Plant Molecular Biology 40: 179–191, 1999.
© 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Characterization of closely related δ-TIP genes encoding aquaporins
which are differentially expressed in sunﬂower roots upon water
deprivation through exposure to air
, Didier Tousch
, Karine Ferrare
, Françoise Cellier
, Carine Alcon
, Jean Marc
, Francine Casse
and Thierry Lamaze
Biochimie & Physiologie Mol´eculaire des Plantes, ENSA-M/INRA/CNRS URA 2133/UM II, 2 place Viala,
34060 Montpellier Cedex 1, France (
author for correspondence);
Rhône-Poulenc Agrochimie, rue Pierre
Baizet, 69009 Lyon, France;
CESBIO (UPS/CNRS/CNES, UMR 56390), Universit´e Paul Sabatier, 118 route
de Narbonne, 31062 Toulouse Cedex, France
Received 21 July 1998; accepted in revised form 7 January 1999
Key words: aquaporin, root, TIP, water deprivation
We isolated ﬁve sunﬂower (Helianthus annuus) cDNAs belonging to the TIP (tonoplast intrinsic protein) family.
SunRb7 and Sunγ TIP (partial sequence) are homologous to tobacco TobRb7 and Arabidopsis γ-TIP, respectively.
SunTIP7, 18 and 20 (SunTIPs) are closely related and homologous to Arabidopsis δ-TIP (SunTIP7 and 20 have
already been presented in Sarda et al., Plant J. 12 (1997) 1103–1111). As was previously shown for SunTIP7 and
20, expression of SunTIP18 and SunRb7 in Xenopus oocytes caused an increase in osmotic water permeability
demonstrating that they are aquaporins. In roots, in situ hybridization revealed that SunTIP7 and 18 mRNAs
accumulate in phloem tissues. The expression of TIP-like genes was studied in roots during 24 h water deprivation
through exposure to air. During the course of the treatment, each SunTIP gene displayed an individual response:
SunTIP7 transcript abundanceincreased, SunTIP18 decreased whereas that of SunTIP20 was transitorily enhanced.
By contrast, SunRb7 and Sunγ TIP mRNA levels did not ﬂuctuate. Due to the changes in their transcript levels, it
is proposed that SUNTIP aquaporins encoded by δ-TIP-like genes play a role in the sunﬂower response to drought.
Aquaporins are water channels which can facilitate the
passage of water across biological membranes. These
proteins belong to the large major intrinsic protein
(MIP) family of transmembrane channels that are rep-
resented in all kingdoms (Chrispeels and Agre, 1994;
Chrispeels and Maurel, 1994; Agre et al., 1995). In
plants, aquaporins have been localized to the tono-
plast (TIP) and the plasma membrane (PIP); a third
subfamily (Nod-MIP) includes proteins homologous
to Nod26: a protein located in the peribacteroid mem-
The nucleotide sequence data reported will appear in the
EMBL, GenBank and DDBJ Nucleotide Sequence Databases under
the accession numbers X95950 (SunTIP7), X95951 (SunTIP18),
X95952 (SunTIP20), X95953 (SunRb7) and X95954 (Sunγ TIP).
branes of symbiotic soybean root nodules (for review
see Maurel, 1997).
Aquaporins are assumed to contribute signiﬁcantly
to the hydraulic conductivity in Chara internode cells
(Henzler and Steudle, 1995; Tazawa et al., 1996). The
high levels of aquaporins present in the tonoplast of
tobacco and maize cells indicate that they could play
an important role in cell osmoregulation (equilibra-
tion between the cytosol and the vacuole) (Maurel,
1997; Barrieu et al., 1998) and TIP-like aquaporins
could be involved in sunﬂower stomatal movements
(Sarda et al., 1997). The high expression of ZmTIP1
in tissues involved in water transport suggests a role in
transcellular water ﬂow through living cells (Barrieu
et al., 1998). Moreover, some aquaporins are preferen-
tially located in the elongation zones of young organs