Radial oxygen loss and root growth under stagnant conditions of four grassland species with different types of aerenchyma

MANZUR MILENA ELISA; GRIMOLDI AGUSTÍN ALBERTO; INSAUSTI PEDRO; STRIKER GUSTAVO GABRIEL

La Plata, Buenos Aires, Argentina

Congreso; XXVIII Reunión Argentina de Fisiología Vegetal; 2010

Asociación Sociedad Argentina de Fisiología Vegetal

Root aerenchyma provides a pathway of lower resistance for longitudinal oxygen transport from the root base towards the root apex, a crucial process for root aeration under anaerobic conditions. However, the oxygen can be lost from the root towards the rhizosphere (i.e. radial oxygen loss: ROL) before reaching the apex. For that reason, the magnitude of ROL along a root may influence its growth by altering the root apex oxygenation. This work investigates the anatomical traits defining the ROL along roots, and their relationship with root growth under stagnant conditions, in species with different types of aerenchyma. Plants of Rumex crispus, Lotus tenuis, Paspalidium geminatum and Cyperus eragrostis were grown under hydroponics culture and subjected to aerated (7.9 mg.O2.L-1) and stagnant (0.5 mg. O2.L-1) conditions for 10-d. Aerenchyma proportion, ROL pattern along roots (0.5–5 cm from apex), suberin deposition in the outer cortex and root growth rate were assessed. Results showed that aerenchyma was higher under stagnant than aerated conditions for all species (54.1% vs. 18.1% in R. crispus, 26.2% vs. 12.9% in L. tenuis, 38.0% vs. 20.8% in P. geminatum and 38.5% vs. 16.9% in C. eragrostis). In stagnant conditions, R. crispus and L. tenuis showed higher ROL along the root (>150 ng.cm-2.min-1), lower suberin deposition in the outer cortex (<2%) and 35-45% lower root growth rates. P. geminatum had constitutive high suberin deposition (>20%), low ROL values (43 ng.cm-2.min-1) and unaffected root growth rate by anoxia. In C. eragrostis, stagnant condition determined a ROL reduction (106 vs. 44 ng.cm-2.min-1) due to an extra suberin deposition at root basal positions (>15%), so that root growth rate was similar between treatments. In conclusion, although all species increased root aerenchyma under anoxia, only those having high contents of suberin in the outer cortex were able to limit ROL from roots and maintain their root growth rate under stagnant conditions.