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Karin Weitbrecht, Dipl.-Biol.

Email: karin.weitbrecht@biologie.uni-freiburg.de
Phone: ++49-761-203-2669 (office group Leubner)
Phone: ++49-761-203-2808 (lab)

Research interests:
  • Seed germination
  • Plant cell walls
  • Plant homones
  • Biomechanics of seed germination
  • Early stages of seed germination

Academic career
Publications and presentations at conferences

My PhD project: vSEED - biomechanics of seed germination
Project background
Seed model systems
Methods used in this project
Puncture-force measurement of endosperm weakening



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My PhD project: vSEED - biomechanics of seed germination

Project summary: The ERA-NET PG project vSEED aims at a dynamic mathematical description of germination and the development of a virtual seed combining data from different research areas.

Our task in Freiburg within the vSEED project is to investigate the biomechanics of Lepidium sativum (cress) and Arabidopsis seed germination. This includes the establishments of methods and measurements of
• puncture-force of micropylar endosperm of cress and Arabidopsis
• tensile strength of strips of the micropylar endosperm of cress
• cell extension and/or separation during radicle growth and endosperm weakening of cress and Arabidopsis
• vacuoloation and turgor pressure in the micropylar endosperm and radicle of cress and Arabidopsis
• water uptake and volume changes during the germination process of cress and Arabidopsis.

A second focus in our research is an investigation of the early stages of seed germination, that is the processes that precede and lead to testa rupture in Arabidopsis and cress.

People: Kerstin Müller as vSEED postdoc and Karin Weitbrecht as vSEED PhD student.

Collaborations: See the vSEED-webpage for further information on the project and collaborating labs.

 


 




 

Academic career

   
     




















 
 




 
Earlier work (Diplomarbeit): Phytopathology - The role of ß-1,3-glucanases in the defense against biotroph pathogens of grapevine.
A collaboration with Dr. Hanns-Heinz Kassemeyer, Staatliches Weinbauinstitut Freiburg, Dept. Biologie & Phytopathologie:
Webpage "Weinbauinstitut"
 
   




 

Seed model systems

 

In this project, we combine the advantages of two model systems: We use the established system Arabidopsis thaliana (Brassicaceae) and the emerging seed model system Lepidium sativum (garden cress, Brassicaceae).

While Arabidopsis has the many advantages resulting from a sequenced genome and a large amount of available data, mutants and method, it has its limits as a seed model system has its limits. Most of these limits are due to the small size of Arabidopsis seeds. It is for example not possible to directly quantify endosperm weakening by measuring puncture force in Arabidopsis. Our solution to this problem was using a closely related species with highly similar seed anatomy and germination pattern, but with bigger seeds. We chose Lepidium sativum which is in the same Brassicaceae subfamily as Arabidopsis, but has seeds are about ten times the size of Arabidopsis seeds.

For further details on these seed model systems see the "Seed structure" and "Endosperm weakening" webpages and the Müller et al. (2006) publication.


Seed size Brassicaceae

 




 

Methods used in this project

Our methods range from physiological and biomechanical to molecular and biochemical approaches:
 
 

Puncture-force measurement of endosperm weakening

 

Puncture force measurements are a useful method requiring a suitable seed system, a detailed description and discussion of the technique is published in Müller et al. (2007). The choice of the seed system for puncture force experiments strongly influences the experimental options the method offers. It is essential that the seeds are large enough to be fixed properly and leave space for the metal probe to be lowered onto the tissue with no or very little friction. In an optimal seed system for puncture force experiments it should be possible to puncture the individual seed coats (testa, endosperm) separately in order to be able to assign the weakening to a specific seed cover.

We measure puncture force of Lepidium seeds by using a custom-made machine (Figure A,B, on the right). A seed is cut in half and the radicle tip carefully removed, leaving the empty but intact endosperm cap. A metal probe shaped roughly like the radicle tip is slowly lowered into the endosperm cap. The force it takes to rupture the endosperm, the puncture force, is calculated from the size of the peak that signifies the pressure on the endosperm tissue. The lower the puncture force, the softer the tissue. (Figure C, below).


Puncture force method

Puncture force machine

Figure. Puncture-force method for measuring endosperm weakening of Lepidium.

Müller K, Heß B, Leubner-Metzger G. A role for reactive oxygen species in endosperm weakening.
In: Adkins S, Ashmore S, Navie S (eds). Seeds: Biology, Development and Ecology.
CAB International, Wallingford, UK. Chapter 30, pp. 287-295 (2007)
 
     




 

Publications and presentations at conferences

   


Peer-reviewed publications


Papers in conference proceedings and poster presentations


Oral presentations



 
     
     


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