Fifteen potato (Solanum tuberosum L.) clones with varying resistance to cold-induced sweetening were analysed for vacuolar acid invertase (AcInv, EC 188.8.131.52) and UDP-Glc pyrophosphorylase (UGPase; EC 184.108.40.206) activities related to their ability to accumulate sugars following cold storage (4 C). The UGPase isozyme profiles for each clone were also determined. Immunoblot analysis demonstrated a 55 kD protein, in seven of the 15 clones, that reacted with UGPase antisera in addition to the 53 kD UGPase subunit previously reported. The UGPase activity of these clones was significantly lower than that of the "single subunit" clones. Basal AcInv activity showed a positive correlation to the Glc:Suc ratio across the clones that was moderately significant before and after cold temperature storage. The activity of UGPase, which limits the rate of Suc formation, was of secondary importance in limiting the rate of hexogenesis when vacuolar AcInv activity was excessive. It is suggested that with the potato clones from this breeding program that AcInv (and its inhibitor) plays a dominant role in the hexogenic pathway by regulating the hexose:Suc ratio. The finding of a new protein that is reactive with UGPase antisera may prove to play an important function in the regulation of Suc formation in potatoes.
Bibliographical noteFunding Information:
We gratefully acknowledge the New Zealand Institute for Crop & Food Research Limited fellowship program for financing MJM's travel and research in Minnesota, as well as the ISAT linkages fund (Royal Society of New Zealand) for its support towards travel costs. We thank Russell Genet (New Zealand Institute for Crop & Food Research Ltd), the principle breeder of 2852.5 and 2885.1, for use of these clones; and Maaike Bendall and Duncan Hedderley for their assistance with the statistical analysis. Finally, a warm thank you to the members of the USDA/ARS Potato Research Worksite, the Minnesota State Seed Laboratory, East Grand Forks, MN, and the Northern Crop Science Laboratory, Fargo, ND, for their hospitality and kindness during the time MJM was there.
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- Cold storage
- Invertase inhibitor