ИСТИНА

We show here that production of extracellular ROS is an integral part of the root hair growth machinery. Cell wall ROS in growing Arabidopsis root hairs was measured using a novel ROS sensor, Oxyburst BSA. This non-permeant molecule is localized to the extracellular space and is nonfluorescent until oxidized by ROS. Therefore, the appearance of Oxyburst fluorescence in the extracellular space indicates the localized production of extracellular ROS. Root hairs elongate via apical growth where cell wall expansion is limited to the apex of the elongating cell, while cell wall extensibility falls to almost zero several mm behind the tip. No ROS production was detected at the very apex of the growing root hair and the highest ROS activity was measured at the cell wall located directly behind the growing root hair apex. There was no significant difference between ROS concentration in the apex and flanks of the terminally elongating root hairs. Treating growing root hairs with antioxidants invariably induced bursting. Conversely, extracellular application of ROS inhibited root hair apical growth. Therefore our data is consistent with extracellular ROS playing an important role in apical growth by rigidifying the cell wall behind the root hair apex. Artificially increasing cytosolic calcium by treating the roots with calcium ionophore A23187 inhibited apical growth and induced production of elevated levels of ROS around the root hair tip. Addition of the calcium channel inhibitor, La3+, caused bursting of growing root hairs. These observations are consistent with the calcium dependent production of extracellular ROS playing a role in root hair apical growth by restricting cell wall extension to the very apex of the root hair.