Biomedical subjects

A. B. Bennett

Publications and source records attributed to A. B. Bennett.

4 recordsLinked to original sources

PubMed1996

Differential Expression of Two Endo-1,4-[beta]-Glucanase Genes in Pericarp and Locules of Wild-Type and Mutant Tomato Fruit.

The mRNA accumulation of two endo-1,4-[beta]-D-glucanase genes, Cel1 and Cel2, was examined in the pericarp and locules throughout the development of normal tomato (Lycopersicon esculentum) fruit and the ripening-impaired mutants rin and Nr. Both Cel1 and Cel2 were expressed transiently at the earliest stages of fruit development during a period corresponding to cell division and early cell expansion. In the pericarp, the mRNA abundance of both genes increased markedly at the breaker stage; the level of Cel1 mRNA decreased later in ripening, and that of Cel2 increased progressively. Cel2 mRNA levels also increased at the breaker stage in locules but after initial locule liquefaction was already complete. In rin fruit mRNA abundance of Cel1 was reduced and Cel2 was virtually absent, whereas in Nr Cel1 was expressed at wild-type levels and Cel2 was reduced. In wild-type fruit ethylene treatment slightly promoted the mRNA accumulation of both genes. In rin fruit ethylene treatment strongly increased the mRNA abundance of Cel1 to an extent greater than in wild-type fruit, but Cel2 mRNA was absent even after ethylene treatment. These two endo-1,4-[beta]-D-glucanase genes, therefore, do not show coordinated expression during fruit development and are subject to distinct regulatory control. These results suggest that the product of the Cel2 gene contributes to ripening-associated cell-wall changes.

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PubMed1996

A Single Gene May Encode Differentially Localized Ca2+-ATPases in Tomato.

Previously, a partial-length cDNA and a complete genomic clone encoding a putative sarcoplasmic reticulum-type Ca2+-ATPase (LCA, Lycopersicon Ca2+-ATPase) were isolated from tomato. To determine the subcellular localization of this Ca2+-ATPase, specific polyclonal antibodies raised against a fusion protein encoding a portion of the LCA polypeptide were generated. Based on hybridization of the LCA cDNA and of the nucleotide sequence encoding the fusion protein to genomic DNA, it appears that LCA and the fusion protein domain are encoded by a single gene in tomato. Antibodies raised against the LCA domain fusion protein reacted specifically with two polypeptides of 116 and 120 kD that are localized in the vacuolar and plasma membranes, respectively. The distribution of vanadate-sensitive ATP-dependent Ca2+ transport activities in sucrose gradients coincided with the distribution of the immunodetected proteins. The ATP-dependent Ca2+ transport activities associated with tonoplast and plasma membrane fractions shared similar properties, because both fractions were inhibited by vanadate but insensitive to carbonyl cyanide m-chlorophenylhydrazone, nitrate, and calmodulin. Moreover, antibodies raised against the LCA domain fusion protein inhibited ATP-dependent Ca2+ uptake activity associated with both the tonoplast and plasma membrane fractions. These data suggest that a single gene (LCA) may encode two P-type Ca2+-ATPase isoforms that are differentially localized in the tonoplast and plasma membrane of tomato roots.

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PubMed1994

Tomato Fruit Polygalacturonase Isozyme 1 (Characterization of the [beta] Subunit and Its State of Assembly in Vivo).

Polygalacturonase isozyme 1 (PG1) is a heterodimer comprising a catalytic and noncatalytic or [beta] subunit, whereas polygalacturonase isozyme 2 (PG2) comprises only the catalytic subunit. To assess the state of assembly of PG1 in vivo, both subunits were purified to homogeneity and used to study assembly of the heterodimer. PG1 could be reconstituted in vitro from purified [beta] subunit and purified PG2 under a wide range of salt and pH conditions, and PG1 reconstituted in vitro was indistinguishable from PG1 isolated from tomato (Lycopersicon esculentum) fruit. Specific antibodies indicated that the [beta] subunit was present in fruit of all developmental stages, but absent in vegetative tissue. The state of assembly of PG1 in vivo was tested based on the differential thermal stability of PG1 and PG2 by heating segments of ripe fruit pericarp tissue. Temperatures well below those required to inactivate PG1 in vitro caused the loss of activity of both PG1 and PG2, suggesting that only heat-labile PG2 is present in vivo. In addition, when extracts of ripe fruit were rigorously maintained and analyzed at 4[deg]C, PG1 was absent or barely detectable. These results are consistent with the hypothesis that PG1 can assemble spontaneously and is essentially absent in intact tomato fruit but forms artifactually from PG2 and the [beta] subunit during the extraction of tomato fruit tissue when low temperatures are not rigorously maintained.

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PubMed1993

Expression of Acid Invertase Gene Controls Sugar Composition in Tomato (Lycopersicon) Fruit.

A wild tomato species, Lycopersicon chmielewskii, accumulates high levels of soluble sugar in mature fruit and, unlike the domesticated tomato species, Lycopersicon esculentum, accumulates sucrose rather than glucose and fructose. Genetic and biochemical analyses of progeny resulting from a cross of L. chmielewskii with L. esculentum have previously indicated that the trait of sucrose accumulation is controlled by a single recessive gene and is associated with low levels of acid invertase protein in the developing fruit. Analysis of progeny from the BC2F3 generation from the L. esculentum x L. chmielewskii cross revealed that sucrose-accumulating fruit accumulate sugar in two phases corresponding to fruit expansion and fruit maturation and that the majority of the sucrose was stored in the latter phase after the fruit had reached maximum size. The only significant enzymic difference between the sucrose-accumulating and hexose-accumulating fruit was the lack of acid invertase activity in sucrose-accumulating fruit. Sucrose phosphate synthase activity did not increase in the sucrose-accumulating fruit during late development when the rate of sucrose accumulation increased. The lack of acid invertase activity in sucrose-accumulating fruit was correlated with inheritance of the L. chmielewskii acid invertase gene and the absence of acid invertase mRNA in developing fruit. This suggests that the L.chmielewskii invertase gene is transcriptionally silent in fruit and that this is the basis for sucrose accumulation in progeny derived from the interspecific cross of L. esculentum and L. chmielewskii.

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