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21.
Highly time-resolved photoacclimation patterns of the chlorophyte microalga Dunaliella tertiolecta during exposure to an off–on–off (block) light pattern of saturating photon flux, and to a regime of consecutive increasing
light intensities are presented. Non-photochemical quenching (NPQ) mechanisms unexpectedly responded with an initial decrease
during dark–light transitions. NPQ values started to rise after light exposure of approximately 4 min. State-transitions,
measured as a change of PSII:PSI fluorescence emission at 77 K, did not contribute to early NPQ oscillations. Addition of
the uncoupler CCCP, however, caused a rapid increase in fluorescence and showed the significance of qE for NPQ. Partitioning
of the quantum efficiencies showed that constitutive NPQ was (a) higher than qE-driven NPQ and (b) responded to light treatment
within seconds, suggesting an active role of constitutive NPQ in variable energy dissipation, although it is thought to contribute
statically to NPQ. The PSII connectivity parameter p correlated well with F′, F
m
′ and NPQ during the early phase of the dark–light transients in sub-saturating light, suggesting a plastic energy distribution
pattern within energetically connected PSII centres. In consecutive increasing photon flux experiments, correlations were
weaker during the second light increment. Changes in connectivity can present an early photoresponse that are reflected in
fluorescence signals and NPQ and might be responsive to the short-term acclimation state, and/or to the actinic photon flux. 相似文献
22.
CO2 acquisition in Chlamydomonas acidophila is influenced mainly by CO2, not phosphorus,availability
The extremophilic green microalga Chlamydomonas acidophila grows in very acidic waters (pH 2.3–3.4), where CO2 is the sole inorganic carbon source. Previous work has revealed that the species can accumulate inorganic carbon (Ci) and exhibits high affinity CO2 utilization under low-CO2 (air-equilibrium) conditions, similar to organisms with an active CO2 concentrating mechanism (CCM), whereas both processes are down-regulated under high CO2 (4.5 % CO2) conditions. Responses of this species to phosphorus (Pi)-limited conditions suggested a contrasting regulation of the CCM characteristics. Therefore, we measured external carbonic anhydrase (CAext) activities and protein expression (CAH1), the internal pH, Ci accumulation, and CO2-utilization in cells adapted to high or low CO2 under Pi-replete and Pi-limited conditions. Results reveal that C. acidophila expressed CAext activity and expressed a protein cross-reacting with CAH1 (the CAext from Chlamydomonas reinhardtii). Although the function of this CA remains unclear, CAext activity and high affinity CO2 utilization were the highest under low CO2 conditions. C. acidophila accumulated Ci and expressed the CAH1 protein under all conditions tested, and C. reinhardtii also contained substantial amounts of CAH1 protein under Pi-limitation. In conclusion, Ci utilization is optimized in C. acidophila under ecologically relevant conditions, which may enable optimal survival in its extreme Ci- and Pi-limited habitat. The exact physiological and biochemical acclimation remains to be further studied. 相似文献
23.
Tian Q Beardall M Xu Y Li J Parker DC Casanova N Bakke AC Chen C 《Journal of immunology (Baltimore, Md. : 1950)》2006,177(4):2412-2422
Despite stringent regulation of disease-associated autoantibodies, a substantial proportion of circulating Abs in sera of healthy individuals exhibit self-reactivity. These Abs are referred to as naturally occurring or natural autoantibodies (NAAs). To understand the origin and function of NAAs, we have generated a new site-directed transgenic mouse model in which a prerearranged VDJ gene coding for the H chain of a typical polyreactive NAA, ppc1-5, is inserted into the IgH locus. This H chain, when combined with its original L chain, the lambda1 L chain, yields a NAA that characteristically binds a variety of self and non-self Ags including ssDNA, actin, ubiquitin, and nitrophenyl phosphocholine. Despite their autoreactivity, B cells expressing ppc1-5H/lambda1 NAA are not negatively selected, but rather are overrepresented in the transgenic mice. The shift toward lambda1 expression mainly occurs during the transition of immature to mature B cells in the spleen, suggesting a BCR selection process. The ppc1-5H/lambda1 B cells exhibit a phenotype that is different from those of the known mature B cell populations, and they are located predominantly in the lymphoid follicles of the spleen and the lymph nodes. These B cells are functionally active, producing high levels of Abs in vivo and responding well to BCR stimulation in vitro. The findings indicate that the ppc1-5/lambda1 natural autoantibodies originate from a distinct B cell subset that may be positively selected by virtue of its poly/autoreactivity. 相似文献
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25.
P. Foster D. Voltolina J. Beardall 《Journal of experimental marine biology and ecology》1982,62(2):93-115
Physical, chemical, and phytoplankton distributions observed in Liverpool Bay during early and terminal stages in development of the spring bloom in May, 1977, are described. Qualitative and quantitative changes in phytoplankton distributions are interpreted with respect to the contemporaneous chemical and physical hydrography and quantified changes in the hydrography between the periods of observation. In early May, a physical discontinuity demarcated the biological, physical, and most of the chemical characteristics of the offshore and coastal waters. Phytoplankton numbers were greatest in the inshore waters and decreased seaward. The diatom bloom was concentrated in coastal areas where the nutrient status of the waters was least favourable to sustain it. The waters bounded by the front and the coast were composed of a number of physically and chemically distinct water types and each had associated with it a qualitatively distinct phytoplankton population. During the early stage of the spring bloom no abnormal concentrations or accumulations of phytoplankton were associated with the front. By late May areas of diverse phytoplankton density had developed in the inshore waters, major differences in qualitative composition were associated with various density fields and the physical discontinuity, separating offshore and coastal waters, had developed into the site of greatest phytoplankton density. The spatial and temporal changes in the phytoplankton populations are shown to be related to the nutrient status of the waters both within and at the boundaries of the various density fields. 相似文献
26.
Daniel W. Pritchard Catriona L. Hurd John Beardall Christopher D. Hepburn 《Journal of phycology》2013,49(5):867-879
Reduced light availability for benthic primary producers as a result of anthropogenic activities may be an important driver of change in coastal seas. However, our knowledge of the minimum light requirements for benthic macroalgae limits our understanding of how these changes may affect primary productivity and the functioning of coastal ecosystems. This knowledge gap is particularly acute in deeper water, where the impacts of increased light attenuation will be most severe. We examined the minimum light requirements of Anotrichium crinitum, which dominates near the maximum depth limit for macroalgae throughout New Zealand and Southern Australia, and is a functional analog of rhodophyte macroalgae in temperate low‐light (deep‐water) habitats throughout the world. These data show that A. crinitum is a shade‐adapted seaweed with modest light requirements for the initiation of net photosynthesis (1.49–2.25 μmol photons · m?2 · s?1) and growth (0.12–0.19 mol photons · m?2 · d?1). A. crinitum maintains high photosynthetic efficiency and pigment content and a low C:N ratio throughout the year and can maintain biomass under sub‐compensation (critical) light levels for at least 5 d. Nevertheless, in situ photon flux is less than the minimum light requirement for A. crinitum on at least 103 d per annum and is rarely sufficient to saturate growth. These findings reinforce the importance of understanding the physiological response of macroalgae at the extremes of environmental gradients and highlight the need to establish minimum thresholds that modification of the subtidal light environment should not cross. 相似文献
27.
Ik?Kyo?ChungEmail author John?Beardall Smita?Mehta Dinabandhu?Sahoo Slobodanka?Stojkovic 《Journal of applied phycology》2011,23(5):877-886
There has been a good deal of interest in the potential of marine vegetation as a sink for anthropogenic C emissions (“Blue
Carbon”). Marine primary producers contribute at least 50% of the world’s carbon fixation and may account for as much as 71%
of all carbon storage. In this paper, we analyse the current rate of harvesting of both commercially grown and wild-grown
macroalgae, as well as their capacity for photosynthetically driven CO2 assimilation and growth. We suggest that CO2 acquisition by marine macroalgae can represent a considerable sink for anthropogenic CO2 emissions and that harvesting and appropriate use of macroalgal primary production could play a significant role in C sequestration
and amelioration of greenhouse gas emissions. 相似文献
28.
Aspects of the physiology of two rhodophyte macroalgae from the Antarctic, Palmaria decipiens and Porphyra endiviifolium, were examined. Both species showed low light compensation points and I
k values. Measurements of the dissolved inorganic carbon dependent kinetics of oxygen evolution gave values for K
0.5 (CO2) of 10.5 and 3.7 μM for Palmaria and Porphyra respectively. These values are lower than expected from the kinetic properties of ribulose 1,5-bisphosphate carboxylase oxygenase
and imply that the two species are capable of the active transport and accumulation of dissolved inorganic carbon by a “CO2 concentrating mechanism”. Both organisms are able to use bicarbonate from the bulk medium. These features are similar to
those found in temperate species and thus, despite the low photon flux, low temperatures and consequent elevated CO2 concentrations in seawater at air-equilibration, the Antarctic rhodophytes examined appeared not to have a diminished capacity
for transport of dissolved inorganic carbon and internal CO2 concentration.
Accepted: 24 October 1998 相似文献
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Climate change is expected to bring about alterations in the marine physical and chemical environment that will induce changes in the concentration of dissolved CO2 and in nutrient availability. These in turn are expected to affect the physiological performance of phytoplankton. In order to learn how phytoplankton respond to the predicted scenario of increased CO2 and decreased nitrogen in the surface mixed layer, we investigated the diatom Phaeodactylum tricornutum as a model organism. The cells were cultured in both low CO2 (390 μatm) and high CO2 (1000 μatm) conditions at limiting (10 μmol L−1) or enriched (110 μmol L−1) nitrate concentrations. Our study shows that nitrogen limitation resulted in significant decreases in cell size, pigmentation, growth rate and effective quantum yield of Phaeodactylum tricornutum, but these parameters were not affected by enhanced dissolved CO2 and lowered pH. However, increased CO2 concentration induced higher rETRmax and higher dark respiration rates and decreased the CO2 or dissolved inorganic carbon (DIC) affinity for electron transfer (shown by higher values for K1/2 DIC or K1/2 CO2). Furthermore, the elemental stoichiometry (carbon to nitrogen ratio) was raised under high CO2 conditions in both nitrogen limited and nitrogen replete conditions, with the ratio in the high CO2 and low nitrate grown cells being higher by 45% compared to that in the low CO2 and nitrate replete grown ones. Our results suggest that while nitrogen limitation had a greater effect than ocean acidification, the combined effects of both factors could act synergistically to affect marine diatoms and related biogeochemical cycles in future oceans. 相似文献