The Impact Of Exogenous Abscisic Acid On Poplar (populus×canescens) Exposed To Cadmium

Cadmium (Cd) is a non-essential element that negatively affects plant growth anddevelopment which could inhibit photosynthesis, cause oxidative stress, change ionabsorption. Industrial development has led to more serious Cd polluted soil, which not onlyaffects the crop yield, but also a threat to the human health. In the process of governance Cdcontaminated soil, Phytoremediation Technology has been widespread attention because it’senvironmental protection, economy and low consumption. Poplars has the potential to achievephytoremediation because it’s fast-growing and it has large biomass and developed rootsystem, in which the Populus×canescens is an excellent candidate.It was reported that Cd stress can stimulate the accumulation of abscisic acid (ABA). Theplant hormone abscisic acid (ABA) is a signal substance produced under stress conditionswhich plays an important role in the regulation of plant physiological status. To study whetherexogenous ABA mediates physiological and molecular responses of poplars to Cd, seedlingsof P.×canescens grown in sand culture were treated with0or400μM Cd for40days incombination with0,5or10μM exogenous ABA. Following results were obtained:(1) Cd treatment increased Cd accumulated in roots and leaves, inhibited the growth ofroots and leaves. The accumulation of Cd inhibited CO2assimilation rate, stomatalconductance and transpiration rate in leaves, decreased photosynthetic pigments content andresulted in leaf chlorosis. Although, exogenous ABA reduced the total amount of Cd in rootsand leaves, but it resulted in lower biomass and more severe yellow dwarf under Cd stress.And along with the concentrations of exogenous ABA increasing, this growth inhibitionstrengthened. So exogenous ABA aggravated the inhibition caused by Cd.(2) Cd treatment increased Fe, Zn and Cu concentrations in roots, decreased Fe, Zn, Cu,Ca and Mg concentrations in leaves, lead to the nutrient deficiency and growth inhibition of P.×canescens. Results of RT-qPCR analysis showed that transcript levels of NRAMP3andNRAMP4were significantly elevated and PCR2and HMA4significantly reduced in poplars exposed to ABA. Thus, exogenous ABA promoted the accumulation of Cd in the cytoplasm ofroots.(3) Cd treatment induced O2-and H2O2accumulation in roots, leading to elevatedmalondialdehyde (MDA), while exogenous ABA increased H2O2accumulation even further,resulting in more severe membrane oxidation. In leaves, Cd treatment had no significanteffect on the accumulation of ROS, but Cd and exogenous ABA treatment leading to O2-andMDA massive accumulation. Therefore, exogenous ABA aggravated the oxidative stressinduced by Cd to some extent.These results suggest that when poplars were exposed to a long-term Cd treatment,exogenous ABA not only aggravated the P.×canescens growth inhibition, but also promotedthe accumulation of Cd2+and other ions in roots, increased the oxidative stress caused by Cd.