Tony Miller

Dr. Tony Miller

Tony Miller now works at the John Innes Centre
Click here for his new page.

Research Leader: Rhizosphere biology and plant nutrition

Welcome to the home pages of the Plant Root Physiology Group, Plant Pathology and Microbiology Department of Rothamsted Research.

In these pages we provide a description of recent research including some details of the techniques used..

Below is a diagrammatic representation of a two-barrelled ion-selective microelectrode impaling and measuring ion concentrations in a plant cell. To find out more about this technology including a full description of how to make these electrodes see the techniques section.

Outline of Current Research

microelectrode measuring nitrate in leaf cells

Nutrient research

Our research uses multidisciplinary approaches to explore the processes sustaining nutrient acquisition and use by plants. It is a part of a Rhizosphere Biology Programme.

The aims of the research are:

The functional characterisation of genes encoding transporter proteins
The electrophysiological analysis of transport phenomenon
The partitioning of nutrients within the plant and their interactions with metabolism
The dynamics of nutrient uptake at the whole plant level and in the field

Maintaining crops with optimal nutrition often requires the application of excess fertiliser resulting in wasteful and damaging loss to the environment. Furthermore, adequate nutrition is important, not only for maintaining growth and yield, but also for optimising plant resistance to other stresses including diseases and pests. Matching the demand of the crop to soil supply to optimise yield by minimising leaching is the goal.

The object of this research is to understand how crops intercept nutrients in the soil and how allocation of nutrients to the different parts of the plant is achieved. An important aspect is the identification of nutrient deficiency stresses and the study of plant mechanisms of adaptation.

A major target for the future is to develop new transgenic cereal crops that can maintain yields under stress and in conditions that would currently constitute nutrient deficiency. In addition, within the programme there are projects aimed at the application of this knowledge to the development of methods for nutrient deficiency diagnosis.

In summary, the programme aims to:

Improve plant processes involved in nutrient uptake and utilisation
Minimise damaging environmental effects of excessive fertiliser use
Develop diagnostic tests for nutrient deficiencies

The work focuses on major UK arable crops such as oilseed (above left), wheat, and barley (below left); with some individual projects on crops such as potato and maize (above right) and on basic research utilising the model plants Arabidopsis (below center) and Chara (below right). N, P and S are the main nutrients under consideration.

Nitrogen research

The efficient use of applied nitrogenous fertilisers depends on understanding how the plant cell senses and responds to changes in the external supply of nitrogen. Several different techniques are being used to measure the nitrogen status of plants, these range from whole tissue digest analysis to single cell sampling methods including the use of ion-selective microelectrode measurements.

In cereals and the model plant Arabidopsis, nitrate- and ammonium-selective microelectrodes are being used to identify how cellular concentrations of these forms of nitrogen change during conditions of N surplus and deficiency.

The genetic manipulation of the expression of nitrate transporters in Arabidopsis is being used to identify the best strategies for the improved N-use in crop plants. This information is also important for conventional breeding programmes aimed at developing more sustainable crops, which can maintain yield and quality but that require lower fertiliser inputs.

The research also links with nitrogen diagnostics research undertaken by Malcolm Hawkesford and Peter Barraclough in the Plant Science Deaprtment. Research on nutrient cycling in the rhizosphere is done in collaboration with Penny Hirsch.

Measuring nutrients in the rhizosphere, the interface between the root and soil, using microelectrodes.

Other nutrient research

Other research in the group includes the characterisation of plant sugar carriers by expressing the proteins in Xenopus oocytes ( see techniques). Photosynthetic carbon fixation in higher plants is an important factor determining plant growth and crop yield. The initial fixation of CO₂ in plants occurs in chloroplasts and the product, usually sucrose, is exported from source tissues into the phloem for long distance transport to sink tissues for either storage or growth. Sucrose concentration in the apoplast has been estimated at about 2-5 mM which is much lower than sucrose concentration (>100 mM) in phloem. Sucrose loading into the phloem and sink tissues therefore requires energy input and occurs by cotransport with protons. The processes which can regulate the activity of these membrane carrier proteins are being resolved.

The effects of salinity on crop plants is also being studied using ion-selective microelectrodes (see techniques) to measure how single cells cope with salt stress. This is an increasing problem in agriculture so an understanding of the cellular mechanisms of tolerating salinity is important for breeding crop species that are better able to withstand this stress. One of the mechanisms of toxicity occurs when cells are no longer able to prevent accumulation of lethal concentrations of salt in the cytoplasm of the cell. The cytoplasm is the important intracellular compartment for the life processes. Ion-selective microelectrodes are used to measure the concentrations of salts (sodium, potassium, chloride) in the cytoplasm.

In depth coverage of Ion-selective microelectrodes

In depth coverage of Heterologous expresion in Xenopus oocytes

Some Current Projects

1. Root Developmental Responses to Heterogeneous Water and Nitrogen Supply

2. Soil Sensors for Nitrogen Availability

3. Establishing the role of IAA and plant indole compounds in nematode infection

4. Engineering rice nitrate transporters to improve N use efficiency

5. Nitrapool: Identification of the factors controlling nitrate pools in plant cells

6. NIP aquaporins: new tools to reduce arsenic accumulation

7. Decreasing arsenic accumulation in rice to reduce health risk.

8. The influence of roots on soil structure: physio-chemical implications

9. Modelling the path to better soil-applied pesticides (Syngenta)

Collaborations