Effects of solar UV radiation on germination of conchospores and morphogenesis of sporelings in Porphyra haitanensis (Rhodophyta)

The effects of ultraviolet radiation (UVR 280-400 nm) on the germination of Porphyra haitanensis conchospores and on the growth and morphogenesis of the subsequent sporelings were investigated by culturing the released conchospores under natural sunlight from 29 September to 6 October 2005. Germination increased with time and was faster when UV-B was excluded using cut-off filters. There were significant negative effects of UV-B radiation on growth and cell division of sporelings, with decreases up to 18% for thallus length, between 6 and 18% for thallus width, up to 29% for thallus area, and between 6 and 14% for cell size as compared to PAR-controls. UV-A had a significant positive effect on morphogenesis, enhancing the formation of sporelings with cells dividing transversely; on the other hand, UV-B delayed the formation of such sporelings. We also tested the effects of solar UVR on the growth of P. haitanensis juveniles and found no significant effects. Our results indicate that UV-A has an important role in the germination and morphogenesis of the species, but on the other hand, sporelings of P. haitanensis are more sensitive to UV-B radiation than juveniles.The effects of ultraviolet radiation (UVR 280-400 nm) on the germination of Porphyra haitanensis conchospores and on the growth and morphogenesis of the subsequent sporelings were investigated by culturing the released conchospores under natural sunlight from 29 September to 6 October 2005. Germination increased with time and was faster when UV-B was excluded using cut-off filters. There were significant negative effects of UV-B radiation on growth and cell division of sporelings, with decreases up to 18% for thallus length, between 6 and 18% for thallus width, up to 29% for thallus area, and between 6 and 14% for cell size as compared to PAR-controls. UV-A had a significant positive effect on morphogenesis, enhancing the formation of sporelings with cells dividing transversely; on the other hand, UV-B delayed the formation of such sporelings. We also tested the effects of solar UVR on the growth of P. haitanensis juveniles and found no significant effects. Our results indicate that UV-A has an important role in the germination and morphogenesis of the species, but on the other hand, sporelings of P. haitanensis are more sensitive to UV-B radiation than juveniles

Combined effects of ultraviolet radiation and temperature on morphology, photosynthesis, and DNA of Arthrospira (Spirulina) platensis (Cyanophyta)

Natural levels of solar UVR were shown to break and alter the spiral structure of Arthrospira (Spirulina) platensis (Nordst.) Gomont during winter. However, this phenomenon was not observed during summer at temperatures of similar to 30 degrees C. Since little has been documented on the interactive effects of solar UV radiation (UVR; 280-400 nm) and temperature on cyanobacteria, the morphology, photosynthesis, and DNA damage of A. platensis were examined using two radiation treatments (PAR [400-700 nm] and PAB [PAR + UV-A + UV-B: 280-700]), three temperatures (15, 22, and 30 degrees C), and three biomass concentrations (100, 160, and 240 mg dwt [dry weight] . L-1). UVR caused a breakage of the spiral structure at 15 degrees C and 22 degrees C, but not at 30 degrees C. High PAR levels also induced a significant breakage at 15 degrees C and 22 degrees C, but only at low biomass densities, and to lesser extent when compared with the PAB treatment. A. platensis was able to alter its spiral structure by increasing helix tightness at the highest temperature tested. The photochemical efficiency was depressed to undetectable levels at 15 degrees C but was relatively high at 30 degrees C even under the treatment with UVR in 8 h. At 30 degrees C, UVR led to 93%-97% less DNA damage when compared with 15 degrees C after 8 h of exposure. UV-absorbing compounds were determined as negligible at all light and temperature combinations. The possible mechanisms for the temperature-dependent effects of UVR on this organism are discussed in this paper

UV-absorbing compounds in Porphyra haitanensis (Rhodophyta) with special reference to effects of desiccation

The intertidal red alga Porphyra haitanensis Chang et Zheng is episodically desiccated and exposed to high levels of solar radiation at low tide during emersion. However, little has been documented on the relationship between the stresses during desiccation and related chemical compounds. We found that P. haitanensis thalli, when desiccated under indoor (artificial radiation) or outdoor (solar radiation) conditions, with or without UV radiation (UVR: 280-400 nm), contained significantly higher concentrations of UV-absorbing compounds (peak at 336 nm) than those maintained submerged (without desiccation). Solar UVR had no effect on the content of UV-absorbing compounds. Even though the concentration of these compounds decreased with time in all treatments, a slower decrease was observed in the desiccated samples. The samples with higher levels of UV-absorbing compounds showed higher photochemical efficiency of photosystem II (PS II) during the exposure or subsequent recovering process than samples with low concentration of UV-absorbing compounds, reflecting their protective role. The concentration of these compounds varied in different parts of the thallus, with the middle and marginal parts containing 60-80% more UV-absorbing compounds than the basal parts in both female and male plants. In addition, the marginal parts of male thalli contained more UV-absorbing compounds than the corresponding parts of female thalli. Our data suggest that desiccation plays a key role in this alga to maintain high concentration of UV-absorbing compounds, and that this might provide a beneficial advantage to compete in the intertidal zone where the organism is normally exposed to high levels of UVR