Isotopic Labeling with Carbon-13

In vivo isotopic labeling is a technique that modifies a growing plant at the molecular level in way that can be later measured. Generation of isotopically labeled plant material is a perquisite to certain proteomic and metabolomic experiments. Isotopic labeling enables analytical techniques to resolve complex relationships between the molecular composition, environment, and phenotype of a plant.

What is an isotope?

Isotopes are variants of elements whose atoms share the same number of protons but differ in their number of neutrons. Isotopic labeling is a method that replaces one or more atoms in a molecule of interest with an isotope. Depending on the specific isotope used, the presence of this alteration can be detected through differences in mass, vibrational modes, gyromagnetic ratios, or radioactive decay.

Why use carbon-13?

The overwhelming occurrence of carbon compounds in biological systems means labeling with a carbon isotope is especially useful. Carbon-13 is often ideal, as it is a stable (nonradioactive) isotope with low natural abundance (~1.1%) and its incorporation causes minimal physiological perturbations. Carbon-13 is particularly useful for plant labeling as it can be introduced via 13CO2 gas and readily assimilated into plant metabolic systems through natural carbon fixation.

How are plants labeled with carbon-13?

Plants are labeled in a isotopic growth chamber that provides a 13CO2 gas environment. It is necessary to perform isotopic labeling in a sealed enclosure to minimize the amount (and cost) of 13CO2 gas required and to protect from atmospheric 12CO2 contamination. However, growth in an isolated environment introduces a variety of obstacles that will result in plant stress or injury if left unmonitored. Climate regulation, nutrient delivery, and waste removal are all required elements to sustain healthy plant growth. We design our growth chambers to overcome these challenges and produce healthy and highly enriched plants.

How is a carbon-13 labeled plant analyzed?

Proteins and metabolites are extracted from plant samples and analyzed with gas chromatography (GC) or liquid chromatography (LC)-mass spectrometry (MS)-coupled methods or nuclear magnetic resonance (NMR). Depending on the labeling and sampling methods, carbon-13 compounds can be traced from a plant’s uptake from the environment and throughout its tissues, cells, and organelles. Labeled molecules are useful in many different contexts, frequently as a standard to which unlabeled molecules may be compared using isotope dilution methodology.

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