ENZYME POLYMORPHISM IN POSIDONIA-OCEANICA, A SEAGRASS ENDEMIC TO THE MEDITERRANEAN

Enzyme polymorphism was used to investigate genetic variability in Pos idonia oceanica (L.) Delile from natural meadows around Nice (Alpes-Ma ritimes and Var) and among eight populations, sampled from the collect ion in the Port-Cros National Park, which had originated in different parts of the Mediterranean. Of the 30 enzyme systems studied only six were found useful in the isozyme studies (peroxidases, PER; glucose-ph osphate isomerases, GPI; superoxide dismutases, SOD; malate dehydrogen ases, MDH; catalases, CAT; glutamate dehydrogenases, GDH). The results showed that of these six only two enzymes showed enzyme polymorphism, indicating low levels of polymorphism, The small intrapopulation isoz yme variability in P. oceanica meadows near Nice concurs with previous suggestions that reproduction is predominantly clonal, corresponding with previously observed infrequency of flowering in meadows. In the F rench meadows studied, one locus out of the eight was found to be poly morphic; this locus, moreover, showed an excess of heterozygotes. This same genetic structure found in all three meadows around Nice suggest s that the greater part of these populations is not isolated, perhaps because of their practically continuous distribution along the Mediter ranean coast, with dissemination by currents both of fruits and of rhi zome fragments.