Carbon isotope ratios of amylose,amylopectin and mutant starches

Carbon isotope ratios (expressed as δ¹³C values) were determined for various sources of starch and the starch fractions amylose and amylopectin. The δ¹³C values of amylose were consistently less negative, 0.4–2.3 ‰, than those of amylopectin in kernal starch from maize (Zea mays) and barley (Hordeum vulgare) and in tuber starch from potato (Solanum tuberosum). Kernel starch isolated from the maize mutants wx1 and ae1, with known genetic lesions in the starch biosynthetic pathway, also showed significant differences in δ¹³C values. Collectively, these results suggest that variation in carbon isotope ratios in the amylose and amylopectin components of starch may be attributed to isotopic discrimination by the enzymes involved in starch biosynthesis.     

Carbon isotope ratios of central Mexican Crassulaceae in natural and greenhouse environments

Summary Measurements of carbon isotope ratios of central Mexican Crassulaceae collected over a broad habitat range show consistent patterns of CAM activity with no indications of substantial flexible photosynthetic pathways between C₃ and CAM. The three genera studied — Echeveria, Pachyphytum, and Graptopetalum — are all closely related to Dudleya in which considerable flexible metabolic response has been demonstrated. Comparative measurements of carbon isotope ratios for field collected and greenhouse reared samples of the same taxa showed a uniform occurrence of slightly more negative ¹³C values, but no indication of substantial flexible metabolic response.     

Contribution of the ear and the fl ag leaf to grain fi lling in durum wheat inferred from the carbon isotope signature: Genotypic and growing conditions eff ects FA

The ear, together with the flag leaf, is believed to play a major role as a source of assimilates during grain filling in C3cereals. However, the intrusive nature of most of the available methodologies prevents reaching conclusive results in this regard. This study compares the carbon isotope composition（d13C） in its natural abundance in the water‐soluble fractions of the flag leaf blade and the ear with the d13C of mature kernels to assess the relative contribution of both organs to grain filling in durum wheat（Triticum turgidum L. var.durum）. The relative contribution of the ear was higher in landraces compared to modern cultivars, as well as in response to nitrogen fertilization and water stress. Such genotypic and environmentally driven differences were associated with changes in harvest index（HI）, with the relative contribution of the ear being negatively associated with HI. In the case of the genotypic differences, the lower relative contribution of the ear in modern cultivars compared with landraces is probably associated with the appearance in the former of a certain amount of source limitation driven by a higher HI. In fact, the relative contribution of the ear was far more responsive to changes in HI in modern cultivars compared with landraces.     

Carbon isotope ratios in crassulacean Acid metabolism plants: seasonal patterns from plants in natural stands

A year round study of photosynthesis and carbon isotope fractionation was conducted with plants of Opuntia phaeacantha Engelm. and Yucca baccata Torr. occurring in natural stands at elevations of 525, 970, 1450 and 1900 m. Plant water potentials and the daytime pattern of ¹⁴CO₂ photosynthesis were similar for all cacti along the elevational gradient, despite significant differences in temperature regime and soil water status. Carbon isotope ratios of total tissue and soluble extract fractions were relatively constant throughtout the entire year. Additionally, the σ¹³C values were similar in all plants of the same species along the elevational gradient, i.e. −12.5 ± 0.86 ‰ for O. phaeacantha and −15.7 ± 0.95 ‰ for Y. baccata. The results of this study indicate Crassulacean acid metabolism predominates as the major carbon pathway of these plants, which do not facultatively utilize the reductive pentose phosphate cycle of photosynthesis as the primary carboxylation reaction.     

Carbon and hydrogen isotope ratios of bryophytes from arid and humid regions

Summary Measurements of carbon isotope ratios of nine taxa of arid zone mosses from North America and 24 taxa of European bryophytes show consistent values indicative of C₃ metabolism. Other morphological, physiological and biochemical characteristics provide the mechanism of adaptation to environmental stresses of heat and extended desiccation in these plants. Analyses of D content indicate that values become less negative with increasing aridity of the habitat.     

Stable isotope labelling and zinc distribution in grains studied by laser ablation ICP-MS in an ear culture system reveals zinc transport barriers during grain filling in wheat

Zinc (Zn) deficiency has been recognized as a potential risk for human health in many developing regions where staple food with low micronutrient density represents a major proportion of the diet. The success of strategies to increase Zn content in the edible part of crops requires better understanding of Zn transport to, and distribution within, the grains. The transfer of Zn from the growth medium to wheat (Triticum aestivum) grains in an ear culture system was investigated by using the stable Zn isotope (70) Zn, and the spatial distribution of Zn within the grains was studied by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Zinc was readily transported in the stem up to the rachis. More Zn accumulated in the stem when higher amounts of Zn were supplied to the medium. Once Zn was transported into the grain, Zn accumulated particularly in the crease vascular tissue. The gradient of (70) Zn concentration between crease vascular tissue, aleurone layer and endosperm demonstrates that Zn is distributed within grain through the crease phloem. These results suggest that two barriers of Zn transport into wheat grains may exist: between the stem tissue rachis and the grain, and the maternal and filial tissues in the grain.     

Carbon isotope ratios of crassulacean acid metabolism species in relation to climate and phytosociology

Summary The ¹³C, values of the two principal, widely distributed CAM species in Big Bend National Park, Texas, were examined and related to phytosociologic and macroclimatic parameters. Samples of Agave lecheguilla and Opuntia engelmannii were collected along an elevational gradient covering 1370 m, and values for both total and insoluble fractions were measured. Linear regressions were used to correlate changes in values with changes in community importance and mean annual precipitation for both species to determine whether or not they became increasingly C₃-like in their photosynthetic mode at more mesic, upper elevations. In addition, values were measured for other Agave and Opuntia species from different locations and for different seasons and for A. lecheguilla following a short laboratory experiment. Results show that there are very small changes in values for both species along the pronounced temperature and precipitation gradients associated with elevational change. The ranges in values for O. engelmannii are only 1.5 (n=7) and 1.2 (n=6) for total and insoluble fractions respectively. The ranges in values for A. lecheguilla are 2.6 (n=9) and 3.1 (n=9). The results for other species confirm this low variability. We conclude that the species examined are obligate CAM species and that wide elevational distributions are not due to shifts in photosynthetic mode.     

Carbon, nitrogen, and hydrogen isotope ratios in creekside trees in western Kansas

Three species of creekside trees were monitored weekly during the 2007 and 2008 growing seasons. The 2007 growing season was wet early, but became drier as the season progressed. In contrast, the 2008 growing season was dry early, but became wetter as the season progressed. Creekside trees were measured to determine effects of changing water regimes on leaf-level processes. Lonicera tatarica plants were compared to Morus alba and Celtis occidentalis trees. Leaves were monitored for changes in stomatal conductance, transpiration, δ¹³C, δ¹⁵N, δD, leaf temperature, and heat losses via latent, sensible, and radiative pathways. δD of creek water was more similar to ground water than to rain water, but the creek was partially influenced by summer rains. δD of bulk leaf material was significantly higher in individuals of C. occidentalis compared to the other species, consistent with source water coming from shallower soil layers. Despite decreasing water levels, none of these tree species showed signs of water stress. There were no significant differences between species in stomatal conductance or transpiration. Leaf δ¹³C was significantly lower in individuals of L. tatarica compared to the other species. Differences in δ¹³C were attributed to a lower carboxylation capacity, consistent with lower leaf nitrogen content in L. tatarica plants. Leaf δ¹⁵N was significantly lower in individuals of L. tatarica compared to the other species, consistent with uptake of a different N source. Two of the three sites appeared to be affected by inorganic N from fertilizer run-off. Evidence is presented that these species acquired water and nitrogen from different sources, resulting from differences in root uptake patterns.     

Carbon and nitrogen isotope ratios, nitrogen content and heterotrophy in New Zealand mistletoes

The carbon isotope ratio ('¹³C) of New Zealand mistletoes (-29.51ǂ.10‰) and their hosts (-28.89ǂ.12‰) is generally more negative, and shows less difference between mistletoes and their hosts, than found in previous studies. In 37% of the examined pairs, the '¹³C of mistletoes was less negative than that of their hosts. These reversals were not associated with the relative position (proximal or distal) of the host material with regard to the mistletoe. Differences between host and mistletoe tended to be greater on hosts with less negative '¹³C. Both nitrogen content and isotope ratio ('¹⁵N) of the mistletoe leaves were strongly correlated with those of their hosts. Nitrogen contents of mistletoe leaves were similar to those of their hosts at low nitrogen contents but proportionately less on hosts with a high nitrogen content, whereas '¹⁵N of mistletoes was consistently similar to that of their hosts. The '¹³C of mistletoes was related to both host nitrogen content and '¹⁵N, but '¹³C in host tissue was related to neither, suggesting that the mistletoes derived both nitrogen and carbon from their hosts. The '¹³C of both hosts and mistletoes were significantly related to leaf conductance and carbon dioxide concentration but relationships with transpiration and water use efficiency were not significant. In all cases there was no clear separation between the responses of hosts and mistletoes. This may be related to the similarity of stomatal conductance, transpiration and photosynthesis in the studied mistletoes and their hosts and is consistent with the small differences in '¹³C between mistletoes and hosts found in this study. Consequently, the estimation of mistletoe heterotrophy from carbon discrimination is confounded, as the small difference between host and mistletoe carbon discrimination could equally well result from either similarities in photosynthesis and water relations or heterotrophic assimilation of host-derived carbon. The differences between our study and previous studies (which are mostly from seasonally dry or semi-arid to arid environments) may be related to the temperate environment in which these mistletoes grow. Water is freely available so that the mistletoe is able to obtain sufficient water and dissolved nutrients without having to maintain the high transpiration rate and low water potentials that are needed to extract water from a water-stressed host. Similarly, mistletoe photosynthesis is less inhibited by water stress. The physiological similarities between mistletoe and hosts from a temperate environment are reflected in their similar '¹³C values.     

Carbon isotope ratios and crop analyses of Arphia (Orthoptera: Acrididae) species in southeastern Wyoming Grassland

Summary Food habits of Arphia conspersa Scudder and Arphia pseudonietana (Thomas) were studied along an altitudinal transect in southeastern Wyoming shortgrass mixed prairie. Stable carbon isotope ratios indicated that diets were significantly different between study sites, between species, and between sexes. These differences were found to be primarily related to the availability of different food plants along the transect, although species with the C₃ pathway of photosynthesis were consumed in greater proportion than their availability in the habitat. The preference for C₃ species is presumably related to their higher nutritional value and digestibility, in spite of the fact that more time and energy must be spent to locate these food plants in some of the habitats studied. This study demonstrates the utility of the carbon isotope method in studying plant-animal interactions in habitats containing both C₃ and C₄ plants.     

Climatic significance of isotope ratios

The hydrogen and oxygen isotope ratios of water, which can be measured by Isotope Ratio Mass Spectrometry (IRMS), exhibit climatic dependencies and are commonly exploited in hydrogeology. More generally, the overall carbon or hydrogen isotope ratios of plant organic matter, and in particular of tree-ring cellulose, have been frequently used for climatic reconstruction. However, since many physicochemical and biochemical fractionation phenomena are likely to contribute to the isotopic values, the interpretation of the climatic significance of isotopic parameters is not always straightforward. In the case of hydrogen and oxygen for instance, the climatic profile of the source meteoric water is not simply transferred to leaf water and many steps of the biosyntheses are accompanied by kinetic and thermodynamic isotope effects that depend on the individual mechanistic pathways. The information brought about by overall isotope ratios determined by IRMS is averaged over all fractionation effects undergone at the different molecular positions. In contrast, the NMR investigation of Site-specific Natural Isotope Fractionation (SNIF-NMR) gives simultaneous access to isotope ratios specific to individual positions in the molecule. Since the different atoms do not necessarily exhibit the same climatic dependency, the method provides complementary responses to the environmental conditions. In particular, the isotopic parameters of ethanol and water obtained by fermenting sugars in standardized conditions reflect climatic influences which took place at different periods of plant growth. As a consequence, statistical analyses based on multi-site isotopic variables provide powerful criteria for distinguishing geographical regions of cultivation characterized by different climatic features. Although the sensitivity to climatic variations is the most pronounced for plant water and for sugars formed at the first step of photosynthesis, other components such as lipids or minor metabolites also exhibit climatic dependencies. The combination of isotopic values pertaining to different atomic species and either averaged over the whole molecule (IRMS) or associated with different molecular sites (SNIF-NMR), provides complementary criteria, which can be exploited in terms of both climatic significance and mechanistic pathways of the individual atoms.     

Brassinosteroids regulate grain filling in rice

Genes controlling hormone levels have been used to increase grain yields in wheat (Triticum aestivum) and rice (Oryza sativa). We created transgenic rice plants expressing maize (Zea mays), rice, or Arabidopsis thaliana genes encoding sterol C-22 hydroxylases that control brassinosteroid (BR) hormone levels using a promoter that is active in only the stems, leaves, and roots. The transgenic plants produced more tillers and more seed than wild-type plants. The seed were heavier as well, especially the seed at the bases of the spikes that fill the least. These phenotypic changes brought about 15 to 44% increases in grain yield per plant relative to wild-type plants in greenhouse and field trials. Expression of the Arabidopsis C-22 hydroxylase in the embryos or endosperms themselves had no apparent effect on seed weight. These results suggested that BRs stimulate the flow of assimilate from the source to the sink. Microarray and photosynthesis analysis of transgenic plants revealed evidence of enhanced CO₂ assimilation, enlarged glucose pools in the flag leaves, and increased assimilation of glucose to starch in the seed. These results further suggested that BRs stimulate the flow of assimilate. Plants have not been bred directly for seed filling traits, suggesting that genes that control seed filling could be used to further increase grain yield in crop plants.     

Stable nitrogen and carbon isotope ratios in wild native honeybees: the influence of land use and climate

The eastern hive bee Apis cerana is a major honeybee species in Asia providing numerous ecosystem services. Understanding how much the honeybees depend on natural and human-influenced plants and landscapes in different climates is important could contribute to evaluate how wild honeybees use food resources and to measure the ecosystem services. We investigated the effects of land use and climate changes on stable nitrogen and carbon isotope ratios in wild populations of A. cerana. In populations from 139 individual sites throughout Japan, we measured nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope ratios and analyzed the effects of land use and climate. Our results showed that forested areas and annual precipitation had significant effects on δ¹⁵N, and that paddy fields and urban areas had significant effects on δ¹³C. These results suggest that A. cerana sensibly uses available food resources in the various environments and that stable nitrogen and carbon isotope ratios clearly reflect the effects of land use and climate changes on the populations of A. cerana. Thus, stable nitrogen and carbon isotope ratios in A. cerana, which widely distributes in Asia, can be used as indicators of the environments, such as land use and climate, of an area within its foraging range.     

Carbon : nitrogen : phosphorus ratios influence biofilm formation by Enterobacter cloacae and Citrobacter freundii

AIMS: To test the effects of C : N : P ratio modification of a well-known nutrient medium formulation, the Endo formulation on biofilm formation by Enterobacter cloacae Ecl and Citrobacter freundii Cf1 in both single-species and binary species biofilms. METHODS AND RESULTS: The C : N : P atom : atom ratio of a well-known nutrient medium formulation, the Endo formulation, that has been applied in fermentative biohydrogen studies, was modified to include two different C concentrations, one containing 17.65 g l(-1) and the other 8.84 g l(-1) sucrose, each containing four different C : N : P ratios, two at higher C : N : P ratios (334 : 84 : 16.8 and 334 : 84 : 3) and two at lower C : N : P ratios (334 : 28 : 5.6 and 334 : 28 : 1). Attached cells were enumerated after dislodging the biofilms that had formed on granular activated carbon (GAC). The modified medium containing 17.65 g l(-1) sucrose and having a C : N : P ratio of 334 : 28 : 5.6 resulted in significantly (P < 0.05) higher counts of attached cells for both single-species biofilms at 7.73 log(10) CFU g(-1) GAC and 9.3 log(10)CFU g(-1) GAC for Ent. cloacae Ecl and Cit. freundii Cf1, respectively, and binary species biofilms at 8.2 log(10) CFU g(-1) GAC and 6.34 log(10) CFU g(-1) GAC for Ent. cloacae Ecl and Cit. freundii Cf1, respectively. Scanning electron micrographs showed qualitative evidence that the 334 : 28 : 5.6 ratio encouraged more complex and extensive biofilm growth for both single-species and binary species biofilms. CONCLUSIONS: The differences in the attachment numbers between the different ratios were found not to be a result of the individual actions of the bacterial isolates involved but rather because of the effects of the various C : N : P ratios. The 334 : 28 : 5.6 ratio showed significantly (P < 0.05) higher counts of attached cells for both single-species and binary species biofilms. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates that C : N : P ratios should be a key consideration with regard to maximizing biofilm formation in shake flask and fluidized bed bioreactor studies as well as understanding fundamental factors affecting biofilm growth in natural environments.     

Carbon and nitrogen stable isotope ratios of deposit-feeding polychaetes in the Nanakita River Estuary, Japan

Two types of deposit-feeding polychaetes, Neanthes japonica and Notomastus sp., and their surrounding sediments were collected from the Nanakita River Estuary and a small brackish lagoon (Gamõ Lagoon) in northeastern Japan. The samples were examined using stable isotope analysis to assess the site specific feeding mode of the animals and their trophic status. N. japonica is a surface deposit-feeder and Notomastus sp. is a subsurface deposit-feeder. In the estuary, the sedimentary ⁵N tended to become isotopically heavier from the upper estuary (2.0 3.9) to the river mouth (4.3 6.2), while sedimentary organic ¹³C constant value (–26.8 –24.4, average –25.6) throughout the river estuary. The ¹³C values of N. japonica were similar to those of the surrounding sediment in the upper estuary, whereas in the lower estuary, N. japonica had a heavier ¹³C value than the surrounding sediment. The ¹³C and dg ¹⁵N values indicated that the carbon, but not the nitrogen, of N. japonica was derived from upland plants in the upper estuary. In the lower estuary, a significant fraction of carbon of N. japonica was derived from phytoplankton. Notomastus sp. exhibited heavier ¹³C values than the surrounding surface sediment throughout the estuary and had heavier ¹³C values than N. japonica in the same location. These results suggest selective utilization of sedimentary carbon by those animals following bacterial processing and subsequent fractionation. The difference in ¹⁵N between sedimentary organics and corresponding polychaetes was 5 ± 1 and rather higher than 3.4 ± 1.1 expected for normal trophic effects in other animals.     

Aerial decay influence on the stable oxygen and carbon isotope ratios in tree ring cellulose

Sub-fossil wood is often affected by the decaying process that introduces uncertainties in the measurement of oxygen and carbon stable isotope composition in cellulose. Although the cellulose stable isotopes are widely used as climatic proxies, our understanding of processes controlling their behavior is very limited. We present here a comparative study of stable oxygen and carbon isotope ratios in tree ring cellulose in decayed and non-decayed wood samples of Swiss stone pine (Pinus cembra) trees. The intra-ring stable isotope variability (around the circumference of a single ring) was between 0.1 and 0.5‰ for δ¹⁸O values and between 0.5 and 1.6‰ for δ¹³C values for both decayed and non-decayed wood. Observed intra-tree δ¹⁸O variability is less than that reported in the literature (0.5–1.5‰), however, for δ¹³C it is larger than the reported values (0.7–1.2‰). The inter-tree variability for non-decayed wood ranges between 1.1 and 2.3‰ for δ¹⁸O values, and between 2 and 4.7‰ for δ¹³C values. The inter-tree differences for δ¹⁸O values are similar to those reported in the literature (1–2‰ for oxygen and 1–3‰ for carbon) but are larger for δ¹³C values. We have found that the differences for δ¹⁸O and δ¹³C values between decayed and non-decayed wood are smaller than the variation among different trees from the same site, suggesting that the decayed wood can be used for isotopic paleoclimate research.     

Replantation of severed ear parts.

We have used a technique whereby a severed ear part is sutured back into place on "shaved" areas on the medical surface of the remaining ear and on the corresponding retroauricular area. After 4 to 6 weeks, the ears are freed and the raw surfaces are skin grafted. We think that replantation of severed ear parts is justifiable, and we recommend this method whereby the supply of blood vessels is increased.     

Plastid DNA during grain filling in wheat

During grain filling in wheat (Triticum aestivum L.) there is a progressive increase in the number of amyloplasts in the endosperm, as well as in cell number, DNA content and nuclear ploidy as the grain increases in size. The plastid DNA content also rises initially, and then there is a levelling off in the amount, with the percentage plastid DNA finally making up approximately 0.9% of the total endosperm DNA.     

Effect of soil salinity on grain filling and grain development in barley

Experiments were conducted with five barley cultivars with the aim of ascertaining the effect of salt stress on grain filling, grain development and bioohemical composition of developing grains. Reduced grain yield under salt stress was found to be due to reduced efficiency per day to fill the grains and consequent more effective days and also due to disturbed starch-sugar balance.