Our aim is to promote gas exchange measurements of whole unscathed plants/shoots in controlled conditions. Measuring whole plants or attached shoots provides a unified picture, where macroscopic plant water relations, transpiration, photosynthesis, water conducting tissues in the plant and microscopic events in the guard cell signaling are all brought together – this is what happens in real plant growing in real field. Using multiple cuvettes simultaneously adds value, as it enables to measure several plants under similar conditions and thus, to get representative datasets.
To achieve this aim, we applied our 40-year experience in constructing different devices for plant gas exchange analyses to develop systems that provide reliable measurements of photosynthesis and transpiration in Arabidopsis and other plants.
Entire unharmed plants are inserted into measurement cuvettes and their water vapour and CO2 exchange patterns are continuously measured. This is done by dividing the air that enters each cuvette into two streams, one going directly to IRGA analyzers, another passing plant cuvette before analysis. Net assimilation rate (Anet) and transpiration (E) are calculated as follows:
Anet=air flow rate*(CO2in-CO2out)/leaf area
E=air flow rate*(H2Oout-H2Oin)/leaf area
Total leaf conductance (Gt) to water vapour is calculated as (von Caemmerer & Farquhar 1981):
where denominator is the difference in water vapour mole fractions between leaf and air.
Air temperature in the cuvettes is measured with temperature-matched NTC resistors and from air temperature, leaf temperature, needed to determine leaf-to-air humidity gradient in the equation above, is calculated using energy budget equation (Parkinson 1985).
From Gt, stomatal conductance (Gs) is calculated after considering the values of boundary layer and cuticular conductances.
For further details, please see:
von Caemmerer S, Farquhar GD (1981) Some relationships between the biochemistry of photosynthesis and the gas exchange of leaves. Planta 153: 376–387
Parkinson KJ (1985) A simple method for determining the boundary layer resistance in leaf cuvettes. Plant Cell Environ 8: 223–226
Kollist T, Moldau H, Rasulov B, Oja V, Rämma H, Hüve K, Jaspers P, Kangasjärvi J, Kollist H (2007) A novel device detects a rapid ozone-induced transient stomatal closure in intact Arabidopsis and its absence in abi2 mutant. Physiol Plant 129: 796–803