2002 Progress Report: DMSP and its Role as an Antioxidant in the Salt Marsh Macrophyte Spartina alternifloraEPA Grant Number: R827072C029
Subproject: this is subproject number 029 , established and managed by the Center Director under grant R827072
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Alabama Center For Estuarine Studies (ACES)
Center Director: Shipp, Robert L.
Title: DMSP and its Role as an Antioxidant in the Salt Marsh Macrophyte Spartina alterniflora
Investigators: Kiene, Ronald P. , Husband, Joseph D.
Institution: University of South Alabama
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 2001 through December 31, 2003
Project Period Covered by this Report: January 1, 2001 through December 31, 2002
RFA: Alabama Center For Estuarine Studies (ACES) (1999) RFA Text | Recipients Lists
Research Category: Targeted Research
The objective of this research project is to test the hypothesis that the osmolyte dimethylsulfoniopropionate (DMSP) and its degradation products, dimethylsulfide (DMS) and dimethylsulfoxide (DMSO), function as antioxidants in the smooth cordgrass Spartina alterniflora. Field and nursery-grown plants will be used to examine natural and experimentally imposed stresses. We focus on the responses of S. alterniflora to natural environmental stress factors, including elevated salinity, high solar radiation, nitrogen limitation, and iron limitation. Additionally, we selectively will impose oxidative stress by administration of the herbicides paraquat and dichlorophenyldimethyl urea (DCMU). Plant responses to be monitored will include DMSP dynamics (along with its degradation products, DMS, DMSO, and methanesulfonic acid), reactive oxygen scavenging enzymes (peroxidase and superoxide dismutase), and the quantum yield of photosystem II. The data gathered will be used to assess whether DMSP production confers advantages to S. alterniflora living in salt marsh habitats.
The production of DMSP by S. alterniflora is well known, but no previous studies had looked for potential oxidation products of DMSP in the tissues of this important salt marsh macrophyte. Our initial efforts focused on adapting assays to measure DMSO in plant tissues. The method proved to work well, and for the first time we have demonstrated that DMSO is present in the leaves of field-collected S. alterniflora. Not only is DMSO present, but its intracellular concentrations were relatively high, in the low mM range, and equivalent to 5-20 percent of the DMSP concentrations. At these concentrations, DMSO could indeed function as a radical scavenger and an antioxidant. This is an important and very exciting finding. In plants from the natural environment, the ratio of DMSO:DMSP was higher in segments of necrotic tissue (0.16) than healthy tissue (0.06) from the same leaf. In addition, we found higher concentrations of DMSO in the spring and summer, when insolation and photosynthetic activity are at a maximum. These periods may correspond to the highest oxidative stress. Furthermore, we found that intracellular DMSP concentrations decreased along the length of leaves from the ligule to the tip. DMSO, in contrast, showed the opposite trend, being highest near the leaf tip. As S. alterniflora leaves tend to senesce from the tip, this further argues that DMSP oxidation may be promoted in stressed tissues.
Direct evidence that DMSP may be involved in oxidative stress response was obtained from experiments in which selected leaves of nursery-grown plants were treated with the herbicide paraquat (methylviologen). Paraquat is known to promote excessive production of reactive oxygen species (ROS) in plants exposed to light. Application of paraquat to leaves held in sunlight caused visible leaf chlorosis within 24 hours. Intracellular DMSP and DMSO concentrations were significantly higher in leaves treated with the paraquat (34.3 µmol/ml and 3.25 µmol/ml leaf water, respectively) compared to untreated control leaves (14.4 µmol/ml and 2.54 µmol/ml leaf water) from the same plant. These findings suggest that S. alterniflora may be able to rapidly increase synthesis of DMSP in response to oxidative stress. Our findings further suggest that DMSP is oxidized during times of stress, such as that caused by natural tissue necrosis or by administration of an oxidative stressor such as paraquat. It remains to be demonstrated, however, whether translocation of DMSP (or DMSO) into stressed areas is responsible for the localized increases that we observed.
We have carried out some tests showing that DMS release from chlorotic or necrotic (i.e., stressed) tissues of S. alterniflora leaves is significantly higher than from healthy green leaves. DMS is a cleavage product of DMSP, and can be produced via the enzyme DMSP lyase. These findings suggest that the stressed leaves are consuming more DMSP to produce DMS. Some of this DMS is volatilized from the leaves, but some is further oxidized to yield DMSO, which explains why higher DMSO was found in chlorotic (yellow) leaf sections and near the leaf tips. At present, we do not know whether the S. alterniflora plants are the source of the DMSP lyase enzyme that may be cleaving DMSP into DMS, or whether microbes (bacteria or fungi) are involved. This will be a subject for further study in the year to come. Preliminary tests for DMSP lyase activity in healthy green leaf sections of S. alterniflora failed to show significant activity. We did find, however, that leaf extracts prepared for these lyase assays rapidly consumed DMS in some cases. Thus, we demonstrated that S. alterniflora tissues have the capability to consume DMS (presumably by oxidation). More tests on potential lyase activity and DMS consumption are planned.
S. alterniflora is native to the East and Gulf Coasts of North America, but it recently has invaded various estuaries on the West Coast. While valued on the East Coast as a stabilizing force on shorelines and as a major source of organic matter and habitat, on the West Coast S. alterniflora is considered an unwelcome invader. There is growing evidence that S. alterniflora is hybridizing with the native West Coast species S. foliosa, providing a further threat to the ecological balance in West Coast marshes. On the European side of the Atlantic, S. alterniflora has crossed with the native species S. maritima, producing the successful hybrid S. anglica. Given the ability of S. alterniflora and its congenerics to dominate some ecosystems, and its apparent ability to invade new areas and cross with closely related species, we need to understand what makes this species so successful in colonizing euryhaline coastal margins. What specific adaptation(s) allows S. alterniflora to dominate under the harsh estuarine conditions where stressors include variable salinity, aerial desiccation, high light exposure, soil/sediment anoxia, sulfide, and anthropogenic pollutants? We believe the high concentration of DMSP in S. alterniflora may help explain this dominance.
We will continue to measure seasonal patterns of DMSP and its oxidation products in natural populations of S. alterniflora throughout the 2002-2003 project period. We will carry out tests using antibiotics and antifungal agents to evaluate whether leaf microbes might be involved in DMSP transformations. Further work on assaying the potential DMSP lyase activity in S. alterniflora tissues will be conducted. To aid in this work, we have initiated a side project involving isolation and purification of DMSP lyase enzyme(s) from the green macroalga Enteromorpha intestinalis. This macroalga has very high DMSP lyase activity, and provides a good opportunity to procure a purified, functional protein. If we can acquire a pure DMSP lyase, we can obtain the N-terminal amino acid sequence and thereby infer the DNA sequence encoding this enzyme. We then would be able to use this information to generate DNA probes that would allow us to test S. alterniflora (and other organisms) for this important enzyme.
Methods are under development to measure methanesulfonic acid (MSA) in leaf tissue samples. MSA is a potential oxidation product of DMSP via DMS and DMSO, and it is a difficult compound to measure in a saline matrix. If we can measure MSA and observe its production in vivo, this would provide unambiguous confirmation that DMSP and its degradation products are scavenging ROS in S. alterniflora.
Other methods under development are assays for ROS scavenging enzymes, including peroxidase and superoxide dismutase. We will use these assays, together with pulsed amplitude modulated fluorometry, to assess the level of oxidative stress experienced by plants.
More experimental work is planned to examine the effects of direct oxidative stressors on DMSP production and dynamics in the S. alterniflora leaves. We will repeat experiments with paraquat and also test DCMU, another herbicide expected to promote oxidative stress in the plants.
Nursery-grown plants will be used for a series of experiments examining how common stresses, including elevated salinity, N-limitation, and iron limitation, affect oxidative stress and DMSP dynamics in the S. alterniflora plants.
Finally, we will investigate the hypothesis that the high concentrations of DMSP found in S. alterniflora confer increased resistance to oxidative stress for this species. To test whether DMSP provides S. alterniflora with greater resistance to oxidative stress (relative to the non-DMSP containing congener S. patens) time series measurements will be made of oxidative stress in paraquat-treated S. alterniflora and S. patens, in parallel with measurements of the concentration of DMSP and its oxidation products in S. alterniflora. A PAM-fluorometer will be used to assess in situ oxidative stress in the paraquat-treated plants.
Journal Articles:No journal articles submitted with this report: View all 1 publications for this subproject
Supplemental Keywords:osmolyte, dimethylsulfoniopropionate, DMSP, dimethylsulfide, DMS, dimethylsulfoxide, DMSO, smooth cordgrass, Spartina alterniflora, field-grown plants, nursery-grown plants, stress factors, salinity, solar radiation, nitrogen limitation, iron limitation, oxidative stress, herbicides, paraquat, dichlorophenyldimethy urea, DCMU, reactive oxygen scavenging enzymes, quantum yield, photosystem II, risk, assessment, indicators, environmental stress, antioxidant, Alabama, AL, ecosystem, ecosystem protection, ecology, ecological effects, ecological indicators, environmental exposure, geographic area, environmental chemistry, chemistry, chemical engineering, salt marsh habitat., RFA, Scientific Discipline, ECOSYSTEMS, Water, Ecosystem Protection/Environmental Exposure & Risk, estuarine research, Aquatic Ecosystems & Estuarine Research, Ecology, Ecosystem/Assessment/Indicators, Ecosystem Protection, Restoration, Aquatic Ecosystem, Aquatic Ecosystems, Ecological Monitoring, Terrestrial Ecosystems, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Ecological Indicators, coastal ecosystem, eutrophication, water use, nursery habitats, estuaries, watersheds, nutrients, osmolyte dimethylsufoniopropionate, fisheries, aquatic plants, submerged aquatic vegetation, dimethylsulfoxide, ecosystem, environmental indicators, water quality, estuarine waters, seagrass
Progress and Final Reports:Original Abstract
Main Center Abstract and Reports:R827072 Alabama Center For Estuarine Studies (ACES)
Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
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R827072C007 Benthic Study Component
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R827072C010 Effects Of Variation in River Discharge and Wind-Driven Resuspension on Lower Trophic Levels of the Mobile Bay Ecosystem
R827072C011 Evaluation of Alabama Estuaries as Developmental Habitat for Juvenile Sea Turtles
R827072C012 Effects of Salinity Stress on Natural and Anthropogenically-Derived Bacteria in Estuarine Environments
R827072C013 The Role of Land-Use/Land-Cover and Sub-estuarine Ecosystem Nitrogen Cycling in the Regulation of Nitrogen Delivery to a River Dominated Estuary; Mobile Bay, Alabama
R827072C014 Environmental Attitudes of Alabama Coastal Residents: Public Opinion Polls and Environmental Policy
R827072C015 Synthesis and Characterization of an Electrochemical Peptide Nucleic Acid Probe
R827072C016 Determinants of Small-Scale Variation in the Abundance of the Blue Crab Callinectes Sapidus
R827072C017 Effects of Estrogen Pollution on the Reproductive Fitness of the Gulf Pipefish, Syngnathus scovelli
R827072C019 A Model for Genetic Diversity Aquatic Insects of the Mobile/Tensaw River Delta
R827072C020 Evaluating Trophic Processes as Indicators of Anthropogenic Eutrophication in Coastal Ecosystems: An Exploratory Analysis
R827072C021 Effects of Anthropogenic Eutrophication on the Magnitude and Trophic Fate of Microphytobenthic Production in Estuaries
R827072C022 Characteristics of Ship Waves and Wind Waves in Mobile Bay
R827072C023 Methods Comparison Between Stripping Voltammetry and Plasma Emission Spectroscopy for Metals in Mobile Bay
R827072C024 Changes in Water Conditions and Sedimentation Rates Associated With Construction of the Mobile Bay Causeway
R827072C025 Cold-Induced Hibernation of Marine Vibrios in the Gulf of Mexico: A Study of Cell-Cell Communication and Dormancy in Vibrio vulnificus
R827072C026 Holocene Sedimentary History of Weeks Bay, AL: Human and Natural Impacts on Deposition in a Gulf Coast Estuary
R827072C027 Shelter Bottlenecks and Self-Regulation in Blue Crab Populations: Assessing the Roles of Nursery Habitats and Juvenile Interactions for Shelter Dependent Organisms
R827072C028 Predicting Seagrass Survival in Nutrient Enriched Waters: Toward a New View of an Existing Paradigm
R827072C029 DMSP and its Role as an Antioxidant in the Salt Marsh Macrophyte Spartina alterniflora
R827072C030 A Preliminary Survey of Aerial and Ground-Dwelling Insects of the Mobile/Tensaw Delta
R827072C031 Natural Biogeochemical Tags of Striped Mullet, Mugil cephalus, Estuarine Nursery Areas in the North Central Gulf of Mexico
R827072C032 Resolution of Sedimentation Rates in Impacted Coastal Environments Using 137Cs and 210Pb Markers: Dog River and Fowl River Embayments
R827072C033 Investigation of the Use of Pulse Amplitude Modulated (PAM) Fluorometry as an Indicator of Submerged Aquatic Vegetation Health in Mobile Bay
R827072C034 Influence of Invasive Plant Species in Determining Diversity of Aquatic Vegetation in the Mobile-Tensaw Delta
R827072C035 The Influence of Shallow Water Hydrodynamics on the Importance of Seagrass Detritus in Estuarine Food Webs
R827072C036 Food Web Interactions, Spatial Subsidies and the Flow of Energy Between the Mobile Bay Delta and Offshore Waters: A SGER Proposal to the Alabama Center for Estuarine Studies
R830651C001 Meteorological Modeling of Hurricanes and Coastal Interactions: A Stability Study For Vertical Pressure Levels
R830651C002 Characterization of Glycoprotein Cues Used by the Parasitic Rhizocephalan Barnacle Loxothylacus texanus To Identify Its Blue Crab Host, Callinectes sapidus
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R830651C004 An Assessment of Environmental Contaminant Levels in Water and Dragonfly Larvae Tissues from the Mobile/Tensaw Delta