Overaccumulation of glycine betaine alleviates the negative effects of salt stress in wheat

To investigate the physiological mechanisms of glycinebetaine (GB) involved in the improvement of salt tolerance of wheat, three transgenic wheat (Triticum aestivum L.) lines-T1, T4, and T6-and the wild-type (WT) line Shi4185 were used. The transgenic lines were generated by introducing the BADH gene encoding betaine aldehyde dehydrogenase, which was cloned from Atriplex hortensis L. The BADH gene induced overexpression of GB in transgenic lines. Salt stress was induced by adding 200 mM NaCl, and the osmotic adjustment (OA), ion homeostasis, and antioxidant characteristics of wheat plants were observed. Under salt stress, the OA in the transgenic wheat lines was significantly higher than that in WT; this may be attributed to GB itself and/or the GB-induced overaccumulation of other osmolytes, such as free proline, soluble protein, and soluble sugar. Moreover, the transgenic lines could maintain the lower Na+ and Cl- concentrations in their leaves by accumulating these ions in the sheaths in order to protect the leaves from ion toxicity; however, these lines maintained a higher K+ concentration in the leaves since K+ functions as an osmolyte and maintains ion homeostasis in the leaf cells. Furthermore, the in vivo overaccumulated GB could enhance or stabilize the activity of antioxidant enzymes that can scavenge reactive oxygen species (ROS) and mitigate oxidative damage of biomembranes. The experimental results suggest that GB overexpression can enhance the salt tolerance of transgenic plants by regulating ion homeostasis, enhancing OA, and scavenging ROS.