Spatial variation in H2O2 response of Arabidopsis thaliana root epidermal Ca2+ flux and plasma membrane Ca2+ channels

Abstract

Summary: Hydrogen peroxide is an important regulatory agent in plants. This study demonstrates that exogenous H 2 O 2 application to Arabidopsis thaliana root epidermis results in dose‐dependent transient increases in net Ca 2+ influx. The magnitude and duration of the transients were greater in the elongation zone than in the mature epidermis. In both regions, treatment with the cation channel blocker Gd 3+ prevented H 2 O 2‐induced net Ca 2+ influx, consistent with application of exogenous H 2 O 2 resulting in the activation of plasma membrane Gd 3+‐sensitive Ca 2+‐influx pathways. Application of 10 m m H 2 O 2 to the external plasma membrane face of elongation zone epidermal protoplasts resulted in the appearance of a hyperpolarization‐activated Ca 2+‐permeable conductance. This conductance differed from that previously characterized as being responsive to extracellular hydroxyl radicals. In contrast, in mature epidermal protoplasts a plasma membrane hyperpolarization‐activated Ca 2+‐permeable channel was activated only when H 2 O 2 was present at the intracellular membrane face. Channel open probability increased with intracellular [H 2 O 2] and at hyperpolarized voltages. Unitary conductance decreased thus: Ba 2+ > Ca 2+ (14.5 pS) > Mg 2+ > Zn 2+ (20 m m external cation, 1 m m H 2 O 2). Lanthanides and Zn 2+ (but not TEA+) suppressed the open probability without affecting current amplitude. The results suggest spatial heterogeneity and differential sensitivity of Ca 2+ channel activation by reactive oxygen species in the root that could underpin signalling.