Photosynthetic Acclimation To Light And Temperature: Excitation Pressure And Redox Sensing

Photosynthetic acclimation to low temperature has been studied extensively. However, since low temperature causes a preferential decrease in the rates of biochemical as compared to photochemical reactions, some alterations brought about by acclimation to low temperature may be the result of the light-harvesting apparatus absorbing more light energy than can be readily dissipated through photosynthesis. This possibility was investigated by using two species of green algae, Chlorella vulgaris and Dunaliella salina and the techniques of chlorophyll a fluorescence, O{dollar}\sb2{dollar}-evolution, protein electrophoresis and Western blotting, high performance liquid chromatography, RNA blot hybridization, and enzyme and metabolite assays. Compared to algae grown at high temperature and moderate irradiance, acclimation to low temperature resulted in a 5-8 fold lower chlorophyll content, a 2-3 fold higher ratio of chlorophyll a/b, increased carotenoid content, lower abundance of light-harvesting polypeptides and cab mRNA, and an acquired resistance to photoinhibition. However, these alterations were found not to be due to low temperature per se. In fact, adjustment in the structure and function of the photosynthetic apparatus upon growth of cells under a low temperature/low light regime mimicked growth under a high temperature/moderate light regime. Similarly, growth of cells under a low temperature/moderate light regime mimicked growth at high temperature and high light.;These results were rationalized in terms of changes in photosystem II excitation pressure which reflects modulation of photosynthetic redox poise. It was shown that growth of cells at either low temperature/moderate light or high temperature/high light caused an increase in the proportion of Q{dollar}\rm \sb{lcub}A{rcub},{dollar} the first stable electron acceptor of PSII, in the reduced state (high excitation pressure) compared to algae growth at either moderate temperature/moderate irradiance or low temperature/low irradiance (low excitation pressure). Increased reduction of PSII was shown to be, in part, due to feedback limitation at the level of photosynthetic carbon metabolism.;These results indicate that functional and structural alterations previously ascribed to changes in either temperature or irradiance are actually the result of altered photosynthetic redox poise. Photosynthetic redox poise represents a central component of the signal transduction pathway which regulates the structure and function of the photosynthetic apparatus

First-best technological strategy in an Nth-BEST economic context: a case-study of the evolution of the Acindar steelplant in Rosario, Argentina""

Includes bibliograph

Steelplant technological development in Latin America: a comparative study of the selection and upgrading of technology in plants in Argentina, Brasil, Colombia, Mexico and Peru

Includes bibliographyDescribe las caracteristicas basicas de la tecnologia e innovacion de la industria siderurgica en Argentina, Brasil, Colombia, Mexico y Peru. Comenta los factores que han influenciado en el aprendizaje llevado a cabo por las firmas y algunas de las determinantes en la seleccion de tecnologia inicial en las nuevas plantas asi como en expansiones subsecuentes

Public and Private Rights and Remedies under the Deceptive Trade Practices - Consumer Protection Act.

Abstract Forthcoming

Key lessons learned on international engagement

This briefing paper summarises shifts in international engagement in South Sudan from humanitarian aid to development and institution-building, and then back again to crisis response. The findings emerge from the recent report, Trajectories of international engagement with state and local actors: Evidence from South Sudan [^] , as well as other SLRC South Sudan research over the life of the programme. In the wake of South Sudan’s Comprehensive Peace Agreement in 2005, optimism abounded that investment in state-building would produce numerous benefits including peace, stability, growth and economic opportunities. But such optimism proved to be unfounded. This paper analyses why current aid frameworks have been mostly unsuccessful in their efforts to promote sustainable institutions and peace in South Sudan. The central argument is that aid actors largely failed because they applied technical solutions to political problems. What is needed is a rethink in approaches, modalities, and time frames, and better use of contextual and political analysis, in order to avoid similar failures in the future