Expression of Vp1 and water channel proteins during seed germination

Germination of seeds from individual seed capsules of Mesembryanthemum crystallinum (common ice plant) is spread out over time with some seeds germinating within 1 d (early, E) and others germinating up to more than 4 weeks after imbibition (late, L). L-seeds are characterized by a lack of expression of Cdc2-related transcripts and an increase of Vp1-transcripts after water uptake, while Cdc2-related transcripts increase early and Vp1 decline early in E-seeds, Maintenance of Vp1 transcription, which can be disrupted by abolishing translation activity, seems to be at the basis of prolonged dormancy in L-seeds. We have in addition characterized the expression of several MIP (water channel) proteins during germination and in organs of adult plants. Using probes specific for individual ice plant Mip, we observed differences during germination that are not exclusively due to water uptake, Mip transcripts increase before L-seeds begin to germinate. Gene-specific probes indicate that the expression of all Mip is high in germinating seedlings, but differences in expression exist in the root, hypocotyl and cotyledon, In adult plants, all Mip-transcripts are expressed at a significantly lower rate than in seedlings, and organ-specific expression of individual Mip transcripts is observed. Their expression, measured by MIP-specific antibodies, indicates developmental specificity of MIP in different organs and highest amounts in actively growing tissues.