2006-present PhD, Physiological Ecology group, Department of Plant Sciences, University of Cambridge.
1999-2006 BSc & MSc, Wageningen University and Research centre, Plant Science, Netherlands. Specialization: Greenhouse Horticulture.
1998-1999 Propedeutical year Horticulture, Hogeschool Delft, Netherlands.
Plants with the C4 pathway minimize photorespiration by concentrating CO2 around Rubisco in bundle sheath (BS) cells. The biochemical pump (C4 cycle) in mesophyll (M) cells uses phosphoenol-pyruvate (PEP) as a substrate and regeneration of PEP accounts for a net consumption of two ATP per CO2 released in BS cells. Retro-diffusion of CO2 through BS cell walls therefore represents an energetic inefficiency of the C4 pathway.
Important steps in CO2 fixation during C4 photosynthesis (Figure by O'Leary MH. (1988) Bioscience, 38 (5): 328-336). In red: ATP for PEP regeneration and retro-diffusion of CO2 from BS cells.
This loss of CO2 from BS cells or 'leakiness' (Φ, leakage relative to PEP carboxylation in C4 cycle) increases at low light intensity. The exact biochemical or biophysical mechanism underlying this increase in Φ is unclear. Since most C4 crop species develop dense canopies, where progressive self-shading of older leaves occurs, Φ could represent a considerable constraint to C4 crop productivity.
The model by Farquhar (1983) has recently been applied in a number of studies (Tazoe et al. 2006, 2008; Cousins et al. 2006, 2008) to estimate Φ, using simultaneous measurements of photosynthetic gas exchange and carbon isotope discrimination (Δ13C). Although these estimates under controlled conditions have shown that Φ could be substantial (15 to 40% of CO2 released in the bundle sheath subsequently leaks out), to date there have been no attempts to quantify Φ under field conditions. In this project we set out to do:
- Measurements under field conditions to estimate Φ both at leaf-level, by coupling gas exchange to Δ13C and at canopy-level by using net ecosystem CO2 exchange (measured by eddy covariance) in combination with diurnal sampling of carbon stable isotopes in canopy air to partition the impact of respiration, photosynthetic uptake and f.
- Measurements under controlled conditions to study the short- medium- and long-term dynamics of bundle sheath leakiness as a function of the surrounding microclimate. In particular, the reasons and possible mechanism underlying changes in Φ caused by low light will be studied extensively.
- Modelling of (steady state) production and (optimal) distribution of ATP and NADPH in C4 photosynthesis under various light intensities, temperatures and O2 concentrations.
Professor Howard Griffiths (Physiological Ecology group, Department of Plant Sciences, University of Cambridge)
Dr Hans Schepers (Seminis, Wageningen, The Netherlands)
Alexander James Keith Studentship.
A unique collaboration with Trinity College Dublin and Teagasc (Irish agricultural research) provides technical and logistical support from the European commission framework programme 'Infrastructure for Measurement of the European Carbon Cycle' to perform field measurements at Teagasc field research stations 'Oak Park' (Carlow) and 'Johnstown Castle' (Wexford), Ireland.
Johannes Kromdijk, Hans E. Schepers, Fabrizio Albanito, Nuala Fitton, Faye Carroll, Michael B. Jones, John Finnan, Gary J. Lanigan, Howard Griffiths (2008). Bundle sheath leakiness and light limitation during C4 leaf and canopy CO2 uptake. Plant Physiology, DOI:10.1104/pp.108.129890.
J. Kromdijk, F. Albanito, N. Fitton, G. Lanigan, J. Finnan, F. Carroll, M. Jones, H. Schepers and H. Griffiths (2008). Is CO2-uptake by C4-grass canopies limited by leakage of CO2 from bundle sheath cells? Geophysical Research Abstracts Vol.10, EGU2008-A-05198. Abstract)
Hans Schepers, Wanne Kromdijk and Olaf van Kooten, The Conveyor Belt Model for fruit bearing vegetables: Application to Sweet Pepper Yield Oscillations. Presented on international symposium 'Hortimodel', on models in protected cultivation, November 2006, Wageningen. In: Acta Horticulturae, 2006.
Hans Schepers, Wanne Kromdijk and Olaf van Kooten, Innovation-oriented Analysis of Critical Control Points (IACCP): Who wishes to solve Sweet Pepper Yield Oscillations? Presented at conference 'Managing Quality in Chains', August 2006, Bangkok. In: Acta Horticulturae, 2006.
Kromdijk, W. (2005) Who wishes to solve Sweet Pepper oscillations? Crop model assisted innovation in horticulture. Agrotechnology & Food Innovations - Wageningen University & Research centre, report 521.
Kromdijk, W. (2003) Overexpression of tomato-phytochromes in Arabidopsis. Photomorphogenesis group, Department Plant Sciences, Wageningen University & Research centre.