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Two TIP-like genes encoding aquaporins are expressed in sunflower guard cells

Sarda, X., Tousch, D., Ferrare, K., Legrand, E., Dupuis, J.M., Casse-Delbart, F., Lamaze, T.
The plant journal 1997 v.12 no.5 pp. 1103-1111
Helianthus annuus, genes, gene expression, histochemistry, guard cells, plant proteins, complementary DNA, amino acid sequences, nucleotide sequences, permeability, water, mercury, leaves, messenger RNA, stomatal movement, leaf conductance, diurnal variation, water stress, water uptake, chemical constituents of plants
SunTIP7 and SunTIP2O are closely related sunflower cDNAs showing a deduced amino acid sequence homologous to proteins of the tonoplast intrinsic protein (TIP) family. Their expression in Xenopus oocytes caused a marked increase in osmotic water permeability (demonstrating that they are water channels) which was sensitive to mercury. In leaves, in situ hybridization revealed that both SunTIP7 and SunTIP2O mRNA accumulated in the guard cells. The possible involvement of SunTIPs in stomatal movement was examined by comparing the time course of transcript accumulation and leaf conductance during the daily cycle and following a water limitation. SunTIP7 mRNA fluctuations fitted changes occurring in leaf conductance. The transcript levels were markedly and systematically increased during stomatal closure. It is suggested that aquaporin SunTIP7 facilitates water exit associated with a decrease in guard cell volume. In the same conditions, the transcript level of SunTIP2O remained constant indicating that SunTIP genes are differentially regulated within the same cell.