Strategies providing success in a variable habitat: II. Ecophysiology of photosynthesis of Cladophora glomerata

Cladophora glomerata (L.) Kütz. is the dominant filamentous algae of the river Ilm, Thuringia, Germany. For most of the year it can be found at open as well as at shaded sites. Photosynthetic acclimation of C. glomerata to different light intensities was detected by chlorophyll fluorescence measurements and pigment analysis. Cladophora glomerata from highlight sites showed decreased values of efficiency of open photosystem II (F_v/F_m) as compared with C. glomerata from low‐light sites. Winter populations revealed higher F_v/F_m values than summer populations. A light‐induced decrease in efficiency of the closed photosystem II was observed at increasing irradiance intensities. The decrease was higher in C. glomerata from shaded sites compared with plants from open sites. Differences in the photosynthetic electron transport rate of different populations of C. glomerata were shown by photosynthesis–irradiance curves. Summer populations from high‐light sites yielded higher maximum electron transport rates than plants from low‐light sites, whereas winter populations exhibited significantly decreased values compared with the summer populations. Results of the analysis of photosynthetic pigments corresponded with data from chlorophyll fluorescence measurements. In addition to these long‐term acclimation effects, C. glomerata expressed its ability to cope with rapid changes in the light environment by the de‐epoxidation of violaxanthin during exposure to high light intensities.     

Ethene (ethylene) production in the marine macroalga Ulva (Enteromorpha) intestinalis L. (Chlorophyta, Ulvophyceae): effect of light-stress and co-production with dimethyl sulphide

Ethene (ethylene; H₂C = CH₂) is one of a range of non-methane hydrocarbons (NMHC) that affect atmospheric chemistry and global climate. Ethene acts as a hormone in higher plants and its role in plant biochemistry, physiology and ecology has been the subject of extensive research. Ethene is also found in seawater, but despite evidence that marine microalgae and seaweeds can produce ethene directly, its production is generally attributed to photochemical breakdown of dissolved organic matter. Here we confirmed ethene production in cultured samples of the macroalga Ulva (Enteromorpha) intestinalis. Ethene levels increased substantially when samples acclimatized to low light conditions were transferred to high light, and ethene addition reduced chlorophyll levels by 30%. A range of potential inhibitors and inducers of ethene biosynthesis were tested. Evidence was found for ethene synthesis via the 1-aminocylopropane-1-acrylic acid (ACC) pathway and ACC oxidase activity was confirmed for cell-free extracts. Addition of acrylate, a potential ethene precursor in algae that contain the compatible solute dimethylsulphoniopropionate, doubled the ethene produced but no acrylate decarboxylase activity was found. Nonetheless the data support active production of ethene and we suggest ethene may play a multifaceted role in algae as it does in higher plants.