Physiological analyses indicate superoxide dismutase, catalase, and phytochelatins play important roles in Pb tolerance in Eremochloa ophiuroides

Low-molecular-weight organic acid-mediated tolerance and Pb accumulation in centipedegrass under Pb stress

Lead (Pb) is one of the most harmful, toxic pollutants to the ecological environment and humans. Centipedegrass, a fast-growing warm-season turfgrass, is excellent for Pb pollution remediation. Exogenous low-molecular-weight organic acid (LMWOA) treatment is a promising approach for assisted phytoremediation. However, the effects of this treatment on the tolerance and Pb accumulation of centipedegrass are unclear. This study investigated these effects on the physiological growth response and Pb accumulation distribution characteristics of centipedegrass. Applications of 400 μM citric acid (CA), malic acid (MA) and tartaric acid (TA) significantly reduced membrane lipid peroxidation levels of leaves and improved biomass production of Pb-stressed plants. These treatments mainly increased peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities and enhanced free protein (Pro), ascorbic acid (AsA) and phytochelatins (PCs) contents, ultimately improving the Pb tolerance of centipedegrass. Their promoting effects decreased as follows: TA>CA>MA. All the treatments decreased root Pb concentrations and increased stem and leaf Pb concentrations, thus increasing total Pb accumulation and TF values. MA had the best and worst effects on Pb accumulation and Pb transportation, respectively. CA had the best and worst effects on Pb transportation and Pb accumulation, respectively. TA exhibited strong effects on both Pb accumulation and transport. Furthermore, all treatments changed the subcellular Pb distribution patterns and distribution models of the chemical forms of Pb in each tissue. The root Pb concentration was more highly correlated with the Pb subcellular fraction distribution pattern, while the stem and leaf Pb concentrations were more highly correlated with the distribution models of the chemical forms of Pb. Overall, TA improved plant Pb tolerance best and promoted both Pb absorption and transportation well and is considered the best candidate for Pb-contaminated soil remediation with centipedegrass. This study provides a new idea for Pb-contaminated soil remediation with centipedegrass combined with LMWOAs.

NTA-assisted mineral element and lead transportation in Eremochloa ophiuroides (Munro) Hack

Lead (Pb) is one of the most toxic and harmful pollutants to the environment and human health. Centipedegrass (Eremochloa ophiuroides (Munro) Hack.), an excellent ground cover plant for urban plant communities, exhibits the outstanding lead tolerance and accumulation. Nitrilotriacetic acid (NTA) is an environmentally friendly chelating agent that strengthens phytoremediation. This study explored the effects of different NTA concentrations on the absorption and transportation of mineral elements and Pb in centipedegrass. Following exposure to Pb (500 μM) for 7 days in hydroponic nutrient solution, NTA increased root Mg, K, and Ca concentrations and shoot Fe, Cu, and Mg concentrations and significantly enhanced the translocation factors of mineral elements to the shoot. Although NTA notably decreased root Pb absorption and accumulation, it significantly enhanced Pb translocation factors, and the Pb TF value was the highest in the 2.0 mM NTA treatment. Furthermore, the shoot translocation of Pb and mineral elements was synergistic. NTA can support mineral element homeostasis and improve Pb translocation efficiency in centipedegrass. Regarding root radial transport, NTA (2.0 mM) significantly promoted Pb transport by the symplastic pathway under the treatments with low-temperature and metabolic inhibitors. Meanwhile, NTA increased apoplastic Pb transport at medium and high Pb concentrations (200-800 μM). NTA also enhanced the Pb radial transport efficiency in roots and thus assisted Pb translocation. The results of this study elucidate the effects of NTA on the absorption and transportation of mineral elements and Pb in plants and provide a theoretical basis for the practical application of the biodegradable chelating agent NTA in soil Pb remediation.

Genetic diversity in centipedegrass [Eremochloa ophiuroides (Munro) Hack.]

Genetic diversity is the heritable variation within and among populations, and in the context of this paper describes the heritable variation among the germplasm resources of centipedegrass. Centipedegrass is an important warm-season perennial C4 grass belonging to the Poaceae family in the subfamily Panicoideae and genus Eremochloa. It is the only species cultivated for turf among the eight species in Eremochloa. The center of origin for this species is southern to central China. Although centipedegrass is an excellent lawn grass and is most widely used in the southeastern United States, China has the largest reserve of centipedegrass germplasm in the world. Presently, the gene bank in China holds ~200 centipedegrass accessions collected from geographical regions that are diverse in terms of climate and elevation. This collection appears to have broad variability with regard to morphological and physiological characteristics. To efficiently develop new centipedegrass varieties and improve cultivated species by fully utilizing this variability, multiple approaches have been implemented in recent years to detect the extent of variation and to unravel the patterns of genetic diversity among centipedegrass collections. In this review, we briefly summarize research progress in investigating the diversity of centipedegrass using morphological, physiological, cytological, and molecular biological approaches, and present the current status of genomic studies in centipedegrass. Perspectives on future research on genetics and genomics and modern breeding of centipedegrass are also discussed.

Exogenous melatonin improves lead tolerance of bermudagrass through modulation of the antioxidant defense system

Lead (Pb) is a major anthropogenic contaminant that can be devastating on both animals and plants. It is essential to develop methods to decrease the Pb contaminant in soil by phytoremediation using plants that are tolerance to Pb. In this study, we investigated the tolerance of bermudagrass (Cynodon dactylon (L.) Pers.) and the role of exogenous application of melatonin for improving its tolerance to Pb. Bermudagrass growing in soil treated with Pb at 1,000 or 2,000 mg kg^-1 were assessed with or without melatonin pretreatment at various concentrations. Under Pb stresses, bermudagrass plants showed stunted growth and increased cellular oxidative stress. Pre-treating bermudagrass plants with melatonin at 20 or 100 μM significantly increased the activities of antioxidant enzymes (superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, and glutathione reductase) and the contents of non-enzymatic antioxidants (ascorbic acid and glutathione), and decreased reactive oxygen species (hydrogen peroxide, superoxide), and ultimately reduced membrane lipid peroxidation and permeability. These changes contributed to improvements in the water status, photosynthetic pigment synthesis, and biomass production of bermudagrass under Pb stresses. Our study provides the first evidence that melatonin may be a promising tool for enhancing Pb tolerance and phytoremediation potential of bermudagrass.

Transgenic Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) Overexpressing S-Adenosylmethionine Decarboxylase (SAMDC) Gene for Improved Cold Tolerance Through Involvement of H2O2 and NO Signaling

Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) is an important warm-season turfgrass species. Transgenic centipedgrass plants overexpressing S-adenosylmethionine decarboxylase from bermudagrass (CdSAMDC1) that was induced in response to cold were generated in this study. Higher levels of CdSAMDC1 transcript and sperimidine (Spd) and spermin (Spm) concentrations and enhanced freezing and chilling tolerance were observed in transgenic plants as compared with the wild type (WT). Transgenic plants had higher levels of polyamine oxidase (PAO) activity and H₂O₂ than WT, which were blocked by pretreatment with methylglyoxal bis (guanylhydrazone) or MGBG, inhibitor of SAMDC, indicating that the increased PAO and H₂O₂ were a result of expression of CdSAMDC1. In addition, transgenic plants had higher levels of nitrate reductase (NR) activity and nitric oxide (NO) concentration. The increased NR activity were blocked by pretreatment with MGBG and ascorbic acid (AsA), scavenger of H₂O₂, while the increased NO level was blocked by MGBG, AsA, and inhibitors of NR, indicating that the enhanced NR-derived NO was dependent upon H₂O₂, as a result of expression CdSAMDC1. Elevated superoxide dismutase (SOD) and catalase (CAT) activities were observed in transgenic plants than in WT, which were blocked by pretreatment with MGBG, AsA, inhibitors of NR and scavenger of NO, indicating that the increased activities of SOD and CAT depends on expression of CdSAMDC1, H₂O₂, and NR-derived NO. Our results suggest that the elevated cold tolerance was associated with PAO catalyzed production of H₂O₂, which in turn led to NR-derived NO production and induced antioxidant enzyme activities in transgenic plants.

Differential Responses of Polyamines and Antioxidants to Drought in a Centipedegrass Mutant in Comparison to Its Wild Type Plants

Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) is an important warm-season turfgrass species with low turf maintenance requirements. However, our knowledge on physiological adaptation of centipedegrass to drought stress is limited. Physiological responses to drought in a gamma-ray-induced mutant 22-1 as compared with two wild type (WT) lines were analyzed for understanding of drought tolerance mechanism of centipedegrass. The mutant showed an elevated drought tolerance with higher levels of relative water content, net photosynthetic rate (A) and stomatal conductance (g_s) and lower levels of ion leakage and malondialdehyde (MDA) under drought stress as compared with WT plants. A showed significant correlation with g_s and MDA. Higher levels of antioxidant enzymes activities, non-enzyme antioxidants, and polyamines including putrescine (Put), spermidine (Spd), and spermine (Spm) were maintained in 22-1 than in WT plants. Superoxide dismutase (SOD), catalase (CAT), ascorbate-peroxidase (APX), and glutathione reductase (GR) activities and ascorbic acid (AsA) content were significantly correlated with both Put and Spd levels, and reduced glutathione level was correlated with Put during drought stress. Exogenous application of Put, Spd, and Spm increased drought tolerance and activities of SOD, CAT, APX, and GR in WT plants. The results suggest that higher levels of polyamines and antioxidant defense system are associated with the elevated drought tolerance in 22-1, which may improve protection on photosynthesis against drought induced oxidative damage.