High expression of putative aquaporin genes in cells with transporting and nutritive functions during seed development in Norway spruce (Picea abies).

Aquaporins mediate the bidirectional passage of water over membranes and are present in tonoplasts (TIPs) and in plasma membranes (PIPs) of plant cells. Knowing their expression in different tissues is valuable when assessing their contribution to plant water relations. A TIP-gene has been cloned from developing female gametophytes of Picea abies, a conifer displaying an embryology different from the angiosperms. Probes were made from conserved regions of the TIP gene and used for in situ hybridization to examine the gene expression pattern in developing female reproductive structures. Early during development high transcript expression was found in the spongy tissue encasing the developing female gametophyte, in cells of the future seed coat of young ovules and in vascular tissue of the ovuliferous scale. At later stages a strong signal was seen in archegonia jacket cells surrounding egg cells and, still later, at the time of storage protein accumulation, in storage parenchyma cells of the gametophyte as well. These aquaporin-homologues probably participate in regulating water balance in the cells although they could also be permeable to other molecules than water.