Beáta Bočová

Impact of the auxin signaling inhibitor p-chlorophenoxyisobutyric acid on short-term Cd-induced hydrogen peroxide production and growth response in barley root tip

Short-term treatment (30 min) of barley roots with a low 10 μM Cd concentration induced significant H(2)O(2) production in the elongation and differentiation zone of the root tip 3h after treatment. This elevated H(2)O(2) production was accompanied by root growth inhibition and probably invoked root swelling in the elongation zone of the root tip. By contrast, a high 60 μM Cd concentration induced robust H(2)O(2) production in the elongation zone of the root tip already 1h after short-term treatment. This robust H(2)O(2) generation caused extensive cell death 6 h after short-term treatment. Similarly to low Cd concentration, exogenously applied H(2)O(2) caused marked root growth inhibition, which at lower H(2)O(2) concentration was accompanied by root swelling. The auxin signaling inhibitor p-chlorophenoxyisobutyric acid effectively inhibited 10 μM Cd-induced root growth inhibition, H(2)O(2) production and root swelling, but was ineffective in the alleviation of 60 μM Cd-induced root growth inhibition and H(2)O(2) production. Our results demonstrated that Cd-induced mild oxidative stress caused root growth inhibition, likely trough the rapid reorientation of cell growth in which a crucial role was played by IAA signaling in the root tip. Strong oxidative stress induced by high Cd concentration caused extensive cell death in the elongation zone of the root tip, resulting in the cessation of root growth or even in root death.

Salicylic acid alleviates cadmium-induced stress responses through the inhibition of Cd-induced auxin-mediated reactive oxygen species production in barley root tips.

Auxin is a master regulator of root growth by modulating its development under the constantly changing environment. Recently, an antagonistic interaction was suggested between SA and IAA signaling. Therefore, the purpose of this work was to analyze and compare the effect of the indole-3-acetic acid (IAA) signaling inhibitor p-chlorophenoxyisobutyric acid (PCIB) and salicylic acid (SA) as a potential IAA signaling inhibitor on the root growth, enzyme activity and reactive oxygen species (ROS) production in Cd- and IAA-treated barley root tips. Exposure of plants to Cd resulted in a more than threefold increase of IAA content in the root apex even 3h after the treatment. In addition, exogenously applied IAA evoked root responses such as root growth inhibition and swelling, ROS generation and activation of lipoxygenase or glutathione peroxidase identical to those induced by Cd. Furthermore, both Cd- and IAA-induced stress responses were markedly reversed by PCIB or SA post-treatment. Similarly to PCIB, SA did not affect the IAA content of root tips, suggesting the action of SA on the IAA signaling pathway in barley roots. SA probably does not alleviate the Cd toxicity in roots, but rather prevents or partially inhibits the root defense response to the presence of Cd through the inhibition of Cd-induced IAA-mediated ROS generation in roots.

Impact of short-term cadmium treatment on catalase and ascorbate peroxidase activities in barley root tips

The aim of this study was to analyse the relationship between root growth inhibition and alterations in catalase (CAT) and ascorbate peroxidase (APX) contents and activities in barley root tips during the recovery after short-term Cd stress. Significant root growth inhibition was observed after a relatively short-term (30 min) exposure of barley roots to low 15 μM Cd concentration. In seedlings treated with 30 μM Cd root growth was renewed 8–9 h after Cd treatment. By contrast, seedlings exposed to 60 μM Cd failed to restore root growth. The CAT activity increased after 15 μM Cd treatment, whereas, higher Cd concentrations inhibited CAT activity. However, APX activity was not affected by Cd treatment. The content of APX1 transcript increased while content of APX2 decreased 3 h after short-term treatment in a concentration dependent manner. While the expression of CAT1 was upregulated after 15 and 30 μM Cd treatment, it was strongly downregulated by 60 μM Cd. By contrast, CAT2 was upregulated in a concentration dependent manner. These results suggest that increased CAT activity is crucial for restoration of root growth after moderate Cd stress while at severe Cd stress its inhibition may lead to the irreversible damages.

Cadmium-induced reactive oxygen species generation, changes in morphogenic responses and activity of some enzymes in barley root tip are regulated by auxin

Abstract Morphogenic responses, ROS generation and changes in enzymes activity induced by the short-term exposure of barley roots to Cd were very similar to those of triiodobenzoic acid (TIBA) treatment. Both Cd and TIBA markedly increased the amount of IAA in root apex. In addition, the treatment of roots with TIBA before Cd treatment had an additive effect on morphogenic responses, changes in enzymes activity and ROS generation. In turn, the application of auxin efflux/influx inhibitor 1-naphthoxyacetic acid (1-NOA) before Cd treatment significantly reduced the Cd-induced ROS generation, root growth inhibition and enzymes activity in spite of the elevated level of IAA in the root apex. The auxin signalling inhibitor p-chlorophenoxyisobutyric acid (PCIB) nearly fully eliminated some of these Cd-induced responses. These results indicated that the short-term Cd treatment-induced ROS generation, morphogenic responses and activity of some enzymes can be attributed to the disturbance of IAA homeostasis in root apex. While auxin efflux inhibitor TIBA evoked similar response to Cd, auxin efflux/influx inhibitor 1-NOA attenuated and auxin signalling inhibitor PCIB blocked these Cd-induced responses suggesting that apart from the elevated level of IAA in root apex its enter and accumulation inside of until closely undetermined cells or tissues is a prerequisite for the induction of characteristic root responses to short-term Cd exposure.