Abstract
Aquaporins influence water flow in plants, yet little is known of their involvement in the water‐driven process of seed germination. We therefore investigated their role in seeds in the laboratory and under field and global warming conditions. We mapped the expression of tonoplast intrinsic proteins (TIPs) during dormancy cycling and during germination under normal and water stress conditions. We found that the two key tonoplast aquaporins, TIP3;1 and TIP3;2, which have previously been implicated in water or solute transport, respectively, act antagonistically to modulate the response to abscisic acid, with TIP3;1 being a positive and TIP3;2 a negative regulator. A third isoform, TIP4;1, which is normally expressed upon completion of germination, was found to play an earlier role during water stress. Seed TIPs also contribute to the regulation of depth of primary dormancy and differences in the induction of secondary dormancy during dormancy cycling. Protein and gene expression during annual cycling under field conditions and a global warming scenario further illustrate this role. We propose that the different responses of the seed TIP contribute to mechanisms that influence dormancy status and the timing of germination under variable soil conditions.
Highlights
Water content in seeds changes dramatically during imbibition to drive radicle extension through its emergence from the seed coat to complete germination
Seeds were surface sterilized in the dark under a green safe light, and 3 × 40 seeds were placed on to nylon strips in boxes set up as used for investigating base water potential above and cold conditioned at 5°C/−1.0 MPa/dark for 28 days to reduce primary dormancy to the point at which dormancy can be completely removed by exposure to light
As laboratory‐based tests showed a role for TIP3 isoforms in dormancy regulation, we examined their response in microarray data where dormancy was set at different levels in the laboratory (Cadman, Toorop, Hilhorst, & Finch‐Savage, 2006; Finch‐Savage, Cadman, Toorop, Lynn, & Hilhorst, 2007)
Summary
Water content in seeds changes dramatically during imbibition to drive radicle extension through its emergence from the seed coat to complete germination. We investigated their role in natural variable environments by extending our analysis to look at TIP3 gene expression and protein accumulation during dormancy cycling under field conditions and under a global warming scenario in a thermogradient tunnel. We discuss the roles of these aquaporins as seed dormancy changes and seeds germinate in response to the environment
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