Alternative electron transfer routes involved in photoprotection of cyanobacteria

In oxygenic photosynthesis, the highly oxidizing reactions of water splitting produce reactive oxygen species (ROS) and other radicals that could damage the photosynthetic apparatus and affect cell viability. Under particular environmental conditions, more electrons are produced in water oxidation than can be harmlessly used by photochemical processes for the reduction of metabolic electron sinks. In these circumstances, the excess of electrons can be delivered, for instance, to O2, resulting in the production of ROS. To prevent detrimental reactions, a diversified assortment of photoprotection mechanisms has evolved in oxygenic photosynthetic organisms. In this thesis, I focus on the role of alternative electron transfer routes in photoprotection of the cyanobacterium Synechocystis sp. PCC 6803. Firstly, I discovered a novel subunit of the NDH-1 complex, NdhS, which is necessary for cyclic electron transfer around Photosystem I, and provides tolerance to high light intensities. Cyclic electron transfer is important in modulating the ATP/NADPH ratio under stressful environmental conditions. The NdhS subunit is conserved in many oxygenic phototrophs, such as cyanobacteria and higher plants. NdhS has been shown to link linear electron transfer to cyclic electron transfer by forming a bridge for electrons accumulating in the Ferredoxin pool to reach the NDH-1 complexes. Secondly, I thoroughly investigated the role of the entire flv4-2 operon in the photoprotection of Photosystem II under air level CO2 conditions and varying light intensities. The operon encodes three proteins: two flavodiiron proteins Flv2 and Flv4 and a small Sll0218 protein. Flv2 and Flv4 are involved in a novel electron transport pathway diverting electrons from the QB pocket of Photosystem II to electron acceptors, which still remain unknown. In my work, it is shown that the flv4-2 operon-encoded proteins safeguard Photosystem II activity by sequestering electrons and maintaining the oxidized state of the PQ pool. Further, Flv2/Flv4 was shown to boost Photosystem II activity by accelerating forward electron flow, triggered by an increased redox potential of QB. The Sll0218 protein was shown to be differentially regulated as compared to Flv2 and Flv4. Sll0218 appeared to be essential for Photosystem II accumulation and was assigned a stabilizing role for Photosystem II assembly/repair. It was also shown to be responsible for optimized light-harvesting. Thus, Sll0218 and Flv2/Flv4 cooperate to protect and enhance Photosystem II activity. Sll0218 ensures an increased number of active Photosystem II centers that efficiently capture light energy from antennae, whilst the Flv2/Flv4 heterodimer provides a higher electron sink availability, in turn, promoting a safer and enhanced activity of Photosystem II. This intertwined function was shown to result in lowered singlet oxygen production. The flv4-2 operon-encoded photoprotective mechanism disperses excess excitation pressure in a complimentary manner with the Orange Carotenoid Protein-mediated non-photochemical quenching. Bioinformatics analyses provided evidence for the loss of the flv4-2 operon in the genomes of cyanobacteria that have developed a stress inducible D1 form. However, the occurrence of various mechanisms, which dissipate excitation pressure at the acceptor side of Photosystem II was revealed in evolutionarily distant clades of organisms, i.e. cyanobacteria, algae and plants.

An investigation into the functional role of the D1:1 and D1:2 polypeptides in photosystem II in cyanobacteria : the effect of changing PSI/PSII ratio on photoinhibition in Synechococcus sp. PCC7942 /

The cyanobacterium Synechococcus sp. PCC 7942 (Anacystis nidulans R2) adjusts its photosynthetic function by changing one of the polypeptides of photosystem II. This polypeptide, called Dl, is found in two forms in Synechococcus sp. PCC 7942. Changing the growth light conditions by increasing the light intensity to higher levels results in replacement of the original form of D 1 polypeptide, D 1: 1, with another form, D 1 :2. We investigated the role of these two polypeptides in two mutant strains, R2S2C3 (only Dl:l present) and R2Kl (only Dl:2 present) In cells with either high or low PSI/PSII. R2S2C3 cells had a lower amplitude for 77 K fluorescence emission at 695 nm than R2Kl cells. Picosecond fluorescence decay kinetics showed that R2S2C3 cells had shorter lifetimes than R2Kl cells. The lower yields and shorter lifetimes observed in the D 1 and Dl:2 containing cells. containing cells suggest that the presence of D 1: 1 results in more photochemical or non-photochemical quenching of excitation energy In PSII. One of the most likely mechanisms for the increased quenching in R2S2C3 cells could be an increased efficiency in the transfer of excitation energy from PSII to PSI. However, photophysical studies including 77 K fluorescence measurements and picosecond time resolved decay kinetics comparing low and high PSI/PSII cells did not support the hypothesis that D 1: 1 facilitates the dissipation of excess energy by energy transfer from PSII to PSI. In addition physiological studies of oxygen evolution measurements after photoinhibition treatments showed that the two mutant cells had no difference in their susceptibility to photoinhibition with either high PSI/PSII ratio or low PSI/PSII ratio. Again suggesting that, the energy transfer efficiency from PSII to PSI is likely not a factor in the differences between Dl:l and Dl:2 containing cells.

Efecto comparado de la radiación gamma sobre fibroblastos humanos diploides derivados del cultivo de pulmón y de adenocarcinoma mamario

Tesis (Maestría en Ciencias con Especialidad en Patología) UANL

Producción y composición quimica del forraje de Huizachillo (Desmanthus virgatus (L) var. de pressus Willd) bajo cultivo.

Tesis (Maestría en Ciencias en Producción Agrícola) UANL

Caracterización de cepas del hongo comestible Pleurotus spp. en medios de cultivo y su evaluación en substratos lignocelulósicos forrajeros para la producción de carpóforos.

Tesis (Maestría en Ciencias con Especialidad en Producción Agrícola) UANL

Producción y toxicidad de cepas nativas de bacillus thuringiensis en diferentes medios de cultivo para control de insectos, plaga lepidopteros

Tesis (Maestría en Ciencias con Especialidad en Microbiología Industrial) UANL

Producción de esporas de Paecilomyces fumosoroseus en diferentes medios de cultivo líquidos

Tesis (Maestría en Ciencias con Especialidad en Microbiología) UANL

Evaluación de la expresión de los genes endógenos hPLs y hGH-v en cultivo primario de placenta

Tesis (Maestría en Ciencias con Especialidad en Biología) UANL

Estudio molecular y celular bajo la influencia de condiciones de cultivo durante la producción de proteínas heterólogas en Pichia pastoris

Tesis (Maestría en Ciencias con Especialidad en Biología Molecular e Ingeniería Genética) UANL

Regulación de la expresión diferencial del gen hGH-V en células en cultivo

Tesis (Maestría en Ciencias con Especialidad en Biología Molecular e Ingeniería Genética) UANL

Uso de técnicas isotópicas de 15 N aplicadas al estudio de la fijación biológica de nitrógeno en el cultivo de alfalfa (Medicago sativa L.) en La Comarca Lagunera, México

Tesis (Maestría en Ciencias con Especialidad en Microbiología) UANL

Efecto de sobrenadantes de cultivo sobre la esporulación de cepas nativas de Clostridium Perfringens tipo A

Tesis (Maestría en Ciencias con Especialidad en Microbiología) UANL

Diagnóstico de elementos secundarios y micronutrimientos en el cultivo de maíz (Zea mays L.) en Anáhuac, Nuevo León

Tesis (Maestría en Ciencias con Especialidad en Producción Agrícola) UANL

Epizootiología de las enfermedades detectadas en el cultivo de camarón azul Litopenaeus stylirostris en el parque acuícola El Siari, Sonora, México

Tesis (Maestría en Ciencias con Especialidad en Parasitología) UANL

Inducción de germinación, crecimiento de plántula y cultivo in vitro de pitahaya Hylocereus undatus (Haworth) Britton and Rose

Tesis (Maestría en Ciencias con Especialidad en Botánica) UANL