Similar temperature requirement for sugar accumulation and for the induction of new forms of sucrose phosphate synthase and amylase in cold-stored potato tubers.
Deiting, U., Zrenner, R. and Stitt, M.
Plant, Cell and Environment, Volume 21, Number 2, February 1998 , pp. 127-138
1998
บทคัดย่อ
The onset of sugar accumulation in cold-stored potato tubers coincides with an activation of sucrose phosphate synthase (SPS) and the appearance of a new form of amylase (Hill et al. 1996; Nielsen et al. 1997). To provide more evidence that these changes are involved in the regulation of cold-induced sugar accumulation we have compared the temperature dependence of sugar accumulation with the temperature dependence of changes in SPS and amylase activity. To do this, we investigated: sugars and metabolites; SPS activity, protein and transcript; invertase activity; and amylolytic activity and amylase forms. during the first 10 d after transferring tubers from room temperature to 3, 5, 7, 9 and 11 degrees C. After 10 d there was negligible accumulation of sugars at 11, 9 and 7 degrees C, and a large accumulation at 5 and 3 degrees C. Activation of SPS was assayed by comparing activity in an assay with limiting substrates and phosphate and an assay with saturating substrate concentrations. The activation state increased slightly at 7 degrees C, 3- to 4-fold at 5 degrees C and 5- to 6-fold at 3 degrees C. The cold-induced change in the kinetic properties of SPS was accompanied by the appearance of a new form of SPS with a slightly higher apparent molecular weight, and by an increase of the SPS transcript. The changes in SPS protein and transcript showed the same temperature dependence as the changes in the kinetic properties. Total starch hydrolysing enzyme activity was unaltered at 7 degrees C, increased at 5 degrees C and increased further (up to 7- to 8-fold) at 3 degrees C. The increase in amylolytic activity correlated with the appearance of a new amylase band on zymograms. Acid invertase activity showed a similar increase at 3, 5, and 7 degrees C, and it did not correlate with the total sugar accumulation. The cold-induced accumulation of sugar can be reversed by transferring tubers back to warmer temperatures. We compared the decline of sugar levels with the changes of SPS, amylolytic activity and metabolites at various times (up to 14 d) after transfer of tubers from a 4 degrees C storage (for 14 d) back to 20 degrees C. SPS activation state is reversed and the cold induced form of SPS virtually disappears during the first 2-4 d at 20 degrees C. The cold-induced amylase activity also vanishes within 2-4 d.