Novel methodology for quantitative assessment of the capacity for photoprotection in photosynthetic organisms

The dissipation of excess excitation energy (NPQ) in the photosynthetic membrane is a fundamental process that prevents damage to the photosynthetic membrane, particularly oxygen-evolving photosystem II reaction centers. However, exploiting NPQ for quantitative assessment, the prediction of plant wellbeing and for the possible improvement of photosynthesis has not occurred, partly due to a lack of knowledge concerning the nature and amplitude of the photoprotective component of NPQ (pNPQ) and its optimal level required for photosynthesis. Indeed, we urgently need methods that routinely separate components of NPQ that are crucially important from those not essential or even detrimental for plant survival and productivity. Here we propose to develop and test innovative, non-destructive and effective fluorescence techniques to isolate the beneficial (protective) component of NPQ in vivo and to determine its optimal level via generation of a number of quantitative parameters of light tolerance. We will use molecular and physiological approaches to apply these methods to leaf photosynthesis of a model plant species, Arabidopsis thaliana, and its various mutants. We will determine the impact of all NPQ components, photoprotective and photoinhibitory, on the state of the PSII reaction centers, electron transport, growth rate and biomass production and using mutant plants we will identify new targets for the forecasting and improvement of light energy utilization, stress resistance and overall plant wellbeing.

Modelling suggests under certain circumstances photoprotective energy dissipation in the photosystem II (PSII) antenna (qE) may be responsible for reducing the yield of photosynthesis by up to 30%. This project will test this idea in two ways. Firstly, we will test whether qE is an unnecessary mechanism for plants grown under constant light intensity (e.g. commercial glasshouses) where photo-oxidative damage is unlikely. To test this we will grow Arabidopsis mutants that possess little or no qE (lut2npq1, npq1 and npq4) under various constant light intensities and compare their productivity, measured in terms of both growth rate, biomass and seed production, to the wild-type. We will quantify leaf area and PSII yield using non-invasive methods such as chlorophyll fluorescence imaging. In addition, the fluorescence lifetime of leaves will be used as an independent and absolute measure of energy storage efficiency and usage by PSII using picosecond time correlated single photon counting. The ability to turn increased PSII yield into carbon gain will be quantified by comparing the levels of stored sugars and carbohydrates in leaf tissue by spectroscopic assay. The second part of the project will test if plants grown under natural light conditions where the light intensity fluctuates rapidly and dramatically throughout the day suffer from the inability of qE to track adequately quickly these fluctuations. The slow relaxation of qE upon transition from high to low light undermines the photosynthetic yield leading to losses in productivity. Here we will compare Arabidopsis and rice mutants that show faster rates of qE relaxation than the wild-type (L17, szl1, asChyB) to understand if these phenotypes result in increases in productivity. To check this Arabidopsis and rice will be grown under fluctuating light conditions mimicking those found in the field and quantify their productivity by seed production, biomass and growth rate.

Who will benefit from this research? How will they benefit from this research?
1. The Environment
The project will benefit the environment in several ways. Firstly, any increase in the productivity of UK agriculture will allow the home-grown share of the fruits and vegetables market to increase, thus reducing the amount imported from overseas. A decrease in fruit and vegetable imports will reduce the carbon footprint of the consumer by reducing food miles. The project also promises to reduce the necessary artificial light energy input into UK glasshouses, again reducing the carbon footprint. In addition, in the very near future, there will be a strongly increasing demand for sustainable energy for our society. The sun is the far biggest source of energy, and photosynthetic organisms in both land and aquatic environments are the foundations of a bio-based economy. Increases in photosynthetic productivity can benefit UK society by increasing the amount of biomass available for conversion into biofuels and increasing food security through higher crop yields.
2. The UK Agriculture Sector
The principle end users of this research will be in the commercial sectors associated with crops, including biofuels. The maximum predicted profit from the improvement of NPQ dynamics in the field for all UK crops could potentially reach £300M. The PI together Professor Conrad Mullineaux (QMUL) was a recipient of a grant from the Carbon Trust on Algal Biofuels Challenge (ABC) to explore certain marine algae for the use in the generation of biodiesel. It is possible that identified NPQ mutants will also be useful for increasing algal photosynthetic productivity especially where controlled environmental conditions are used in biorectors etc.
3. The UK Economy
In addition to increased profits from enhanced crop plant productivity the UK economy will also benefit from the project by providing training and experience for UK scientists and technicians in a multidisciplinary array of microscopic, spectroscopic, biochemical and other practical techniques. The skills they acquire will enable them to think of innovative, cross-discipline solutions to the crucial biological and environmental problems of the present and future, and to play a part in developing a successful bio-based economy.
4. Agrobiotech companies such as Syngenta
The project will benefit agrobiotechnology companies at home and abroad, who will be interested in genes identified by the project as targets for increased photosynthetic productivity. Potentially these companies can create mutants currently only available in Arabidopsis for crop plants and sell these under license to the domestic and global agriculture sector.
What will be done to ensure that they benefit from this research?
Dissemination of results: Publications in peer-reviewed international journals; Oral and poster contributions at international scientific meetings and workshops; the project will be described on the PI's website; (http://webspace.qmul.ac.uk/aruban); publicity of important finding via press releases from QMUL. We will also actively engage with a range of agrobiotech companies providing them with presentations of our findings, opening a dialogue on the future application of our research to crop plants.
Training: The training opportunities provided by this project will be greatly augmented by the participation of the PI in the HARVEST Marie Curie training Network of the EU FP7 programme. HARVEST brings together 15 top institutes from various disciplines working on the elementary regulation mechanisms in oxygenic photosynthesis, as well as academic groups and commercial enterprises working on new methodologies suitable for industrial and commercial exploitation of biosolar energy.