Photoperiodic response in the formation of gametangia of the long-day plant Sphacelaria rigidula (Phaeophyceae)

The effect of daylength and irradiance on the formation of gametangia in the male gametophyte of Sphacelaria rigidula Kutz (= S. furcigera Kutz [Prud'homme van Reine 19821) was investigated. Formation of gametangia was restricted to long-day conditions: In light-dark regimes with 12 h of light per day or less, no gametangia were formed. In long-day regimes high irradiances caused a suboptimal response, especially near the critical daylength. Interruption of a long dark period with a light break promoted gametangia formation. Light breaks were most effective when given at about the 6th hour of darkness. Nine inductive long-day cycles were required to induce the formation of gametangia, which appeared after ca. 15 d. The plants remained in the induced state only for a very short time. In regimes with very long days and at high irradiance the number of fertile plants decreased after some time, when vigorous vegetative growth started without any further formation of gametangia

A METHOD FOR OBTAINING AXENIC ALGAL CULTURES USING THE ANTIBIOTIC CEFOTAXIME WITH EMPHASIS ON CLADOPHOROPSIS-MEMBRANACEA (CHLOROPHYTA)

Axenic cultures of the tropical green seaweed Cladophoropsis membranacea (C. Agardh) Boergesen were obtained by cutting 2-mm apical tips from fast-growing unialgal filaments and incubating them in 1/2PES containing 100-mu-g.mL-1 cefotaxime. After 1 week, apical tips were cut from the newly grown plantlets, washed through a series of sterile drops of seawater, and incubated in sterile 1/2PES. Plantlets were screened for the presence of bacteria by incubating droplets of the culture medium on peptone agar plates and by examining DAPI-stained filaments. Ninety to one hundred percent of the plantlets obtained with this treatment were axenic. Cefotaxime was also effective against cyanobacteria but of only limited value in rhodophytes

Genotypic relationships between Prochloron samples from different localities and hosts as determined by DNA-DNA reassociations

Genotypic relationships between seven Prochloron samples isolated from different didemnid ascidian hosts collected at the Palau archipelago and Munda (Solomon Islands) and one cyanobacterial (Synechocystis) strain were determined by DNA-DNA reassociations. Thermal stability values of DNA-DNA hybrids indicate that all Prochloron samples involved are mutually very closely related and only slightly related with the Synechocystis strain. It is concluded that the Prochloron samples tested are representatives of one and the same species