Leaf anatomy and photosynthesis

294 Pages·2016·10.43 MB·English

by  Herman Berghuijs

Leaf anatomy and photosynthesis:
Unravelling the CO diffusion pathway in C leaves
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Herman Nicolaas Cornelis Berghuijs
Thesis committee

Promotors
Prof. Dr P.C. Struik
Professor of Crop Physiology
Wageningen University

Prof. Dr B.M. Nicolaï
Professor of Biosystems Engineering
KU Leuven, Belgium

Co-promotor
Dr X. Yin
Senior scientist, Centre for Crop Systems Analysis
Wageningen University

Other members
Prof. Dr J. Molenaar, Wageningen UR
Prof. Dr B.M. Mulder, Wageningen UR
Prof. Dr M. de Proft, KU Leuven, Belgium
Prof. Dr W. Saeys, KU Leuven, Belgium

This research was conducted under the joined auspices of the C.T. de Wit Graduate School
for Production Ecology and Resource Conservation and the Arenberg Doctoral School.
Leaf anatomy and photosynthesis:
Unravelling the CO diffusion pathway in C leaves
2 3

Herman Nicolaas Cornelis Berghuijs

Thesis
submitted in fulfilment of the requirements for the joint degree of doctor at
Wageningen University
by the authority of the Rector Magnificus
Prof. Dr A.P.J. Mol
and doctor in de bio-ingenieurswetenschappen van de
KU Leuven
by the authority of the Director of the Arenberg Doctoral School
Prof. Dr G. Govers
in the presence of the
thesis committee appointed by
the Academic Board of Wageningen University
and
the Director of the Arenberg Doctoral School of the KU Leuven
to be defended in public
on Wednesday May 25, 2016
at 1:30 p.m. in the Aula, Wageningen University
Berghuijs, H.N.C.
Leaf anatomy and photosynthesis; unravelling the CO diffusion pathway in C leaves
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Joint PhD thesis, Wageningen University, Wageningen, NL; KU Leuven, Leuven, BE (2016),
286 pages
With references, with summaries in English and Dutch
DOI: 10.18174/379249
ISBN: 978-94-6257-794-7
Abstract
Herman Nicolaas Cornelis Berghuijs (2016). Leaf anatomy and photosynthesis;
unravelling the CO diffusion pathway in C leaves. PhD thesis. Wageningen
2 3
University, Wageningen, The Netherlands, with summaries in English and Dutch. 286
pages
Optimizing photosynthesis can contribute to improving crop yield, which is necessary
to meet the increasing global demand for food, fibre, and bioenergy. One way to
optimize photosynthesis in C plants is to enhance the efficiency of CO transport
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from the intercellular air space to Rubisco. The drawdown of CO between these
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locations is commonly modelled by Fick's first law of diffusion. This law states that
the flux from the air spaces to Rubisco is proportional to the difference in partial
pressure between these locations. The proportionality constant is the mesophyll
conductance. Its inverse is mesophyll resistance. Mesophyll resistance is a complex
trait, which lumps various structural barriers for CO transport and processes that add
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or remove CO along the diffusion pathway. In order to better understand how and to
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what extent these factors affect photosynthesis, it is necessary to find a more
mechanistic description of CO transport in the mesophyll. The aim of this dissertation
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is to investigate how leaf anatomical properties and CO sources and sinks along the
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CO diffusion pathway in C leaves affect the photosynthetic capacity of these leaves.
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In this study, Solanum lycopersicum was used as a model organism. In a first
approach, we developed a model in which we partitioned mesophyll resistance into
two sub-resistances. The model assumed that CO produced by respiration and
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photorespiration was released between the two sub-resistance components. By
quantifying these resistances using measured thicknesses, exposed mesophyll and
chloroplast surfaces, and assumed diffusive properties, we were able to simulate the
effect of various anatomical properties on photosynthesis. A disadvantage of this two-
resistance approach is that it assumes either that (photo)respiratory CO release takes
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place in the outer cytosol or that there is no CO gradient in the cytosol. Therefore, in
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a second approach we modelled CO transport, production and consumption by use of
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a reaction-diffusion model. This model is more flexible in terms of determining the
v
Abstract
location of CO sources and sinks. We developed methods to estimate physiological
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parameters of this model using combined gas exchange and chlorophyll fluorescence
measurements on leaves. The results suggest that the rate of respiration depends on the
oxygen partial pressure, which is often not considered in previous photosynthesis
models. We also presented a method to calculate the fraction of (photo)respiratory
CO that is re-assimilated. We found that this fraction strongly depends on both
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environmental factors (CO , irradiance), the location of mitochondria relative to the
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chloroplast, stomatal conductance and various physiological parameters. The reaction-
diffusion model and associated methods presented in this study provide a more
mechanistic framework to describe the CO diffusion pathway in C leaves. This
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model could, therefore, contribute to identifying targets to increase mesophyll
conductance in future research.
Keywords: CO diffusion, C photosynthesis, mesophyll conductance, mesophyll
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resistance, re-assimilation, photorespiration, respiration, tomato

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Table of contents

Chapter 1 General introduction 1

Chapter 2 Reaction-diffusion models extend our understanding of C leaf 13
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photosynthesis: opportunities and challenges.

Chapter 3 Modelling the relationship between CO assimilation and leaf 45
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anatomical properties in tomato leaves

Chapter 4 Localization of (photo)respiration and CO re-assimilation in 95
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tomato leaves investigated with a reaction-diffusion model

Chapter 5 Quantitative analysis of the effects of environmental and 145
physiological factors on the re-assimilation of (photo)respired CO ,
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using a reaction-diffusion model

Chapter 6 General discussion 221

References 245

Summary 259

Samenvatting 267

Acknowledgements 275

Curriculum vitae 281

List of publications 283

PE&RC Training and Education Statement 285

Funding 286

CHAPTER 1
General introduction
Chapter 1
1.1 Introduction
Photosynthesis can be defined as the process in which light energy is converted into
chemical energy (Reece et al., 2011). This process is of vital importance for life on
Earth; photosynthesis allows phototrophic organisms to convert sun light and
inorganic carbon into biomass. More specifically, in green plants, photosynthesis
refers to the conversion of CO from the atmosphere into sugars and other organic
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compounds. This assimilation of CO consumes energy. Green plants obtain this
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energy by the absorption of photosynthetically active radiation (PAR). Understanding
the mechanisms of photosynthesis in green plants is of interest from an agronomical
perspective. In 2009, the Food and Agricultural Organization (FAO) expected the
global population to increase by 34% to 9 billion people in 2050 (FAO, 2009a). In
order to fulfil this global demand for more food and production due to the growing
world population, the FAO estimated that the global food production had to increase
by 70% from 2009 to 2050 to meet the global demand for food, feed, and fibres (FAO,
2009b). This can be achieved in two ways; using larger areas of land for crop
production or increasing the efficiency of the production process (Ort et al., 2015).
Increasing of the efficiency of the process can be done by increasing the efficiency of
light absorption by crops, by increasing the conversion of absorbed light energy into
biomass and by increasing the harvest index (Long et al., 2006). During the second
half of the 20th Century, there have already been major improvements in increasing the
efficiency of the production process. Between 1960 and 2005, the global food
production has been increased by 160%, while the total area of cropland has only
increased by 27% (Burney et al., 2010). This increase of the global food production
can mainly be explained by the increase in harvest index. Although there is some
potential to further increase the efficiency of light absorption and the harvest index, the
scope of possibilities to further improve these is very limited (Long et al., 2006).
Therefore, further increase of crop yield can mainly be achieved by increasing the
conversion efficiency of absorbed light into biomass; i.e. by optimizing
photosynthesis. Zhu et al. (2010) identified several possibilities to further increase the
efficiency of photosynthesis. These possibilities include alterations at the canopy level,
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