Response of hrpZPsph-transgenic N. benthamiana plants under cadmium stress

Cadmium stimulated cooperation between bacterial endophytes and plant intrinsic detoxification mechanism in Lonicera japonica thunb

Due to the intimate association between plant physiology and metabolism, the internal colonizing microbe (endophytes) community must be adjusted to support plant productivity in response to cell damage in plants under stress. However, how endophytes coordinate their activities with plant intrinsic mechanisms such as antioxidative systems and detoxification pathways during Cd accumulation remains unknown. In this hydroponic pot study, we investigated how exposure of Lonicera japonica. thunb. to different levels of Cd (0.5, 2.5, 5, 10, and 20 mg kg^-1) affected plant growth, metabolic pathways, and endophyte community structure and function. Although Cd accumulation increased at 5 mg kg^-1 Cd, the biomass and height of L. japonica increased in association with elevated endophyte-involved plant detoxification activities. Endophytes, such as Sphingomonas, Klenkia, and Modestobacter, expressed major antioxidative regulators (superoxide dismutase and ascorbate acid) to detoxify Cd in L. japonica. Furthermore, L. japonica and its endophytes synergistically regulated the toxic effects of Cd accumulation via multiple plant metabolic defensive pathways to increase resistance to metal-induced stress.

Effects of an Arbuscular Mycorrhizal Fungus on the Growth of and Cadmium Uptake in Maize Grown on Polluted Wasteland, Farmland and Slopeland Soils in a Lead-Zinc Mining Area

Arbuscular mycorrhizal fungi (AMF) exist widely in soil polluted by heavy metals and have significant effects on plant growth and cadmium (Cd) uptake. Cd contents differ among wasteland, farmland and slopeland soils in a lead-zinc mining area in Yunnan Province, Southwest China. The effects of AMF on maize growth, root morphology, low-molecular-weight organic acid (LMWOA) concentrations and Cd uptake were investigated via a root-bag experiment. The results show that AMF increased maize growth on Cd-polluted soils, resulting in increases in root length, surface area, volume and branch number, with the effects being stronger in farmland than in wasteland and slopeland soils; increased malic acid and succinic acid secretion 1.3-fold and 1.1-fold, respectively, in roots on farmland soil; enhanced the iron- and manganese-oxidized Cd concentration by 22.6%, and decreased the organic-bound Cd concentration by 12.9% in the maize rhizosphere on farmland soil; and increased Cd uptake 12.5-fold and 1.7-fold in shoots and by 25.7% and 86.6% in roots grown on farmland and slopeland soils, respectively. Moreover, shoot Cd uptake presented significant positive correlations with root surface area and volume and LMWOA concentrations. Thus, these results indicated the possible mechanism that the increased maize Cd uptake induced by AMF was closely related to their effect on root morphology and LMWOA secretion, with the effects varying under different Cd pollution levels.

Potassium and Silicon Synergistically Increase Cadmium and Lead Tolerance and Phytostabilization by Quinoa through Modulation of Physiological and Biochemical Attributes

Cadmium (Cd) and lead (Pb) contaminated soils have increased recently, resulting in limited crop productivity. The ameliorative role of potassium (K) and silicon (Si) is well established in plants under heavy metals stress; however, their combined role under the co-contamination of Cd and Pb is not well understood. We hypothesized that the synergistic application of K and Si would be more effective than their sole treatment for increasing the Pb and Cd tolerance and phytostabilization potential of quinoa (Chenopodium quinoa Willd.). In the current study, quinoa genotype ‘Puno’ was exposed to different concentrations of Cd (0, 200 µM), Pb (0, 500 µM) and their combination with or without 10 mM K and 1.0 mM Si supplementation. The results revealed that the combined stress of Cd and Pb was more detrimental than their separate application to plant biomass (66% less than the control), chlorophyll content and stomatal conductance. Higher accumulation of Pb and Cd led to a limited uptake of K and Si in quinoa plants. The supplementation of metal-stressed plants with 10 mM K and 1.0 mM Si, particularly in combination, caused a significant increase in the growth, stomatal conductance and pigment content of plants. The combined stress of Cd and Pb resulted in an overproduction of H₂O₂ (11-fold) and TBARS (13-fold) and a decrease in membrane stability (59%). Oxidative stress induced by metals was lessened by 8-fold, 9-fold, 7-fold and 11-fold increases in SOD, CAT, APX and POD activities, respectively, under the combined application of K and Si. It is concluded that the exogenous supply of K and Si in combination is very promising for increasing Cd and Pb tolerance and the phytostabilization potential of quinoa.