Photoinhibition of Photosystem II. Kinetics, Photoprotection and Mechanism

Photosystem II (PSII) is susceptible to light-induced damage defined as photoinhibition. In natural conditions, plants are capable of repairing the photoinhibited PSII by on-going degradation and re-synthesis of the D1 reaction centre protein of PSII. Photoinhibition is induced by both visible and ultraviolet light and photoinhibition occurs under all light intensities with the same efficiency per photon. In my thesis work, I studied the reaction kinetics and mechanism of photoinhibition of PSII, as well as photoprotection in leaves of higher plants. Action spectroscopy was used to identify photoreceptors of photoinhibition. I found that the action spectrum of photoinhibition in vivo shows resemblance to the absorption spectra of manganese model compounds of the oxygen evolving complex (OEC) suggesting a role for manganese as a photoreceptor of photoinhibition under UV and visible light. In order to study the protective effect of non-photochemical quenching, the action spectrum was measured from leaves of wild type Arabidopsis thaliana and two mutants impaired in nonphotochemical quenching of chlorophyll a excitations. The findings of action spectroscopy and simulations of chlorophyll-based photoinhibition mechanisms suggested that quenching of antenna excitations protects less efficiently than would be expected if antenna chlorophylls were the only photoreceptors of photoinhibition. The reaction kinetics of prolonged photoinhibition was studied in leaves of Cucurbita maxima and Capsicum annuum. The results indicated that photoinhibitory decrease in both the oxygen evolution activity and ratio of variable to maximum fluorescence follows firstorder kinetics in vivo. The persistence of first-order kinetics suggests that already photoinhibited reaction centres do not protect against photoinhibition and that the mechanism of photoinhibition does not have a reversible intermediate. When Cucurbita maxima leaves were photoinhibited with saturating single-turnover flashes and continuous light, the light response curve of photoinhibition was found to be essentially a straight line with both types of illumination, suggesting that similar photoinhibition mechanisms might function during illumination with continuous light and during illumination with short flashes.Siirretty Doriast

Short flashes and continuous light have similar photoinhibitory efficiency in intact leaves

Lincomycin-treated pumpkin leaves were illuminated with either continuous light or saturating single-turnover xenon flashes to study the dependence of photoinactivation of photosystem II (PSII) on the mode of delivery of light. The flash energy and the time interval between the flashes were varied between the experiments, and photoinactivation was measured with oxygen evolution and the ratio of variable to maximum fluorescence (Fv/Fm). The photoinhibitory efficiency of saturating xenon flashes was found to be directly proportional to flash energy and independent of the time interval between the flashes. These findings indicate that a low-light-specific mechanism, based on charge recombination between PSII electron acceptors and the oxygen-evolving complex, is not the main cause of photoinactivation caused by short flashes in vivo. Furthermore, the relationship between the rate constant of photoinactivation and photon flux density was similar for flashes and continuous light when Fv/Fm was used to quantify photoinactivation, suggesting that continuous-light photoinactivation has a mechanism in which the quantum yield does not depend on the mode of delivery of light. A similar quantum yield of photoinhibition for flashes and continuous light is compatible with the manganese-based photoinhibition mechanism and with mechanisms in which singlet oxygen, produced via a direct photosensitization reaction, is the agent of damage. However, the classical acceptor-side and donor-side mechanisms do not predict a similar quantum yield for flashes and continuous light

Magnetic field protects plants against high light by slowing down production of singlet oxygen

Recombination of the primary radical pair of photosystem II (PSII) of photosynthesis may produce the triplet state of the primary donor of PSII. Triplet formation is potentially harmful because chlorophyll triplets can react with molecular oxygen to produce the reactive singlet oxygen (1O(2)). The yield of 1O(2) is expected to be directly proportional to the triplet yield and the triplet yield of charge recombination can be lowered with a magnetic field of 100-300 mT. In this study, we illuminated intact pumpkin leaves with strong light in the presence and absence of a magnetic field and found that the magnetic field protects against photoinhibition of PSII. The result suggests that radical pair recombination is responsible for significant part of 1O(2) production in the chloroplast. The magnetic field effect vanished if leaves were illuminated in the presence of lincomycin, an inhibitor of chloroplast protein synthesis, or if isolated thylakoid membranes were exposed to light. These data, in turn, indicate that 1O(2) produced by the recombination of the primary charge pair is not directly involved in photoinactivation of PSII but instead damages PSII by inhibiting the repair of photoinhibited PSII. We also found that an Arabidopsis thaliana mutant lacking alpha-tocopherol, a scavenger of 1O(2), is more sensitive to photoinhibition than the wild-type in the absence but not in the presence of lincomycin, confirming that the target of 1O(2) is the repair mechanism

Light Variability Illuminates Niche-Partitioning among Marine Picocyanobacteria

Prochlorococcus and Synechococcus picocyanobacteria are dominant contributors to marine primary production over large areas of the ocean. Phytoplankton cells are entrained in the water column and are thus often exposed to rapid changes in irradiance within the upper mixed layer of the ocean. An upward fluctuation in irradiance can result in photosystem II photoinactivation exceeding counteracting repair rates through protein turnover, thereby leading to net photoinhibition of primary productivity, and potentially cell death. Here we show that the effective cross-section for photosystem II photoinactivation is conserved across the picocyanobacteria, but that their photosystem II repair capacity and protein-specific photosystem II light capture are negatively correlated and vary widely across the strains. The differences in repair rate correspond to the light and nutrient conditions that characterize the site of origin of the Prochlorococcus and Synechococcus isolates, and determine the upward fluctuation in irradiance they can tolerate, indicating that photoinhibition due to transient high-light exposure influences their distribution in the ocean

Frequently asked questions about chlorophyll fluorescence, the sequel

[EN] Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122: 121-158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additionalChl a fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of F-V/F-M values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl a fluorescence in biosensor applications and the application of neural network approaches for the analysis of fluorescence measurements. The answers draw on knowledge fromdifferent Chl a fluorescence analysis domains, yielding in several cases new insights.Kalaji, H.; Schansker, G.; Brestic, M.; Bussotti, F.; Calatayud, A.; Ferroni, L.; Goltsev, V.... (2017). Frequently asked questions about chlorophyll fluorescence, the sequel. 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Biochim Biophys Acta 1553:302–308Debus RJ (1992) The manganese and calcium ions of photosynthetic oxygen evolution. Biochim Biophys Acta 1102:269–352Degl’Innocenti E, Guidi L, Soldatini GF (2002) Characteriz

Isännöinti- ja tilipalvelu Makarin asiakastyytyväisyyskysely

Tämän opinnäytetyön tarkoituksena on selvittää asiakkaiden tyytyväisyyttä isännöinti- ja tilipalvelu Makariin sekä kehittää sen toimintaa. Tutkimuksen tavoitteena on selvittää nykyinen tilanne asiakkaiden näkökulmasta ja parantaa heikkoja kohtia. Kyselyllä selvitettiin asiakastyytyväisyyttä yleisesti sekä toiminnan eri osa- alueittain. Tutkimus toteutettiin kirjekyselynä. Kyselylomakkeet lähetettiin aivan uusimpia taloyhtiöitä lukuun ottamatta kaikille puheenjohtajille. Kysely lähetettiin yhteensä 47 puheenjohtajalle, joista 32 vastasi siihen. Vastausprosentiksi muodostui 68,1 %. Kyselylomake laadittiin Microsoft Word- ohjelmalla ja tulokset analysoitiin Microsoft Excel- ohjelmalla. Tämän tutkimuksen tulokset antavat toimeksiantajalle suuntaa yrityksen tilanteesta. He eivät ole aikaisemmin tehneet tutkimuksia, joten tämä tutkimus luo pohjan seuraaville tutkimuksille ja kertoo missä tällä hetkellä mennään. Vastaukset olivat pääosin erittäin positiivisia, joten mihinkään radikaaleihin toimenpiteisiin ei ole tarvetta. Tulokset osoittivat, että etenkin isännöitsijän toimintaan ollaan erittäin tyytyväisiä. Kävi myös ilmi, että ei ole mahdollista muuttaa viestintää (esim. kokouskutsuja) asukkaiden kanssa täysin sähköiseksi. Mikään osa- alue ei saanut erityisen huonoja arvosanoja. Toiminta on kokonaisuudessaan hyvää nykyisellään, mutta pieniä parannuksia tekemällä on mahdollisuus vielä parantaa.The purpose of this thesis is to find out about the customer satisfaction with the services of Makari Property Management and Accounting Agency as well as develop the company´s services. The objective is to explain the situation from the customers' point of view and to improve the weaknesses. A survey was carried out to study customer satisfaction in general and considering various business areas. The survey was conducted by using a questionnaire. The questionnaires were sent to chairmen of the board in all housing companies except the most recent ones. The questionnaire was sent to the total of 47 chairmen of whom 32 rep-lied. The response rate was 68.1 %. The questionnaire template was made up by using Microsoft Word program and the results were analyzed in Microsoft Excel. The results of this survey give good understanding of the performance and development needs of the company. The company has not carried out any customer satisfaction surveys before, so this one creates the foundation for future development and gives a clear picture of the present level of service from the customers' point of view. The answers were generally very positive, so there is no need for any major actions as for the company's operations today. The results show especially that customers are very satisfied with the property management. It also became clear that it is not possible to change the communication with the customers to be fully conveyed through electronic channels. None of the business areas received very critical results. The entire business as it is today, received good feedback but with some small improvements there is a possibility to do better

Markkinointiviestintäsuunnitelma kiintokalusteita valmistavalle yritykselle

Opinnäytetyön tarkoituksena oli suunnitella Carolina Keittiö Oy:n uuden toimipisteen lanseerausvaiheen markkinointiviestintää. Opinnäytetyön ensimmäisenä tavoitteena oli perehtyä markkinointiviestinnän suunnittelun eri vaiheisiin. Opinnäytetyön toisena tavoitteena oli perehtyä markkinointiviestinnän keinoihin. Opinnäytetyön kolmantena tavoitteena oli laatia toimeksiantajalle markkinointiviestintäsuunnitelma. Teoriaosuudessa opinnäytetyössä käydään läpi markkinointiviestintäsuunnitelman suunnitteluprosessi, sen vaiheet ja erilaiset markkinointiviestinnän keinot. Markkinointiviestinnän suunnitteluprosessin vaiheet ovat tilanneanalyysit, kohderyhmien määrittely, budjetin määrittely, markkinointiviestinnän keinojen valinta, organisointi ja aikataulutus sekä seuranta ja arviointi. Teoriaosuudessa käsitellään ne markkinointiviestinnän keinot, jotka ovat toimeksiantajayrityksen markkinointiviestinnässä tärkeimpiä ja toimivimpia. Teoriaosuuden pohjalta toimeksiantajayritykselle laadittiin markkinointiviestintäsuunnitelma. Suunnitelmassa hyödynnettiin valittuja markkinointiviestinnän keinoja. Keinoja olivat sosiaalinen media, josta Facebook ja Instagram, verkkosivut, hakukonemarkkinointi sekä suoramainonta. Toimeksiantajayritykselle laadittiin suunnitelma, jossa oli keinoja markkinointiviestintään ennen uuden toimipisteen avausta ja avajaisissa. Liite salaisena liitteenä.