Aluminum interference in leaf hydration in citrus limonia and in photosynthetic performance of Vochysia tucanorum

Abstract

Aluminum (Al) is toxic to most plants. In acidic soils (pH < 5) it is found in one of its phytotoxic forms, Al3 +. In plants sensitive to Al, the first and most conspicuous toxicity symptom is the inhibition of root growth, where Al is chemically retained. In addition, Al also causes indirect symptoms such as reduced shoot growth. Sensitive plants exposed to Al show reduced CO2 assimilation rate (A) and impairment of photochemical responses, as well as low stomatal conductance (gs). This indicates that retained in the root, Al could change the hydration of the mesophyll, like in soil water deficit situations. In addition, it is also possible that water transport is impaired due to changes in the root xylem vessels that become fibrous in the presence of Al. This suggests a decrease in water transport capacity from roots to the shoots of plants exposed to Al. On the other hand, native Cerrado plants accumulate high concentration of Al in their tissues without structural or physiological damages. In some of these species, it has been found that Al is accumulated in the mesophyll, raising the question that, somehow, Al may be involved in photosynthetic processes. In the present study, we chose 'Rangpur' lime plants (Citrus limonia L.), a sensitive species to Al, and an Al-accumulating species from the Cerrado vegetation, Vochysia tucanorum Mart. (Vochysiaceae). 'Rangpur' lime plants will be grown in nutrient solution with 0 and 1480 ¼M Al, for 90 days. Sap flow sensors (HMR) will be installed in their stems and we hypothesize that plants exposed to Al will show reduced sap flow, as well as reductions in A, gs, transpiration rate (E), leaf water potential (¨w), Relative Water Content (RWC), biomass and shoot growth. All these measurements will be performed at 1, 7, 15, 30, 45, 60 and 90 Days After Planting (DAP). V. tucanorum plants will be grown in nutrient solution with contrasting Al concentrations. For these plants, measurements of leaf gas exchange rates and photochemical responses will be measured at the same dates described above. We hypothesize that V. tucanorum plants exposed to Al in nutrient solution show higher photosynthetic performance in relation to those not exposed to Al. In addition, V. tucanorum plants will be grown in pots containing calcareous soil and also in nutrient solution absent in Al, and after spraying Al on their leaves we expect that greater photosynthetic performance occur in these plants. At the beginning and at the end of the experiments, plant organ samples will be collected and the concentration of Al will be measured in routine laboratory by the colorimetric method. (AU)