(Carbon isotope fractionation inplants)

Abstract

_apleuroticCO F_._ti0n in Ca.._a_o£_ (Melzer and O'LeaD,, 1987, 1991). Although Cs plants use RuBP carboxylase to fix CO2, these plants also contain significant amounts of PEP carboxylase. The role of this latter enzyme in C_photosynthesis is unknown. The role of PEP carboxylase in photosynthesis in the C3 plant Nicotiana tabacum, has been probed by measurement of the _3Ccontent of various materials. Whole leaf and purified RuBP carboxylase are within the range expected for C.. s plants. Aspartic acid purified following acid hydrolysis of this RuBP carboxylase is enriched in t3C compared to whole protein. Carbons 1-3 of this aspartic acid are in the normal Ca range, but carbon4 (analyzed by treatment of the aspartic acid with aspartate _..decarboxylase) has an isotopic composition in the range expected for products of C4 photosynthesis (-5 o/oo), and it appears that more than half of the aspartic acid is synthesized by PEP carboxylase using atmospheric CO2/HCO3In subsequent work, we have extended this study to other species and have studied aspartate derived from protein, free aspartate, malate, and citrate. Enzymatic degradations nave been performed in all c_es to recover the carbon that might have arisen front CO 2 via PEP carboxylase. The isotopic data from tobacco, spinach, and soybean are similar, and age effects are small. The soybean data are shown in Table I. The isotopic content of whole protein is similar to that of the leaves. Carbon-4 of protein-derived aspartic acid is invariably 15.-20°/oo more positive than the protein, indicating that most of this carbon is derived from action of PEP carboxylase. This presumably happens principally during leaf development, when protein synthesis is rapid and PEP carboxylase concentration is relatively high.The isotopic content of the pool of free aspartic acid, malic acid, and citric acid indicates that in the mature leaf, these compounds are synthesized principally via the C3 cycle, although small contributions from PEP carboxylase can be seen. Thus, a principal role of PEP carboxylase in C3plants is the synthesis of four-carbon skeletons (principally aspartate) for use in protein synthesis early in development.Isotop_e__Fractionationin A___.artateSynthesi_ in .M__a.i_. We have used the same approach in maize, in order to determine the isotopic pattern of metabolites in C4plants. The results are summarized in Table I. The very positive value observed for carbon-4 of aspartate and malate in these plants is presumably due to the isotope fractionation associated with decarboxylation of four-carbon acids in the bundle sheath cells. _ ,-.uk. klM6NT t6 UNLItvt_TL-D

Integrating buccal and occlusal dental microwear with isotope analyses for a complete paleodietary reconstruction of Holocene populations from Hungary

“…In brief, δ 13 C is primarily used to identify the consumption of plants that use different metabolic pathways for fixing carbon during photosynthesis and the animals raised on them. These δ 13 C differences can then be used to identify the consumption of C 3 versus C 4 terrestrial resources in past diets 68 – 70 . Values of carbon ratios may also inform about the consumption of marine foods 71 – 74 and freshwater resources 75 – 77 .…”

Characterization of L-theanine in tea extracts and synthetic products using Stable Isotope Ratio Analysis

“…This behaviour is in line with the botanical origin of the matrices. Indeed, Camellia sinensis is an evergreen shrub belonging to the group of C3 photosynthetic cycle plants that show a typical stable isotopic range of δ 13 C of between −30 and −23‰ [ 28 – 30 ]. As already mentioned, in the tea plant, L-theanine is biosynthesized from glutamic acid and ethylamine by the theanine synthetase enzyme [ 31 ].…”

“…δ 15 N cannot be considered as the only parameter in the evaluation of the source of L-theanine, but it seems to add further information to that provided by the carbon isotope ratio. In synthetic L-theanine, the lower δ 15 N values obtained are probably due to the addition of ammonium sulphate (δ 15 N = −3.1 ± 0.66) [ 37 ] to the yeast broth as a source of nitrogen [ 28 , 29 ].…”