Tomato cell wall studies

The psubunit has been purified from PGl by ourselves and others and is a heat stable, acidic, heavily glycosylated protein with an apparent molecular mass of 37-39 kD (19, 26). No enzymatic activity has been identified for the protein. The psubunit can be extracted from the cell walls of both green and ripe tomato fruit by high salt buffers (13, 14, 18, 19, 20), and in the latter case is associated with PG2 polypeptide(s) in the form of PGl. Purified psubunit can also associate with and convert PG2 in vitro into an isoenzyme that closely resembles PGl (13, 14, 24). Biochemical studies have shown that in vivo and in vitro formation of PGl by the association of PG2 with the p-subunit alters the biochemical and enzymic properties of the associated catalytic PG2 polypeptide including its pH optima, response to cations and thermal stability (summarized in Table 1). This later property provides a convenient assay for the levels of PGl and PG2 in total cell wall protein extracts. 

Colonization of tomato root tissues by FORL is associated with striking modifications of host cell walls, as it has been shown by ultrastructural studies which have been carried out describing the penetration of the fimgus through... 

The effect of a reduced polygalacturonase activity in cell walls of transgenic tomatoes was studied by I3C CPMAS NMR in order to investigate the ripening... 

Studies with ABA mutants have not yet contributed substantially to the expansion of our knowledge concerning the molecular action of ABA. Studies with tomato mutants indicate an important role for ABA in regulating membrane and cell wall structure [see 18 for review]. During seed development applied ABA stimulates protein synthesis both by maintaining levels of mRNA stability and promoting RNA synthesis [19]. The aba abi3 recombinant may allow these experiments to be shifted to an in vivo situation. 

Methylation analysis of the tetra-arabinosides isolated from primary cell walls of tomato and sycamore indicates that the arabinosyl residues are terminal and 2- and 3-linked (71, 123). Akiyama and Kato (2) have studied the hydroxyproline arabinosides obtained from suspension-cultured cells of tobacco (Nicotiana tabacum). These workers used periodate oxidation (Smith degradation), methylation analyses, NMR, and optical rotation to show that the structure of the hydroxyproline tetra-arabinoside is Araf-(1 3)-Araf-(l - 2)-Arar(l - 2)-Arar(l - 4)-hydroxyproline. 

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