To obtain RNA from root hairs, the root hairs are physically isolated and purified from the roots of seedling plants using a method modified from that published in Lee et al, 2008.

1. Seedlings are grown under sterile conditions and the root portion is cut away from the shoot portion.
2. Next, depending on the root diameter, the roots are either:

(a) grasped with tweezers and quickly stirred in liquid nitrogen to break off the root hairs (used for smaller diameter roots)

OR

(b) placed into liquid nitrogen and stirred with glass rods to cause root hairs to break off from the roots (used for larger diameter roots).

3. Root hairs are then purified by filtration through a 250 um-mesh filter.
4. RNA is extracted using the RNeasy^® Plant Mini Kit (QIAGEN).
5. The purity of the root hair RNA preparations can be assessed by analyzing expression of root-cell-specific genes, such as isoforms of actin, expansin, scarecrow, shortroot, and/or plethora genes.

Reference:

Lee, Y., Bak, G., Choi, Y., Chuang, W.-I., Cho, H.-T., Lee, Y. (2008) Roles of phosphatidylinositol 3-kinase in root hair growth.  Plant Physiology 147:624-635.