ABSTRACT
I. 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 water 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 environment that maintains the macromolecular structure and function of proteins [5]. They are hypothesized 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], protecting membrane structure [17], and general maintenance of physiological stability under stressful conditions [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 engineering
This 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 accumulate) and the limitations associated with this approach are discussed.
