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.Abbreviations: MIPs, major intrinsic proteins; NIPs, nodulin 26-like intrinsic proteins; PIPs, plasma membrane intrinsic proteins; SIPs, small, basic intrinsic proteins; TIPs, tonoplast intrinsic proteins

The role of water channel proteins and nitric oxide signaling in rice seed germination

“…The mRNA of PsPIP1;1 or its possible homologs was detected in the dry and germinating seeds, suggesting that they could play a role in water absorption during seed imbibition [35]. It was also shown previously that the water channel proteins, BnPIP1and BnTIP2, play a role in seed germination [9].…”

Arabidopsis NIP2;1, a Major Intrinsic Protein Transporter of Lactic Acid Induced by Anoxic Stress

“…These observations, along with the general finding that aquaporin activities in roots are suppressed by flooding stress (45), suggest that AtNIP2;1 likely does not function as an aquaporin in vivo. In addition, unlike soybean nodulin 26 and other NIP aquaglyceroporins (5,(11)(12)(13)(14), AtNIP2;1 shows low permeability to glycerol. The surprising finding is that the protein mediates the flux of lactic acid.…”

“…AtNIP2;1F-expressing oocytes were tested for the uptake of lactic acid by incubation in bath solutions containing modified Frog Ringer's solution with 14 C-labeled lactic acid (20 mM) as described under "Experimental Procedures." A, 14 C-labeled lactic acid transport rate of control or AtNIP2;1F-expressing oocytes as a function of the media pH. Error bars show S.E.…”

“…As a final note, the transport properties of AtNIP2;1 are noteworthy from a structural and functional perspective of 14 C-labeled lactic acid uptake by oocytes expressing AtNIP2;1F or Nod26F or control oocytes injected with RNase-free water was done as described in Fig. 7.…”

A single locus confers tolerance to continuous light and allows substantial yield increase in tomato

“…RNA was extracted from a 3-week-old CLT tomato plant according to ref. 65 and purified with silica membranes columns. In short, 50 mg of frozen pulverized leaf tissue was homogenized with 500 ml of extraction buffer (350 mM glycine, 48 mM NaOH, 340 mM NaCl, 40 mM EDTA and 4% SDS) at 50°C.…”