Effect of cobalt chloride on soybean seedlings subjected to cadmium stress

Abstract

Contamination of the environment with heavy metals such as Cd is a serious problem of modern world. Exposure of plants to Cd leads to oxidative stress, inhibition of respiration and photosynthesis, increased rate of mutation and, as a consequence, stunted growth and yield decrease. One of the common reactions of plants to cadmium stress is over-production of ethylene, however the exact role of this hormone in plants response to Cd is still unrecognized. The aim of the present study is evaluation of the impact of an ethylene synthesis inhibitor, Co, on the response of soybean seedlings to cadmium stress. The experiments included measurements of growth, cell viability, ethylene production and expression of genes associated with cellular signaling in soybean seedlings exposed to CdCl 2 (with Cd in a concentration of 223 μM) and/or CoCl 2 (with Co in concentration of 4.6 μM). Surprisingly, the results show that Co has no effect on ethylene biosynthesis, however, it affects cell viability and expression of Cd-induced genes associated with plant signaling pathways. The affected genes encode mitogen-activated protein kinase kinase2 (MAPKK2), nitrate reductase and DOF1 and bZIP2 transcription factors. The role of Co in plants response to cadmium stress and its potential use as an ethylene inhibitor is discussed.

Role of Ethylene and Its Cross Talk with Other Signaling Molecules in Plant Responses to Heavy Metal Stress

“…The accumulation of ethylene and ROS, and the diminution of NO, led to Cd-induced senescence processes in pea (Rodríguez-Serrano et al, 2006). Moreover, ethylene, polyamines, NO, MAPKs, and several transcription factors, including MYBZ2, bZIP62, and DOF1, were proposed to integrate the responses to short-term Cd stress in young soybean seedlings (Chmielowska-Bąk et al, 2014). Together, these findings further suggest a possible role of NO in the HM-induced ethylene pathway.…”

“…Co, a beneficial metal for plant development at moderate levels, is known as an inhibitor of ethylene production (Palit et al, 1994;Yıldız et al, 2009;Chmielowska-Bąk et al, 2014). Although many studies showed that Cd, Cu, Fe, and Zn induce ethylene production in plants (Wise and Naylor, 1988;Maksymiec, 2007), excessive Co treatment of HM-stressed plants does not lead to enhanced ethylene levels, since Co inhibits the ACO enzymatic activity in the ethylene synthetic pathway.…”

“…Several studies have proved that the application of ethylene biosynthesis modulators adjusted endogenous stress-induced ethylene content to an optimized level and, consequently, resulted in beneficial effects in plants treated with Ni and Zn Khan and Khan, 2014), Cd (Iakimova et al, 2008;Sun et al, 2010;Chmielowska-Bąk et al, 2014), or Al (Sun et al, 2010). Additionally, S application has proved to be effective in the alleviation of Cd stress, which was related to the reduction of undesirable stress-induced ethylene production in mustard, suggesting that S might be used to optimize the ethylene level for developing HM stress-tolerant cultivars as well (Asgher et al, 2014;Khan et al, 2015a).…”

“…Although many studies showed that Cd, Cu, Fe, and Zn induce ethylene production in plants (Wise and Naylor, 1988;Maksymiec, 2007), excessive Co treatment of HM-stressed plants does not lead to enhanced ethylene levels, since Co inhibits the ACO enzymatic activity in the ethylene synthetic pathway. Thus, Co has been widely used as an ethylene biosynthesis inhibitor to study the effects of ethylene on plant responses to HM stress (Sun et al, 2010;Chmielowska-Bąk et al, 2014). However, in soybean (Glycine max) seedlings, coapplication of Co and Cd negatively affected cell viability as well as the expression of Cd-induced genes encoding MAPK KINASE2, DNA BINDING WITH ONE FINGER1 (DOF1), and BASIC LEUCINE ZIPPER2 (bZIP2) transcription factors, suggesting that Co increased Cd toxicity to soybean plants and that this happened independently from ethylene action (Chmielowska-Bąk et al, 2014).…”

“…Thus, Co has been widely used as an ethylene biosynthesis inhibitor to study the effects of ethylene on plant responses to HM stress (Sun et al, 2010;Chmielowska-Bąk et al, 2014). However, in soybean (Glycine max) seedlings, coapplication of Co and Cd negatively affected cell viability as well as the expression of Cd-induced genes encoding MAPK KINASE2, DNA BINDING WITH ONE FINGER1 (DOF1), and BASIC LEUCINE ZIPPER2 (bZIP2) transcription factors, suggesting that Co increased Cd toxicity to soybean plants and that this happened independently from ethylene action (Chmielowska-Bąk et al, 2014). Moreover, excessive Co also increased oxidative stress and photosynthesis inhibition as well as caused alterations in germination, sex ratio, photoperiodism, and uptake of other elements (Yıldız et al, 2009;Hasan et al, 2011).…”