PARENT SESSION
Posters P1C Photosynthate transport and transporters. Abstracts (612-613)

Diurnal changes in gene expression and enzymatic activity of starch phosphorylase in rapidly-bulking potato tubers. Xiu-Qing Li^*,1, Chang-Ai Xu¹, Muhammad Haroon¹, Merideth Bonierbale², Dapeng Zhang², Fan-Rui Meng³, ¹ Agriculture and Agri-Food Canada, Fredericton, New Brunswick, Canada^{2 3}

ABSTRACT- Enzymes involved in converting sucrose to starch in rapidly bulking potato tubers are expected to have diurnal changes in their gene expression and enzymatic activity patterns because of the diurnal nature of sucrose import from photosynthetic leaves. Starch phosphorylase (STPase) catalyzes a reversible reaction that can degrade as well as synthesize starch. However, despite the reporting of the importance of this enzyme in starch degradation, it is still unclear whether this enzyme plays also a positive role in starch accumulation. To gain insight into the role of STPase in starch accumulation in potatoes (Solanum tuberosum), we compared the diurnal change pattern of STPase gene expression behavior with that of ADP-glucose pyrophosphorylase (AGPase), which is known to be very important for starch accumulation. Greenhouse plants of two potato varieties (cv Shepody, a tetraploid; and cv 11379-03, a diploid) at the rapid tuber-bulking phase were used to analyze gene expression, enzyme activity, photosynthesis, and dry matter content. Sampling of leaves and tubers was conducted at 5 AM, 9 AM, noon, and 9 PM. Expression of STPase was found to be much more active in starch-accumulating tubers than that of AGPase. STPase enzymatic activity had a similar diurnal pattern to that of AGPase in both leaves and tubers, within the resolution limit of the sampling intervals. The results suggest that STPase plays a positive role in starch accumulation in these rapidly bulking potato tubers and that the transport of photosynthate sucrose from leaves to tubers is relatively rapid.

KEY WORDS: photosynthate partition and accumulation, storage organ, photosynthate transport, starch synthesis