| Results All tested hexaploid species and subspecies have 3 PDE isoenzymes with the same electrophoretic mobility. Each of the two faster moving bands in always about twice as active as the slowest one. The tetraploids contain only one band, which is identical with the fastest band of the hexaploids. The band of three diploid species and one subspecies was fast moving, and under standard conditions it was difficult to decide whether this band and that of the tetraploids moved electrophoretically as fast or at a different rate as the fastest of the hexaploids. Unambiguous results were obtained only by coelectrophoresis at a prolonged separation time (5 1/2 hours). Thus, by coelectrophoresis of partially purified extracts of T. aestivum ssp. vulgare var. wernerianum and extracts of the four diploid species or subspecies, it was shown that the diploid band was not identical with the fastest band of the hexaploids. Coelectrophoresis also demonstrated that the slow-moving band of Ae. squarrosa is identical with the slowest band of the hexapoids. These results imply that the PDE isoenzymes of the four diploid species or subspecies are also not identical with the PDE of the tetraploids. Coelectrophoresis of extracts of T. aestivum ssp. vulgare var. wernerianum with extracts of the other hexaploid species and with those of the tetraploids also confirmed the results obtained under standard conditions; that is, all the bands of the hexaploids are identical and the fastest of these is identical with the band of the tetraploids. Discussion The use of seed proteins and of many of the enzymes employed in genetic investigations of wheat presents several problems. The seed proteins are very numerous and only characterized by their electrophoretic mobility. Some enzymes, e.g., the phosphatases and esterases, also give many bands, and their substrate specifity is not well defined. With other enzymes, such as esterase, alcohol dehydrogenase, catalase or aminopeptidase, the picture may be complicated by polymorphism (MACDONALD and BREWBAKER, 1972). Phosphodiesterase, however, has a well-defined substrate specifity and occurs in the Triticinae only in the form of at most three isozymes, which are not composed of dissociable subunits (WOLF, unpublished). Therefore, in our opinion, it is particularly suited for genome analysis. It is striking that the pattern of the isoenzymes of phosphodiesterase is the same within the di-, tetra-, and hexaploid group. Assuming the validity of the one-gene, one-protein hypothesis and considering the PDE as a genome marker, we draw the following conclusions from a comparison of the isoenzyme pattern: 1 . Tne identity of the slowest moving band of the hexaploids and the band of Aegilops squarrosa confirms Ae. squarrosa as the donor of the D genome. 2. The identity of the band of the tetraploids and the fastest migrating band of the hexaploids confirms that the hexaploids derive from a tetraploid species. 3. No band corresponding to the middle band of the hexaploids could be found in the di- and tetraploids. However, the synthetic hexaploid T. durum x Ae. squarosa displayed three isoenzymes of phosphodiesterase. As the parents possess only one band each, we conclude that the middle band in the hexaploids is a hybrid enzyme (WOLF, unpublished). 4. The occurrence of only one band in the tetraploids can be explained best by the hypothesis of autotetraphloidy (CAMARA, 1935). The hypothesis is supported further by the observation that the fastest band of the hexaploids (originating from the tetraploids) contains about twice the activity of the slowest one (originating from Ae. squarrosa). 5. T. monococcum, T. aegilopoides, and Ae. speltoides, which are said to possess the genomes A or B, have an identical band which is different, however, from that of Ae. squarrosa and does not correspond to any band of the tetra- or hexaploids. We therefore conclude that the tetraploids have originated from a diploid species as yet unknown. Studies on occurrence and properties of hybrid enzymes of PDE in Triticum are nearly completed and will be published elsewhere. |
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