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  • 1
    ISSN: 1432-2048
    Keywords: Key words: Aquaporin (γ-TIP) ; Brassica ; Gene expression ; Meristematic cell ; Tonoplast intrinsic protein ; Vacuole (membrane)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The vacuolar membrane (tonoplast) of plant cells contains aquaporins, protein channels that facilitate the selective transport of water. These tonoplast intrinsic proteins (TIPs) of 23–29 kDa belong to the ancient major intrinsic protein (MIP) family. A monospecific polyclonal antiserum directed against a 26 kDa intrinsic protein from the tonoplast of meristematic cells from cauliflower (Brassica oleracea L. var. botrytis) was used to screen a cDNA library. Two distinct cDNAs have been isolated. Both clones, c26-1 and c26-2, encode closely related TIPs. The c26-1 insert, consisting of 933 bp upstream of the poly(A) tail, is a full-length cDNA with an open reading frame encoding a protein of 251 amino acids with a calculated Mr of 25 500. The c26-2 insert is a 5′ truncated cDNA. The two cDNAs share 90.5% sequence identity within their overlapping coding regions but only 35% sequence identity in the 3′␣untranslated regions, indicating that highly related TIP-encoding genes are expressed in meristematic cells. Although TIPs have previously been found in a variety of cell types, they have not been found in meristems. The derived amino acid sequences (BobTIP26-1 and BobTIP26-2, respectively) closely resemble the aquaporin γ-TIP from Arabidopsis thaliana. Northern blot analysis and in situ hybridization show that BobTIP26 mRNAs preferentially accumulate in highly meristematic cells, mostly before and during cell enlargement, and in the living cells of the xylem. This differential pattern of expression is also found by immunodetection of BobTIP26 polypeptides. The gene expression patterns are discussed with respect to the probable function of the gene products.
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  • 2
    ISSN: 1432-2048
    Keywords: Key words: Aquaporin ; Brassica (cauliflower) ; Gene regulation ; Tonoplast ; Vacuole ; Water stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Changes in vacuolar structure and the expression at the RNA level of a tonoplast aquaporin (BobTIP26-1) were examined in cauliflower (Brassicaoleracea L. var. botrytis) under water-stress conditions. Gradual drying out of slices of cauliflower floret tissue caused its collapse, with a shrinkage in tissue and cell volumes and an apparent vesiculation of the central vacuole, whereas osmotic stress resulted in plasmolysis with a collapse of the cytoplasm and the central vacuole within. Osmotic stress caused a rapid and substantial increase in BobTIP26 mRNA in slices of floret tissue. Exposure of tissue slices to a regime of desiccation showed a slower but equally large rise in BobTIP26 mRNA followed by a rapid decline upon rehydration. In situ hybridization showed that BobTIP26-2 mRNA is expressed most highly in meristematic and expanding cells of the cauliflower florets and that desiccation strongly increased the expression in those cells and in differentiated cells near the xylem vessels. These data indicate that under water-deficit conditions, expression of the tonoplast aquaporin gene in cauliflower is subject to a precise regulation that can be correlated with important cytological changes in the cells.
    Type of Medium: Electronic Resource
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