Abstract
The accumulation of compatible solutes such as glycine betaine (betaine) and proline is one of the adaptive strategies for salt and drought stresses. It was shown that betaine is translocated in barley plants. However, little is known about the mechanisms of betaine transport at molecular level in barley plants. We have previously isolated the gene encoding a betaine/proline transporter, HvGB/ProT1 from barley plants. The purpose of this study is to elucidate the physiological role of HvGB/ProT1.
The transport assays using yeast strain 22574d showed that HvGB/ProT1 transports betaine and proline coupled with H+. Onion epidermal cells expressing HvGB/ProT1:GFP fusion protein indicated that HvGB/ProT1 is localized at the plasma membrane. The expression level of HvGB/ProT1 was higher in old leaves than in young leaves. On the other hand, the expression level was low in roots. Moreover, we determined the tissue-specific expression of HvGB/ProT1 by in situ hybridization. HvGB/ProT1 was expressed in xylem parenchyma cells and mestom sheath in leaves. On the other hand, in root tip, cross sections showed that expression of HvGB/ProT1 is restricted mainly to lateral root cap.
