Jibiao Fan

Effect of Heavy Metals Pollution on Soil Microbial Diversity and Bermudagrass Genetic Variation

Heavy metal pollution is a serious global environmental problem as it adversely affects plant growth and genetic variation. It also alters the composition and activity of soil microbial communities. The objectives of this study were to determine the soil microbial diversity, bermudagrass genetic variation in Cd contaminated or uncontaminated soils from Hunan province of China, and to evaluate Cd-tolerance of bermudagrass at different soils. The Biolog method, hydroponic experiments and simple sequence repeat markers were used to assess the functional diversity of microorganisms, Cd-tolerance and the genetic diversity of bermudagrass, respectively. Four of the sampling sites were heavily contaminated with heavy metals. The total bioactivity, richness, and microbial diversity decreased with increasing concentration of heavy metal. The hydroponic experiment revealed that bermudagrass populations collected from polluted sites have evolved, encompassing the feature of a higher resistance to Cd toxicity. Higher genetic diversity was observed to be more in contaminated populations than in uncontaminated populations. Heavy metal pollution can result in adverse effects on plant growth, soil microbial diversity and activity, and apparently has a stronger impact on the genetic structure. The results of this study provide new insights and a background to produce a genetic description of populations in a species that is suitable for use in phytoremediation practices.

Alleviation of cold damage to photosystem II and metabolisms by melatonin in Bermudagrass

As a typical warm-season grass, Bermudagrass [Cynodon dactylon (L).Pers.] is widely applied in turf systems and animal husbandry. However, cold temperature is a key factor limiting resource utilization for Bermudagrass. Therefore, it is relevant to study the mechanisms by which Burmudagrass responds to cold. Melatonin is a crucial animal and plant hormone that is responsible for plant abiotic stress responses. The objective of this study was to investigate the role of melatonin in cold stress response of Bermudagrass. Wild Bermudagrass pre-treated with 100 μM melatonin was subjected to different cold stress treatments (−5°C for 8 h with or without cold acclimation). The results showed lower malondialdehyde (MDA) and electrolyte leakage (EL) values, higher levels of chlorophyll, and greater superoxide dismutase and peroxidase activities after melatonin treatment than those in non-melatonin treatment under cold stress. Analysis of chlorophyll a revealed that the chlorophyll fluorescence transient (OJIP) curves were higher after treatment with melatonin than that of non-melatonin treated plants under cold stress. The values of photosynthetic fluorescence parameters increased after treatment with melatonin under cold stress. The analysis of metabolism showed alterations in 46 metabolites in cold-stressed plants after melatonin treatment. Among the measured metabolites, five sugars (arabinose, mannose, glucopyranose, maltose, and turanose) and one organic acid (propanoic acid) were significantly increased. However, valine and threonic acid contents were reduced in melatonin-treated plants. In summary, melatonin maintained cell membrane stability, increased antioxidant enzymes activities, improved the process of photosystem II, and induced alterations in Bermudagrass metabolism under cold stress.

Effects of Cadmium Exposure on Growth and Metabolic Profile of Bermudagrass [Cynodon dactylon (L.) Pers.]

Metabolic responses to cadmium (Cd) may be associated with variations in Cd tolerance in plants. The objectives of this study were to examine changes in metabolic profiles in bermudagrass in response to Cd stress and to identify predominant metabolites associated with differential Cd tolerance using gas chromatography-mass spectrometry. Two genotypes of bermudagrass with contrasting Cd tolerance were exposed to 0 and 1.5 mM CdSO4 for 14 days in hydroponics. Physiological responses to Cd were evaluated by determining turf quality, growth rate, chlorophyll content and normalized relative transpiration. All these parameters exhibited higher tolerance in WB242 than in WB144. Cd treated WB144 transported more Cd to the shoot than in WB242. The metabolite analysis of leaf polar extracts revealed 39 Cd responsive metabolites in both genotypes, mainly consisting of amino acids, organic acids, sugars, fatty acids and others. A difference in the metabolic profiles was observed between the two bermudagrass genotypes exposed to Cd stress. Seven amino acids (norvaline, glycine, proline, serine, threonine, glutamic acid and gulonic acid), four organic acids (glyceric acid, oxoglutaric acid, citric acid and malic acid,) and three sugars (xylulose, galactose and talose) accumulated more in WB242 than WB144. However, compared to the control, WB144 accumulated higher quantities of sugars than WB242 in the Cd regime. The differential accumulation of these metabolites could be associated with the differential Cd tolerance in bermudagrass.

Physiological and Molecular Responses to Salt Stress in Wild Emmer and Cultivated Wheat

Salinity severely influences growth and grain yield of wheat. Modern breeding efforts have contributed to severe loss of genetic diversity and reduced tolerance to salt stress in cultivated plants. Wild emmer wheat (Triticum dicoccoides), the progenitor of cultivated wheat, is well-adapted to a wide range of environments and exhibits tolerance to abiotic stress. However, there is lack of fundamental knowledge of the mechanism of salt stress tolerance in wild emmer wheat and how it differs from that of the cultivated wheat. By screening wild emmer genotypes, we identified a promising salt-tolerant line from Gitit in the eastern Samaria steppes. We investigated the physiological difference of wild emmer and cultivated wheats in response to salt stress. Our results revealed that salt stress resulted in an increase in lipid peroxidation (malondialdehyde) content and electrolyte leakage, to a greater extent in cultivated wheat genotype, Zheng 9023, than in salt-resistant wild emmer wheat genotype 18-35, but the latter had higher relative dry weight. Differential expression analysis showed that higher transcript induction folds of genes encoding transcription factor were detected in the resistant plants (wild emmer) than in sensitive plants (cultivated wheat) after salt treatment. In conclusion, wild emmer wheat demonstrated better tolerance to salt stress than cultivated wheat, and the higher tolerance of wild emmer wheat is because of high expression of stress-responsive genes encoding transcription factor, including NAC2F, NAC8, DREB3A, MYB3R, and MYB2A. Therefore, our results suggest that wild emmer wheat is an important germplasm for salt tolerance breeding in cultivated wheat.

Differential Acclimation of Enzymatic Antioxidant Metabolism and Photosystem II Photochemistry in Tall Fescue under Drought and Heat and the Combined Stresses

Quality inferiority in cool-season turfgrass due to drought, heat, and a combination of both stresses is predicted to be more prevalent in the future. Understanding the various response to heat and drought stress will assist in the selection and breeding of tolerant grass varieties. The objective of this study was to investigate the behavior of antioxidant metabolism and photosystem II (PSII) photochemistry in two tall fescue genotypes (PI 234881 and PI 578718) with various thermotolerance capacities. Wide variations were found between heat-tolerant PI 578718 and heat-sensitive PI 234881 for leaf relative water content, malondialdehyde and electrolyte leakage under drought, high-temperature or a combination of both stresses. The sensitivity of PI 234881 exposed to combined stresses was associated with lower superoxide dismutase activity and higher H2O2 accumulation than that in PI 578718. Various antioxidant enzymes displayed positive correlation with chlorophyll content, but negative with membrane injury index at most of the stages in both tall fescue genotypes. The JIP-test analysis in PI 578718 indicated a significant improvement in ABS/RC, TR0/RC, RE0/RC, RE0/ABS values as compared to the control regime, which indicated that PI 578718 had a high potential to protect the PSII system under drought and high temperature stress. And the PS II photochemistry in PI 234881 was damaged significantly compared with PI578718. Moreover, quantitative RT-PCR revealed that heat and drought stresses deduced the gene expression of psbB and psbC, but induced the expression of psbA. These findings to some extent confirmed that the various adaptations of physiological traits may contribute to breeding in cold-season turfgrass in response to drought, high-temperature, and a combination of both stresses.

Physiological and Molecular Mechanism of Nitric Oxide (NO) Involved in Bermudagrass Response to Cold Stress

Bermudagrass is widely utilized in parks, lawns, and golf courses. However, cold is a key factor limiting resource use in bermudagrass. Therefore, it is meaningful to study the mechanism of bermudagrass response to cold. Nitric oxide (NO) is a crucial signal molecule with multiple biological functions. Thus, the objective of this study was to investigate whether NO play roles in bermudagrass response to cold. Sodium nitroprusside (SNP) was used as NO donor, while 2-phenyl-4,4,5,5-tetramentylimidazoline-l-oxyl-3-xide (PTIO) plus NG-nitro-L-arginine methyl ester (L-NAME) were applied as NO inhibitor. Wild bermudagrass was subjected to 4 °C in a growth chamber under different treatments (Control, SNP, PTIO + L-NAME). The results indicated lower levels of malondialdehyde (MDA) content and electrolyte leakage (EL), higher value for chlorophyll content, superoxide dismutase (SOD) and peroxidase (POD) activities after SNP treatment than that of PTIO plus L-NAME treatments under cold stress. Analysis of Chlorophyll (Chl) a fluorescence transient displayed that the OJIP transient curve was higher after treatment with SNP than that of treated with PTIO plus L-NAME under cold stress. The values of photosynthetic fluorescence parameters were higher after treatment with SNP than that of treated with PTIO plus L-NAME under cold stress. Expression of cold-responsive genes was altered under cold stress after treated with SNP or PTIO plus L-NAME. In summary, our findings indicated that, as an important strategy to protect bermudagrass against cold stress, NO could maintain the stability of cell membrane, up-regulate the antioxidant enzymes activities, recover process of photosystem II (PSII) and induce the expression of cold-responsive genes.

Cotton GhERF38 gene is involved in plant response to salt/drought and ABA

ERF (ethylene-responsive factor) transcription factors play important roles in plant stress signaling transduction pathways. However, their specific roles during diverse abiotic stresses tolerance in Gossypium hirsutum are largely unknown. Here, a novel ERF transcription factor, designated GhERF38, homologous to AtERF38 in Arabidopsis, was isolated from cotton (Gossypium hirsutum L). GhERF38 expression was up-regulated by salt, drought and ABA treatments. Subcellular localization results indicated that GhERF38 was localized in the cell nucleus. Over-expression of GhERF38 in Arabidopsis reduced plant tolerance to salt and drought stress as indicated by a decline of seed germination, plant greenness frequency, primary roots length and the survival rate in transgenic plants compared to those of wild type plants under salt or drought treatment. Besides, stress tolerance related physiological parameters such as proline content, relative water content, soluble sugar and chlorophyll content were all significantly lower in transgenic plants than those of wild type plants under salt or drought treatment. Furthermore, over-expression of GhERF38 in Arabidopsis resulted in ABA sensitivity in transgenic plants during both seed germination and seedling growth. Interestingly, the stomatal aperture of guard cells in the transgenic plants was larger than that in transgenic plant after ABA treatment, suggesting that GhERF38-overexpressing plants were insensitive to ABA in terms of stomatal closure. Furthermore, expressions of the stress-related genes were altered in the GhERF38 transgenic plants under high salinity, drought or ABA treatment. Together, our results revealed that GhERF38 functions as a novel regulator that is involved in response to salt/drought stress and ABA signaling during plant development.

Genetic diversity and association mapping of cadmium tolerance in bermudagrass [Cynodon dactylon (L.) Pers.]

Background and aimsIdentification of the association between Cd tolerance-related traits and molecular markers facilitates an efficient selection of the tolerant cultivars. The objectives of this study were to analyze the Cd tolerance and the genetic diversity of native bermudagrass accessions in China, and to identify marker-trait association with wild bermudagrass.MethodsA countrywide collection of 120 bermudagrass [Cynodon dactylon (L.) Pers.] accessions were evaluated for Cd tolerance and genetic diversity with simple sequence repeat (SSR) markers.ResultSignificant variations in 7 physiological parameters were observed among the accessions under Cd conditions. The 104 SSR primers amplified 1474 alleles. The average gene diversity and polymorphic information content (PIC) for the whole sample was 0.2270 and 0.1894, respectively. Clustering analysis showed that the distance of genetic relationship was affected by the cultivars of natural habitats and the edaphic conditions. Thirty one SSR markers were associated with more than one trait (P < 0.01), while 37 markers were identified by corrected P values (P < 3.5 × 10−4).ConclusionThirty one SSR markers were associated with a reduction in 7 traits under Cd stress. These markers can be used for genetic improvement of Cd tolerance of bermudagrass after further validation.

TdCBL6, a calcineurin B-like gene from wild emmer wheat (Triticum dicoccoides), is involved in response to salt and low-K+ stresses

The calcineurin B-like proteins (CBLs), a unique family of calcium sensors in plants, have been shown to be involved in abiotic stresses, such as salt, drought and cold. Although extensive studies and remarkable progress have been made in Arabidopsis (Arabidopsis thaliana) CBLs, very little is known about the role of CBL genes in wheat. In this study, a CBL gene, designated TdCBL6, was cloned and characterized from wild emmer wheat (Triticum dicoccoides), the progenitor of cultivated wheat. Sequence alignment revealed that TdCBL6 shares high sequence homology with rice OsCBL6. Phylogenetic analysis also revealed that TdCBL6 protein has the closest evolutionary relationship with rice OsCBL6 protein. TdCBL6 transcription was induced by NaCl, polyethylene glycol and abscisic acid. Further differential expression analysis revealed that TdCBL6 expression was much higher in the salt-tolerant line than in the salt-sensitive line when they were subjected to salt treatment. Transgenic Arabidopsis ectopic expression of the TdCBL6 gene displayed higher levels of photosynthetic efficiency (Fv/Fm) and lower ion leakage (EL) than wild-type (WT) plants under NaCl stress conditions. Moreover, TdCBL6-overexpressing lines showed low-K+ (LK)-sensitive phenotypes compared with WT plants. Further experiments revealed that ectopic expression of TdCBL6 resulted in reduction of H2O2 content, and affected expression of K+-responsive/H2O2-regulated genes under LK stress. Taken together, we demonstrated that heterologous expression of TdCBL6 in Arabidopsis confers salt tolerance by reducing membrane injury and improving photosynthetic efficiency, and that the TdCBL6 gene may be involved in response to LK stress by regulating the reactive oxygen species-mediated LK signaling pathway.

Melatonin: A Multifunctional Factor in Plants

Melatonin (N-acetyl-5-methoxy-tryptamine) is a universal molecule that is present in animals and plants. It has been detected in different kinds of plants and organs in different levels. Melatonin in plants shares the same initial biosynthesis compound with auxin, and therefore functions as indole-3-acetic acid like hormones. Moreover, melatonin is involved in regulating plant growth and development, protecting plants against biotic and abiotic stresses, such as salt, drought, cold, heat and heavy metal stresses. Melatonin improves the stress tolerance of plants via a direct pathway, which scavenges reactive oxygen species directly, and indirect pathways, such as increasing antioxidate enzymes activity, photosynthetic efficiency and metabolites content. In addition, melatonin plays a role in regulating gene expression, and hence affects performance of plants. In this review, the biosynthesis pathway, growth and development regulation, and the environment stress response of melatonin in plants are summarized and future research directions and priorities of melatonin in plants are speculated.