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Techniques
Chlorophyll fluorescence
Chlorophyll fluorescence analysis is very widely used in plant physiology as it provides the ability to monitor with great precision processes occurring in the chloroplast in a completely non-invasive manner. Simply applying a flash of light to a leaf is enough to rapidly assess the efficiency with which the leaf is performing photosynthesis. Fluorescence arises primarily from Photosystem II and by examining changes in fluoresence yield over time we can both follow changes in photosynthesis, in the ability of the plant to dissipate light energy as heat and in the extent of damage to Photosystem II (photoinhibition). A detailed discussion of this analysis can be found in Maxwell and Johnson (2000) To measure chlorophyll fluorescence in the lab we use Walz PAM-101 fluorimeters. These are incorportated into data acquisition systems using National Instruments M-series data acquisition cards combined with laboratory written software (available here )
Transient absorption spectroscopy
Many of the components of the photosynthetic apparatus undergo optical changes depending on their redox state. This allows us to follow electron flow through multiple components of the electron transport chain, including cytochrome f, cytochrome b, P700 and plastocyanin. The absorbtion changes occurring are however very small and occur in a background that is both highly absorbing and highly scattering, therfore specialised, purpose built spectrophotometers. We have a system that is specially designed for leaf measurements and which was developed for us by Daniel Beal and Pierre Joliot . A commercial version of this system should be available shortly. For routine measurements of photosystem I turnover, we use a Walz PAM-101 with a dual wavelength NIR detector.
