The Plant Respiratory Redox Group
Allan Rasmusson, P.I.
Project descriptions
Molecular physiology of plant respiratory energy bypasses
 In plant respiration, carbon compounds are broken down in order to synthesise ATP, which provides the energy needed for cellular processes. Click on the image to the left to get a larger view. Carbohydrates and lipids are broken down to organic acids, which are transported to the mitochondria. These are small ex-bacteria that have been part of the eukaryotic cell for more than a billion years. Mitochondria oxidise the organic acids while reducing NAD+ to NADH. The NADH is oxidised and the electrons transferred to oxygen by the respiratory chain in the inner mitochondrial membrane (depicted in the image below). In this process, the complexes pumps protons across the membrane, creating a membrane potential used for the synthesis of ATP. The mitochondrially produced ATP is the main energy source for chemical reactions in virtually all eukaryotic cells (exceptions include some unicellular species that do not have mitochondria). However, plants have enzymes that prevent the conservation of energy.
 |
| General scheme for the respiratory chain and ATP synthesis in mitochondria. |
|
The first step of the electron transfer chain in animal mitochondria, the oxidation of NADH, is carried out by the proton-pumping complex I. Plant mitochondria differ by having additional non-proton-pumping enzymes - alternative NAD(P)H dehydrogenases and oxidases - in the electron transfer chain. Electron transfer through these enzymes will not be coupled to ATP synthesis and the efficiency of the respiratory process will be lower. So these enzymes bypass the energy conservation steps.
 |
| The respiratory chain in plants have energy bypass enzymes that are absent in animals. These allow larger flexibility in energy efficiency, in which substrates will be used, and in regulation. |
|
The project aims at elucidating cellular and physiological functions of different energy bypasses, especially the alternative NAD(P)H dehydrogenases, present in plants. Since these enzymes are not bound to energy conservation they have the possibility to regulate the levels of redox compounds like NADH and NADPH in different compartments in the cell. We recently demonstrated that one energy bypass enzyme is able to do this.
We have in later years defined the setup of genes that code for the NAD(P)H dehydrogenases, and assigned genes to particular enzymatic activities and regulation mechanisms. At the same time we have studied how the expression is affected by changes in major plant growth conditions like light, temperature and nitrogen, to see what processes the enzymes are associated with, and what processes may need cellular redox balancing by mitochondrial activity. Since changes in for example photosynthesis will cause large metabolic changes in the cell, efficient photosynthetic carbon dioxide fixation and sugar production need collaboration by the whole cell, also the mitochondrion.
The major approaches used is to:
- Follow expression of energy bypass genes under variable growth conditions and stressful challenges.
- Biochemically, search for novel regulatory mechanisms.
- In transgenic plants, find and directly verify the importance of the different energy bypasses for other processes in the plant.
Plant cell sensing and response to pH and redox
(Ida Lager)
Plants live in soils that vary considerably spatially and in time regarding nutrient composition and pH. Consistently, plants have to recognise and adapt to these changes by altering their structure and metabolism. The goal of this project is to characterize the responses to external pH and nitrogen source changes in plant roots. Plants encounter both nitrate ions and ammonium ions in the soil. The transcriptional effects of the nitrate ion have been investigated, but little is known about the effects of the ammonium ion. Addition of ammonium ions is inherently associated with pH changes. Bacteria and fungi have well developed external pH signalling systems that are involved in regulating many genes. In the plant field this is an area which to date is almost unexplored.
General aspects
Of major importance for these projects is that we have a wide knowledge of techniques, including for example transgenic plant construction and growth, but also that we can isolate, quantitate and/or study in isolation RNA, organelles, proteins and enzymes.
However, a small group of people cannot know everything. We collaborate with several other groups, including plant biologists and microbiologists at our Department, colleagues in other departments at Lund University, as well as several other groups in other countries that specialise in important subjects and/or methods that are needed for bringing the projects further.
The work in the group have in recent years been supported by Carl Tesdorpf's Foundation, the Swedish Research Council, Wenner-Gren Foundations, and Stiftelsen A. W. Bergstens donation.
Additional information about plants biology and respiration can be found in the textbook "Plant Physiology" that we contribute to. You can visit the homepage of this book.
Top of this page
Group home page
Department Home Page
 |
| Contact: Allan Rasmusson, Professor in Plant Physiology |
| Address: |
Department of Cell and Organism Biology,
Biology Building, Sölvegatan 35,
SE-223 62 Lund, Sweden |
Phone: +46 46 222 93 81 Fax: +46 46 222 41 13
E-mail:
Updated: 23 March 2008
Webmaster: |
|
