These instructions are stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T).

        validate

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      6. To prove something is accurate. With remote sensing, it is a comparison of data obtained via satellite or other imaging with data collected by conventional means.

        dose

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      8. The amount of a substance that comes into contact with a living organism or some part of a living organism.

        vitamin

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      10. An organic compound required as a nutrient in tiny amounts by an organism.

        control

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      12. 1. Part of a scientific experiment in which no treatment has been applied in order to see whether there are any detectable differences to the experiment that did receive a treatment.

        2. To hold in check or to curb.

        marker

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      14. A short sequence of DNA within a genome that can be readily detected. Markers are usually associated with a known gene and provide information about which allele(s) of the gene an individual is likely to carry.

        enzyme

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      16. A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.

        genes

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      18. A segment of a DNA molecule that carries the information needed to make a specific protein. Genes determine the traits (phenotype) of the individual.

        biosynthesis

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      20. The production of a new molecule by a living organism.