Functional organization and plasticity of the photosynthetic unit of the cyanobacterium Anacystis nidulans (original) (raw)
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Microbiology, 1983
Photosynthetic membrane and chlorophyll content of the cyanobacterium Anacystis nidulans were determined after growth at different light intensities in Mg2+-limited and non-Mg2+limited continuous cultures. Decreasing the light intensity from 445 to 3 1 pE m-2 s-' resulted in a threefold increase of chlorophyll per unit cell volume. The photosynthetic lamellar structure, on the other hand, increased twofold under the same conditions. The specific chlorophyll content of the photosynthetic membrane increased when the light intensity was decreased from 445 to 282 pE m-2 s-' and was constant at lower light intensities. The results indicate that the maximum chlorophyll content in the thylakoids of A. nidulans was about 1.5 fg pm-2, which means that the membrane contained 1 chlorophyll molecule per nm2 under these conditions.
PLANT PHYSIOLOGY, 1993
The filamentous nitrogen-fixing cyanobacterium Anabaena variabilis ATCC 29413 is capable of heterotrophic growth in complete darkness. After 6 months of continuous dark growth, both the autotrophic and heterotrophic cultures were found to have the same doubling time of 14 h. On a cellular basis, the chlorophyll content remained the same and the phycobilin content showed an increase in the dark-grown cultures. Fluorescence emission spectra at 77 K of dark-grown cells indicated that the phycobilisomes are functionally associated with photosystem II (PSII). Moreover, upon transfer to light, the dark-grown cells readily evolved oxygen. Although photosystem I (PSI) and whole chain-mediated electron transfer rates were comparable in both types of cultures, the rate of PSII-mediated electron transfer was found to be 20% higher in dark-grown cells. The PSI to PSI1 ratio changed from 6 1 in autotrophic cultures to 4:l in the dark-grown cells. These changes in the rate of PSI1 electron transfer and in the stoichiometry between the two photosystems under dark, heterotrophic growth conditions were brought about by a preferential increase in the number of PSI1 units while the number of PSI units remained unchanged. The advantages of using this organism in the selection of PSI-deficient mutants are discussed.
Light quality, oxygenic photosynthesis and more
Photosynthetica
Keywords: Chl fluorescence induction; chromatic acclimation of cyanobacteria; photoreceptors; photosynthetic pigments; photosystems I and II; stomatal and chloroplast photoinduced movements. Note a: See Allakhverdiev et al. (2016) for an article honoring the lifetime achievements of George C. Papageorgiou. Note b: One of us (Govindjee) is very proud to remember George Papageorgiou to be his first PhD student, whose 1968 PhD thesis in Biophysics, at the University of Illinois at Urbana-Champaign (UIUC), was extraordinarily unique, for that time; it was on 'Fluorescence induction in Chlorella pyrenoidosa and Anacystis nidulans and its relation to photophosphorylation' (available at: https://www.life. illinois.edu/govindjee/theses.html); it is equally unique that together with George, Govindjee recently paid a tribute to the father of biophysics, the prophet of photosynthesis, at UIUC, Eugene Rabinowitch, who had been on George's PhD committee (see Govindjee et al. 2019). † Lazar and Stirbet had equal contribution. Conflict of interest: The authors declare that they have no conflict of interest.
The role of growth temperature and growth irradiance on the regulation of the stoichiometry and function of the photosynthetic apparatus was examined in the cyanobacterium Plectonema boryanum UTEX 485 by comparing mid-log phase cultures grown at either 29°C/150 micromol m-2 s-1, 29°C/750 micromol m-2 s-1, 15°C/150 micromol m-2 s-1, or 15°C/10 micromol m-2 s-1. Cultures grown at 29°C/750 micromol m-2 s-1 were structurally and functionally similar to those grown at 15°C/150 micromol m-2 s-1, whereas cultures grown at 29°C/150 micromol m-2 s-1 were structurally and functionally similar to those grown at 15°C/10 micromol m-2 s-1. The stoichiometry of specific components of the photosynthetic apparatus, such as the ratio of photosystem (PS) I to PSII, phycobilisome size and the relative abundance of the cytochrome b6/f complex, the plastoquinone pool size, and the NAD(P)H dehydrogenase complex were regulated by both growth temperature and growth irradiance in a similar manner. This indicates that temperature and irradiance may share a common sensing/signaling pathway to regulate the stoichiometry and function of the photosynthetic apparatus in P. boryanum. In contrast, the accumulation of neither the D1 polypeptide of PSII, the large subunit of Rubisco, nor the CF1 a-subunit appeared to be regulated by the same mechanism. Measurements of P700 photooxidation in vivo in the presence and absence of inhibitors of photosynthetic electron transport coupled with immunoblots of the NAD(P)H dehydrogenase complex in cells grown at either 29°C/750 micromol m-2 s-1 or 15°C/150 micromol m-2 s-1 are consistent with an increased flow of respiratory electrons into the photosynthetic intersystem electron transport chain maintaining P700 in a reduced state relative to cells grown at either 29°C/150 micromol m-2 s-1 or 15°C/10 micromol m-2 s-1. These results are discussed in terms of acclimation to excitation pressure imposed by either low growth temperature or high growth irradiance.
Journal of Phycology, 2002
The photosynthesis-irradiance response (PE) curve, in which mass-specific photosynthetic rates are plotted versus irradiance, is commonly used to characterize photoacclimation. The interpretation of PE curves depends critically on the currency in which mass is expressed. Normalizing the light-limited rate to chl a yields the chl a -specific initial slope ( ␣ chl ). This is proportional to the light absorption coefficient (a chl ), the proportionality factor being the photon efficiency of photosynthesis ( m ). Thus, ␣ chl is the product of a chl and m . In microalgae ␣ chl typically shows little ( Ͻ 20%) phenotypic variability because declines of m under conditions of high-light stress are accompanied by increases of a chl . The variation of ␣ chl among species is dominated by changes in a chl due to differences in pigment complement and pigment packaging. In contrast to the microalgae, ␣ chl declines as irradiance increases in the cyanobacteria where phycobiliproteins dominate light absorption because of plasticity in the phycobiliprotein:chl a ratio. By definition, light-saturated photosynthesis (P m ) is limited by a factor other than the rate of light absorption. Normalizing P m to organic carbon concentration to obtain P m C allows a direct comparison with growth rates. Within species, P m C is independent of growth irradiance. Among species, P m C covaries with the resource-saturated growth rate. The chl a :C ratio is a key physiological variable because the appropriate currencies for normalizing light-limited and light-saturated photosynthetic rates are, respectively, chl a and carbon. Typically, chl a :C is reduced to about 40% of its maximum value at an irradiance that supports 50% of the species-specific maximum growth rate and light-harvesting accessory pigments show similar or greater declines. In the steady state, this down-regulation of pigment content prevents microalgae and cyanobacteria from maximizing photosynthetic rates throughout the light-limited region for growth. The reason for down-regulation of light harvesting, and therefore loss of potential photosynthetic gain at moderately limiting irradiances, is unknown. However, it is clear that maximizing the rate of photosynthetic carbon assimilation is not the only criterion governing photoacclimation.
2002
A diverse group of anoxygenic phototrophic bacteria thrive in habitats characterized by extremes of temperature, pH, or salinity. These ‘extremophilic ’ anoxygenic phototrophs are optimally adapted to the conditions of their habitats and are ideal model systems for defining the physiochemical limits of photosynthesis. Extremophilic phototrophs have provided new insight into the evolution of photosynthesis and play ecological roles as primary producers in their unusual habitats. Abbreviations: BChl – bacteriochlorophyll; LH – light-harvesting; topt – optimal temperature for growth Species of anoxygenic phototrophic bacteria that inhabit extreme environments have become increasingly popular as models for the study of basic problems in photosynthesis. These organisms are the ‘extremophilic’ phototrophs. In this minireview I will describe extremophilic anoxygenic phototrophs, including a brief history of their discovery and the extent of their diversity. I conclude with a discussion of ...