Selenium compartmentalization in arbuscular mycorrhizal fungi associated with brachiaria grass

ABSTRACT Selenium (Se) is essential for humans and other animals and beneficial to plants. However, high Se concentrations cause toxicity in living organisms. Arbuscular mycorrhizae are a symbiotic interaction between arbuscular mycorrhizal fungi (AMF) and plants that can alleviate metal phytotoxicity. This study used synchrotron X-ray fluorescence (S-XRF) microanalyses to identify Se compartmentalization in AMF structures as a possible protection mechanism against Se phytotoxicity. Our experiments investigated the Se exposure in brachiaria (Urochloa decumbens) plants under AMF inoculation (pot experiment) and AMF spores (Petri dish experiment). In the pot experiment, the treatments consisted of five doses of Se in soil (0, 2, 4, 6, and 8 mg kg-1) combined with four inoculation conditions (Acaulospora morrowiae, Dentiscutata heterogama, Rhizophagus clarus, and not inoculated). In the Petri dish experiment, seven spores of D. heterogama were grown in an agar medium with the same Se doses described previously. The inoculated plants showed shoot dry matter production 26% higher than the not inoculated under 8 mg kg-1 Se. The R. clarus inoculation decreased the Se concentration in shoots by 37% compared to the other conditions under the highest Se dose. In addition, the S-XRF analysis identified a R. clarus vesicle inside a root fragment, showing a Se concentration ten times higher than in root tissues. The S-XRF analysis identified 35 mg kg-1 Se in spores of D. heterogama cultivated with 8 mg L-1 Se. The results indicated that AMF inoculation can protect brachiaria against Se toxicity due to Se compartmentalization in vesicles and spores.