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N V Karapetian

Publications and source records attributed to N V Karapetian.

At least 19 recordsLinked to original sources
PubMed1982

[Effects of pyridazinones and cerulenin on the biosynthesis and functional state of photosystem 2 in barley leaves].

The effects of pyridazinones and cerulenin on the formation of photosystem 2 in etiolated barley leaves and its functional state in green leaves were studied. It was shown that the reaction centers of photosystem 2 in greening leaves are formed after 2.5--3.0 hrs of illumination independently of herbicide treatment. In the leaves greening in the presence of pyridazinones and cerulenin and in green leaves treated by these substances a change in the chlorophyll state takes place, which is detected by a shortwave shift of the low temperature fluorescence maximum at 740 nm. Long-term treatment of greening and green leaves by pyridazinones increases variable fluorescence at 20 degrees. The inhibition of carotene synthesis by pyridazinones SAN 6706 and SAN 9789 during the greening is accompanied by a decrease of variable fluorescence at - 196 degrees and of its reversible part, as well as by an appearance of a light-induced dip of the fluorescence yield at 20 degrees slowly reversible in the dark. It is suggested that pyridazinones produce a 3-fold effect on the photosynthetic apparatus: 1) they block electron transport in the acceptor part of photosystem 2 and affect directly the reaction centers of this photosystem; 20 SAN 6706 and SAN 9789 inhibit carotene biosynthesis during greening of leaves, resulting in a formation of a photounstable pigment apparatus with a low amount of the reaction centers of photosystem 2; 3) pyridazinones which damage the membrane structure and probably the lipid composition of chloroplasts cause significant changes of the chlorophyll state; this effect is similar to that exerted by cerulenin.

Antifungal Agents↗
PubMed1981

[Dark and photo-induced changes in absorption and fluorescence spectra of phycobilisomes in the presence of dithionite].

In order to test the possibility of photochemical participation of phycobilin pigments in photosynthesis, the ability of phycobilisomes for reversible photo-induced redox reactions was studied. The photo-induced fast reversible changes in the absorption and fluorescence spectra of phycobilisomes in the presence of dithionite were found. Simultaneously dithionite induced dark changes revealed by the decrease of the absorption and fluorescence yields. However, the dark and photo-induced changes differ in spectral parameters depending on dithionite concentration. The ability of phycobilisomes to photosensitive redox reactions was demonstrated. A possible nature of dark and photo-induced changes in the absorption and fluorescence spectra of phycobilisomes is discussed.

Cyanobacteria↗
PubMed1981

[Effect of pyridazinone herbicides on the photosynthetic electron transport chain of chloroplasts and Chlorella].

In order to establish the site of pyridazinone herbicides action on the photosynthetic electron transport chain, their effect on the photochemical activity of chloroplasts and Chlorella was studied. It was shown that these compounds similar to diuron inhibit the delta F of chloroplasts but enhance the delta F and cause the disappearance of slow transient processes in Chlorella and change the light-off time course of delta F both in Chlorella and in the chloroplasts. The inhibiting effect is observed at herbicide concentration of 5 x 10(-6) M and is maximal at 10(-4) M. However, in contrast to diuron the herbicides enhance the msec afterglow in Chlorella cells; besides, even at concentration as high as 10(-4) M they only partly block photosynthetic oxygen evolution and the light-induced change of pH. Pyridazinone herbicides retard the delay of light-off delta F at-196 degrees C more efficiently than diuron. It is suggested that the herbicides under study inhibit the photosynthetic electron transport chain, however less efficiently than diuron; the inhibiting effect is decreased in the following order: SAN 9785, SAN 6706, SAN 9789. The herbicides affect mainly the acceptor part of the photosystem 2, retarding the electron transport from the intermediary acceptor to plastoquinone. In addition these herbicides may also have other sites of action in the region of photosystem 2.

Chlorella↗
PubMed1979

[Photoinduced changes in adsorption at 800 nm related to photosystem I functioning].

The spectra and kinetics of light-induced absorbance changes in the near-infrared region of subchloroplast fragments enriched by P700 were studied. An increase in absorbancy within the region of 725--900 nm upon illumination was characterized by a maximum around 810 nm and by "shoulders" around 760 and 870 nm. Similar effects of thermal inactivation and low temperatures on the duration of dark recovery of light-induced absorbance changes at 700 nm and within the region of 725--900 nm suggest that the absorbance changes in the near-infrared region are due to photooxidation of P700. The values of P700 differential extinction coefficients at 810 nm are 8,2.10(3) M-1.cm-1 for digitonin fragments and 7,7.10(3) M-1.cm-1 for fragments prepared with the use of diethyl ester. It was shown that the value of midpoint oxidation-reduction potential measured for the absorbance changes at 810 nm (+492 mv) is higher than that measured at 700 nm (+475 mv).

Digitonin↗
PubMed1978

[Nature of changes in the fluorescence process of P700-enriched chloroplast fragments].

Spectral and photochemical properties of P700-enriched chloroplast fragments, obtained by ether treatment of liophylized digitonin fragments, were studied. It was shown that time course of fluorescence changes of isolated fragments (in contrast to digitonin fragments) at 20 degrees does not correspond to time course of absorption changes at 700 nm. Differences in low temperature fluorescence spectra of fragments, initially distinguished by redox states of photosystem 1 reaction centers were found. However, the fragments under study were incapable of light-induced changes of fluorescence yield at--196 degrees, independently of spectral region of measured fluorescence (lambda greater than 660 nm or lambda greater than 710 nm), though these fragments reveal phototransformation of P700. Thus changes in the low temperature fluorescence spectra cannot be accounted for by redox changes of P700. The fragments, isolated by ether treatment at 20 degrees as well at--196 degrees do not reveal light-induced fluorescence changes caused by redox changes of P700. The fluorescence changes observed may be due to accessory photoprocesses of chlorophyllprotein complex.

Cell Fractionation↗
PubMed1977

[Characteristics of photosystem I from grana thylakoids and from stroma lamellae].

Photochemical and spectral properties of photosystem I particles isolated from grana thylakoids and stroma lamellae of chloroplasts of higher plants are studied. The similarity of P700 content in these particles and the same dependence of P700+ reduction on temperature and the time course of variable fluorescence from artificial electron donors and acceptors indicate on the same type of reaction center for both photosystems I. Stroma particles have a higher rate of dark relaxation of variable fluorescence and a higher rate of dark reduction of P700+ at room temperature, than grana particles. Moreover, on the basis of data on low temperature fluorescence spectra, the stroma particles contain less shortwave chlorophyll a forms than grana particles. Thus, photosystem I from grana thylakoids and from stroma lamellae have the same type of reaction centers and can differ only by their nearest environment.

Chloroplasts↗
PubMed1976

[Bacteriochlorophyll fluorescence changes related to the bacteriopheophytin photoreduction in the chromatophores of purple sulfur bacteria].

It is shown that illumination of chromatophores of sulfur bacterium Chromatium minutissimum at Eh of the medium --200 mV divided by --620 mV (when the photooxidation of pigment P890 is completely inhibited) induces a decrease in bacteriochlorophyll fluorescence yield, reversible in the dark. Under these conditions a reversible photoreduction of bacteriopheophytin is detected (bleaching of absorption bands at 543 and 760 nm and development of a band at 650 nm), which is accompanied by a blue shift of the absorption band at 8 nm. As a possible interpretation of these effects the suggestion is made on the function of bacteriopheophytin as a primary electron acceptor in reaction centers of bacteria. The bacteriopheophytin photoreduction, followed by a decrease in fluorescence yield, is also observed in other sulfur bacteria, Thiocapsa roseopersicina and Ectothiorodospira shaposhnikovii, but it is not detected in nonsulfur bacteria, Rhodospirillum rubrum and Rhodopseudomonas spheroides. This is considered as an evidence for the difference in the functional organization of the reaction centers of these two groups of bacteria,

Bacterial Chromatophores↗