Circadian rhythm of photosynthetic oxygen evolution in Kappaphycus alvarezii (Rhodophyta): dependence on light quantity and quality

The rate of oxygen evolution of the tropical red alga Kappaphycus alvarezii was measured for 6 days in the laboratory using a computer-aided method for long-term recording. In cool white light Kappaphacus exhibited a robust circadian rhythm of O2 evolution in the irradiance range of 100 to 1000 µmol m-2 s-1. With increasing irradiance the period of the free-running rhythm, tau, decreased in blue and increased in red light, but did not change significantly in green light. The accelerating or slowing action of blue or red light, respectively, points to two photoreceptors used in the light transduction pathway of the circadian oscillator controlling oxygen evolution or the light reactions of photosynthesis in Kappaphycus. No significant changes of tau were observed with increasing irradiance in cool white light, possibly due to the additive, opposing responses caused by blue and red light

Effect of dark and salinity treatment in the yield and quality of agar from Gracilaria cornea (Rhodophyceae)

The alkali treatment used previous to agar extractions from the Gracilaria genus reduces, among other reactions, the sulphate content and improves the gel strength; however, at an industrial level it requires expensive effluent processing to reduce its polluting charge. The red alga Gracilaria cornea was cultivated under dark and salinity treatments to replace this alkali treatment. The different treatments tested were: (a) darkness and 33‰ salinity for 8 days, [dark treatment]; (b) darkness and 50‰ salinity for 4 days, followed by darkness and 25‰ salinity for 4 days, [4+4]; and (c) darkness and 50‰ salinity for 8 days, followed by darkness and 25‰ salinity for 4 days, [8+4]. The treatment [4+4] increased the agar yield in 26% (from 36.6 to 46.1%). All treatments reduced the sulphate content of the agar in approximately 24% when compared with agar obtained without any treatment. For G. cornea the [4+4] treatment might become in the future an additional treatment to a mild alkali treatment using less alkaline reagents for agar extraction

Responses of the kelp Saccharina latissima (Phaeophyceae) to the warming Arctic: from physiology to transcriptomics

The Arctic region is currently facing substantial environmental changes due to global warming. Melting glaciers cause reduced salinity environments in coastal Arctic habitats, which may be stressful for kelp beds. To investigate the responses of the kelp Saccharina latissima to the warming Arctic, we studied the transcriptomic changes of S. latissima from Kongsfjorden (Svalbard, Norway) over a 24-hour exposure to two salinities (Absolute Salinity [S-A] 20 and 30) after a 7-day pre-acclimation at three temperatures (0, 8 and 15 degrees C). In addition, corresponding physiological data were assessed during an 11-days salinity/temperature experiment. Growth and maximal quantum yield for photosystem II fluorescence were positively affected by increased temperature during acclimation, whereas hyposalinity caused negative effects at the last day of treatment. In contrast, hyposalinity induced marked changes on the transcriptomic level. Compared to the control (8 degrees C - S-A 30), the 8 degrees C - S-A 20 exhibited the highest number of differentially expressed genes (DEGs), followed by the 0 degrees C - S-A 20. Comparisons indicate that S. latissima tends to convert its energy from primary metabolism (e.g. photosynthesis) to antioxidant activity under hyposaline stress. The increase in physiological performance at 15 degrees C shows that S. latissima in the Arctic region can adjust and might even benefit from increased temperatures. However, in Arctic fjord environments its performance might become impaired by decreased salinity as a result of ice melting