I am assuming you are asking this in the context of chemical analysis of the tissues. You can use liquid nitrogen - it is by far the best method to prevent biochemical activity.

In terms of drying either Refractance Window drying or Atmospheric Freeze Drying will give equivalent results to conventional freeze drying yet being more economical. I hope I answered you.

Some people also use silica gels to dry plant tissues. What are you going to do later with those materials?

Following.