Characterization and expression of plasma and tonoplast membrane aquaporins in primed seed of Brassica napus during germination under stress conditions
1999
Gao, Y.P. | Young, L. | Bonham-Smith, P. | Gusta, L.V.
Two aquaporin genes were isolated from a cDNA library of canola (Brassica napus L.). The first aquaporin, BnPIPl of 1094 bp, encoding a putative polypeptide of 287 amino acids with a predicted molecular mass of 30.4 kDa and a pI of 7.8, belongs to the family of plasma membrane intrinsic protein (PIPs) aquaporins. The B. napus aquaporin showed 85-94% identity to the Arabidopsis thaliana PIPs. ABA priming of seed induced high levels of BnPIPl transcript which remained after subsequent re-drying of the seed. The second aquaporin, Bngamma-TIP2 of 1020 bp, encoded a putative polypeptide of 253 amino acids with a predicted molecular mass of 25.8 kDa and a pI of 5.8. Bngamma-TIP2 showed 83-90% identity to gamma-TIP genes from a variety of plant species. Bngamma-TIP2 was expressed only when radicle protrusion occurred in either untreated or primed seeds. Seeds primed with PEG or ABA germinated earlier and showed a higher final percentage of germination than unprimed seed, particularly under salt and osmotic stresses at low temperature. Transcripts of both BnPIPl and Bngamma-TIP2 genes were present earlier during germination of primed seeds than non-primed seed. From these results, we conclude that BnPIPl is related to the water transportation required for enzymatic metabolism of storage nutrients at the early stages of canola seed germination whereas Bngamma-TIP2 expression is related to cell growth associated with radicle protrusion. Priming induced the expression of BnPIPl but had no effect on Bngamma-TIP2.
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