Fotossíntese em Clusia hilariana Schlechtendal (Clusiaceae): respostas ao estresse salino e à alta irradiância

• Autor(a) principal: Godoy, Alice Gontijo de
• Data de Publicação: 2010
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4316
• topic: Fotossíntese; Clusia; Fluorescência; Salinidade; Photosynthesis; Clusia; Fluorescence; Salinity; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

Clusia hilariana is a species with CAM photosynthesis that occurs in areas of brazillian restingas. Little is known about the adaptive strategies used by C. hilariana to tolerate the adverse conditions to which it is exposed in its natural environment, and about how the CAM photosynthesis would perform these processes. The aim of this study was to characterize and understand the responses of the photosynthetic apparatus of C. hilariana to contrasting light environments, as well as to the excess of NaCl in the solution in contact with the roots. To assess the effects of high irradiance and salt stress, it was designed a factorial experiment with three light and two salt conditions. Plants of C. hilariana were grown in half-strength Hoagland solution under conditions of full sun and 70% shading. It was added 400mM of NaCl to the nutrient solution of half the plants in each shading condition, than half of the plants grown in the shade were transferred to full sun. Individuals in control nutrient solution showed daily pattern of gas exchange typical of CAM plants. The values of photosynthetic rate (A), stomatal conductance (gs), ratio between internal and atmospheric CO2 (Ci/Ca) and transpiration (E) varied according to different lighting conditions, as well as the duration of the phases of CAM photosynthesis. Plants in saline solution showed changes in all variables of gas exchange when compared to plants in the control solution, with A, gs, E, and Ci/Ca close to zero. Among the plants in control solution, the highest values of potential quantum yield of photosystem II (Fv/Fm) were observed for sun and shade plants, with little change throughout the day. A transfer from shade to sun caused reduction in Fv/Fm, as well as treatment with NaCl, which resulted in an increase on initial fluorescence and a decrease on maximum fluorescence and rate of electron transport, especially in transferred plants. The contents of Na and Cl in plants’ leaves under all treatments do not resulted in toxic effects, also with no deficiency of K, Ca and Mg. The effects of NaCl were osmotic, with values of osmotic potential of plants in saline solution less negative than that of saline solution itself. The application of NaCl leaded to degradation of chlorophyll a in transferred plants, but not of chlorophyll b. Higher levels of carotenoids were observed in plants under osmotic or light. Plants with greater A also showed higher succulence. Differences in the photosynthetic pattern of C. hilariana showed that this species may have great plasticity in response to changing light and salinity conditions, through changes in the duration and intensity of each CAM phase. It was also noted the existence of interaction between the osmotic and light stresses effects in the metabolism of C. hilariana, resulting in increases of photoinhibitory damage when compared to the effects of individual stresses. Plants grown in full sun showed metabolic changes that allowed greater tolerance to conditions of high irradiance and salinity than plants grown in the shade. Although plants of C. hilariana resort to strategies that could lead to acclimation under stressful situation, for the stresses combined these strategies do not appear as efficient as for individual stresses.