Date: July 2000
Creator: Haritatos, Edith Emily, 1969-; Ayre, Brian G. & Turgeon, Robert
Description: This article discusses identification of phloem. Abstract: The definition of "minor" veins in leaves is arbitrary and of uncertain biological significance. Generally, the term refers to the smallest vein classes in the leaf, believed to function in phloem loading. The authors found that a galactinol synthase promoter, cloned from melon (Cucumis melo), directs expression of the gusA gene to the smallest veins of mature Arabidopsis and cultivated tobacco (Nicotiana tabacum) leaves. This expression pattern is consistent with the role of galactinol synthase in sugar synthesis and phloem loading in cucurbits. The expression pattern in tobacco is especially noteworthy since galactinol is not synthesized in the leaves of this plant. Also, the authors unexpectedly found that expression in tobacco is limited to two of three companion cells in class-V veins, which are the most extensive in the leaf. Thus, the "minor" vein system is defined and regulated at the genetic level, and there is heterogeneity of response to this system by different companion cells of the same vein.
Contributing Partner: UNT College of Arts and Sciences