Photosynthetic organisms often face rapid and large fluctuations in light intensity. High light exposure increases the fraction of "unused" excitation in the photosynthetic membrane which is potentially harmful, resulting in a long-term reduction in plant/algal productivity called photoinhibition . The most sensitive to light component of photosynthesis is Photosystem II (PSII) reaction center (RCII). Hence PSII has evolved a mechanism that works to protect RCII against excess light via a prompt opening of a channel which dissipates excess absorbed light energy harmlessly as heat, a process called NPQ . A knowledge of the effectiveness of photoprotection (NPQ) is of paramount importance to predict the consequences of climate change to our planet’s plant communities and, most importantly, for the possible improvement of their survival during periods of drastic environmental perturbations .
NPQ and photoinhibition both diminish the efficiency of PSII. The Ruban laboratory is one of the leading groups in the world that works on protection of the photosynthetic apparatus against photodamage. It has developed a methodology that enables to separate these effects and most importantly quantify the extent of light tolerance by plants [4-7]. Monitoring the dependence of PSII efficiency and NPQ during the progressive increase in the illuminating light intensity produces unique experimental data that can be analysed in order to obtain critical light intensity that causes photoinhibition and maximum levels of NPQ that can pant develop in order to protect all RCII’s. The novel methodology uses pulse modulated chlorophyll fluorescence technique (PAM) that tracks the onset of photoinhibition. As a result of the use of this approach a number of new physiological quantitative parameters reflecting the functional state of PSII can be obtained: a) the maximum tolerable light intensity; b) the light intensity which would damage 100% of reaction centers; c) the minimum amount of NPQ required to protect plants from photodamage at a given light intensity. The effectiveness of the fast tracking of environmental light intensity by NPQ will be studied on various plant species, including crops like rice and wheat. Interactions between slow, acclimatory changes in the structure and functions of PSII and adjustments in the effectiveness of photoprotection will be investigated. Combination of cold and high light stress will be a special focus of this project.
Plant growth in a controlled environment (high vs low light acclimation). Cold acclimation. Plant physiology techniques based on chlorophyll fluorescence measurements (PAM). Techniques in analytical and computational modelling. Electron microscopy. Low-temperature and time-resolved fluorescence spectroscopy. Preparation of chloroplasts. Preparation of membrane proteins. Pigment analysis: HPLC.
The Ruban laboratory (http://webspace.qmul.ac.uk/aruban/research.htm) possesses a spectrum of instrumental and biochemical approaches that study the physiology, biochemistry and structure of the whole plant, cell, chloroplast, photosynthetic membrane and individual proteins and pigments. You will receive an extensive training in plant growth in a controlled environment; plant physiology techniques based on chlorophyll fluorescence measurements (PAM) and oxygen evolution; low-temperature and time-resolved fluorescence spectroscopy; analytical and preparatory biochemistry of membrane proteins, pigments and lipids (SDS gel electrophoresis, isoelectric focusing, FPLC, HPLC, westerns); electron microscopy techniques (freeze-fracture, thin sections, negative staining), confocal fluorescence microscopy and computational modeling.
KEYWORDS: light harvesting, photosynthetic membrane, reaction center, Photosystem II, photoinhibition, photoprotection, electron microscopy, fluorescence
Applicants wishing to apply for PhD funding through Science without Borders, CONACYT or the China Scholarship Council are welcomed, as are those applicants who can self-fund.
Applicants should be able to demonstrate that they can cover the cost of living expenses and tuition fees for a minimum of 3.5 years.
1. Ohad, I., D. J. Kyle, and C. J. Arntzen. 1984. Membrane protein damage and repair: removal and replacement of inactivated 32-kilodalton polypeptides in chloroplast membranes. J. Cell Biol. 99:481–485.
2. Ruban, A.V., Johnson, M.P. and Duffy, C.D.P. (2012) Photoprotective molecular switch in photosystem II. Biochim. Biophys. Acta, 1817, 167-181.
3. Ruban, A. (2013) The Photosynthetic Membrane: Molecular Mechanisms and Biophysics of Light Harvesting. Wiley-Blackwell, Chichester, ISBN: 978-1-1199-6053-9.
4. Ruban, A.V. and Belgio, E. (2014) The relationship between maximum tolerated light intensity and non-photochemial chlorophyll fluorescence quenching: chloroplast gains and losses. Phil. Trans. Royal Society of London B, 369, 20130222.
5. Ware, M.A., Belgio, E., Ruban, A.V. (2014) Comparison of the protective effectiveness of NPQ in Arabidopsis plants deficient in PsbS protein and zeaxanthin. Journal of Experimental Botany 66, 1259-1270.
6. Carvalho, F.E.L., Ware, M.A., Ruban, A.V. Quantifying the dynamics of light tolerance in Arabidopsis plants during ontogenesis. Plant
Cell & Environment, doi: 10.1111/pce.12574.
7. Ware, M.A., Belgio, E., Ruban, A.V. (2015) Photoprotective capacity of non-photochemical quenching in plants acclimated to different light intensities. Photosynth. Research, doi10.1007/s11120-015-0102-4.
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FTE Category A staff submitted: 23.39
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