A Strategy for the Proliferation of Ulva prolifera, Main Causative Species of Green Tides, with Formation of Sporangia by Fragmentation

Ulva prolifera, a common green seaweed, is one of the causative species of green tides that occurred frequently along the shores of Qingdao in 2008 and had detrimental effects on the preparations for the 2008 Beijing Olympic Games sailing competition, since more than 30 percent of the area of the games was invaded. In view of the rapid accumulation of the vast biomass of floating U. prolifera in green tides, we investigated the formation of sporangia in disks of different diameters excised from U. prolifera, changes of the photosynthetic properties of cells during sporangia formation, and development of spores. The results suggested that disks less than 1.00 mm in diameter were optimal for the formation of sporangia, but there was a small amount of spore release in these. The highest percentage of area of spore release occurred in disks that were 2.50 mm in diameter. In contrast, sporangia were formed only at the cut edges of larger disks (3.00 mm, 3.50 mm, and 4.00 mm in diameter). Additionally, the majority of spores liberated from the disks appeared vigorous and developed successfully into new individuals. These results implied that fragments of the appropriate size from the U. prolifera thalli broken by a variety of factors via producing spores gave rise to the rapid proliferation of the seaweed under field conditions, which may be one of the most important factors to the rapid accumulation of the vast biomass of U. prolifera in the green tide that occurred in Qingdao, 2008

CO2 and light effects on growth, photosynthesis, carbon acquisition and nitrogen fixation of the diazotrophic cyanobacteria Trichodemium

Recent studies on the diazotrophic cyanobacteria Trichodesmium showed a pronounced CO2 dependency in N2- and C-fixation. However, significant uncertainties remain as to the degree of sensitivity to CO2, modification of these responses by other environmental factors, and the underlying processes. To this end, we investigated carbon acquisition and nitrogen fixation in Trichodesmium IMS101 under different CO2 and light levels. In these acclimations, growth rates, cellular C and N content, and respective isotopic values were measured. In vivo activities of photosynthetic O2 evolution, O2 uptake, CO2 and HCO3- fluxes were obtained using membrane inlet mass spectrometry methods (MIMS). Nitrogen fixation rates were determined using the acetylene reduction assay, and chlorophyll a fluorescence was measured via fluorescence induction and relaxation method (FIRe). Photosynthesis and N2-fixation increased with CO2 and this effect was even more pronounced under high light. Moreover, our data suggest a shift in the distribution of metabolic energy between photosynthesis, carbon acquisition and N2-fixation in Trichodesmium. The observed stimulation in photosynthesis and N2-fixation may enhance the productivity in N-limited oligotrophic regions

Fluorescence as a tool to understand changes in photosynthetic electron flow regulation

International audienceThe physiological state of a chloroplast is stronglyinfluenced by both biotic and abiotic conditions.Unfavourable growth conditions lead to photosyntheticstress. Chlorophyll a fluorescence is a widelyused probe of photosynthetic activity (specificallyPSII), and therefore stress which specifically targetsthe electron transport pathway and associated alternativeelectron cycling pathways. By manipulating theprocesses that control photosynthesis, affecting thechlorophyll a fluorescence, yields detailed insight intothe biochemicalpathways. Light that is captured by achlorophyll molecule can be utilised in three competingprocesses; electron transport, energy dissipation(via heat) and chlorophyll a fluorescence emission.Electrons produced by water-splitting are not alwaysused in carbon fixation; if the incident irradiancegeneratesmore electrons than the dark reactionscan use in carbon fixation, damage will occur to the photosynthetic apparatus. If carbon fixation is inhibitedby temperature or reduced inorganic carbon (Ci), ATPor NADPH availability, then the photosystem dynamicallyadjusts and uses alternate sinks for electrons, suchas molecular oxygen (water-water cycle or Mehler ascorbateperoxidase reaction). The process of stress acclimationleads to a number of photoprotective pathwaysand we describe how inhibitors can be used to identifythese particular processes. In this chapter, we describethe processes controlling electron transport as influencedby light-induced stress