Observations on the effect of salinity and photon fluence rate on the induction of sporulation and rhizoid formation in the green alga Enteromorpha prolifera (Muller) J.!Agardh (Chlorophyta, Ulvales)

Although most members of the genus Enteromorpha are important edible green algae, some species are also potentially economically valuable crops. Samples of E. prolifera were obtained from the Yoshino River estuary, Tokushima, Japan and cultured in laboratory conditions at 10degreesC, a salinity of 20 psu, under white light with 12 h light: 12 h dark cycle and at a photon fluence rate (PFR) of 40 mumol/m(2) pers for 30days. In the present study, the effect of salinity and PFR on the induction of reproductive cells and rhizoid formation were investigated. Synchronous formation of swarmers by thalli was induced in excised disks of 1.2 mm diameter after 2-5 days incubation. The optimum salinity for maturation of reproductive cells was between 5.0 and 52.0 psu, and between 13.2 and 45.3 psu for swarmer release, although the lower limit for swarmer release was 5.0 psu. Maturation of reproductive cells and swarmer release required a PFR higher than 16 mumol/m(2) per s. The minimum PFR for swarmer release was 8 mumol/m(2) per s. Many rhizoids were formed between 1.6 and 52.0 psu and photon fluence rates between 8 and 320 mumol/m(2) pers. Rhizoids were formed in a polarized manner.