Expression of the PmSUC1 sucrose carrier gene from Plantago major L. is induced during seed development

A cDNA clone of the plasma membrane sucrose-H⁺ sym- porter PmSUC1 from Plantago major L. has been isolated and expressed in Saccharomyces cerevisiae . The PmSUC1 protein was characterized in transgenic yeast and in proteoliposomes with an artificial proton-motive-force (pmf) generator. PmSUC1 catalyzes the active uptake of sucrose or maltose in the presence of pmf and is sensitive to uncouplers. Unlike the extremely pH-dependent PmSUC2 sucrose-H⁺ symporter, PmSUC1 is relatively insensitive to changes of the extracellular pH. In leaves and petioles of P. major , expression of PmSUC1 mRNA is restricted to the vascular system. The important new feature about PmSUC1 is that the highest mRNA levels are found in non-vascular tissue of P. major flowers where the gene is transiently expressed during the early stages of seed development. In situ hybridization experiments show that PmSUC1 is expressed only in young ovules; the putative physiological role of PmSUC1 is discussed.