Cadmium Disrupts the Balance between Hydrogen Peroxide and Superoxide Radical by Regulating Endogenous Hydrogen Sulfide in the Root Tip of Brassica rapa

Abstract

Cd (cadmium) stress always alters the homeostasis of ROS (reactive oxygen species) including H2O2 (hydrogen sulfide) and O2•– (superoxide radical), leading to the oxidative injury and growth inhibition in plants. In addition to triggering oxidative injury, ROS has been suggested as important regulators modulating root elongation. However, whether and how Cd stress induces the inhibition of root elongation by differentially regulating endogenous H2O2 and O2•–, rather than by inducing oxidative injury, remains elusive. To address these gaps, histochemical, physiological, and biochemical approaches were applied to investigate the mechanism for Cd to fine-tune the balance between H2O2 and O2•– in the root tip of Brassica rapa. Treatment with Cd at 4 and 16 μM significantly inhibited root elongation, while only 16 μM but not 4 μM of Cd induced oxidative injury and cell death in root tip. Fluorescent and pharmaceutical tests suggested that H2O2 and O2•– played negative and positive roles, respectively, in the regulation of root elongation in the presence of Cd (4 μM) or not. Treatment with Cd at 4 μM led to the increase in H2O2 and the decrease in O2•– in root tip, which may be attributed to the up-regulation of Br_UPB1s and the down-regulation of their predicted targets (four peroxidase genes). Cd at 4 μM resulted in the increase in endogenous H2S in root tip by inducing the up-regulation of LCDs and DCDs. Treatment with H2S biosynthesis inhibitor or H2S scavenger significantly blocked Cd (4 μM)-induced increase in endogenous H2S level, coinciding with the recovery of root elongation, the altered balance between H2O2 and O2•–, and the expression of Br_UPB1s and two peroxidase genes. Taken together, it can be proposed that endogenous H2S mediated the phytotoxicity of Cd at low concentration by regulating Br_UPB1s-modulated balance between H2O2 and O2•– in root tip. Such findings shed new light on the regulatory role of endogenous H2S in plant adaptions to Cd stress.

Interaction between the signaling molecules hydrogen sulfide and hydrogen peroxide and their role in vacuolar H+‐ATPase regulation in cadmium‐stressed cucumber roots

“…This increase was related to the enhanced activity of both L‐CD and D‐CD, suggesting that endogenous production of H 2 S in cucumber occurs enzymatically in response to Cd. The present results are consistent with those demonstrating elevated H 2 S synthesis upon Cd stress in Medicago sativa (Cui et al ) and A. thaliana (Qiao et al ) as well as increased expression of genes encoding H 2 S synthesizing enzymes in Cd‐treated Brassica rapa (Zhang et al , Lv et al ).…”

“…However, modulation of the H 2 S level by adding NaHS or PAG did not significantly change Cd‐induced accumulation of H 2 O 2 . In the other plants subjected to Cd stress, it was found that H 2 S could be responsible for both an increase (Lv et al ) as well as a decrease in H 2 O 2 level (Mostofa et al , Zhang et al ). Mostofa et al () suggested that reduced H 2 O 2 production, together with a lowered malondialdehyde level, indicates that H 2 S alleviates Cd‐induced oxidative damage.…”

Characterization, expression, and functional analysis of polyamine oxidases and their role in selenium‐induced hydrogen peroxide production in Brassica rapa

“…Intracellular H 2 O 2 in roots was detected in situ using a specific fluorescent probe, 3′‐(p‐hydroxyphenyl) fluorescein (HPF), based on our previously published method . Roots were incubated in 5 µmol L −1 of HPF solution for 20 min at 25 °C, followed by washing with distilled water to remove excessive HPF on the root surface.…”

“…Intracellular H 2 O 2 in roots was detected in situ using a specific fluorescent probe, 3 ′ -(p-hydroxyphenyl) fluorescein (HPF), based on our previously published method. 32 Roots were incubated in 5 μmol L −1 of HPF solution for 20 min at 25 ∘ C, followed by washing with distilled water to remove excessive HPF on the root surface. Roots were visualized and photographed under a fluorescent microscope (ECLIPSE, TE2000-S, Nikon, Melville, NY, USA) at an excitation wave length of 490 nm and emission of 515 nm.…”

Evaluation of three wheat (Triticum aestivum L.) cultivars as sensitive Cd biomarkers during the seedling stage

“…Also, the boosted NO and O 2− production is required for Cd-induced programmed cell death that is in turn induced by Cd in Lupinus luteus L. roots (Arasimowicz-Jelonek et al, 2012). Cd accumulation induces oxidative injury and cell death in the root tips of Brassica rapa (Lv et al, 2017), suggesting that Cd exposure would alter root growth through oxidative stress alteration. Secondly, the damaged root tip restricts the further root elongation under Cd exposure was supposed to be another important reason for the root growth inhibition.…”