THE EXPRESSION OF AN AQUAPORIN PROMOTER FROM MESEMBRYANTHEMUM-CRYSTALLINUM IN TOBACCO

The promoter region of the MipB gene encoding an aquaporin from Mesemb ryanthemum crystallinum was isolated and used in st transcriptional fu sion to control uidA expression in tobacco. The sequence of tile promo ter,vas determined for 2 kb upstream of the translation initiation sit e, Three start sites were utilized with approximately equal frequency, located 176, 170, and 161 bases, respectively, upstream of the transl ation initiation site. As judged by analysis of GUS expression, promot er MipB retains its specificity in transgenic tobacco, In germinating seedlings, all cells showed GUS expression of different intensifies wi th the strongest signals in root meristems, In older seedli ngs, GUS s taining was observed in rapidly expanding cells-root and apical merist em, and lateral root primordia. In mature plants, strong GUS activity was located to glandular trichomes, subepidermal cells of the stem and petioles, to cells surrounding vascular tissues as well as in xylem p arenchyma cells. In immature floral organs, GUS expression was strong in sepals, petals, stamen, and pistil, The intensity declined as they matured. In general, this promoter was active in rapidly expanding cel ls and cells with high water Aus capacity, especially in the xylem par enchyma.