Ethylene Potentiates Sulfur-Mediated Reversal of Cadmium Inhibited Photosynthetic Responses in Mustard.

Nafees A. Khan,M. I. R. Khan,Mohd Asgher,Tasir S. Per,Mehar Fatma,Asim Masood

doi:10.3389/fpls.2016.01628

Abstract

The potential of exogenous ethylene and sulfur (S) in reversal of cadmium (Cd)-inhibited photosynthetic and growth responses in mustard (Brassica juncea L. cv. Pusa Jai Kisan) were studied. Plants grown with 50 μM Cd showed increased superoxide and H2O2 accumulation and lipid peroxidation together with increased activity of 1-aminocyclopropane carboxylic acid synthase (ACS) and ethylene production and inhibition of photosynthesis and growth. Application of 1 mM SO42- or 200 μL L-1 ethephon (ethylene source) influenced photosynthetic and growth performance equally in presence or absence of Cd. However, their combined application synergistically improved photosynthetic performance more in presence of Cd and reduced oxidative stress (lower superoxide and H2O2 accumulation) by decreasing ethylene and glucose sensitivity with the increase in cysteine and methionineand a non-proteinogenic thiol (reduced glutathione; GSH) contents. The central role of ethylene in potentiating S-mediated reversal of Cd-induced oxidative stress was evident with the use of ethylene action inhibitor, norbornadiene (NBD). The application of NBD resulted in decreased thiol production and photosynthetic responses. This suggests that ethylene promotes the effects of S in reversal of adverse effects of Cd, and thus, ethylene modulation may be considered as potential tool to substantiate the S effects in reversal of Cd inhibited photosynthesis and growth in mustard.

Highlights

Cadmium (Cd) with long biological half-life and potentially toxic even at low concentration has become one of the most challenging threats due to its increasing concentration in agricultural system (Choppala et al, 2014; Asgher et al, 2015; Khan et al, 2015a; Wahid and Khaliq, 2015)
Activity of ATP-S and serine acetyltransferase (SAT) increased with Cd treatment by 42.3 and 33.5%, respectively, whereas S content decreased by 27.0% in comparison to control
The study provides evidence that ethephon and S influenced the accumulation of ROS in the plants. These findings demonstrated that the GSH synthesis was upregulated when ethephon and S were applied to Cd treated plants, which in turn induced a strong ROS scavenging capacity and decreased production rate of O·2−

Summary

Introduction

Cadmium (Cd) with long biological half-life and potentially toxic even at low concentration has become one of the most challenging threats due to its increasing concentration in agricultural system (Choppala et al, 2014; Asgher et al, 2015; Khan et al, 2015a; Wahid and Khaliq, 2015). Inhibits nutrients uptake, inactivates enzymes of CO2 fixation and negatively affects various cellular functions through displacement of essential elements from proteins (Mobin and Khan, 2007; DalCorso et al, 2008; Masood et al, 2012b; Choppala et al, 2014). It accumulates to high levels in leaves and adversely impacts chlorophyll (Chl) biosynthesis and photosynthetic process by disrupting the electron transport chain, and aggregation of pigment protein complexes of the photosystems (Baryla et al, 2001; Liu et al, 2011; Shukla et al, 2014). Sulfur (S) limitations resulted in the chlorosis of young leaves and inhibition of photosynthetic activity (Hawkesford, 2000), whereas S supply increases photosynthetic capacity of leaves through an increase in stromal and thylakoid protein and regulating stomatal movement under Cd stress (Masood et al, 2012b; Asgher et al, 2014; Khan et al, 2015b)

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