Hi Alex,

RNA later or simlar formulations from differen companies are available for conserve plant material for some days. These chemicals even at room temperature ....You may use such chemicals for tissue collection on field and later RNA isolation in the lab

bye

I asked a colleague and his opinion was that you might take a pestle and mortal, and grind some fresh sample into CTAB buffer (as you might for DNA extraction). The idea being that the buffer would separate the RNA from the RNAse proteins that do most of the damage. When you get back to the lab you can do an RNA extraction from the buffer mixture. I guess you'd need to try it out, sorry I don't have a reference for this method.

If you have the resources to buy a very nice dewar (eg http://sementanks.com/) they will hold liquid nitrogen for several weeks. We do this for our field studies- even in the salt marsh, but this may be difficult at very remote field sites.