Mark A. Teece

Increased Accumulation of Cuticular Wax and Expression of Lipid Transfer Protein in Response to Periodic Drying Events in Leaves of Tree Tobacco

Cuticular wax deposition and composition affects drought tolerance and yield in plants. We examined the relationship between wax and dehydration stress by characterizing the leaf cuticular wax of tree tobacco (Nicotiana glauca L. Graham) grown under periodic dehydration stress. Total leaf cuticular wax load increased after each of three periods of dehydration stress using a CH2Cl2 extraction process. Overall, total wax load increased 1.5- to 2.5-fold, but composition of the wax was not altered. Homologous series of wax components were classified into organic groups; n-hentriacontane was the largest component (>75%) with alcohols and fatty acids representing <10% of the entire wax load. An increase in density, but no change in the three-dimensional shape, of leaf wax crystals was evident under low-kV scanning electron microscopy after each drying event. Leaves excised from plants subjected to multiple drying events were more resistant to water loss compared to leaves excised from well-watered plants, indicating that there is a negative relationship between total wax load and epidermal conductance. Lipid transfer proteins (LTPs) are thought to be involved in the transfer of lipids through the extracellular matrix for the formation of cuticular wax. Using northern analysis, a 6-fold increase of tree tobacco LTP gene transcripts was observed after three drying events, providing further evidence that LTP is involved in cuticle deposition. The simplicity of wax composition and the dramatic wax bloom displayed by tree tobacco make this an excellent species in which to study the relationship between leaf wax deposition and drought tolerance.

Isotopic fractionation associated with biosynthesis of fatty acids by a marine bacterium under oxic and anoxic conditions

Shewanella putrefaciens (Strain MR-4), a gram negative facultative marine bacterium, was grown to stationary phase under both aerobic and anaerobic conditions using lactate as the sole carbon source. Aerobically-produced cells were slightly enriched in 13C (+1.5‰) relative to the lactate carbon source, whereas those from anaerobic growth were depleted in 13C (−2.2‰). The distribution of fatty acids produced under aerobic conditions was similar to that resulting from anaerobic growth, being dominated by C16:1 ω7 and C16:0 fatty acids with a lesser amount of the C18:1 ω7 component. Low concentrations of saturated even numbered normal fatty acids in the C14 to C18 range, and iso-C15:0 were synthesized under both conditions. Fatty acids from anaerobic cultures (average δ13C=−37.8‰) were considerably depleted in 13C relative to their aerobically-synthesized counterparts (−28.8‰). The distinct differences in isotopic composition of both whole cells and individual fatty acid components result from differences in assimilation pathways. Under aerobic conditions, the primary route of assimilation involves the pyruvate dehydrogenase enzyme complex which produces acetyl-CoA, the precursor to lipid synthesis. In contrast, under anaerobic conditions formate, and not acetate, is the central intermediate in carbon assimilation with the precursors to fatty acid synthesis being produced via the serine pathway. Anaerobically-produced bacterial fatty acids were depleted by up to 12‰ relative to the carbon source. Therefore, detection of isotopically depleted fatty acids in sediments may be falsely attributed to a terrestrial origin, when in fact they are the result of bacterial resynthesis.

Diversity of cuticular wax among Salix species and Populus species hybrids.

The leaf cuticular waxes of three Salix species and two Populus species hybrids, selected for their ability to produce high amounts of biomass, were characterized. Samples were extracted in CH(2)Cl(2) three times over the growing season. Low kV SEM was utilized to observe differences in the ultrastructure of leaf surfaces from each clone. Homologous series of wax components were classified into organic groups, and the variation in wax components due to clone, sample time, and their interaction was identified. All Salix species and Populus species hybrids showed differences in total wax load at each sampling period, whereas the pattern of wax deposition over time differed only between the Salix species. A strong positive relationship was identified between the entire homologous series of alcohols and total wax load in all clones. Similarly strong relationships were observed between fatty acids and total wax load as well as fatty acids and alcohols in two Salix species and one Populus species hybrid. One Salix species, S. dasyclados, also displayed a strong positive relationship between alcohols and alkanes. These data indicate that species grown under the same environmental conditions produce measurably different cuticular waxes and that regulation of wax production appears to be different in each species. The important roles cuticular waxes play in drought tolerance, pest, and pathogen resistance, as well as the ease of wax extraction and analysis, strongly suggest that the characteristics of the cuticular wax may prove to be useful selectable traits in a breeding program.

Preparation of Ecological and Biochemical Samples for Isotope Analysis

Publisher Summary This chapter presents an overview of the applications of stable isotope techniques to addressing ecological questions. The technological advancements in the elemental analyzers linked to isotope ratio mass spectrometers; stable isotope analysis is quickly becoming a standard measurement for interpretation of various biological and environmental parameters. The main power of isotopic analyses is the ability to study both specific processes and also to trace sources of materials and flows of energy through complex ecological webs. It focuses on the proper sampling protocols for accurately determining the natural abundance and distribution of stable isotopes, particularly carbon and nitrogen, in ecological systems and does not address methods that include the addition of isotopically labeled compounds at enriched levels. Different types of samples require different methods of collection and storage, and the choice of methods will be influenced by the location of the ecosystem, the availability of cold storage, and the kinds of analyses to be performed. The materials used are biological materials, aquatic particulate material, collection of water samples, storage of samples, and sample preparation for isotope analysis.

Taxonomic and Environmental Variation of Metabolite Profiles in Marine Dinoflagellates of the Genus Symbiodinium

Microorganisms in terrestrial and marine ecosystems are essential to environmental sustainability. In the marine environment, invertebrates often depend on metabolic cooperation with their endosymbionts. Coral reefs, one of the most important marine ecosystems, are based on the symbiosis between a broad diversity of dinoflagellates of the genus Symbiodinium and a wide phyletic diversity of hosts (i.e., cnidarian, molluscan, poriferan). This diversity is reflected in the ecology and physiology of the symbionts, yet the underlying biochemical mechanisms are still poorly understood. We examined metabolite profiles of four cultured species of Symbiodinium known to form viable symbioses with reef-building corals, S. microadriaticum (cp-type A194), S. minutum (cp-type B184), S. psygmophilum (cp-type B224) and S. trenchii (cp-type D206). Metabolite profiles were shown to differ among Symbiodinium species and were found to be affected by their physiological response to growth in different temperatures and light regimes. A combined Random Forests and Bayesian analysis revealed that the four Symbiodinium species examined primarily differed in their production of sterols and sugars, including a C29 stanol and the two sterols C28Δ5 and C28Δ5,22, as well as differences in metabolite abundances of a hexose and inositol. Inositol levels were also strongly affected by changes in temperature across all Symbiodinium species. Our results offer a detailed view of the metabolite profile characteristic of marine symbiotic dinoflagellates of the genus Symbiodinium, and identify patterns of metabolites related to several growth conditions.

Urea is a dynamic pool of bioavailable nitrogen in coral reefs

Urea may be an important source of nitrogen in low nutrient coral reef environments because corals and other organisms can assimilate it easily and it is found throughout ocean waters. We measured the distribution and concentrations of urea in seagrass beds, areas of schooling fish, coral formations and bottom sediments in the Upper Florida Keys Reef Tract. The flux of urea from bottom sediments was also measured. Ambient concentrations of urea in the offshore reefs were similar to the concentrations of nitrate and ammonium. Seagrass beds, areas of schooling fish and coral formations had elevated concentrations of urea that were up to eight times higher than nitrate in the system. Numerous ephemeral hotspots of urea that were 8–20 times the ambient urea concentration existed in seagrass beds, areas of schooling fish, and above sediments. Coastal areas and inland canals had high urea concentrations where urban runoff and septic effluents were prevalent, but there was no anthropogenic influence in the offshore habitats. Urea concentrations above bottom sediments were not different from ambient concentrations and benthic flux chamber incubations showed biological activity in carbonaceous sediments but no net urea production. The decrease in urea concentrations from coasts and inland waterways to a consistent ambient concentration in the offshore reef system and ephemeral hotspots of high urea concentration suggest that urea is a dynamic pool of bioavailable nitrogen in the reefs of the Upper Florida Keys.

Ontogenetic resource-use strategies in a rare long-lived cycad along environmental gradients.

We studied carbon and nitrogen acquisition and water-use efficiency across the ontogeny of a rare cycad in relation to environmental gradients. Increased water-use efficiency at lower drier elevations and nitrogen fixation at upper elevations with nutrient poor soils may help maintaining the lower and upper altitudinal species range limits

Resource partitioning by evergreen and deciduous species in a tropical dry forest

Niche differentiation can lead to coexistence of plant species by partitioning limiting resources. Light partitioning promotes niche differentiation in tropical humid forests, but it is unclear how niche partitioning occurs in tropical dry forests where both light and soil resources can be limiting. We studied the adult niche of four dominant evergreen (cycad, palm) and drought-deciduous (legume, oak) species co-occurring along environmental gradients. We analyzed light intensity and soil fertility effects on key functional traits related to plant carbon and water economy, how these traits determine species’ functional strategies, and how these strategies relate to relative species abundance and spatial patterns. Light intensity was negatively associated with a key trait linked to plant water economy (leaf δ13C, a proxy for long-term water-use efficiency—WUE), while soil fertility was negatively associated with a key trait for plant carbon economy (LNC, leaf nitrogen content). Evergreens were highly sclerophyllous and displayed an efficient water economy but poor carbon economy, in agreement with a conservative resource-use strategy (i.e., high WUE but low LNC, photosynthetic rates and stature). Conversely, deciduous species, with an efficient carbon economy but poor water economy, exhibited an exploitative resource-use strategy (i.e., high LNC, photosynthetic rates and stature, but low WUE). Evergreen and deciduous species segregated spatially, particularly at fine-scales, as expected for species with different resource-use strategies. The efficient water economy of evergreens was related to their higher relative abundance, suggesting a functional advantage against drought-deciduous species in water-limited environments within seasonally dry tropical forests.

Lipid metabolism during embryonic development of the common snapping turtle, Chelydra serpentina

The metabolism of lipids and fatty acids during embryonic development of Chelydra serpentina (common snapping turtle) was investigated. Substantial changes in lipid class and fatty acid composition occurred as lipids were transferred from the yolk to the yolk sac membrane (YSM) and then to the brain, eyes, heart, and lungs of the hatchling. Lipids were hydrolyzed in the yolk prior to transport to the YSM, shown by a large increase in free fatty acids (FFAs) during the second half of development. Triglyceride-derived docosahexaenoic acid (DHA) was utilized preferentially to phospholipid-derived DHA. In the YSM, arachidonic acid (ARA) was selectively incorporated into phospholipids while DHA was preferentially incorporated into triglycerides. Selective incorporation of DHA and ARA into the brain and eyes, and ARA into the heart was observed, indicating the importance of these PUFAs for organ development and function. The amount of DHA and ARA in each organ was less than 1% of that measured in the yolk of the freshly laid egg, indicating that only a small portion of yolk PUFAs were incorporated into the hatchling organs studied. We discuss the differences in the mechanisms and utilization of yolk lipids in turtles compared with lipid uptake during embryonic development in birds.

Spatial mobilization of calcium and magnesium from the eggshell of the snapping turtle, Chelydra serpentina

Abstract Reptilian eggshells are a potential source of nutrients for developing embryos. Embryonic Snapping Turtles (Chelydra serpentina) used calcium and magnesium from the eggshell during development. This supplemental source of calcium provided more than twice the amount of calcium present in freshly laid egg yolk to developing embryos. Calcium was preferentially mobilized from the sides and bottom of the eggshell. Scanning electron micrographs of eggshells indicated that this preferential use affected the structural integrity of the eggshell, which presumably facilitates pipping. The mass and concentration of calcium in the chorioallantoic membrane increased significantly during later development, suggesting that this membrane plays a critical role in mobilization of calcium during development. This is the first study to demonstrate mobilization of eggshell magnesium by embryonic turtles.