Determination of depth of immersion of chlorophyll P680, pheophytin, and a secondary electron donor in the subchloroplast preparations of photosystem II from pea

The immersion depths (r) of the main functional components of the reaction centres of the Photosystem 2 in the thylakoid membranes were determined by ESR at 77K. It was shown that P680(+), Pheo(-) (pheophytin), and Z(+) (secondary electron donor) the r value was 2-4, 4-7 and 14-20 A, respectively. On the basis of these and reference data a model of location of the Photosystem 2 reaction centre components in the photosynthetic membrane was suggested.     

Study of oxygen accumulation in pea chloroplasts with spin labels

Oxygen evolution in chloroplasts was studied by nitroxide fatty probes, introduced into chloroplasts membranes. The values of K(e)[O2] were determined from the measuring kinetics of nitroxide reduction under permanent illumination at two values of the microwave field, where K(e) was the constant of spin exchange between nitroxide and oxygen, [O2] --oxygen concentration. It was shown that in chloroplasts membranes, in contrast to liposomes there was no oxygen in the dark. This observation can be explained by oxygen consumption in various biochemical reactions. The values of K(e)[O2] were measured under permanent illumination. The highest value of K(e)[O2]=1.2.10(-5) s(-2) was observed in the middle of the membrane. At temperatures above 40?C and below -20?C oxygen was not evolved.     

Variable chlorophyll fluorescence and its use for assessing physiological condition of plant photosynthetic apparatus

Analysis of plant behavior under diverse environmental conditions would be impossible without the methods for adequate assessment of the processes occurring in plants. The photosynthetic apparatus and its reaction to stress factors provide a reliable source of information on plant condition. One of the most informative methods based on monitoring the plant biophysical characteristics consists in detection and analysis of chlorophyll a fluorescence. Fluorescence is mainly emitted by chlorophyll a from the antenna complexes of photosystem II (PSII). However, fluorescence depends not only on the processes in the pigment matrix or PSII reaction centers but also on the redox reactions at the PSII donor and acceptor sides and even in the entire electron transport chain. Presently, a large variety of fluorometers from various manufacturers are available. Although application of such fluorometers does not require specialized training, the correct interpretation of the results would need sufficient knowledge for converting the instrumental data into the information on the condition of analyzed plants. This review is intended for a wide range of specialists employing fluorescence techniques for monitoring the physiological plant condition. It describes in a comprehensible way the theoretical basis of light emission by chlorophyll molecules, the origin of variable fluorescence, as well as relations between the fluorescence parameters, the redox state of electron carriers, and the light reactions of photosynthesis. Approaches to processing and analyzing the fluorescence induction curves are considered in detail on the basis of energy flux theory in the photosynthetic apparatus developed by Prof. Reto J. Strasser and known as a “JIP-test.” The physical meaning and relation of each calculated parameter to certain photosynthetic characteristics are presented, and examples of using these parameters for the assessment of plant physiological condition are outlined.     

Inactivation of photosynthetic oxygen evolution by o-phenanthroline and LiClO4 in Photosystem 2 of the pea

We examined the effects of o-phenanthroline and LiClO₄ on oxygen evolution and electron transport in the Photosystem 2 complex of the pea. Treatment of Photosystem 2 particles with a combination of 3.0 mM o-phenanthroline and 1.0 M LiClO₄ for 30–40 min at 0°C decreased the oxygen-evolving activity with the electron acceptor (either phenyl-p-benzoquinone or 2,6-dichlorophenol indophenol) to less than 5% of the original level. However with the same treatment, the electron-transport activity from an artificial electron donor, 1,5-diphenylcarbohydrazide, to 2,6-dichlorophenol indophenol remained at 60% of the original activity. The amount of manganese in the Photosystem 2 complex decreased in parallel with the loss of oxygen evolution following treatment. These observations suggest that the treatment of the Photosystem 2 complex with o-phenanthroline and LiClO₄ inhibits electron transport on the oxygen-evolving side much more significantly than on the electron-acceptor side.Abbreviations Chl chlorophyll - DCPIP 2,6-dichlorophenol indophenol - DPC 1,5-diphenylcarbo hydrazide - EDTA ethylenediaminetetraacetic acid - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - Mes 4-morpholineethanesulfonic acid - PBQ phenyl-p-benzoquinone - PS 2 Photosystem 2     

Honoring eight senior distinguished plant biologists from India

Photosynthesis Research - We summarize here research contributions of eight stalwarts in photosynthesis research from India. These distinguished scientists (Shree Kumar Apte, Basanti Biswal, Udaya...     

Application of low temperatures during photoinhibition allows characterization of individual steps in photodamage and the repair of photosystem II

Recent investigations of photoinhibition have revealed that photodamage to photosystem II (PSII) involves two temporally separated steps: the first is the inactivation of the oxygen-evolving complex by light that has been absorbed by the manganese cluster and the second is the impairment of the photochemical reaction center by light that has been absorbed by chlorophyll. Our studies of photoinhibition in Synechocystis sp. PCC 6803 at various temperatures demonstrated that the first step in photodamage is not completed at low temperatures, such as 10°C. Further investigations suggested that an intermediate state, which is stabilized at low temperatures, might exist at the first stage of photodamage. The repair of PSII involves many steps, including degradation and removal of the D1 protein, synthesis de novo of the precursor to the D1 protein, assembly of the PSII complex, and processing of the precursor to the D1 protein. Detailed analysis of photodamage and repair at various temperatures has demonstrated that, among these steps, only the synthesis of the precursor to D1 appears to proceed at low temperatures. Investigations of photoinhibition at low temperatures have also indicated that prolonged exposure of cyanobacterial cells or plant leaves to strong light diminishes their ability to repair PSII. Such non-repairable photoinhibition is caused by inhibition of the processing of the precursor to the D1 protein after prolonged illumination with strong light at low temperatures.     

Reconstitution of the water-oxidizing complex in manganese-depleted photosystem II preparations using synthetic binuclear Mn(II) and Mn(IV) complexes: production of hydrogen peroxide

Reconstitution of Mn-depleted PSII particles with synthetic binuclear Mn complexes (one Mn(II)₂ complex and one Mn(IV)₂ complex) was examined. In both cases the electron-transfer rates in the reconstituted systems were found to be up to 75–82% of that measured in native PSII but the oxygen evolution activity remained lower (<5–40%). However, hydrogen peroxide was also produced by the reconstituted samples. These samples therefore represent a new type of reconstituted PSII that generates hydrogen peroxide as the final product in reconstituted PSII centers.     

Glycinebetaine alleviates the inhibitory effect of moderate heat stress on the repair of photosystem II during photoinhibition

Transformation with the bacterial gene codA for choline oxidase allows Synechococcus sp. PCC 7942 cells to accumulate glycinebetaine when choline is supplemented exogenously. First, we observed two types of protective effect of glycinebetaine against heat-induced inactivation of photosystem II (PSII) in darkness; the codA transgene shifted the temperature range of inactivation of the oxygen-evolving complex from 40-52 degrees C (with half inactivation at 46 degrees C) to 46-60 degrees C (with half inactivation at 54 degrees C) and that of the photochemical reaction center from 44-55 degrees C (with half inactivation at 51 degrees C) to 52-63 degrees C (with half inactivation at 58 degrees C). However, in light, PSII was more sensitive to heat stress; when moderate heat stress, such as 40 degrees C, was combined with light stress, PSII was rapidly inactivated, although these stresses, when applied separately, did not inactivate either the oxygen-evolving complex or the photochemical reaction center. Further our studies demonstrated that the moderate heat stress inhibited the repair of PSII during photoinhibition at the site of synthesis de novo of the D1 protein but did not accelerate the photodamage directly. The codA transgene and, thus, the accumulation of glycinebetaine alleviated such an inhibitory effect of moderate heat stress on the repair of PSII by accelerating the synthesis of the D1 protein. We propose a hypothetical scheme for the cyanobacterial photosynthesis that moderate heat stress inhibits the translation machinery and glycinebetaine protects it against the heat-induced inactivation.     

International conference on “Photosynthesis Research for Sustainability-2016”

During June 19–26, 2016, an international conference (http://photosynthesis2016.cellreg.org/) on “Photosynthesis Research for Sustainability-2016” was held in honor of Nathan Nelson and Turhan Nejat Veziro?lu at the Institute of Basic Biological Problems, Russian Academy of Sciences, formerly Institute of Photosynthesis, Academy of Sciences of the USSR, Pushchino, Russia. Further, this conference celebrated the 50th anniversary of the Institute. We provide here a brief introduction and key contributions of the two honored scientists, and then information on the conference, on the speakers, and the program. A special feature of this conference was the awards given to several young investigators, who are recognized in this Report. Several photographs are included to show the excellent ambience at this conference. We invite the readers to the next conference on “Photosynthesis and Hydrogen Energy Research for Sustainability-2017”, which will honor A.S. Raghavendra (of University of Hyderabad), William Cramer (of Purdue University) and Govindjee (of University of Illinois at Urbana-Champaign); it will be held during the Fall of 2017 (from October 30 to November 4), at the University of Hyderabad, Hyderabad, India. See <https://prs.science>.