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61.
Chemeris Yu. K. Korol'kov N. S. Seifullina N. Kh. Rubin A. B. 《Russian Journal of Plant Physiology》2004,51(6):754-760
Inactivation of photosystem II (PSII) in the alga Chlorella pyrenoidosa Chick induced by photoinhibition (high light illumination at an intensity 10 times higher than photosynthesis-saturating light) or by incubation at a supraoptimum temperature (41°C) in darkness, resulted in a decrease in the relative yield of variable fluorescence due to a selective suppression of the slow phase of its rise. This indicates that low-activity PSII complexes, with a low efficiency of QA
– formation are inactivated first. We suppose that the transition of normal PSII complexes to a low-activity state precedes the complete loss of their photochemical activity. The existence of some common stages of PSII inactivation, when induced by photoinhibition or incubation at supraoptimum temperature in darkness, is discussed. We suggest a scheme of the sequential stages in the regulation of photosynthetic light reactions involving a reversible redox-dependent PSII inactivation. 相似文献
62.
Hajnalka Laczkó-Dobos Bettina Ughy Szilvia Z. Tóth Ottó Zsiros Árpád Párducz Masayuki Komura Zoltán Gombos 《BBA》2008,1777(9):1184-1194
To analyze the role of phosphatidylglycerol (PG) in photosynthetic membranes of cyanobacteria we used two mutants of Synechocystis sp. PCC6803: the PAL mutant which has no phycobilisomes and shows a high PSII/PSI ratio, and a mutant derived from it by inactivating its cdsA gene encoding cytidine 5'-diphosphate diacylglycerol synthase, a key enzyme in PG synthesis. In a medium supplemented with PG the PAL/ΔcdsA mutant cells grew photoautotrophically. Depletion of PG in the medium resulted (a) in an arrest of cell growth and division, (b) in a slowdown of electron transfer from the acceptor QA to QB in PSII and (c) in a modification of chlorophyll fluorescence curve. The depletion of PG affected neither the redox levels of QA nor the S2 state of the oxygen-evolving manganese complex, as indicated by thermoluminescence studies. Two-dimensional PAGE showed that in the absence of PG (a) the PSII dimer was decomposed into monomers, and (b) the CP43 protein was detached from a major part of the PSII core complex. [35S]-methionine labeling confirmed that PG depletion did not block de novo synthesis of the PSII proteins. We conclude that PG is required for the binding of CP43 within the PSII core complex. 相似文献
63.
PHOTOSYNTHETIC FUNCTION IN DUNALIELLA TERTIOLECTA (CHLOROPHYTA) DURING A NITROGEN STARVATION AND RECOVERY CYCLE 总被引:1,自引:0,他引:1
Phytoplankton can be exposed to periods of N starvation with episodic N resupply. N starvation in Dunaliella tertiolecta (Butcher) measured over 4 days was characterized by slow reduction in cell chl and protein content and chl/carotenoid ratio and a decline in photosynthetic capacity and maximum quantum yield of photosynthesis (Fv/Fm). In the early stages of N starvation, cell division was maintained despite reduction in cellular chl. Chl content was more sensitive than carotenoids to N deprivation, and cellular chl a was maintained preferentially over chl b under N starvation. NO3? resupply stimulated rapid and complete recovery of Fv/Fm (from 0.4 to 0.7) within 24 h and commencement of cell division after 10 h, although N‐replete levels of cell chl and protein were not reestablished within 24 h. Recovery of Fv/Fm was correlated with increases in cell chl and protein and was more related to increases in Fm than to changes in F0. Recovery of Fv/Fm was biphasic with a second phase of recovery commencing 4–6 h after resupply of NO3?. Uptake of NO3? from the external medium and the recovery of Fv/Fm, cell chl, and protein were inhibited when either cytosolic or chloroplastic protein synthesis was inhibited by cycloheximide or lincomycin, respectively; a time lag observed before maximum NO3? uptake was consistent with synthesis of NO3? transporters and assimilation enzymes. When both chloroplastic and cytosolic translation was inhibited, Fv/Fm declined dramatically. Dunaliella tertiolecta demonstrated a capacity to rapidly reestablish photosynthetic function and initiate cell division after N resupply, an important strategy in competing for limiting inorganic N resources. 相似文献
64.
Studies of the variability of enhancement in Chlorella pyrenoidosa confirm the existence of two types of variability: a very slow diurnal variation linked to the growth cycle and a much more rapid adaptive response to the immediate incident light conditions (State I–State II transitions). Measurements of the wavelength dependencies and relative contributions of these two types of variability suggest that they may be linked.A close examination of the enhancement signals associated with the State I–State II transition reveals that the transitions can take place in any one of three ways: by a change in Photosystem II efficiency alone, by a change in Photosystem I efficiency alone or by a simultaneous change in the efficiencies of both photosystems.Measurements of the rates of transition between State I, State II and the dark adapted state, Dark, suggest that the behaviour of State II and Dark are normally, but not always, identical. The transitions between the three states were found to be first order. For those samples exhibiting the same behaviour in Dark and State II, the rate of the State I–State II transition was found to be independent of the wavelength of Light II, suggesting that the return from State I to State II is essentially a dark process and that the driving force for the adaptive transition is the over-stimulation of Photosystem I.Finally, a model is proposed, involving an antagonistic control of the quantum yields of photochemistry of the two photosystems, that is capable of explaining the links between the two types of variability, their wavelength dependencies and the shapes of the individual enhancement signals. 相似文献
65.
C. Lu F.G. Acién Fernández E. Cañizares Guerrero D.O. Hall E. Molina Grima 《Journal of applied phycology》2002,14(5):331-342
The outdoor production of Monodus subterraneus wasstudied in bubble column and helical reactors, mainly analysing the influenceofdilution rate, air flow rate and solar irradiance on growth rate andbiochemicalcomposition. Photoinhibition and photo-oxidation phenomena were also analysed.The cultures were stressed at high solar irradiance and dissolved oxygenconcentrations. A clear relationship between stress of the cultures and thefluorescence from PSII measurements was observed, the Fv/Fm ratio being lowerinthe helical reactor than in the bubble column. Growth rate and biomassproductivity were both a function of the average irradiance and the Fv/Fmratio;maximum values of 0.040 h–1 and 0.54 gL–1 d–1 were measured. The influenceofphotoinhibition and average irradiance was modelled, the model also fitting theexperimental data reported by another author. The chlorophyll contenthyperbolically decreased, whereas the carotenoid content decreased linearlywiththe average irradiance. The higher the dilution rate the higher the protein andcarbohydrate content of the biomass, and the lower the lipid content. Theeicosapentaenoic acid (EPA) content ranged from 2.3 to 3.2% d.wt, the higherthe dilution rate, the lower EPA content, although the higher the EPAproportion. Maximum EPA productivity was only 9 mg L–1d–1, due to the stress to which the cultures wereexposed. 相似文献
66.
《Bioorganic & medicinal chemistry》2020,28(11):115492
Effective chemotherapy for solid cancers is challenging due to a limitation in permeation that prevents anticancer drugs from reaching the center of the tumor, therefore unable to limit cancer cell growth. To circumvent this issue, we planned to apply the drugs directly at the center by first collapsing the outer structure. For this, we focused on cell–cell communication (CCC) between N-glycans and proteins at the tumor cell surface. Mature N-glycans establish CCC; however, CCC is hindered when numerous immature N-glycans are present at the cell surface. Inhibition of Golgi mannosidases (GMs) results in the transport of immature N-glycans to the cell surface. This can be employed to disrupt CCC. Here, we describe the molecular design and synthesis of an improved GM inhibitor with a non-sugar mimic scaffold that was screened from a compound library. The synthesized compounds were tested for enzyme inhibition ability and inhibition of spheroid formation using cell-based methods. Most of the compounds designed and synthesized exhibited GM inhibition at the cellular level. Of those, AR524 had higher inhibitory activity than a known GM inhibitor, kifunensine. Moreover, AR524 inhibited spheroid formation of human malignant cells at low concentration (10 µM), based on the disruption of CCC by GM inhibition. 相似文献
67.
Jan Sielewiesiuk 《Acta Physiologiae Plantarum》2002,24(4):399-406
An explanation of photodamages to PS II at low light intensities is proposed. The explanation is based on the two following
postulates: 1. Intermediate states of the water-oxidizing complex can undergo parasitic reduction to lower degrees of oxidation.
2. Photosynthetic apparatus can minimize the unfavorable effect of such reduction by changes in the number of active reaction
centers of PS II. Some steady-state characteristics were calculated under these assumptions. The results obtained show that
the frequency of P680 excitations at low light intensities becomes as high as that at saturating light provided that the rate
of parasitic reduction is comparable with the rate of the slowest reaction in the cycle of the water- oxidizing complex conversions. 相似文献
68.
《Biocatalysis and Biotransformation》2013,31(1-2):119-128
The lipases (triacyglycerol hydrolases EC 3.1.1.3) of Candida cylindracea and Mucor miehei were found to be highly enantioselective for the biocatalytic resolutions of enantiomers possessing multi-chiral centers. An important optically-active building block (?)-15 (with five consecutive chiral centers), for Venturicidin synthesis has been successfully prepared. 相似文献
69.
William E. Davis Christine L. Foster Meredith K. Holub Rosina C. Krecek Audra W. Richburg 《Anthrozo?s》2018,31(2):211-219
The purpose of this study was to examine the characteristics, motivations, and expectations of humans who enroll their dogs, cats, and other pets into pet life-care centers. Pet life-care centers are groups or institutions that provide a permanent home for pets in the event of the owner’s illness, inability to care for their pet, or death. The long-term pet care industry has grown in the quality and type of care available to pet owners and is a classic example of the human–animal bond in action. This bond is well-documented in the literature, with most research focusing on physical, emotional, and mental health benefits to the pet owner. Few studies have examined how the human–animal bond affects the animal, and little is known about the motives and expectations of owners who enroll their pet in a life-care center. We conducted a study using a mail questionnaire sent to 163 current clients of a pet life-care center in Texas, USA. Of 101 respondents, whose ages ranged from 30 to over 70, most were female, married, and college-educated. Respondents strongly endorsed a variety of reasons for enrolling their pet in the center, with quality of veterinary care and satisfaction of their pet’s basic needs being the most highly rated. Coding of open-ended responses was consistent with these ratings and identified having no other options as another frequently endorsed reason. The open-ended responses also indicated that respondents expected that their pet would enjoy extensive social interaction, receive high-quality medical attention, and be treated like they were at home. Respondents who had previously visited the center were more willing to adopt a pet in the future than those who had not visited the center. With the dramatic growth of pet life-care centers in the United States and lack of existing literature, further studies in this area are advised. 相似文献
70.
Irena Trbojević-Akmačić Frano Vučković Marija Vilaj Andrea Skelin Lennart C. Karssen Jasminka Krištić Julija Jurić Ana Momčilović Jelena Šimunović Massimo Mangino Manuela De Gregori Maurizio Marchesini Concetta Dagostino Jerko Štambuk Mislav Novokmet Richard Rauck Yurii S. Aulchenko Dragan Primorac Gordan Lauc 《Biochimica et Biophysica Acta (BBA)/General Subjects》2018,1862(10):2124-2133