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Chromosome Isolation in Wheat

  1. Harvest root tips (1 cm) and transfer them into deionized H2O.
  2. Immediately transfer root tips into 25 ml of 2 % formaldehyde fixative and fix at 5°C for 20 min.
  3. Wash roots in 25 ml of Tris buffer three times for 5 min at 5°C.
  4. Excise root meristems and transfer them into 5-ml polystyrene tube containing 1 ml of LB01 lysis buffer (pH 9.0).
  5. Isolate chromosomes by homogenising at 20000 rpm for 10 sec.
  6. Filter the suspension through a 50-µm nylon mesh into 5-ml polystyrene tube.
  7. Store the suspension on ice.
  8. Transfer 50 µl of chromosome suspension into a 0.5-ml PCR tube.
  9. Add 1 µl of DAPI stock solution.
  10. Place a small drop (~ 10 µl) of DAPI-stained suspension on a microscope slide.
  11. Observe under a fluorescence microscope with low magnification (10 - 20x lens). Do not cover by a coverslip.

Notes

Approximately 30 root tips are used to prepare one sample (1 ml of chromosome suspension). 
The suspension should contain intact nuclei and chromosomes. The concentration of chromosomes in the sample should be 5 x 105 / ml or higher. If the chromosomes are damaged (broken and/or appear as long extended fibres) than the formaldehyde fixation was too weak and should be prolonged. If the chromosomes are aggregated and/or the cells remain intact, then the fixation was too strong and should be shortened. 
Although the chromosome suspension can be stored overnight, it is recommended to analyse the chromosomes on the same day of isolation. 

References 

Vrana J, Kubalakova M, Simkova H, Cihalikova J, Lysak MA, Dolezel J. Flow-sorting of mitotic chromosomes in common wheat (Triticum aestivum L.). Genetics 156: 2033 - 2041 (2000) Abstract PDF 
Kubalakova M, Vrana J, Cihalikova J, Simkova H, Dolezel J. Flow karyotyping and chromosome sorting in bread wheat (Triticum aestivum L.). Theoretical and Applied Genetics 104: 1362 - 1372 (2002) Abstract