Arbuscular mycorrhizal fungi induce differential activation of the plasma membrane and vacuolar H⁺ pumps in maize roots

Roots undergo multiple changes as a consequence of arbuscular mycorrhizal (AM) interactions. One of the major alterations expected is the induction of membrane transport systems, including proton pumps. In this work, we investigated the changes in the activities of vacuolar and plasma membrane (PM) H⁺ pumps from maize roots (Zea mays L.) in response to colonization by two species of AM fungi, Gigaspora margarita and Glomus clarum. Both the vacuolar and PM H⁺-ATPase activities were inhibited, while a concomitant strong stimulation of the vacuolar H⁺-PPase was found in the early stages of root colonization by G. clarum (30 days after inoculation), localized in the younger root regions. In contrast, roots colonized by G. margarita exhibited only stimulation of these enzymatic activities, suggesting a species-specific phenomenon. However, when the root surface H⁺ effluxes were recorded using a noninvasive vibrating probe technique, a striking activation of the PM H⁺-ATPases was revealed specifically in the elongation zone of roots colonized with G. clarum. The data provide evidences for a coordinated regulation of the H⁺ pumps, which depicts a mechanism underlying an activation of the root H⁺-PPase activity as an adaptative response to the energetic changes faced by the host root during the early stages of the AM interaction.