Evidence for Post‐translational Modification of Triose Phosphate Isomerase (Tpi) in Isoëtes (Isoëtaceae)

Abstract

As part of an electrophoretic study on Isoëtes, a number of Neotropical and North American species were examined for allozyme variation in TPI. Three of these species—I. storkii, I. flaccida, and I. mexicana—exhibit three distinct zones of TPI activity. The two most anodally migrating zones are comparable to the two zones found in most angiosperms and in several other species of Isoëtes. The single or three‐banded phenotypes produced at these loci correspond, respectively, to the homozygous and heterozygous patterns typical of a dimeric enzyme. The most cathodal zone (zone III) differs in producing either single or two‐banded phenotypes. Analyses of these three zones indicate a nearly perfect correlation between zones II and III in putative allelic constitution and relative allelic mobility. Explanations involving TPI gene duplications and/or null alleles fail to account for the peculiar banding characteristics and origin of activity zone III. An alternative hypothesis involving a protease duplication and differential post‐translational modification is postulated. This hypothesis adequately explains the zone III phenotypes and fixation of the third activity zone in the species examined. Amino acid sequencing is suggested as the most direct test of this hypothesis. The taxonomic distribution of TPI III generally supports a previous, morphologically‐based, hypothesis on species relationships in Isoëtes. The presence of this zone is regarded as an independent synapomorphy for a major clade of Neotropical Isoëtes.

Morphological Stasis abd Molecular Divergence in the Intercontinental Disjunct Genus Datisca (Datiscaceae)

“…The dimeric condition is typical ofvascular plants (Gottlieb 1981). However, a similar "monomeric" TPI locus has been recently reported in Isoetes (Hickey, Guttman, and Eshbaugh 1989) and evidently results from a post-translational modification of the TPI enzyme. Activity for Tpi-1 was not observed in the absence of the substrate dihydroxyacetone phosphate, indicating that it was not a nonspecific protein.…”

Esterase polymorphism marking cultivars of Manihot esculenta, Crantz

“…Our results showed that additives such as sodium metabisulfite and ascorbic acid, which are important to reverse or prevent the oxidative formation of quinones (Loomis, 1974), were needed to solubilize and maintain a higher number of esterase isozymes. Metabisulfite can form a stable covalent complex with phenols that does not react with PVP-40 (Arulsebar et al, 1986;Buckley et al, 1988); ascorbic acid will reduce quinones (Loomis, 1969), not reducible by β-mercaptoethanol (Shaw et al, 1987;Buckley et al, 1988;Hickey et al, 1989;Krebs and Hancock, 1989;Laguidah and Hanna, 1989). Thus, the extraction solution for esterase analysis in young leaves of M. esculenta required two phenolcomplexing agent and four antioxidant agents.…”

The Hybrid Cystopteris fragilis x C. tenuis (Dryopteridaceae) and the Relationship Between Its Tetraploid Progenitors

“…TPI in Cystopteris is composed of two comigrating isozymes, TPI1 and TPI2, that apparently are sequestered in different cellular compartments and thus do not interact (Haufler et al 1990). TPI1 is a typical dimeric protein and TPI2 has been interpreted as a dimeric protein with post-translational modification (Gastony 1988;Hickey et al 1989;Kephart 1990 We inferred that the three distinct, multilocus band patterns observed in PGI2 and TPI correspond to C. fragilis, C. tenuis, and C. fragilis…”

“…Two allozymes, denoted a and b, were observed at both TPI1 and TPI2. TPI2 shows a sixbanded pattern attributed to post-translational modification(Gastony 1988;Hickey et al 1989). For TPI2, "mp," a letter, and a number correspond to "modified individuals taken from three widely separated populations; in each case the sporophytes had aborted spores.…”