Expression analysis of genes encoding plasma membrane aquaporins during seed and fruit development in tomato

Aquaporins facilitate water flux across biomembranes in plant cells, and are involved in various physiological phenomena in several plant tissues. To determine whether aquaporins have physiological roles during seed development, we analyzed the expression of genes encoding plasma membrane intrinsic proteins (PIPs) during seed and fruit development in tomato (Lycopersicon esculentum Mill.). Six genes encoding PIPs were detected in mature tomato seeds by RT-PCR using PCR primers corresponding to conserved transmembrane domains and NPA motifs. The expression of these genes in developing seeds and fruit was analyzed by RT-PCR using primers specific for nine tomato PIPs, including the six PIPs detected and an additional three PIPs from the tomato EST database. Increased expression of seven PIPs was detected during the earlier phase of seed development [12–32 days after flowering (DAF)], and the expression of these genes decreased during the later phase (36–56 DAF). Each tomato PIP showed a distinct expression pattern during fruit development. In addition, the water content of the cells was calculated. The seed water content decreased gradually in the earlier phase of seed development (12–32 DAF), and was subsequently maintained at 44–50% from 36 to 56 DAF, whereas the water content of the fruit remained at 90% throughout fruit development. These results suggest that plasma membrane aquaporins play a physiological role during seed and fruit development in tomato.