Project 1 - Characterising the plant fluorome - analysis of chlorophyll induction kinetics of Arabidopsis mutants
Following the onset of illumination, leaves display a polyphasic increase in chlorophyll fluorescence to a maximum level before gradually declining to a lower, steady-state as the leaf adapts to the ambient light conditions. Similar fluorescence transients are generated following transfer from a lower to a higher light intensity. At physiological temperatures this florescence arises principally from chlorophyll associated with Photosystem II. The size and shape of the fluorescence transient is related to the light intensity, the composition and organisation of the photochemical apparatus, and the metabolic and physiological state of the leaf. Theoretical analysis of the fluorescence induction has led to the development of an approach to estimate key photosynthetic parameters from fast direct fluorescence measurements of dark-adapted leaves (referred to as the "JIP-test", see reference for details).
The aim of this project is to examine the chlorophyll fluorescence induction kinetics of Arabidopsis mutants with defined genetic lessons known to influence photosynthetic metabolism. The study will establish the applicability of the "fluorome" as a rapid measure of the physiological status of a plant and the feasibility of exploiting a rapid fluorescence screen for identifying novel arabidopsis mutants. The project will involve the following steps.(i) Determine the extent of variation in fluorescence characteristics within, and between, individual wildtype plants by monitoring the induction curves of all leaves on each of several plants at different developmental stages. (ii) Compare fluorescence characteristics of wildtype plants and mutants known to be defective in specific reactons affecting photosynnthesis. At present I envisage studying (a) cue-1, defective in synthesis of carotenoids (photoprotective pigments) and plastoquinone (a critical component of chloroplast electron transport), (b) ape-2, a recently isolated (and, as yet, unpublished) mutant defective in export of triose phosphates from the chloroplast through the tiose-phosphate translocator, (c) adg1, a mutant lacking ADPglucose pyrophosphorylase, a key enzyme of starch synthesis. The study will involve the collection and analysis of a large amount of data. (Typically, a fluorescence induction curve contains 1200 data points over 1 s and takes about 20 s to collect, thus about 100 data sets can be collected each hour.) These will be analysed in two ways: (i) by extraction of key photosynthetic parameters from the induction curves using the (ii) by adapting statistical procedures (such as Principal Component Analysis - used in ecology and, more recently, metabolomics) to identify distinguishing features between plant lines and/or growth conditions. Familiarity in the use of Excel spreadsheets, confidence in the application of new programmes and a reasonable degree of mathematical competence is required for this project. Getting the data will be easy, it is the analysis that will be the clever part!