hortonp

Em Prof Peter Horton FRS

Emeritus Professor of Biochemistry
+44 (0) 7714202652
p.horton@sheffield.ac.uk

General

Career History

  • 2014 - present: Chief Research Advisor, Grantham Centre for Sustainable Futures, University of Sheffield
  • 2008 - present: Emeritus Professor of Biochemistry, Department of Molecular Biology and Biotechnology, University of Sheffield
  • 2008 - 2014: Research Advisor, Project Sunshine, Faculty of Science, University of Sheffield
  • 1990 - 2008: Professor of Plant Biochemistry, University of Sheffield
  • 1989 - 2003: Chairman, Robert Hill Institute, University of Sheffield
  • 1978 - 1990: Lecturer/Reader, Department of Molecular Biology and Biotechnology University of Sheffield
  • 1975 - 1978: Assistant Professor, Department of Cell and Molecular Biology, State University of New York at Buffalo, USA
  • 1973 - 1975: Postdoctoral Research Associate, Department of Biological Sciences, Purdue University, USA
  • 1970 - 1973: D.Phil student, Department of Biology, University of York
Research

Interdisciplinary approaches to sustainable food security

fig1

Food is a basic human need and its production and consumption are embedded in all aspects of our society. Food Security has been defined as a situation that exists when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life. Characteristics of achieving food security include: high agricultural productivity; stability to changes in weather and markets; resilience to stresses and shocks; and equity in supply. Sustainability is a term also broadly set out, as meaning meeting the needs and aspirations of the present without compromising the ability of future generations to meet theirs. Therefore Sustainable Food Security means reconciliation of the frequently conflicting environmental, social equity and economic demands. Successful research aimed at reaching this goal is unlikely to be confined within single disciplines but will inevitably have to integrate many, in science, engineering, social science and medicine. Whilst enhanced agricultural production with new technology is a pre-requisite it will not on its own be sufficient. The challenge is how to integrate research across disciplines such that farmers, agri-food industries, policy makers and consumers have the evidence upon which to make the best decisions and interventions.


1. Delivering sustainable food security: analysis of agri-food ecosystems

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It is now widely accepted that our food supply systems are in crisis, whether on the national or global scale. The implementation of an agri-tech strategy takes place in the context of a food supply system in crisis. Disruptions in supply due to extreme weather events, over-reliance on scarce or expensive inputs, increased energy costs, increasing demand from an increasing population, major contributions to greenhouse gas emissions, changing food consumption patterns, growing number of links between human health and the food we eat, and the increased complexity of global food supply chains are some of the factors involved. Current systems and practices not only deliver insufficient food but are economically and environmentally unsustainable, and risk social upheaval, political unrest and a human health disaster.

Achieving adequate food production, ensuring environmental sustainability and promoting human health, impinge on all aspects of the food supply chain. Despite these constraints, farmers, producers and retailers have to retain adequate profit margins whilst food prices stay within the budgets of the consumer. However, forming effective business strategies, coherent agrifood policies and appropriate research and development programmes across such a complex system presents major challenges. How do we take the right actions in the right place at the right time? How do we optimise such actions for maximum benefit and desired outcome? How do we decide which are the most desirable outcomes? Inevitably there will be trade-offs, throughout the food supply chain. eg high yield potential of a crop variety may be incompatible with maximum stress tolerance; maximum levels of production may not be environmentally sustainable; low food prices may be inconsistent with farm profitability or high nutritional value. Making decisions about what trade-offs are practical and acceptable is the critical challenge we face and needs a multidisciplinary effort in which scientists, engineers and social scientists work together in collaboration with farmers, food producers, retailers and consumers to provide specific and practical solutions. Such an unprecedented level of integration in the agri-food sector is a significant challenge.

Extension of the agroecological approach to encompass the entire food production and consumption chain is a promising way forward. Such an agri-food ecosystem would have four key elements: agricultural and land use strategy; crop production and harvesting; processing, storage and distribution; retailing and consumption, and would require:

1. Description of all the people, components and processes within a unified internally consistent framework
2. Analysis to understand how it evolved (by selection or design) and how it works (dynamics, feedbacks)
3. Systems approaches to quantify it in a transparent accessible form
4. Simple models to predict outcomes under a range of scenarios

Waste and losses can then be identified and measured together with all of the environmental and social penalties. The impact of actions of key stakeholders (landowners, farmers, agricultural centres, agrifood industry, distributers, traders, consumers) and the external factors (governments, international agencies, markets, lobbyists; NGOs; science and technology, education, media, culture) can all be assessed.

It is only by reaching this level of analysis and understanding can we hope to implement the right innovation at the right time in the right place. The effects of intervention and change could be predicted and key questions answered. eg What might be the effect of a change in a particular aspect of consumer choice on crop production and resource use. What would be the implications for the food producer, retailer and consumer of a change to a more sustainable and resilient crop production, through a new plant variety or agronomic practice. Where are the pressure points or sites of greatest sensitivity to change? Where are the hotspots in terms of resource use, environmental effects or waste? How do we adapt to climate change? What are the barriers to uptake of new technologies? How can we accommodate the huge diversity of crops and farms?


2. Optimisation of photosynthesis for increasing crop yield

fig3Measurements of rice leaf photosynthesis carried out at the International Rice Research Institute in the Philippines show that for significant periods of the day, photosynthetic activity was far below capacity. Causative factors included: closure of the stomata shutting off the supply of carbon dioxide to the leaves; reduction in the efficiency of light collection by the chloroplasts; and feedback from the accumulation of carbohydrate products of photosynthesis.


To provide more crop yield on less land with fewer inputs undoubtedly requires alteration to the fundamental physiological attributes of plants. Included in these is the increase in efficiency of photosynthesis. Many approaches are being taken to achieve this goal, most of which involve alteration of parts of the basic photosynthetic machinery. An alternative approach arises from observation made on rice photosynthesis, done in collaboration with the International Rice Research Institute. This work revealed some striking insights, mainly how poor photosynthesis was in the field, even under conditions widely regarded as optimum. The conclusion from this study is important: there is enough photosynthetic activity in the existing cellular machinery to sustain a much larger yield if only plants could be induced to perform at their full potential. So why don’t plants perform at their full potential? One reason why photosynthetic activity is not maximally expressed could be inappropriate optimisation. Put simply, stability and survival (a low risk strategy) in the natural environment are driving forces of evolution, not necessarily high growth rate and photosynthetic rate (a high risk strategy) even though there is potential for high grain yield. Photosynthesis is held back below its potential because growth is optimised in the face of the particular properties of the plant’s habitat. Therefore, we have to consider the evolution and basic biology of each crop species.

Particularly important is that the environment is never constant- there are fluctuations in levels of sunlight, temperature and rainfall. Plants record, memorise and (try to) predict their environments to ensure that they always have enough energy storage from photosynthesis to power their growth and development. For example, plants have to determine the size of their reproductive sinks (i.e. grain capacity) in advance, predicting what the photosynthetic rate will be to give maximum grain filling. Over-estimation of future photosynthesis results in poor grain filling and/or poor quality grain; under-estimation of future photosynthesis results in a decrease in the efficiency of solar energy use and losses of potential productivity. Trade-offs inevitably result from optimisation of the internal regulatory mechanisms involved (dynamic range, kinetics, precision), and this readily explains the apparent under-performance of photosynthesis. Consequently, there may be opportunities for the breeding of higher yielding crops by tailoring regulatory responses to specific agricultural scenarios, where man’s intervention has moderated some of the environmental constraints on productivity, by irrigation, provision of fertilisers and elimination of weeds. A key point is that optimisation will vary according to plant species or variety, the climate and season, the agronomic practice, the locality and so on. Thus, significant benefits will come from understanding at the molecular and genetic levels how to alter the optimisation of the biochemistry and physiology of individual leaves, their performance in the whole plant, and the way individual plants interact in the crop canopy. Indeed, such knowledge may also be necessary to offset the inherent conservatism of plants that could thwart current attempts to increase photosynthetic efficiency, and hence yield, by manipulation of with the basic biochemical processes of carbon assimilation.


3. Understanding photoprotection in plants

fig4The photosystem II complexes undergo reversible changes in lateral organisation in the chloroplast thylakoid membrane in response to excess light intensity: in the dissipation mode their aggregation creates a cluster of complexes in which the xanthophyll pigments are brought closer to chlorophylls, creating a new energy transfer pathway leading to non-radiative decay of excited states.


Molecular transitions regulate the structure and function the photosynthetic membrane in order to adapt its function to different environmental and metabolic conditions. Multidisciplinary investigations have provided insights into these transitions, combining biochemical and structural analysis of purified proteins with spectroscopic, physiological and genetic analyses of intact systems. In order to maximise their use of light energy in photosynthesis, plants have light-harvesting antennae, which collect light quanta and deliver them to the reaction centres, where energy conversion takes place. The functioning of the antenna responds to the changes in the intensity of sunlight encountered in nature. In shade, light is efficiently harvested in photosynthesis. However, in full sunlight or whenever there is a restriction on the metabolic demand for photosynthetic product (eg in cold conditions), much of the energy absorbed is not needed and vitally important switches to specific antenna states safely dissipate the excess energy as heat. This is essential for plant survival because it provides protection against the potential photo-damage of the photosynthetic membrane. The understanding the molecular mechanisms involved in photoprotection has the potential to be exploited to produce crops plant better adapted to harsh environmental and climatic conditions.


Selected publications

Horton P, Koh SCL, Shi Guang V (2016) An integrated theoretical framework to enhance resource efficiency, sustainability and human health in agri-food systems. Journal of Cleaner Production 120: 164-1269

Horton P (2012) Optimisation of light harvesting and photoprotection – molecular mechanisms and physiological consequences. Philosophical Transactions of the Royal Society London B 367: 3455-3465

Kruger T, Ilioaia C, Johnson MP, Ruban AV, Papagiannakis E, Horton P, van Grondelle R (2012) Controlled disorder in plant light-harvesting complex II explains its photoprotective role. Biophysical Journal 102: 2669-2676

Murchie EH, Pinto M, Horton P (2009) Agriculture and the new challenges for photosynthesis research. New Phytologist 181: 532-552

Ruban AV, Berera R, Ilioaia C, van Stokkum IHM, Kennis JTM, Pascal AA, van Amerongen H, Robert B, Horton P, van Grondelle R (2007) Identification of a mechanism of photoprotective energy dissipation in higher plants. Nature 450: 575-578

Kovács L, Damkjær J, Kereïche S, Ilioaia C, Ruban AV, Boekema EJ, Jansson S, Horton P. (2006) Lack of the light harvesting complex CP24 affects the structure and function of the grana membranes of higher plant chloroplasts. The Plant Cell 18: 3106-3120

Wentworth M, Murchie EH, Gray JE, Villegas D, Pastenes C, Pinto M, Horton P. (2006) Differential adaptation of two varieties of common bean to abiotic stress. II. Acclimation of photosynthesis. Journal of Experimental Botany 57: 699-709

Ruban AV, Wentworth M, Yakushevska AE, Andersson J, Lee PJ, Keegstra W, Dekker JP, Boekema EJ, Jansson S, Horton P (2003) Plants lacking the main light harvesting complex retain PSII macro-organisation. Nature 421: 648-652

Horton P (2000) Prospects for crop improvement through the genetic manipulation of photosynthesis: morphological and biochemical aspects of light capture. Journal of Experimental Botany 51: 475-485









































Publications

Journal articles

Chapters

Conference proceedings papers

  • Kruger T, Ilioaia C, Johnson M, Ruban A, Papagiannakis E, Horton P & van Grondelle R (2012) Controlled disorder in plant light harvesting complex II explains its photoprotective role. ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, Vol. 243
  • Ilioaia C, Kruger T, Johnson MP, Horton P, Ruban AV & van Grondelle R (2011) Fluorescence dynamics of plant light harvesting complexes studied by single molecule spectroscopy. EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, Vol. 40 (pp 176-177)
  • Romano P, Hisabori T & Horton P (2006) The role of immunophilins in the regulation of the composition of the photosynthetic apparatus. PLANT AND CELL PHYSIOLOGY, Vol. 47 (pp S105-S105)
  • Horton P (1996) Nonphotochemical quenching of chlorophyll fluorescence. LIGHT AS AN ENERGY SOURCE AND INFORMATION CARRIER IN PLANT PHYSIOLOGY, Vol. 287 (pp 99-111)
  • Pascal AA, Ruban AV, Young AJ & Horton P (1995) The effect on pH on LHCII. PHOTOSYNTHESIS: FROM LIGHT TO BIOSPHERE, VOL I (pp 247-250)
  • Ruban AV & Horton P (1995) Regulation of Non-Photochemical Quenching of Chlorophyll Fluorescence in Plants. Australian Journal of Plant Physiology, Vol. 22(2) (pp 221-221)
  • Ruban AV, Young AJ & Horton P (1995) Quenching of chlorophyll fluorescence in the minor chlorophyll A/B binding proteins of photosystem II. PHOTOSYNTHESIS: FROM LIGHT TO BIOSPHERE, VOL I (pp 295-298)
  • McAuley CA, Dyer TA & Horton P (1995) Genetic manipulation of LHCB4, a gene encoding one of the minor light-harvesting complexes, in Arabidopsis thaliana.. PHOTOSYNTHESIS: FROM LIGHT TO BIOSPHERE, VOL I (pp 327-330)
  • Walters RG & Horton P (1995) DCCD binds to lumen-exposed glutamate residues in LHCIIc - Implications for the mechanism of photoprotective energy dissipation. PHOTOSYNTHESIS: FROM LIGHT TO BIOSPHERE, VOL I (pp 299-302)
  • Webster JI, Young AJ & Horton P (1995) Carotenoid composition of Digitalis purpurea in relation to non-photochemical quenching.. PHOTOSYNTHESIS: FROM LIGHT TO BIOSPHERE, VOL I (pp 123-126)
  • HORTON P, NOCTOR G & REES D (1990) REGULATION OF LIGHT HARVESTING AND ELECTRON-TRANSPORT IN PHOTOSYSTEM-II. PERSPECTIVES IN BIOCHEMICAL AND GENETIC REGULATION OF PHOTOSYNTHESIS, Vol. 10 (pp 145-158)
  • WRIGHT DP, SCHOLES JD, HORTON P, BALDWIN BC & SHEPHARD MC (1990) THE RELATIONSHIP BETWEEN THE DEVELOPMENT OF HAUSTORIA OF ERYSIPHE-GRAMINIS AND THE ENERGY STATUS OF LEAVES. CURRENT RESEARCH IN PHOTOSYNTHESIS, VOLS 1-4 (pp D223-D226)