Effects of UV-B radiation on tetraspores of Chondrus ocellatus Holm(Rhodophyta),and effects of red and blue light on repair of UV-B-induced damage

We evaluated the effects of red and blue light on the repair of UV-B radiation-induced damage in tetraspores of Chondrus ocellatus Holm. Tetraspores of C. ocellatus were treated with different UV-B radiation levels(0,36,72,108,144 and 180 J/m2),and thereafter subjected to PAR,darkness,or red or blue light during a 2-h repair stage,each day for 48 days. The diameters and cellular contents of cyclobutane pyrimidine dimmers(CPDs),chlorophyll a(Chl a),phycoerythrin,and UV-B-absorbing mycosporinelike amino acids(MAAs) contents of the tetraspores were determined. Our results show that low doses of UV-B radiation(36 and 72 J/m 2) promoted the growth of C. ocellatus; however,increased UV-B radiation gradually reduced the C. ocellatus growth(greater than 72 J/m2). The MAAs(palythine and asterina-330) in C. ocellatus were detected and analyzed by LC/MS. Our results suggest that moderate red light could induce the growth of this alga in aquaculture. In addition,photorepair was inhibited by red light,so there may be some other DNA repair mechanism activated by red light. Blue light promoted the activity of DNA photolyase,greatly improving remediation efficiency. Red and blue lights were found to reduce the capacity of C. ocellatus to form MAAs. Therefore,PAR,red light,and blue light play different roles during the repair processes for damage induced by UV-B radiation.

Effects of temperature and irradiance on early development of Chondrus ocellatus Holm (Gigartinaceae,Rhodophyta)

Chondrus is a type of commercially produced red seaweed that widely used for food and carrageen extraction. Although the natural life history of the alga had been well understood, the factors influencing development of the tetraspore and carpospore remain poorly understood. In the perspective of seedling resources, the regulation of early development is crucial for the seedlillg nursing; therefore, it is necessary to understand the physiological influences during its early development. In this study, we studied the effects of temperature and irradiance on the early development of Chondrus ocellatus Holm under laboratory conditions. The released tetraspores and carpospores were cultivated at different temperatures （10-28℃） and irradiances （10, 60 μmol photons m^-2s^-1） with a photoperiod of 12L： 12D. The results indicate that both tetraspores and carpospores are tolerant to temperatures of 10-25℃, and have the highest relative growth rate at 20℃. Irradiance variances influenced the growth of the discoid crusts, and the influence was more significant with increasing temperature; 60 μmol photons m^-2s^-1 was more suitable than 10 μmol photons m^-2s^-1. The optimum temperature and irradiance for the development of seedlings was 20℃ and 60 μmol photons m^-2s^-1, respectively.

Early development of Chondrus ocellatus Holm(Gigartinaceae,Rhodophyta)

Chondrus is an economically important red algae widely used for food and biochemical purpose.It early development is crucial for the culture and seedling propagation.We chose tetraspores and carpospores of Chondrus ocellatus as examples for experiment of the culture,induction and release in laboratory condition,aiming to understand early development of C.ocellatus and to apply in seedling production.Mature C.ocellatus were collected in Qingdao,China,from Nov.to Dec.2004.After the gametophyte and tetrasporophyte were brushed and washed with sterilized seawater,the algal materials were treated in 1.5%KI for 20 min,then were dried for lh to stimulate the releasing of spores.After the spores released overnight,it were cultured in PES medium,incubated at 18℃,10±2μmol/(m^(2).s^(1))in 12:12h(light:dark).The observation and recording under microscope were carried out.Continuous observation of the early development showed that both tetraspore and carpospore are similar to each other.In general,three stages of the early development were shown being division,discoid crust and seedling stages.To the division stage,the most obvious feature was the increasing of cell number;during the discoid crust stage,the discoid crust had a three-dimensional axis,and it began to differentiate into two types of cells:the basal cells and the apical cells;and to the seedling stage,several protuberances-like appeared on the discoid crusts and formed juvenile seedlings.Carpospores and tetraspores exhibited a similar development process that included division stage,discoid crust stage and seedling stage.

Effects of different light conditions on repair of UV-B-induced damage in carpospores of Chondrus ocellatus Holm

We evaluated the effects of ultraviolet-B （UV-B） radiation and different light conditions on the repair of UV-B-induced damage in carpospores of Chondrus ocellatus Holm （Rhodophyta） in laboratory experiments. Carpospores were treated daily with different doses of UV-B radiation for 48 days, when vertical branches had formed in all treatments; after each daily treatment, the carpospores were subjected to photosynthetically active radiation （PAR）, darkness, red light, or blue light during a 2-h repair stage. Carpospore diameters were measured every 4 days. We measured the growth and cellular contents of cyclobutane pyrimidine dimers （CPDs）, chlorophyll a, phycoerythrin, and UV-B-absorbing mycosporine-like amino acids （MAAs） in carpospores on Day 48. Low doses of UV-B radiation （36 and 72 J/m2） accelerated the growth of C. ocellatus. However, as the amount of UV-B radiation increased, the growth rate decreased and morphological changes occurred. UV-B radiation significant damaged DNA and photosynthetic pigments and induced three kind of MAAs, palythine, asterina-330, and shinorine. PAR conditions were best for repairing UV-B-induced damage. Darkness promoted the activity of the DNA dark- repair mechanism. Red light enhanced phycoerythrin synthesis but inhibited light repair of DNA. Although blue light, increased the activity of DNA photolyase, greatly improving remediation efficiency, the growth and development of C. ocellatus earpospores were slower than in other light treatments.