GENETIC EVIDENCE FOR DIPLOIDY IN EQUISETUM

Sporophytes and gametophytes of Equisetum arvense, E. laevigatum, and E. telmateia were analyzed using enzyme electrophoresis to estimate isozyme number. Despite their uniformly high chromosome numbers (2n = 216), these three species exhibited isozyme numbers typical of diploid seed plants for the enzymes AAT, ADH, ALD, GDH, [NADP]IDH, LAP, MDH, [NADP]ME, PGI, PGM, SkDH, and 6PGDH. All three species exhibited an additional isozyme for TPI. There is, therefore, no genetic evidence for low base numbers such as x = 9 and x = 12 suggested for Equisetum. Intact chloroplasts were isolated from E. arvense and the chloroplast extract compared electrophoretically to whole plant extracts. The single enzymes observed for LAP, GDH, [NADP]IDH, and [NADP]ME were absent from the chloroplast extract. Isozymes AAT-1, ALD-2, MDH-3, PGI-1, PGM-2, SkDH-2, 6PGDH-2, TPI-2, and TPI-3 were active in the chloroplast fraction; 6PGDH-1, PGI-2, PGM-1, and TPI1 were lacking from the chloroplast fraction and were considered cytosolic. Isozymes AAT-2, MDH1, MDH-2, MDH-4, and SkDH1 were also lacking from the chloroplast fraction but because AAT, MDH, and SkDH have been reported from several subcellular compartments, their localization is unknown. These findings indicate that isozymes in Equisetum species are subcellularly compartmentalized as has also been demonstrated for homosporous ferns, gymnosperms, and angiosperms. DUE TO THEIR high chromosome numbers, homosporous ferns traditionally have been considered highly polyploid (Klekowski and Baker, 1966; Vida, 1976; Wagner and Wagner, 1979; Grant, 1981). However, genetic evidence compiled using enzyme electrophoresis indicates that homosporous ferns with high chromosome numbers may be diploid (Gastony and Darrow, 1983; Gastony and Gottlieb, 1985; Haufler, 1985; Werth, Guttman and Eshbaugh, 1985 a, b; Haufler and Soltis, 1986; Soltis and Soltis, 1986). That is, ongoing electrophoretic surveys indicate that homosporous fern species representing basic generic chromosome numbers have the number of isozymes considered typical of diploid gymnosperms and angiosperms. In addition, Gastony and Darrow (1983) demonstrated for the fern Athyrium filix-femina that isozymes are subcellularly compartmentalized as has been demonstrated for gymnosperms and angiosperms (Gottlieb, 1982). All Equisetum species so far investigated cytologically have 2n = 216 (Manton, 1950; Mehra and Bir, 1959; Bir, 1960; Love, Love and Pichi Sermolli, 1977). Due to their uniformly high chromosome numbers, Equisetum ' Received for publication 17 September 1985; revision accepted 22 November 1985. The assistance and helpful comments of Pam Soltis, Leslie Gottlieb, and Loren Rieseberg are gratefully acknowledged. The comments of Gerald Gastony and Richard Hauke are also appreciated. This research was supported by NSF grant BSR 8315098. species, like the homosporous ferns, have been considered highly polyploid (Vida, 1976; Love et al., 1977; Tryon and Tryon, 1982). Love et al. (1977), for example, considered the base chromosome number of Equisetum to be x = 9. However, since the basis of polyploidy is the number of genomes and not simply the number of chromosomes, other lines of evidence are needed to test the hypothesis that Equisetum species are highly polyploid. Ploidal levels can also be estimated by determining isozyme number. As reviewed by Gottlieb (1981, 1982), polyploid angiosperm species (those having chromosome numbers greater than x = 14) generally have more isozymes per enzyme than do diploids. Since isozyme data have already provided important genetic insights for homosporous ferns (Gastony and Darrow, 1983; Gastony and Gottlieb, 1985; Haufler, 1985; Werth et al., 1985 a, b; Haufler and Soltis, 1986), isozyme number was estimated for several enzymes for Equisetum arvense L., E. laevigatum A. Br., and E. telmateia Ehr. All three species have 2n = 216 (L6ve et al., 1977). Furthermore, enzyme localization studies were conducted using E. arvense to determine whether isozymes in Equisetum species are subcellularly compartmentalized as has been demonstrated for other groups of vascular plants (Gottlieb, 1981, 1982; Gastony and Darrow, 1983). MATERIALS AND METHODS-Five to ten sporophytes each of Equisetum arvense, E. lae-