Dissecting the Role of Glycine Betaine in Plants under Abiotic Stress

Among the compatible solutes, glycine betaine (GB) is particularly an effective osmolyte against abiotic stress. Metabolic acclimation of GB is regarded as a basic strategy for the protection and survival of plants in harsh environmental conditions. Plant species vary in their capacity to synthesize GB. Some plants, such as spinach and barley, accumulate relatively higher levels of GB in their chloroplasts while others, like Arabidopsis and tobacco, lack this compound. The accumulation of GB is induced under stress conditions and the level of GB is correlated with the degree of tolerance to stress. Genetic engineering has allowed the introduction of genes of its biosynthetic pathway into GB-deficient species from both microorganisms and higher plants. This approach has facilitated investigation of the importance of GB in stress protection. However, the level of GB in transgenic plants is relatively low. An alternative approach of exogenous application of GB to plants under stress has gained some attention. In this review, the protective role of GB in conferring tolerance to plants against various abiotic stresses through both exogenous application and genetic engineering has been summarized. _____________________________________________________________________________________________________________