title: Members of the aquaporin family in the developing pea seed coat include representatives of the PIP, TIP, and NIP subfamilies.
abstract: Water and nutrients required by developing seeds are mainly supplied by the phloem and have to be released from a maternal parenchyma tissue before being utilized by the filial tissues of embryo and endosperm. To identify aquaporins that could be involved in this process four full-length cDNAs were cloned and sequenced from a cDNA library of developing seed coats of pea (Pisum sativum L.). The cDNA of PsPIP1-1 appeared to be identical to that of clone 7a/TRG-31, a turgor-responsive gene cloned previously from pea roots. PsPIP1-1, PsPIP2-1, and PsTIP1-1, or their possible close homologues, were also expressed in cotyledons of developing and germinating seeds, and in roots and shoots of seedlings, but transcripts of PsNIP-1 were only detected in the seed coat. In mature dry seeds, high hybridization signals were observed with the probe for PsPIP1-1, but transcripts of PsPIP2-1, PsTIP1-1, and PsNIP-1 were not detected. Functional characterization after heterologous expression in Xenopus oocytes showed that PsPIP2-1 and PsTIP1-1 are aquaporins whereas PsNIP-1 is an aquaglyceroporin. PsNIP-1, like several other NIPs, contains a tryptophan residue corresponding with Trp-48 in GlpF (the glycerol facilitator of Escherichia coli) that borders the selectivity filter in the permeation channel. It is suggested that PsPIP1-1 and/or its possible close homologues could play a role in water absorption during seed imbibition, and that PsPIP2-1, possibly together with PsPIP1-1, could be involved in the release of phloem water from the seed coat symplast, which is intimately connected with the release of nutrients for the embryo.
authors.affiliation: Transport Physiology, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, Netherlands.
authors.forename: Jolanda A M J
authors.initials: JA
authors.lastname: Schuurmans
authors.forename: Joost T
authors.initials: JT
authors.lastname: van Dongen
authors.forename: Bas P W
authors.initials: BP
authors.lastname: Rutjens
authors.forename: Alex
authors.initials: A
authors.lastname: Boonman
authors.forename: Corné M J
authors.initials: CM
authors.lastname: Pieterse
authors.forename: Adrianus C
authors.initials: AC
authors.lastname: Borstlap
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020346:Aquaporins / Q000235:genetics* / Q000378:metabolism; D015152:Blotting, Northern; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D008845:Microinjections; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D009865:Oocytes / Q000378:metabolism; D009995:Osmosis; D018532:Pisum sativum / Q000235:genetics* / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018075:RNA, Complementary / Q000008:administration & dosage / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000235:genetics* / Q000254:growth & development; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014867:Water / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D020346:Aquaporins; D018076:DNA, Complementary; D010940:Plant Proteins; D018075:RNA, Complementary; D012333:RNA, Messenger; D014867:Water