Fotossintese e Aclimatacao a Temperaturas Elevadas em Lupinus albus L. e Vitis vinifera L

The main objective of this work was the study of the effects of high temperature, applied separately or in combination with high light and water deficit, on the photosynthetic response of Lupinus albus L. and Vitis vinifera L., species native from the Mediterranean zone. In order to determine the effects on the photosynthetic activities and to evaluate the heat tolerance and acclimation to high temperature, experiments under laboratory and field conditions were carried out. It became apparent from the photosynthesis/temperature curves, the chlorophyll a fluorescence q-analyse and the critical temperatures for heat-induced fluorescence rise (T_c) that V. vinifera L. is a species more adapted and more resistant to high temperatures than L. albus L. The results show that photosystem II is highly heat resistant and well protected against injury by energy dissipative non-radiative processes. The reductions in Rubisco activation shown in leaves of L. albus L. grown at high temperature indicates that the down-regulation at Calvin cycle contributes to the decrease in photosynthetic rates. The experiments on the interaction between high temperature, high light and water stress showed that the high-temperature effects are modified by others stresses. In L. albus L. grown under laboratory conditions the data confirm that photosystem II is highly drought-resistant and photosynthetic capacity decreases only at leaf relative water content (#theta#) around 60% at optimal temperature. For supraoptimal temperatures however, mesophyll photosynthesis is affected at #theta# of c.a. 80%. However, it is noteworthy that T_c increased in water-stressed plants by c.a. 2.5degC as compared to well watered plants, showing that water stress may have some protective effect against extreme heat stress. Studies done in the field with Vitis vinifera L. show similar results; however the adaptive strategy is more efficient and these plants support better environmental constraints. It is doubtful that photoinhibition occur under field situation unless several stress coincide, because the protection by down-regulation at the photochemical and the Calvin cycle levels and by photorespiration seems to be very effectiveAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga