Role of ABA in water relations in species sensitive to Al3+

Author(s)

Marina Alves Gavassi

• Document type: Doctoral Thesis
• Press: Rio Claro. 2020-01-27.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2020-01-20
• Advisor: Gustavo Habermann

Abstract

Aluminum (Al) is the most abundant metal in the Earth's crust. In acidic soils (pH < 5.0) it is found mostly as Al3+, which is toxic to most plants. In Al-sensitive plants, the first and most conspicuous symptom is the inhibition of the growth of the root system, where most of Al is covalently retained. Aluminum also causes indirect symptoms, such as reduced shoot growth. In Al-sensitive plants, Al-reduced CO2 assimilation rate (A) is observed, and there is evidence suggesting the impairment of photochemical reactions, as well as 30 to 80% reduction in stomatal conductance (gs). In addition, Al has also been associated with a reduction in mesophyll hydration, as occurs under water-limited conditions. Based on these facts, we tested the hypothesis that part of Al symptoms in sensitive plants, especially those related to low shoot growth and development, as well as low gas exchange, occur in response to activation of mechanisms closely associated with the perception of water deficiency, especially as signalled by abscisic acid (ABA) biosynthesis. We used two Al-sensitive species, whose symptoms of toxicity are induced by significantly different concentrations, such as Solanum lycopersicum (100 M Al) and Citrus limonia (1480 M Al). Plants were grown in nutrient solution with and without Al, in independent experiments of 10 and 90 days, for S. lycopersicum and C. limonia, respectively. In the experiments with both species, biometric parameters, root system morphology, biomass, gas exchange (especially gs), leaf water potential (leaf) and ABA quantification in leaves and roots were evaluated. Additionally, root hydraulic conductance (Lpr), pH and ABA concentration in xylem sap were evaluated in S. lycopersicum plants. For C. limonia, the relative leaf water content (CRA), estimated conductivity from roots to the leaf (KL) and the expression of a key genes for ABA biosynthesis, NCED1, NCED3 and NCED5 in leaves and roots, were also evaluated. Both species showed reduction in leaf area associated to lower root growth, but this reduction was not enough to maintain leaf hydration, as evidenced by the decrease in w, CRA and gs. KL and Lpr decreased significantly in plants exposed to Al, thus indicating impairment in water transport from roots to the shoots. In C. limonia, NCED3 expression was induced in the presence of Al in both organs, while NCED1 and NCED5 were induced especially in leaves, where the highest accumulation of ABA was also verified. ABA signaling is likely to modulate stomatal closure under Al toxicity. (AU)

• FAPESP's process: 15/25409-4 - Role of ABA in water relations in metabolisms with contrasting sensitivities to Al3+
• Grantee: Marina Alves Gavassi
• Support Opportunities: Scholarships in Brazil - Doctorate