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- Physiological responses of Plantago algarbiensis and P. almogravensis shoots and plantlets to low pH and aluminum stressPublication . Martins, Neusa; Osório, Maria Leonor; Gonçalves, Sandra; Osório, Júlio; Palma, Tânia; Romano, AnabelaWe investigated the impact of low pH and aluminum (Al) stress on the growth, nutrients concentration, chlorophyll a fluorescence, photosynthetic pigment contents, proline and carbohydrate accumulation in shoots and plantlets (leaves and roots) of Plantago almogravensis and P. algarbiensis. Both species accumulated considerable and similar amounts of Al in their tissues, mainly in the roots. The presence of Al caused a significant reduction on root elongation in P. algarbiensis. Low pH and Al induced significant changes on nutrient accumulation, but no significant alterations on the maximum efficiency of PSII (Fv/Fm), quantum yield of PSII photochemistry (FiPSII), quantum yield of regulated energy dissipation (FiNPQ) and quantum yield of non-regulated energy dissipation (FiNO) were detected in both species in response to these stresses. However, Al increased significantly the nonphotochemical quenching and the hlorophyll b content and decreased the PSII excitation pressure (1 - qp) in P. almogravensis leaves. Both stress treatments induced carbohydrate accumulation in the shoots and roots of this species, but not in leaves. In P. algarbiensis, low pH and Al decreased the photosynthetic pigment contents in the shoots, whereas Al stimulated the carbohydrate accumulation in the leaves. Although our data showed that both species are tolerant to Al3+ and H+, P. almogravensis appeared to be more adapted to maintain cellular physiology and growth under those conditions.
- 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.