Food Biochemistry and Food Processing

11

Starch Synthesis in the Potato Tuber

P. Geigenberger* and A. R. Fernie

253

Introduction

What is Starch?

Routes of Starch Synthesis and Degradation and Their

Regulation

Manipulation of Starch Yield

Manipulation of Starch Structure

Conclusions and Future Perspectives

References

INTRODUCTION

Starch is the most important carbohydrate used for

food and feed purposes and represents the major

resource of our diet. The total yield of starch in rice,

corn, wheat, and potato exceeds 10^9 tons per year

(Kossmann and Lloyd 2000, Slattery et al. 2000). In

addition to its use in a nonprocessed form, due to the

low cost incurred, extracted starch is processed in

many different ways. Processed starch is subse-

quently used in multiple forms, for example in high-

fructose syrup, as a food additive, or for various tech-

nical processes based on the fact that as a soluble

macromolecule it exhibits high viscosity and adhe-

sive properties (Table 11.1). The considerable im-

portance of starch has made increasing the content

and engineering the structural properties of plant

starches major goals of both classical breeding and

biotechnology over the last few decades (Smith et al.

1997, Sonnewald et al. 1997, Regierer et al. 2002).

Indeed, since the advent and widespread adoption of

transgenic approaches some 15 years ago gave rise to

the discipline of molecular plant physiology, much

information has been obtained concerning the po-
tential to manipulate plant metabolism. For this chap-
ter we intend to review genetic manipulation of
starch metabolism in potato (Solanum tuberosum).
Potato is one of the most important crops world-
wide, ranking fourth in annual production behind
the cereal species rice (Oryza sativa),wheat (Triti-
cum aestivum),and maize (Zea mais).Although in
Europe and North America the consumption of pota-
toes is mainly in the form of processed foodstuffs
such as fried potatoes and chips, in less developed
countries it represents an important staple food and
is grown by many subsistence farmers. The main
reasons for the increasing popularity of the potato in
developing countries are the high nutritional value
of the tubers combined with the simplicity of its
propagation by vegetative amplification (Fernie and
Willmitzer 2001). Since all potato varieties are true
tetraploids and display a high degree of heterozy-
gosity, genetics have played only a minor role in
metabolic studies in this species. However, because
the potato is a member of the Solanaceaefamily, it
was amongst the first crop plants to be accessible to
transgenic approaches. Furthermore, due to its rela-
tively large size and metabolic homogeneity, the pota-
to tuber represents a convenient experimental sys-
tem for biochemical studies (Geigenberger 2003a).
In this chapter we will describe transgenic at-
tempts to modify starch content and structure in po-
tato tubers that have been carried out in the last two
decades. In addition to describing biotechnologic-
ally significant results we will also detail fundamen-
*Corresponding author. tal research in this area that should enable future

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing