TRIreagent

Any..... cell homogenization is your main problem

Try the Plant Total RNA Purification Kit from Norgen, it's pretty robust... be sure to ask for a sample kit so you can test it out before investing anything :)

Jaroslaw Krol Thank you for your suggestion. Do you know which method is more efficient in plant cells disruption, grinding plant tissues with mortar and pestle using liquid nitrogen or using ceramic beads and vortex or homogenizer?

Malgorzata Majewska Hi, well If you ask me what I would do to be sure .... I would take my frozen samples and grind them first with liquid nitrogen .... then collect everything and homogenize cells using smaller beads. this way you should brake all the cells and extracting RNA should be easy using any method.

Jaroslaw Krol Thank you a lot.

Thank you all of you for your help.

You might give a try to Qiagen Plant RNeasy kit, this gave me the best results in wheat leaves and roots, i also tried http://m.biobudget-shop.de/p/rnamagic--/0/1

and a home made protocol with citric acid buffer (Oñate,2008).

I think is very critical the homogenization method... i have noticed that when some melting is produced in grounded samples, RNA degrades very fast... so better only to used mechanical grounding methods that keeps the samples frozen