CHLOROPLASTIC AND CYTOSOLIC ISOZYMES OF THE HOMOSPOROUS FERN ATHYRIUM FILIX-FEMINA L

Intact chloroplasts isolated from mature leaf tissue of the homosporous fern Athyrium filixfemina were osmotically ruptured and subjected to starch gel electrophoresis in side by side comparisons with whole leaf extracts. The single enzyme activities of reportedly cytosolic NADP]IDH and NADP]ME were not expressed in the chloroplast fraction, and these were used as controls ensuring the cytosol-free quality of the chloroplast preparations. Isozymes F1,6DP-1, PGI-1, PGM-1, 6PGDH-1, ALDO-1, TPI-2, NAD(P)]G3PDH-1, and NAD(P)]G3PDH-2 are active in the chloroplast fraction, whereas Fl,6DP-2, PGI-2, PGM-2, 6PGDH-2, ALDO-2, and TPI-1 were lacking from the chloroplast fraction and are considered cytosolic. The single enzyme activities observed for AAT and SkDH, are chloroplastic. These data indicate that the two isozymes of certain enzymes in Athyrium filix-femina are not the products of duplicated loci resulting from polyploidy, but are distinct and subcellularly compartmentalized as demonstrated in heterosporous plants. Thus A. filix-femina is functionally diploid in spite of its high chromosome number of 2n = 80.