Cyanobacteria are photosynthetic prokaryotes that able to produce oxygen. They have light harvesting complexes called phycobilisomes (PBS). PBS are generally composed of an allophycocyanin core with phycocyanin and phycoerythrin rods connected to the core. PBS are able to efficiently harvest light energy from different wavelengths of visible light due to the evolution of PBP. Phycoerythrin has five chromophores that are attached to six cysteine residues and is essential for efficient green light capture and transfer of energy for use in photosynthesis. The attachment of these chromophores to PBP is facilitated by enzymes known as bilin lyases. In this study, we characterize and explore the role of enzymes that are involved in the biosynthesis of phycoerythrin in cyanobacteria. Biochemical and molecular techniques were used in the characterization of these proteins to gain a better understanding of their roles in the post-translational modification of phycobiliprotein. In F. diplosipohon, the lyase activity of CpeT was characterized and studied using a heterologous, co-expression system in E. coli. It was determined that CpeT was able to ligate PEB to Cys-165 of CpeB in the presence of CpeZ, a chaperone-like protein. Next, the roles of three proteins, MpeY from RS9916 and MpeQ and MpeW from A15-62, were analyzed using a combination of gene-interruption mutants and recombinant protein expression techniques. The absence of mpeY resulted in the reduction of PEB chromophorylation of MpeA in green light conditions, and recombinant protein coexpression confirmed that MpeY was responsible for PEB attachment to Cys-83 of MpeA. The interruption of mpeQ in A15-62 resulted in a reduced PUB phenotype in MpeA in blue light. Recombinant protein expressions revealed that MpeQ was a lyase-isomerase responsible for the attachment of PUB to Cys-83 of MpeA. Two regulatory proteins located in two conserved configurations of a genomic island present in species that are able to change their phycobilin content in response to different light environments, known as Type-IV chromatic acclimation (CA4), were investigated. FciA and FciB from RS9916 were studied using gene interruption mutants from RS9916 and they were found to be responsible for the CA4 response in CA4-A containing species of Synechococcus.

High schools have undertaken numerous approaches to reduce the number of first-time 9th grade students who do not move to 10th grade with their cohort. The purpose of this study was to determine if a summer program successfully transitioned 9th grade students from middle school to high school environments. Guided by the stage-environment fit conceptual framework, this study explored the effectiveness of a summer transition program at acclimating first time 9th grade students to physical, social, and academic environments. A mixed-method design was used in the study. A t test was used with a sample of approximately 400 archival 9th grader student responses to the Delaware School Climate Survey-Student. Statistical differences in familiarity with physical environments and perceptions of school climate were found between attendees and nonattendees, with attendees reporting better acclimation. A chi-square revealed greater course success for first-time 9th graders in the first marking period and lower 9th grader retention rate for attendees. Acclimation of 9th grade students as perceived by a sample of 10 teachers was explored through individual interviews and analyzed using the constant comparative method. Narratives from teacher interviews suggested acclimation to physical and social environments was greater for attendees. Study results led to development of a 1-day transition program aimed at utilizing effective transition program strategies with the entire upcoming 9th grade cohort. Long-term data collection and disaggregation is recommended to determine lasting effects of the program. Effective 9th grade transition programs may result in social change through increased promotion rates and higher graduation rates.

Plant acclimation to natural and intensified solar UV-B irradiance was investigated in three species, Oenothera stricta Ledeb., Rumex obtusifolius L., and R . patientia L. The objectives of this study were to determine: (1) the relationship between plant sensitivity and epidermal UV attenuation, (2) the effect of phenotypic changes in the leaf epidermis, resulting from UV-B exposure, on plant sensitivity to UV radiation, and (3) the plasticity of these changes in the epidermis leading to plant acclimation to UVB radiation. Epidermal UV transmittance was found to differ in magnitude and spectral distribution among the three species examined in this study. Epidermal tissue from the leaves of Oenothera stricta, Rumex obtusifolius, and R. patientiaattenuated up to 951, 90%, and 851 of the UV-B radiation incident on the leaf, respectively. The spectral distribution of transmittance appeared to be characteristic of each species. The capacity of the epidermis to attenuate UV-B radiation was found to have some degree of plasticity in Oenothera stricta and Rumex obtusifolius. After exposure to UV-B radiation for periods of 11 to 15 days, at a mean dose rate of approximately 2050 biologically effective J·m·-2d-1 , epidermal UV-B transmittance was significantly reduced by up to 36% in mature leaves of O. stricta. Increased capacity of the epidermis to attenuate UV-B radiation was not observed in young leaves of this species. These leaves only transmitted about 4% of the UV-8 radiation incident on the leaf, The transmittance of shorter wavelengths of visible radiation was reduced by 6 to 14% in young and mature leaves after UV-B irradiation. A similar reduction in epidermal UV-8 transmittance in the leaves of R. obtusifolius was also observed. Ultraviolet absorbance in leaf epidermal and mesophyll tissue of Oenothera stricta generally increased in response to UV-B irradiation. Absorbance increased more in young leaves than mature leaves after UV-B irradiation. This increase in UV absorbance was also found in mature leaves of Rumex obtusifolius and R. patientia after UV-B irradiation. The increase in absorbance was most likely caused by an increase in flavonoid and related phenolic compounds in leaf tissues. The rate of photosynthesis was used as an indicator of the degree of plant sensitivity to UV-B radiation. In general, photosynthesis was not significantly depressed in the leaves of any of the three species. A trend toward photosynthetic depression in response to UV-B irradiation was found, however, and thus some degree of UV-B sensitivity is suggested in these species. A limited degree of plant acclimation was suggested in plants that were exposed to a low UV-B dose rate prior to a higher dose rate. A mechanism of UV-B attenuation, possibly involving the biosynthesis of UV-ab sorbing flavonoid compounds in the epidermis and mesophyll under the stress of UV-B radiation, and a subsequent increase in the UV-B attenuation capacity of the epidermis, is suggested. The degree of plant sensitivity and acclimation to natural and intensified solar UV-B radiation may involve a dynamic balance between the capacity for UV-B attenuation and UV-radiation-repair mechanisms in the leaf.

<p>In the natural environment plants are confronted to a multitude of biotic and abiotic stress factors that must be perceived, transduced, integrated and signaled in order to achieve a successful acclimation that will secure survival and reproduction. Plants have to deal with excess excitation energy (EEE) when the amount of absorbed light energy is exceeding that needed for photosynthetic CO2 assimilation. EEE results in ROS formation and can be enhanced in low light intensities by changes in other environmental factors.</p><p>The lesions simulating disease resistance (lsd1) mutant of Arabidopsis spontaneously initiates spreading lesions paralleled by ROS production in long day photoperiod and after application of salicylic acid (SA) and SA-analogues that trigger systemic acquired resistance (SAR). Moreover, the mutant fails to limit the boundaries of hypersensitive cell death (HR) after avirulent pathogen infection giving rise to the runaway cell death (rcd) phenotype. This ROS-dependent phenotype pointed towards a putative involvement of the ROS produced during photosynthesis in the initiation and spreading of the lesions.</p><p>We report here that the rcd has a ROS-concentration dependent phenotype and that the light-triggered rcd is depending on the redox-state of the PQ pool in the chloroplast. Moreover, the lower stomatal conductance and catalase activity in the mutant suggested LSD1 was required for optimal gas exchange and ROS scavenging during EEE. Through this regulation, LSD1 can influence the effectiveness of photorespiration in dissipating EEE. Moreover, low and high SA levels are strictly correlated to lower and higher foliar H2O2 content, respectively. This implies an essential role of SA in regulating the redox homeostasis of the cell and suggests that SA could trigger rcd in lsd1 by inducing H2O2 production.</p><p>LSD1 has been postulated to be a negative regulator of cell death acting as a ROS rheostat. Above a certain threshold, the pro-death pathway would operate leading to PCD. Our data suggest that LSD1 may be subjected to a turnover, enhanced in an oxidizing milieu and slowed down in a reducing environment that could reflect this ROS rheostat property. Finally, the two protein disulphide isomerase boxes (CGHC) present in the protein and the down regulation of the NADPH thioredoxin reductase (NTR) in the mutant connect the rcd to a putative impairment in the reduction of the cytosolic thioredoxin system. We propose that LSD1 suppresses the cell death processes through its control of the oxidation-reduction state of the TRX pool. An integrated model considers the role of LSD1 in both light acclimatory processes and in restricting pathogen-induced cell death.</p>

<p>During the smoltification the Atlantic salmon (Salmo salar) develop different adaptations to survive in oceanic environment. One of the most important adaptations is the ability to excrete the surplus of salt through the gills. The excretion is controlled by an enzyme called Na+/K+-ATPase which is produced in an α-subunit by two gene isoforms called α1a and α1b. Enzyme activity is increasing during the smoltification process and is a strong indicator for that the process is taking place. The aim of this study was to investigate a landlocked strain of Atlantic salmon and see how the enzyme activity is developing in comparison with the gene expression of the mRNA that is coded for the enzyme. The study was carried out between March and May in the hatchery in Brattfors, Värmland. Fish were sampled at four occasions. The enzyme activity was compared between two groups of salmon where one group had full ration of food, 100% and the other group had a 15% food ration. The enzyme activity for the 100% group was then compared with the gene expression from the same group. The hypothesis was that food availability should effect smoltification and that the 15% group would have a faster increase in activity compared with the 100% group. There should also be some correlation between enzyme activity and gene expression. Na+/K+-ATPase enzyme activity showed no major differences between the groups except for a significant difference at the last sampling. Both groups had a large increase in activity from the second to the third sampling with a peak on 3.16 µmol ADP/mg/h at most. This was followed by a drop in activity at the last sampling date. The gene expression showed a fast increase of the α1b gene over the study with drop in the last sampling and the α1a gene had a constant increase from the first to the last sampling. The comparison with enzyme activity and gene expression showed a weak correlation. Compared with studies done on anadromous salmon and the land locked salmon in this study had a different development in gene expression. This could be explained that the different life strategies play an important role how the genes are expressed.</p> / <p>Under smoltifieringen utvecklar atlantlaxen (Salmo salar) olika anpassningar för att överleva i havsmiljö. En av de vikigaste anpassningarna är att utsöndra överskott av salt via gällarna. Exkretionen är kontrollerad av ett enzym som heter Na+/K+-ATPas som produceras i en α-subenhet av två isoformer av gener som heter α1a och α1b. Enzym aktiviteten ökar under smoltifieringen och är en stark indikator på att processen sker. Målet med denna studie var att undersöka en sjövandrande stam av atlantlax och se hur enzymaktiviteten utvecklas i jämförelse med gen expressionen av mRNA som kodar för produktionen av enzymet. Studien genomfördes vid fiskodlingen i Brattfors, Värmland där prover togs vid fyra tillfällen. Enzymaktiviteten jämfördes mellan två grupper av lax där en grupp fick full matranson 100 % och en grupp fick 15 % matranson. Senare jämfördes enzymaktiviteten för 100 % gruppen med gen expressionen inom samma grupp. Hypotesen var att tillgängligheten på mat skulle påverka smoltifieringen och att 15 % gruppen skulle ha en snabbare ökning i jämförelse med 100 % gruppen. Det skulle också vara en viss korrelation mellan enzymaktivitet och gen expression. Na+/K+-ATPas enzym aktiviteten visade inga större skillnader mellan grupperna förutom vid sista provtagningen. Båda grupperna hade en stor ökning från den andra till den tredje provtagningen med den högsta aktiviteten på 3.16 µmol ADP/mg/h. Detta följdes av ett fall i aktivitet vid sista provtagningen. Gen expressionen visade en snabb ökning av α1b genen över studien med en nedgång vid sista provtagningen och α1a hade en konstant men mindre ökning från första till sista provtagningen. Jämförelsen mellan enzymaktivitet och gen expression visade på en svag korrelation. Det fanns en skillnad i gen expression mellan studier gjorda på anadrom lax och sjövandrande lax i denna studie. Detta kan förklaras av att de olika livsstrategierna spelar en betydande roll i hur generna uttrycks.</p>

During the smoltification the Atlantic salmon (Salmo salar) develop different adaptations to survive in oceanic environment. One of the most important adaptations is the ability to excrete the surplus of salt through the gills. The excretion is controlled by an enzyme called Na+/K+-ATPase which is produced in an α-subunit by two gene isoforms called α1a and α1b. Enzyme activity is increasing during the smoltification process and is a strong indicator for that the process is taking place. The aim of this study was to investigate a landlocked strain of Atlantic salmon and see how the enzyme activity is developing in comparison with the gene expression of the mRNA that is coded for the enzyme. The study was carried out between March and May in the hatchery in Brattfors, Värmland. Fish were sampled at four occasions. The enzyme activity was compared between two groups of salmon where one group had full ration of food, 100% and the other group had a 15% food ration. The enzyme activity for the 100% group was then compared with the gene expression from the same group. The hypothesis was that food availability should effect smoltification and that the 15% group would have a faster increase in activity compared with the 100% group. There should also be some correlation between enzyme activity and gene expression. Na+/K+-ATPase enzyme activity showed no major differences between the groups except for a significant difference at the last sampling. Both groups had a large increase in activity from the second to the third sampling with a peak on 3.16 µmol ADP/mg/h at most. This was followed by a drop in activity at the last sampling date. The gene expression showed a fast increase of the α1b gene over the study with drop in the last sampling and the α1a gene had a constant increase from the first to the last sampling. The comparison with enzyme activity and gene expression showed a weak correlation. Compared with studies done on anadromous salmon and the land locked salmon in this study had a different development in gene expression. This could be explained that the different life strategies play an important role how the genes are expressed. / Under smoltifieringen utvecklar atlantlaxen (Salmo salar) olika anpassningar för att överleva i havsmiljö. En av de vikigaste anpassningarna är att utsöndra överskott av salt via gällarna. Exkretionen är kontrollerad av ett enzym som heter Na+/K+-ATPas som produceras i en α-subenhet av två isoformer av gener som heter α1a och α1b. Enzym aktiviteten ökar under smoltifieringen och är en stark indikator på att processen sker. Målet med denna studie var att undersöka en sjövandrande stam av atlantlax och se hur enzymaktiviteten utvecklas i jämförelse med gen expressionen av mRNA som kodar för produktionen av enzymet. Studien genomfördes vid fiskodlingen i Brattfors, Värmland där prover togs vid fyra tillfällen. Enzymaktiviteten jämfördes mellan två grupper av lax där en grupp fick full matranson 100 % och en grupp fick 15 % matranson. Senare jämfördes enzymaktiviteten för 100 % gruppen med gen expressionen inom samma grupp. Hypotesen var att tillgängligheten på mat skulle påverka smoltifieringen och att 15 % gruppen skulle ha en snabbare ökning i jämförelse med 100 % gruppen. Det skulle också vara en viss korrelation mellan enzymaktivitet och gen expression. Na+/K+-ATPas enzym aktiviteten visade inga större skillnader mellan grupperna förutom vid sista provtagningen. Båda grupperna hade en stor ökning från den andra till den tredje provtagningen med den högsta aktiviteten på 3.16 µmol ADP/mg/h. Detta följdes av ett fall i aktivitet vid sista provtagningen. Gen expressionen visade en snabb ökning av α1b genen över studien med en nedgång vid sista provtagningen och α1a hade en konstant men mindre ökning från första till sista provtagningen. Jämförelsen mellan enzymaktivitet och gen expression visade på en svag korrelation. Det fanns en skillnad i gen expression mellan studier gjorda på anadrom lax och sjövandrande lax i denna studie. Detta kan förklaras av att de olika livsstrategierna spelar en betydande roll i hur generna uttrycks.

Temperature variation affects most biological parameters from the molecular level to community structure and dynamics. Current studies on thermal biology assess how populations vary in response to environmental temperature, which can help determine how populations differentially respond to climate change. To date, temperature fluctuation effects on endothermic poikilotherms such as the common eastern bumblebee (Bombus impatiens) are unknown even though bumblebees are the most important natural pollinators in North America. A cold-acclimation experiment with B. impatiens colonies revealed individuals acclimated to 5°C or 10°C at night did not differ in resting metabolic rate, flight metabolic rate, wingbeat frequency, or morphological measurements, compared to the control group. Moreover, an infrared camera showed that all colonies maintained maximum nest temperature consistently above 36.8°C. A latitudinal sampling of flight metabolic rate and morphological measurements of B. impatiens from four locations spanning Ontario (N 45°; W 75°) to North Carolina (N 34°; W 77°) indicated no latitudinal trend in the measured variables. This study shows that bumblebees are well equipped to face a wide range of environmental temperatures, both in the short term and long term, and can use a combination of behavioural and physiological mechanisms to regulate body and nest temperatures. These results are reassuring on the direct effects of climate change on bumblebee ecology, but further studies on the indirect effect of temperature variation on North American bumblebees are required to predict future ecosystem dynamics.

Soil salinity affects over 20% of the worlds irrigated land. Potato (Solanum tuberosum L.), the most important vegetable crop worldwide, is relatively salt sensitive. However, relatively little work has been done on salt tolerance of the potato plant. This thesis investigated the methodology of treatment application and scion/rootstock effects on subsequent salt stress responses of four contrasting potato genotypes: Norland, 9506, 9120-05 [ABA-deficient mutant], and 9120-18 [ABA-normal sibling] grown hydroponically in sand. The effect of incremental salt stress were studied, using NaCl, CaCl2 and combined NaCl + CaCl2 pre- treatments as well as varying methods of ABA application with a specific focus on the role of rootstock and scion. Physiological responses of various potato genotypes to salt stress differed depending on how the salt stress was applied. An incremental salt stress regime was able to more effectively differentiate genotypes based on salt stress resistance and greater salt tolerance compared to a sudden salt shock. Generally, the ability to produce ABA was positively related to the degree of salt stress resistance, with higher ABA levels induced under incremental salt stress treatments compared to salt shock. The method of ABA application also had a marked effect on potato responses to salt stress. Slowly increasing concentrations of exogenous ABA maintained growth rates, enhanced root water content and induced more lateral shoot growth compared to a single ABA dose. The degree of salt tolerance induced by the grafted rootstock was primarily modulated by salt acclimation and was manifested in the scion as increased water content, stem diameter, dry matter accumulation, stomatal conductivity, and osmotic potential and was associated with reduced leaf necrosis. Using the salt-resistant 9506 line as a scion also significantly increased root fresh and dry weight and stem diameter as well as root water content of salt-sensitive ABA-deficient mutant rootstocks. Exogenous ABA appeared to enhance plant water status via the roots under salt stress beyond that of grafting alone. This was verified by more positive stomatal conductivity and greater upward water flow in ABA treated grafted and non-grafted plants as compared to the absence of upward water flow in non-treated grafted plants as measured via micro NMR imaging. NaCl pre-treatment produced greater salt stress resistance compared to pre-treatment with CaCl2 and was associated with a specific Na+ ion effect rather than a non-specific EC-dependent response. However, the presence of both ABA and CaCl2 appears to be necessary in order to enhance Na+ exclusion from the shoot and increases the K+/Na+ ratio.

Soil salinity affects over 20% of the worlds irrigated land. Potato (Solanum tuberosum L.), the most important vegetable crop worldwide, is relatively salt sensitive. However, relatively little work has been done on salt tolerance of the potato plant. This thesis investigated the methodology of treatment application and scion/rootstock effects on subsequent salt stress responses of four contrasting potato genotypes: Norland, 9506, 9120-05 [ABA-deficient mutant], and 9120-18 [ABA-normal sibling] grown hydroponically in sand. The effect of incremental salt stress were studied, using NaCl, CaCl2 and combined NaCl + CaCl2 pre- treatments as well as varying methods of ABA application with a specific focus on the role of rootstock and scion. Physiological responses of various potato genotypes to salt stress differed depending on how the salt stress was applied. An incremental salt stress regime was able to more effectively differentiate genotypes based on salt stress resistance and greater salt tolerance compared to a sudden salt shock. Generally, the ability to produce ABA was positively related to the degree of salt stress resistance, with higher ABA levels induced under incremental salt stress treatments compared to salt shock. The method of ABA application also had a marked effect on potato responses to salt stress. Slowly increasing concentrations of exogenous ABA maintained growth rates, enhanced root water content and induced more lateral shoot growth compared to a single ABA dose. The degree of salt tolerance induced by the grafted rootstock was primarily modulated by salt acclimation and was manifested in the scion as increased water content, stem diameter, dry matter accumulation, stomatal conductivity, and osmotic potential and was associated with reduced leaf necrosis. Using the salt-resistant 9506 line as a scion also significantly increased root fresh and dry weight and stem diameter as well as root water content of salt-sensitive ABA-deficient mutant rootstocks. Exogenous ABA appeared to enhance plant water status via the roots under salt stress beyond that of grafting alone. This was verified by more positive stomatal conductivity and greater upward water flow in ABA treated grafted and non-grafted plants as compared to the absence of upward water flow in non-treated grafted plants as measured via micro NMR imaging. NaCl pre-treatment produced greater salt stress resistance compared to pre-treatment with CaCl2 and was associated with a specific Na+ ion effect rather than a non-specific EC-dependent response. However, the presence of both ABA and CaCl2 appears to be necessary in order to enhance Na+ exclusion from the shoot and increases the K+/Na+ ratio.

Cold hardiness and resistance in winter are key factors determining the geographical distribution of plants. In addition, these factors have a huge impact on harvest of cultural plants. Strawberries, which are among the most important berry plants in the world and in Lithuania, are vulnerable to cold because of unstable snow cover, which is more and more often occurring during variable wintering conditions. Insufficient resistance of strawberries in winter, absence of clear criteria, which enable to select the most resistant varieties during a shorter time than the few year period, impedes the development and introduction of new, adaptive, fertile, and of high-quality berries strawberry cultivars. The mechanisms of cold hardiness were intensively investigated using model plants. However, there is a lack of knowledge about the genetic regulation mechanisms of winterhardiness of cultural plants. For the selection of resistant to cold plants, the knowledge about plants cold acclimation and factors determining cold resistance and controlling genes is necessary. Investigating the plants under controlled conditions in vitro, it is possible to investigate the influence of individual factors on acclimation and cold hardiness by disassociating from the influence of many different factors, which is unavoidable under natural conditions. The cold acclimation and cold hardiness of strawberries are important not only for breeding. Preservation of plant genetic resources for future... [to full text] / Atsparumas šalčiui ir ištvermingumas žiemą – pagrindiniai veiksniai, lemiantys augalų geografinį pasiskirstymą. Be to, šie veiksniai turi didžiulę įtaką kultūrinių augalų derlingumui. Braškės, kurios yra tarp svarbiausių uoginių augalų pasaulyje ir Lietuvoje, stipriai pašąla esant nepastoviai sniego dangai, vis dažniau pasitaikančiomis permainingomis žiemojimo sąlygomis. Nepakankamas braškių ištvermingumas žiemą, aiškių kriterijų, kurie leistų per trumpesnį nei kelių metų laikotarpį atrinkti ištvermingas veisles nebuvimas, apsunkina naujų, adaptyvių, derlingų, kokybiškomis uogomis, braškių veislių sukūrimą ir introdukciją. Atsparumo šalčiui mechanizmai intensyviai tirti naudojant modelinius augalus, tačiau žinių apie žiemojančių kultūrinių augalų, kurių įvairovė labai didelė, ištvermingumo žiemą mechanizmus ir jo genetinį reguliavimą labai trūksta. Atsparių šalčiui augalų atrankai vykdyti reikalingos žinios apie augalų užsigrūdinimą, apie atsparumą šalčiui lemiančius veiksnius ir juos kontroliuojančius genus. Tiriant augalus kontroliuojamomis sąlygomis in vitro, galima ištirti atskirų veiksnių įtaką užsigrūdinimui ir atsparumui šalčiui, atsiribojant nuo, neišvengiamo natūraliomis sąlygomis, daugelio įvairių veiksnių poveikio. Braškių užsigrūdinimas ir atsparumas šalčiui svarbūs ne vien tik atrankai. Genetinių išteklių išsaugojimas ateities kartoms - svarbus šiuolaikinės biologijos uždavinys. Didelių kolekcijų išsaugojimą palengvina ir sąnaudas sumažina, augalų laikymas... [toliau žr. visą tekstą]