Instant Isotopes: Mass Measurements online in real time

photo: Belinda Pratten/freeswimmers

Measuring carbon dioxide (CO₂) and (O₂) fluxes from a living plant allows scientists to better understand the carbon metabolism that underlies plant growth. Traditionally, these measurements have been made by trapping air before and after it passes over a photosynthesising leaf, then cryogenically purifying the CO₂. Sampling and batch processing then gives an indication of the time evolution of the plant's underlying metabolic processes. This entire process is labour intensive and limited in its sensitivity.

Professors Murray Badger and Susanne von Caemmerer and their colleagues in the Molecular Plant Physiology group at the School of Biology have set about devising a better way to make gas exchange measurements on living plants that will expand the sensitivity and versatility of the technique. To do this they have developed a highly modified version of a mass spectrometer that can analyse stable isotopes of carbon and oxygen in real time. This research represents a cutting edge development in global plant science.

This enables determination of isotopic discrimination in either an O₂-consuming, or a CO₂-consuming reaction that might be occurring within a test leaf. In effect, this research makes use of a photosynthesising plant's ability to show a subtle discrimination (or preference) between different isotopic forms of CO₂ (with respect to both carbon and oxygen) during gas exchange. Miniscule changes in the function of the photosynthesising leaf are now both measurable and instructive. This includes aspects of CO₂ transfer for stomates to the chloroplast, CO₂ fixation into sugars, and the functioning of respiratory O₂ uptake processes. This approach to measurement can also be applied to reactions within an aqueous phase used in other photosynthesis and respiratory measurements.

Over the past three years, the team has refined this unique measuring facilities and it now represents the cutting edge of global plant science energetics. For example, this facility is revolutionising photosynthesis research, studies of the Rubisco carboxylase reaction, respiratory oxidase reactions, and whole-leaf gas exchange.

Further Info Online:

• http://www.rsbs.anu.edu.au/Profiles/Murray_Badger