45
Glycine Betaine Accumulation: Its Role in Stress
Resistance in Crop Plants
G. V. Subbarao*, Lanfang He Levine, and Gray W. Stutte
Dynamac Corporation, Kennedy Space Center, Florida
Raymond M. Wheeler
National Aeronautics and Space Administration, Kennedy Space Center, Florida
881I. INTRODUCTION
The concept of compatible solutes was first introduced by Brown and Simpson [1] to define substances
that accumulate in the cytoplasm that are noninhibitory to metabolism when subjected to low external wa-
ter potentials. Compatible solutes that accumulate in higher plants include glycerol, sucrose, trehalose,
pinitol, proline, and betaines [2–8]. Plants accumulate these solutes as an adaptive mechanism to stresses
such as salinity, water deficit, and temperature extremes [5,9]. Compatible solutes provide a cellular en-
vironment that maintains the macromolecular structure and function of proteins [5]. They are hypothe-
sized to have functions including cytoplasmic osmotic adjustment [2,10], protecting cytoplasm and
chloroplasts from Na damage, hydroxyl radical scavenging [11], stabilization of proteins [12–16], pro-
tecting membrane structure [17], and general maintenance of physiological stability under stressful con-
ditions [5,8,18]. Information on the adaptive role of glycine betaine (GB) in plant stress resistance comes
from studies on
Foliar application of GB to plants
Enhancing GB levels through traditional breeding or genetic engineeringThis chapter summarizes the current state of knowledge and understanding of GB accumulation and
distribution in plants. Areas covered include distribution among plant species, biosynthetic pathway, and
GB’s adaptive significance to stress environments. Analytical methodologies for GB are also reviewed.
The potential for introducing the GB biosynthetic pathway into crop plants (that do not naturally accu-
mulate) and the limitations associated with this approach are discussed.
A. Glycine Betaine Accumulation in Higher Plants
Several families of flowering plants have the ability to synthesize GB (Table 1). However, osmotically
significant amounts are detected in only a few families. Glycine betaine synthesis appears to be constitu-
tive as significant amounts are produced under nonstress growing conditions [21]. In GB-accumulating
species, GB synthesis can increase severalfold under stress (Table 2). Several GB-nonaccumulating
species have the ability to synthesize this compound but at very low levels ( 1 mol g^1 dwt), about 100
to 1000 times less than GB accumulators [8,36]. Accumulators and nonaccumulators are often found
- Current affiliation: Japan International Research Center for Agricultural Sciences, Ibaraki, Japan