Springer Online Journal Archives 1860-2000
Abstract We isolated five sunflower (Helianthus annuus) cDNAs belonging to the TIP (tonoplast intrinsic protein) family. SunRb7 and SunγTIP (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 abundance increased, SunTIP18 decreased whereas that of SunTIP20 was transitorily enhanced. By contrast, SunRb7 and SunγTIP 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.
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