Membrane water permeability of maize root cells under two levels of oxidative stress

Changes in the total water permeability of two cell membranes (plasmalemma and tonoplast), estimated by the effective diffusion coefficient of water (D (ef)), were controlled using the NMR method. The time dynamics of D (ef) in maize (Zea mays L.) root cells was studied in response to (i) root excision from seedling and the following 6-h incubation in the growth medium (wound stress) and (ii) the superposition of wound stress plus paraquat, which induces the excess of reactive oxygen species (ROS). The dynamics of lipid peroxidation, oxygen consumption, and heat production was studied to estimate general levels of oxidative stress in two variants of experiments. Under wound stress (the weak oxidative stress), the reversible by dithiothreitol increase in cell membrane water permeability was observed. The applicability of mercury test to aquaporin activity in our experiments was verified. The results of wound stress effect, obtained using this test, are discussed in terms of oxidative upregulation of aquaporin activity by ROS. The increase of oxidative stress in cells (wound-paraquat stress), contrary to wound stress, was accompanied by downregulation of membrane water permeability. In this case, ROS is supposed to affect the aquaporins not directly but via such processes as peroxidation of lipids, inactivation of some intracellular proteins, and relocalization of aquaporins in cells.