Tissue specificity of glycinebetaine synthesis in barley

Glycinebetaine is a major compatible solute accumulated in response to salt stress in barley plants. In this study, we investigated the glycinebetaine content and tissue localization of mRNA of two betaine aldehyde dehydrogenase (BADH) genes, BBD1 and BBD2, and of BADH proteins in barley plants grown under control and saline conditions. Glycinebetaine was increased by salt treatment, and accumulated more in younger leaves than in older ones under both control and saline conditions. While BBD1 and BBD2 genes were constitutively expressed in mesophyll cells of leaves under both control and saline conditions, the signal of BBD2 transcripts increased strongly in vascular parenchyma cells in salt-stressed leaves. In roots under saline conditions, BBD1 transcripts were detected in epidermal cells, and BBD2 transcripts were detected in the pericycle. Moreover, BADH proteins were detected around the xylem vessels of leaves, and in the pericycle and epidermal cells of roots grown under a saline condition. These results suggested that glycinebetaine is synthesized in vascular tissues of leaves and the pericycle of roots in barley plants grown under salt stress.