Is the frequency of apomeiosis in the Rhodophyta a genetic character?
The small rhodophyte Antithamnionella sarniensis Lyle (Ceramiaceae), a very common species on the Atlantic coast of France, has a normal Polysiphonia-like life cycle (Sundene, 1964), but some tetraspores can give new tetrasporophytes directly (L'Hardy-Halos, 1985). This phenomenon has now been studied in detail (Magne, 1986). Twenty strains were prepared starting from sterile plants collected in various places along three hundred kilometers of shoreline. The strains were kept in stock cultures at a low temperature (14 C) with dim natural light and were propagated only by cutting. Exceptionally, one of these strains originated from an apomeiotic tetraspore, and another one is the original strain of von Stosch (1969), who kindly provided it. All the strains proved to be tetrasporophytic, in accordance with the dominance of tetrasporophytes in the field. The progenies of the different strains have been investigated. For each, material from the stock culture was cultivated in monitored conditions (20°C with cool white light of 20 tE.-m-2.s 1, 12 h.d ') to produce tetraspores. Plantlets issuing from the spore-sets were picked randomly, individually transferred in small glass jars and cultivated until reproductive organs were formed; one hundred plantlets were used of each strain. In numerous strains, the progeny is a mixture of gametophytes and tetrasporophytes; the proportions of tetrasporophytes differ from one strain to another over a range from 0% to 100% and show many intermediate values (Magne, 1986). It can be sup-
Seasonal occurrence and reproduction of Hypnea charoides (Rhodophyta) in Tung Ping Chau, N.T., Hong Kong SAR, China
Seasonal occurrence and reproduction in populations of Hypnea charoides Lamouroux were investigated along two coastal shores, A Ma Wan and Lung Lok Shui, in Tung Ping Chau, N. T., Hong Kong SAR, China, from 1996 to 1999. Annual growth of these populations was initiated in early winter (November–December) and ended in late spring (April–May). Mean length of H. charoides in A Ma Wan was significantly negatively correlated with photoperiod (r=−0.359, n=38, p<0.05) and seawater temperature (r=−0.669, n=38, p<0.05). Vegetative plants were dominant but relatively high abundance in tetrasporic plants was observed at the end of each growing season. Percentage occurrence of tetrasporic plants was significantly positively correlated with seawater temperature in samples collected at −1 m CD (r=0.635, n=19, p<0.05), −2 m CD (r=0.690, n=13, p<0.05) and from drifted populations (r=0.705, n=17, p<0.05), suggesting that increase in seawater temperature might induce tetrasporogenesis of H. charoides in A Ma Wan. Plants in Lung Lok Shui were mostly vegetative but 100% tetrasporic samples were collected at −1 m CD during an unusual growth period in October 1998. High abundance of tetrasporic plants was also observed at a depth of −10 m CD on 9 April 1998 (97.5%) and 22-April 1999 (90%). Significantly negative correlation was found in percentage occurrence of vegetative plants at −10 m CD with photoperiod (r=−0.553, n=14, p<0.05) and seawater temperature (r=−0.855, n=8, p<0.05). Dominance of vegetative and tetrasporic plants and rarity of cystocarpic plants in both A Ma Wan and Lung Lok Shui suggested that the life span of H. charoides might be very short and/or majority of the plants underwent apomeiosis to complete their life cycles in Tung Ping Chau.
Etude des possibilités d'adaptation de l'algue rouge Eucheuma Spinosum aux côtes du territoire français des Afars et des Issas
Parmi les nombreuses substances extraites des algues, les carraghenanes occupent une place preponderante. Leur faculte de donner des gels elastiques en fait des concurrents de l'agar ; leur pouvoir de creer des solutions visqueuses leur permet de remplacer, dans certains cas, les alginates ; leur propriete de reagir avec les proteines, et plus particulierement avec la caseine du lait, les a fait largement adopter dans l'industrie laitiere. Aussi ces composes trouvent-ils de larges applications dans des domaines aussi divers que l'alimentation, la cosmetique, la pharmacie, la tannerie, la fabrication des colles et des peintures, la synthese d'explosifs etc...