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Hydraulic, metabolic and molecular aspects of Al3+ interference in above ground plant hydration in citrus limonia

Grant number: 17/26144-0
Support type:Regular Research Grants
Duration: July 01, 2018 - June 30, 2020
Field of knowledge:Agronomical Sciences - Agronomy
Principal Investigator:Gustavo Habermann
Grantee:Gustavo Habermann
Home Institution: Instituto de Biociências (IB). Universidade Estadual Paulista (UNESP). Campus de Rio Claro. Rio Claro , SP, Brazil
Assoc. researchers:Douglas Silva Domingues

Abstract

Aluminum (Al) is the third most available chemical element in the Earth's crust. In acidic soils (pH < 5.5) its phytotoxic form (Al3+) is found. The first and most conspicuous phytotoxic symptom is the growth inhibition of the roots, where Al covalently binds to the cell wall. Al also reduces leaf gas exchange rates, decreasing stomatal conductance (gs). Although the reduction in gas exchange rates might be associated with a smaller root system that could lead to low water uptake, the Al also reduces the growth and development of the above ground organs, compensating this effect. Therefore, retained in the root system, the Al could interfere with the mesophyll hydration as in a water deficiency situation, considering that Al-induced dysfunction in xylem vessels in the roots has already been reported. Following this reasoning, aquaporins and abscisic acid (ABA), a water deficiency signalling in above ground plant organs, could be also involved. Here, we study 'Rangpur' lime plants (Citrus limonia), a tree species that is sensitive to Al and an important rootstock in the Brazilian rain-fed Citrus industry. In plants exposed to Al, we expect to find a low transcription profile of aquaporins (PIPs subfamily), decreased values of estimated hydraulic conductivity from the soil to the leaves (KL), reduced sap flow rates in the stem, as well as increased concentration of ABA and its metabolites. Young plants (15 cm) will be grown in a greenhouse, in nutrient solution containing 0 and 1480 ¼M Al, for 90 days. At 1, 7, 15, 30, 60 and 90 days after treatments (DAT) root tips will be collected to extract RNA for measuring transcriptional profiles (qRT-PCR) of PIPs. On these dates, predawn (¨pd) and midday (¨md) leaf water potential, leaf gas exchange in the morning (9:00h-11:00h) and in the afternoon (13:00h-15:00h), as well as leaf relative water content (RWC) in the afternoon will be measured. Using transpiration rates (E) measured in the afternoon, ¨pd and ¨md it will be possible to calculate KL. Roots and leaves for ABA quantification (LC-ESI-MS/MS, by an outsourced service in Canada) will be also collected on these dates. Sap flow sensors (HRM) will be set on stems for measuring the sap flow rate in order to support the other ecophysiological results. At the beginning (0 DAT) and at the end (90 DAT) of the study, biometric parameters, plant organ biomass and total content of Al in leaves, stems and roots will be also assessed. Up to eight replicates (plants) will be used and data will be checked for its homogeneity and homocedasticity. Parametric data from both treatments will be compared, separately, for each evaluation date by student T test (alpha = 5%). (AU)