[Antenna replacement in the evolutionary origin of chloroplasts].

Endosymbiotic origin of chloroplasts from unicellular cyanobacteria is presently beyond doubt. Oxygenic photosynthesis is based on coordinated action of two photosystems (PS), PS I and PS II, cooperating with several variants of the pigment antenna. In cyanobacteria, red algae, and glaucophytes, phycobilisomes (PBS) act as antennae, while in terrestrial plants, as well as most macro- and microalgae antennae are formed by chlorophyll a/b- and chlorophyll a/c-containing proteins. Advantages and disadvantages of the PBS antenna compared to other light-gathering complexes form the basis for adaptive variations of the antenna in the course of development of eukaryotic photosynthesis. During the evolution of the "green" and "chromophyte" lineages of the chloroplasts, PBS, in spite of their optimal features of light absorption,were replaced by chlorophyll a/b- and chlorophyll a/c-containing light-gathering complexes. Development of the cell wall associated with limited motility and with tissue formation in photosynthetic eukaryotes were the factors responsible for the antenna shift. The subsequent redistribution of cell resources in favor of cellulose biosynthesis required increased for CO2 consumption, higher PS II levels, and greater number and density of the thylakoids in the chloroplasts, got incompatible with the energy-consuming and overly large PBS antenna.

[Changes in parameters of Ascophyllum nodosum dark respiration induced by different salinities]. / izmenenie parametrov temnovogo dykhaniia Ascophyllum nodosum pri deistvii razlichnykh solenostei.

The changes in the rates of O2 consumption and CO2 release by Ascophyllum nodosum thalli in the dark were studied during a 12 day incubation at 34, 20, and 10/1000 salinity as well as at different pH. Depending on the initial pH of the medium, the algae demonstrated antipodal functional responses to the same salinities and, as a consequence, different capacity to overcome hypoosmotic stress. In addition, we observed a more pronounced effect of pH on the rate of O2 consumption than on the rate of CO2 release. Simultaneous desalination and acidification of the medium (pH 7-8) increased O2 consumption in the dark, which activated oxidative processes in the cells and increased their energy status. Forced pH stabilization (8.2) of the medium coupled with its desalination inhibited dark respiration of the algae, which, in our opinion, decreased their energy status. Specific manifestation of hypoosmotic stress and adaptation in A. nodosum are discussed considering the assumed differences in algal energy status.

[The influence of salinity on the rate of dark respiration and structure of the cells of brown algae thallus from the Barents sea littoral]. / Vliianie izmeneniia solenosti na temnovoe dykhanie i strukturu kletok tallomov burykh vodoroslei litorali Barentseva moria.

We studied the changes in the rate of dark respiration (DR) and structure of the cells in Ascophyllum nodosum and Fucus vesiculosus thalluses during the incubation at 40, 34, 20, 10, and 2@1000 salinity for 14 days. The changes in salinity affect the rate of DR and the structure of the thallus apical cells: the organelles swell and later are destroyed. The effect of decreased salinity on the algae was more pronounced as compared to the increase. The stress intensity directly increased with the rate of desalination. Further adaptation of the algae to low salinity enhanced DR and, hence, was an energy-dependent process. Despite higher DR rates (during the stress and adaptation) in F. vesiculosus as compared to A. nodosum, the seaweeds had similar pattern of adaptation to the changed salinity. Different primary response of the seaweeds to 20@1000 salinity was an important exception; apparently, the salinity around 20@1000 is the limit of these species distribution in desalination zones.