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- Photosynthesis, energy partitioning, and metabolic adjustments of the endangered Cistaceae species Tuberaria major under high temperature and droughtPublication . Osório, Maria Leonor; Osório, Júlio; Romano, AnabelaIn view of predicted climatic changes for the Mediterranean region, study of high temperature and drought impacts on physiological responses of endangered species regains relevance. In this context, micropropagated plants of Tuberaria major, a critically endangered species, endemic of Algarve, were transferred to a controlled-environment cabinet with day/night temperatures set at 25/18A degrees C (Reference) or 32/21A degrees C (HT). After 15 days of HT acclimation, some plants were subjected to progressive drought followed by rewatering. The enhancement of temperature alone did not affect water relations and photosynthetic rates (P (N)) but the stomatal conductance (g (s)) exhibited a 3-fold increase in comparison with reference plants. The maximum quantum yield of photosystem (PS) II (F-v/F-m), the effective quantum yield of PSII photochemistry (I broken vertical bar(PSII)), carotenoid (Car) and anthocyanin content enhanced, whereas the quantum yields of regulated (I broken vertical bar(NPQ)) and nonregulated (I broken vertical bar(NO)) energy dissipation decreased. Drought combined with HT reduced predawn leaf water potential to values of about -1.3 MPa, which had adverse effects on gas exchange and PSII activity. Values of P (N) and g (s) were 71 and 79% lower than those of HT plants. An impairment of photochemical activity was also observed: the decrease in I broken vertical bar(PSII) and the increase of I broken vertical bar(NPQ). However, an irreversible photoinhibitory damage had not occurred. Carotenoid and anthocyanin content remained elevated and soluble sugars (SS) increased twice, whereas proline and MDA accumulation was not detected. On the first 24 h after water-stress relief, g (s), P (N), I broken vertical bar(PSII), and I broken vertical bar(NPQ) did not recover, but SS returned to the reference level. Overall, T. major acquired an adequate capacity for a protection against the development of oxidative stress during drought and water recovery under HT. These findings suggest that T. major is prepared to deal with predicted climate changes.
- Differences in Al tolerance between Plantago algarbiensis and P. almogravensis reflect their ability to respond to oxidative stressPublication . Martins, Neusa; Osório, Maria Leonor; Gonçalves, Sandra; Osório, Júlio; Romano, AnabelaWe evaluated the impact of low pH and aluminum (Al) on the leaves and roots of Plantago almogravensis Franco and Plantago algarbiensis Samp., focusing on energy partitioning in photosystem II, H2O2 levels, lipid peroxidation, electrolyte leakage (EL), protein oxidation, total soluble protein content and antioxidant enzyme activities. In both species, Al triggered more changes in oxidative metabolism than low pH alone, particularly in the roots. We found that Al increased the levels of H2O2 in P. algarbiensis roots, but reduced the levels of H2O2 in P. almogravensis leaves and roots. Neither low pH nor Al affected the spatial heterogeneity of chlorophyll fluorescence, the maximum photochemical efficiency of PSII (F-v/F-m), the actual quantum efficiency of PSII (I center dot(PSII)) or the quantum yields of regulated (I center dot(NPQ)) and nonregulated (I center dot(NO)) energy dissipation, and there was no significant change in total soluble protein content and EL. In P. algarbiensis, Al increased the carbonyl content and the activities of superoxide dismutase (SOD) and catalase (CAT) in the roots, and also CAT, ascorbate peroxidase and guaiacol peroxidase activities in the leaves. In P. almogravensis, Al reduced the level of malondialdehyde in the roots as well as SOD activity in the leaves and roots. We found that P. almogravensis plantlets could manage the oxidative stress caused by low pH and Al, whereas the P. algarbiensis antioxidant system was unable to suppress Al toxicity completely, leading to the accumulation of H2O2 and consequential protein oxidation in the roots.
- Influence of enhanced temperature on photosynthesis, photooxidative damage, and antioxidant strategies in Ceratonia siliqua L. seedlings subjected to water deficit and rewateringPublication . Osório, Maria Leonor; Osório, Júlio; Vieira, Ana; Gonçalves, Sandra; Romano, AnabelaPredicted future climatic changes for the Mediterranean region give additional importance to the study of photooxidative stress in local economic species subjected to combined drought and high-temperature conditions. Under this context, the impact of these stresses on photosynthesis, energy partitioning, and membrane lipids, as well as the potential ability to attenuate oxidative damage, were investigated in Ceratonia siliqua L. Two thermal regimes (LT: 25/18ºC; HT: 32/21ºC) and three soil water conditions (control, water stress, and rewetting) were considered. HT exacerbated the adverse effects of water shortage on photosynthetic rates (PN) and PSII function. The decrease in PN was 33% at LT whereas at HT it was 84%. In spite of this, the electron transport rate (ETR) was not affected, which points to an increased allocation of reductants to sinks other than CO2 assimilation. Under LT conditions, water stress had no significant effects on yield of PSII photochemistry (ΦPSII) and yields of regulated (ΦNPQ) and nonregulated (ΦNO) energy dissipation. Conversely, drought induced a significant decrease of ΦPSII and a concomitant increase of ΦNO in HT plants, thereby favouring the overproduction of reactive oxygen species (ROS). Moreover, signs of lipid peroxidation damage were detected in HT plants, in which drought caused an increase of 40% in malondialdehyde (MDA) content. Concurrently, a marked increase in proline content was observed, while the activities of catalase (CAT) and ascorbate peroxidase (APX) were unaffected. Despite the generation of a moderate oxidative stress response, C. siliqua revealed a great capability for photosynthetic recovery 36 h after rewatering, which suggests that the species can cope with predicted climate change.