Post-translational regulation of acid invertase activity by vacuolar invertase inhibitor affects resistance to cold-induced sweetening of potato tubers

Authors

  • MARIAN J. MCKENZIE,

    Corresponding author
    1. The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Private Bag 11600, Palmerston North 4442, New Zealand
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  • RONAN K. Y. CHEN,

    1. The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Private Bag 11600, Palmerston North 4442, New Zealand
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  • JOHN C. HARRIS,

    1. The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Private Bag 11600, Palmerston North 4442, New Zealand
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    • Present address: Australian Centre for Plant Functional Genomics, Waite Campus, University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.

  • MATTHEW J. ASHWORTH,

    1. Institute of Environmental Science and Research Limited, PO Box 29-181, Christchurch 8540, New Zealand
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  • DAVID A. BRUMMELL

    Corresponding author
    1. The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Private Bag 11600, Palmerston North 4442, New Zealand
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M. J. McKenzie. Fax: +64 6 351 7050; e-mail: marian.mckenzie@plantandfood.co.nz; or D. A. Brummell. E-mail: david.brummell@plantandfood.co.nz

ABSTRACT

Cold-induced sweetening (CIS) is a serious post-harvest problem for potato tubers, which need to be stored cold to prevent sprouting and pathogenesis in order to maintain supply throughout the year. During storage at cold temperatures (below 10 °C), many cultivars accumulate free reducing sugars derived from a breakdown of starch to sucrose that is ultimately cleaved by acid invertase to produce glucose and fructose. When affected tubers are processed by frying or roasting, these reducing sugars react with free asparagine by the Maillard reaction, resulting in unacceptably dark-coloured and bitter-tasting product and generating the probable carcinogen acrylamide as a by-product. We have previously identified a vacuolar invertase inhibitor (INH2) whose expression correlates both with low acid invertase activity and with resistance to CIS. Here we show that, during cold storage, overexpression of the INH2 vacuolar invertase inhibitor gene in CIS-susceptible potato tubers reduced acid invertase activity, the accumulation of reducing sugars and the generation of acrylamide in subsequent fry tests. Conversely, suppression of vacuolar invertase inhibitor expression in a CIS-resistant line increased susceptibility to CIS. The results show that post-translational regulation of acid invertase by the vacuolar invertase inhibitor is an important component of resistance to CIS.

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