EFFECTS OF SALINITY ON TURGOR PRESSURE AND FERTILITY IN TOLYPELLA (CHARACEAE)

We present the first experimental results on salinity tolerance and re gulation mechanisms in the genus Tolypella. The two species investigat ed, T. nidifica and T. glomerata, regulate turgor pressure with almost complete effectiveness by adjustment of K+ and Cl- concentrations. Su crose is also involved. The mechanism is basically identical to the me chanism of turgor pressure regulation previously identified in represe ntatives of the genera Chara and Lamprothamnium. Since Chara and Lampr othamnium on the one hand and Tolypella on the other belong to differe nt phylogenetic branches that separated early in the geological histor y of the Characeae, the K+ regulation mechanism can be assumed to repr esent an ancient pattern derived from a salt-tolerant common ancestor. Furthermore, our experiments provide evidence that salinity is a limi ting factor for fertility in both T. nidifica and T. glomerata. Althou gh the onset of gametangia covers the whole range of salinities tested here (0-29 psu), 12 psu was the inhibitory level for the formation of mature oospores. Fertilization is probably disturbed by an increase i n salinity. An inability to reproduce sexually under euryhaline condit ions could explain why the distribution of the two species is restrict ed to oligo- and mesohaline environments, despite the wide range of sa linity tolerance of their vegetative apparatus.