Fangdong Zhan

Cadmium and lead accumulation and low-molecular-weight organic acids secreted by roots in an intercropping of a cadmium accumulator Sonchus asper L. with Vicia faba L.

Sonchus asper L. and Vicia faba L. are a local cadmium (Cd) accumulator and a main winter crop, respectively, found in the Huize lead–zinc mining area in Yunnan Province, Southwest China. The biomass and low-molecular-weight organic acids (LMWOAs) secreted by the roots of these plants, Cd and lead (Pb) contents and their accumulation in a S. asper monoculture, V. faba monoculture and S. asper/V. faba intercrop were investigated in a field experiment at 35, 80 and 180 d after planting. The results showed that (1) intercropping had no notable influences on plant biomass and grain yields of V. faba but led to a significant increase in the amount of stem and leaf biomass of S. asper at 180 d after planting. (2) The major LMWOAs secreted by the roots of both V. faba and S. asper were oxalic acid, tartaric acid and citric acid. Intercropping resulted in an increase and decrease in the LMWOA contents secreted by V. faba and S. asper roots, respectively. (3) Along with plant growth, the available Cd content decreased and the available Pb contents did not exhibit obvious changes in the soil samples of a V. faba monoculture. The amount of available Cd and Pb both increased in the soil of the S. asper monoculture, but decreased in that of the S. asper/V. faba intercrop. (4) Intercropping resulted in a decrease in the contents and accumulation of Cd and Pb in V. faba plants, but an increase in both the contents and accumulation of Cd and Pb in S. asper plants. Moreover, intercropping enhanced the enrichment and translation coefficients of Cd for S. asper. The remediation efficiency was the highest at 180 d after planting. (5) There were significant negative correlations between the contents of citric acid, malic acid (secreted by V. faba roots), oxalic acid and tartaric acid (secreted by S. asper roots) and the available Cd content in the soil samples. In addition, there was a significant positive correlation between the available Cd content in the soil and the Cd contents in the roots and grains of V. faba. Intercropping reduced the Cd contents in the plants and grains of V. faba and was closely related to the decrease in the available Cd content in the soil samples, which was mediated by plant roots that secreted LMWOAs.

Identification and cloning of molecular markers for UV-B tolerant gene in wild sugarcane (Saccharum spontaneum L.)

Previously we have selected wild sugarcane (Saccharum spontaneum L.) sterile lines that are tolerant or susceptible to UV-B radiation based on response index (RI) in a field screening test. The RI was established according to plant height, tiller number, leaf index, total biomass and brix under enhanced ultraviolet-B (UV-B, 280-310 nm) radiation. In this experiment, molecular markers linked to the UV-B tolerant and susceptible genes were identified and cloned. RAPD (Randomly amplified polymorphic DNAs) assay using 100 arbitrary primers followed by clustering analysis separated the tolerant and susceptible lines into two groups at the genetic distance of 0.380. The UV-B tolerant and susceptible gene pools were constructed and compared using the Bulked Segregate Analysis (BSA) approach. Of the 100 arbitrary RAPD primers, primer OPR16 produced polymorphic DNA banding patterns from both gene pools. The OPR16-1200 bp DNA fragment was only amplified from the tolerant lines and the OPR16-800 bp from the susceptible ones. These two PCR fragments were cloned onto T-vector. DNA sequence alignment analysis determined that 42% homology existed between the reverse and forward sequences of the OPR16-1200 bp clone, and 36% homology between the forward sequences of the OPR16-800 bp and OPR16-1200 bp clones. The two DNA clones were determined to be linked to the UV-B tolerant and susceptible genes, and they can be used to develop molecular markers for the associated traits.

Subcellular distribution and chemical form of Pb in hyperaccumulator Arenaria orbiculata and response of root exudates to Pb addition

Solution culture was conducted in order to understand accumulation characteristics and chemical forms of Pb in Arenaria orbiculata (A. orbiculata) and the response of root exudates to Pb addition. The results showed that: 1) Pb contents in the shoot and root of A. orbiculata increased with increasing in Pb concentrations in solution. 2) The contents of Pb chemical forms under Pb addition followed as: HAc extractable fraction (FHAC)> HCl extractable fraction (FHCl)> NaCl extractable fraction (FNaCl)> ethanol-extractable fraction (FE)>water extractable fraction (FW). 3) Increased Pb level in the medium caused increases in Pb contents in the four subcellular fractions of shoots and roots, with most accumulation in FIV (Fraction IV, soluble fraction) in shoots and FI (Fraction I, cell wall fraction) in roots. 4) Contents of soluble sugar and free amino acid of root exudates increased with increasing Pb concentration in solution. Significantly positive correlations between Pb and contents of soluble sugar and free amino acid were observed. 5) With Pb concentrations in solution, low molecular weight organic acids (LMWOAs) contents followed the tendency: tartaric acid>acetic acid>malic acid>citric acid. Significantly positive correlation was observed between Pb and citric acid contents. The results indicate that soluble sugars, free amino acid and citric acid in root exudates of A.orbiculata facilitate the absorption and accumulation of Pb, which exist in NaCl-, HCl- and HAc- extractable Pb forms, FI and FIV fractions, resulting in tolerance of A.orbiculata to Pb.

Resistance-related physiological response of rice leaves to the compound stress of enhanced UV-B radiation and Magnaporthe oryzae

ABSTRACT An enhanced UV-B radiation (5.0 kJ m−2) was supplied before, during, and after Magnaporthe oryzae infection. The effects of single and compound stress of the UV-B radiation and M. oryzae on the resistance physiology and gene expression of rice leaves were examined. Results revealed that UV-B radiation given before M. oryzae infection (UV-B → M.) significantly increased the pathogenesis-related proteins (PRs) activities of phenylalanine ammonialyase (PAL), lipoxygenase (LOX), chitinase (CHT), and β-1,3-glucanase, the resistance-related substances (flavonoids and total phenols) content, and resistance-related genes (OsPAL and OsCHT) expression, thereby improving the disease resistance of rice leaves. Simultaneous exposure to UV-B radiation and M. oryzae (UV-B/M.) significantly increased the OsLOX2 expression and the PRs activities. Exposure to UV-B radiation after M. oryzae infection (M. → UV-B) decreased the flavonoid content, did not improve the PRs activity, and increased OsLOX2 expression. Compound treatments of UV-B → M., UV-B/M., and M. → UV-B reduced the disease index by 62.3%, 40.2%, and 26.6%, respectively, indicating UV-B radiation inhibited the occurrence of M. oryzae disease, but its inhibitory effect weakened when it was provided after M. oryzae infection. Hence, rice responded to the compound stress of UV-B radiation and M. oryzae through a resistance-related physiological mechanism associated with the sequence of stress occurrence.

Arbuscular mycorrhizal fungi enhance antioxidant defense in the leaves and the retention of heavy metals in the roots of maize

In this study, we investigated the effects of the arbuscular mycorrhizal fungi (AMF) Funneliformis mosseae and Diversispora spurcum on the growth, antioxidant physiology, and uptake of phosphorus (P), sulfur (S), lead (Pb), zinc (Zn), cadmium (Cd), and arsenic (As) by maize (Zea mays L.) grown in heavy metal-polluted soils though a potted plant experiment. F. mosseae significantly increased the plant chlorophyll a content, height, and biomass; decreased the H2O2 and malondialdehyde (MDA) contents; and enhanced the superoxide dismutase (SOD) and catalase (CAT) activities and the total antioxidant capacity (T-AOC) in maize leaves; this effect was not observed with D. spurcum. Both F. mosseae and D. spurcum promoted the retention of heavy metals in roots and increased the uptake of Pb, Zn, Cd, and As, and both fungi restricted heavy metal transfer, resulting in decreased Pb, Zn, and Cd contents in shoots. Therefore, the fungi reduced the translocation factors for heavy metal content (TF) and uptake (TF′) in maize. Additionally, F. mosseae promoted P and S uptake by shoots, and D. spurcum increased P and S uptake by roots. Moreover, highly significant negative correlations were found between antioxidant capacity and the H2O2, MDA, and heavy metal contents, and there was a positive correlation with the biomass of maize leaves. These results suggested that AMF alleviated plant toxicity and that this effect was closely related to antioxidant activation in the maize leaves and increased retention of heavy metals in the roots.

Effects of Intercropping of Sonchus asper and Vicia faba on Plant Cadmium Accumulation and Root Responses

Abstract The cadmium (Cd) pollution of farmland soil is serious in the world. The present study investigated the effects of intercropping Vicia faba and the hyperaccumulator Sonchus asper on the Cd accumulation and root responses (morphology and secreted organic acids) of plants grown on soil from a mining area in Yunnan Province, China, under different Cd stress levels (0, 50, 100, and 200 mg kg–1). Intercropping increased the biomass of both S. asper and V. faba, as well as the Cd accumulation and Cd transfer coefficient from roots to shoots of S. asper, but decreased those of V. faba in the 200 mg kg–1 Cd treatment. The Cd concentrations in roots, shoots, and grains from intercropped V. faba plants were positively correlated (P

Effects of a root-colonized dark septate endophyte on the glutathione metabolism in maize plants under cadmium stress

ABSTRACT A high Cd-tolerant dark septate endophyte (DSE), Exophiala pisciphila, was inoculated into maize (Zea mays L.) roots under Cd stress. The Cd content, enzymes activity and thiol compound content relevant to glutathione (GSH) metabolism in maize leaves were analyzed. The Cd content in maize shoots increased with increasing Cd stress, but the DSE significantly reduced the Cd content at the 40 mg/kg Cd treatment. Cd stress increased the enzyme activity of glutathione reductase (GR), glutathione S-transferase (GST) and glutathione peroxidase (GSH-Px) as well as the thiol compound contents of sulfur, thiols (-SH) and oxidized glutathione (GSSG). The content of reduced GSH and the GSH/GSSG ratio reached a peak at the 5 mg/kg Cd treatment but then decreased with increasing Cd stress. Furthermore, the DSE significantly enhanced the GR and GSH-Px activity and increased the contents of -SH and GSH under low Cd stress (5 and 10 mg/kg), but decreased the γ-glutamylcysteine synthetase and GST activity under high Cd stress (20 and 40 mg/kg). Highly positive correlations between the Cd content with enzymes activity and enzymes activity with thiol compound content were observed. Results indicated that DSE played a role in activating GSH metabolism in maize leaves under Cd stress.