RESUMO
Styrax camporum Pohl. (Styracaceae) is a woody species that grows on acidic soils from the Brazilian savanna with high aluminum (Al) saturation (m% > 50%), where it accumulates ~ 1500 mg Al per kg dry leaves. Using nutrient solution, a previous study showed that 1480 µM Al causes toxicity symptoms, which raises the question whether less than 1480 µM Al could cause beneficial effects on this species. Here, we checked possible altered gas exchange rates, damage to organelles in root tips and the association between Al exposure and mitochondria occurrence in cells of root tips, once organic acids from Krebs cycle exuded by the roots of this species when exposed to Al have been recently evidenced. Five-month-old plants were grown in nutrient solution with 0, 740 and 1480 µM Al for 90 days. Plants exposed to 1480 µM Al showed less developed root system, reduced plant height and low gas exchange rates in relation to those exposed to 0 and 740 µM Al, confirming that 1480 µM Al is toxic to S. camporum. However, plants exposed to 0 and 740 µM Al had similar number of leaves, plant height, root biomass, root length, total plant biomass and gas exchange rates, indicating that no beneficial effects from 740 µM Al could be noted on this species. In plants exposed to 0 and 740 µM Al, mitochondria were noted at the root tip, while at 1480 µM Al these organelles were not evident due to the conspicuous vacuolation of root cells. S. camporum shows limited tolerance to Al in nutrient solution. In addition, this species is not dependent on Al to grow and develop because the plants grew well under 0 and 740 µM Al.
Assuntos
Alumínio , Styrax , Alumínio/toxicidade , Brasil , Raízes de Plantas , Styrax/efeitos dos fármacos , Styrax/crescimento & desenvolvimento , MadeiraRESUMO
In acidic soils, aluminium (Al) occurs as Al3+, which is phytotoxic. One of the most conspicuous symptoms of Al toxicity is the root growth inhibition, which can lead to low water uptake and consequent reduction in leaf hydration and gas exchange. However, fibrous xylem vessels have been observed in roots of 'Rangpur' lime plants (Citrus limonia L.) when exposed to Al, which could affect the functioning of aquaporins, ultimately reducing their expression. We confirmed a decrease of CO2 assimilation (A), stomatal conductance (gs), transpiration (E) and relative leaf water content (RWC) in 3-month-old C. limonia plants exposed to 1480 µM Al in nutrient solution for 90 days. The estimated hydraulic conductivity from soil to the leaf (KL) and leaf water potential (Ψw) also showed low values, although not consistently reduced over time of Al exposure. The relative expression of aquaporin genes belonging to PIP family (PIP1-1, PIP1-2 and PIP2) showed downregulation for ClPIP1-1 and ClPIP2 and upregulation for ClPIP1-2 in plants exposed to Al. Furthermore, ClPIP1-1 was positively correlated with A and gs in plants exposed to Al. Therefore, downregulation of ClPIP1-1 and ClPIP2 in roots of 'Rangpur' lime plants could be associated with the low leaf hydration of this species when exposed to Al.