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Novel imaging technique looks inside starch granules

11 February 2011

Starch is the major storage compound in plants, and a major component of cereal grains and so is an important part of our food.  For this reason BBSRC-funded scientists are keen to understand how it is made and stored by the plant, and how changes to the plants genes could affect the composition and properties of the starch in the grain.  IFR scientists have developed a method of visualising and measuring the properties of the starch in a developing maize kernel, revealing previously unidentified properties.  This could have a practical application in screening varieties for novel starch properties, or help in the selection of novel starches for industrial applications.

Starch is made up of a mix of two long sugar chains (polysaccharides), amylose and amylopectin.  Amylose is a long chain molecule, whilst amylopectin is much more branched.  The two different molecules combine to form starch granules within the cell, with amylopectin located in ordered, crystallised regions in the granule and amylose located in more unstructured regions. 

IFR scientists Klaus Wellner, Mary Parker and Vic Morris together with Dominique Georget at the University of East Anglia have developed a novel high-resolution method of characterising the properties of starch granule within seeds, and have used it to examine starch in a high-amylose maize mutant lacking an enzyme that adds branches to amylopectin molecules.  Examining starch granules in the intact seeds means that the effects of isolating starch do not change the properties of the granules and the patterns of heterogeneity within the seed are maintained.

The technique, Raman microscopy, uses the way molecules absorb and re-emit light to give information about the chemical and physical structure of the molecules.  This allows the structure of individual starch granules to be measured and compared with other granules in the seed.  The versatility of using Raman microscopy allows a number of different chemical and physical parameters to be mapped within the sample.

The researchers showed that the starch granules in normal maize are all very similar to each other, but the mutant starch granules showed large differences both within and between granules in the same cell, and between different cells in the seed.  The technique shows that marked differences can occur between starch properties in neighbouring cells.  The degree of heterogeneity was found to be much greater than had previously been reported for studies of isolated granules extracted from seeds. 

The spatial difference in the properties within seeds provides information on the structure of starch over time and during growth.  Analysis of the data suggested that the mutation in the branching enzyme leads to defects in the way the granules self-assemble that accumulate to produce the observed heterogeneity, rather than simply producing new homogeneous granular structures with different relative amounts of amylose and amylopectin.

The technique can be developed to provide more quantitative data, and the researchers believe that it could also be used to produce 3D image data sets for seeds.  Using Raman microscopy in this way could have a practical application in screening varieties for novel starch properties, potentially aiding in the selection of novel starches for specific industrial applications.

These imaging methods can also be used to study many other biological tissues. There is interest in using chemical imaging for determination of inflammatory status and cancer detection in intestinal tissue. Initial infrared mapping studies together with IFR scientist Anastasia Sobolewski have shown that it is possible to map the distribution of protein and polysaccharide in gut sections. Raman imaging could be applied to obtain high resolution images and to identify the changes in chemical composition for individual cells in normal and diseased tissue.

ENDS

Notes to editors

Reference: In situ Raman microscopy of starch granule structures in wild type and ae mutant maize kernels.  Wellner et al, Starch/Stärke (2010) DOI 10.1002/star.201000107

About BBSRC

BBSRC is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £470M in a wide range of research that makes a significant contribution to the quality of life in the UK and beyond and supports a number of important industrial stakeholders, including the agriculture, food, chemical, healthcare and pharmaceutical sectors.

BBSRC provides institute strategic research grants to the following:

  • The Babraham Institute
  • Institute for Animal Health
  • Institute for Biological, Environmental and Rural Studies (Aberystwyth University)
  • Institute of Food Research
  • John Innes Centre
  • The Genome Analysis Centre
  • The Roslin Institute (University of Edinburgh)
  • Rothamsted Research

The Institutes conduct long-term, mission-oriented research using specialist facilities. They have strong interactions with industry, Government departments and other end-users of their research.For more information visit: www.bbsrc.ac.uk

About Global Food Security

Global Food Security is a multi-agency programme bringing together the research interests of the Research Councils, Executive Agencies and Government Departments.

Through Global Food Security the partners are working together to support research to meet the challenge of providing the world’s growing population with a sustainable,  and secure supply of safe, nutritious and affordable high quality food from less land and with lower inputs.

Partner and sponsor organisations are:

  • Research Councils UK – comprising:
    • Biotechnology and Biological Sciences Research Council
    • Economic and Social Research Council
    • Engineering and Physical Sciences Research Council
    • Medical Research Council
    • Natural Environment Research Council
  • Department for Business, Innovation and Skills
  • Department for Environment, Food and Rural Affairs
  • Department for International Development
  • Food Standards Agency
  • Government Office for Science
  • Scottish Government
  • Technology Strategy Board

For more information about the food security challenge and Global Food Security visit: www.foodsecurity.ac.uk

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