Agriculture Reference
In-Depth Information
Chapter 13
Sugars as Antioxidants in Plants
Darin Peshev and Wim Van den Ende
1 Plant Carbohydrates: An Introduction
Typical plant carbohydrates consist of carbon, hydrogen and oxygen. Their empiri-
cal formula is C
m
(H
2
O)
n
. (m and n ≥ 3, m ≥ n). They are polyhydroxy aldehydes and
ketones with different degrees of polymerization (DP). On this basis, monosaccha-
rides (DP1), disaccharides (DP2), oligosaccharides (DP ≤ 10), and polysaccharides
(DP>10) can be distinguished. Some biomolecules do not strictly obey the empiri-
cal formula (e.g., chitin), but they are still considered as carbohydrates.
Carbohydrates are the most abundant biomolecules on the planet. They ful-
fill numerous functions in living beings (He and Liu
2002
), especially in plants
(Lewis
1984
). Polysaccharides are often used to store energy (e.g., starch, glycogen,
fructans), or to make up structural components (e.g., cellulose and chitin). Ribose
and deoxyribose form an integral part of RNA and DNA. Ribose is also a part of
NAD(P)H and ATP which are important cellular metabolites.
Numerous carbohydrates are recognized participants in stress responses in plants
and other living beings. This chapter will discuss in detail the relations between
carbohydrates and plant stress responses, particularly focusing on their role in
the plant antioxidant network. First, the plant stresses are introduced. Second, the
metabolism of stress-related sugars is highlighted. Third, the actual functions of
different types of sugars in plants will be discussed, with special attention on the
emerging “sugar as antioxidant” concept in which sugars act as true ROS scaven-
gers in plants. Finally, how these insights might be exploited to create stress-tolerant
crops in the near future is discussed.
