Rapid plastic embedding is compatible with colorimetric detection following whole mount in situ hybridization in plant specimens

In performing in situ hybridizations, nonisotopic nucleic acid labeling cou pled with colorimetric detection offers a safer, easier and more rapid alte rnative to using radioactively labeled nucleic acid probes and microscopic autoradiography. Whole mount in situ hybridization is also advantageous, be cause many samples can be processed identically and the reduced handling of specimens greatly reduces the risk of exposing tissues to RNase(s). The th ickness of whole mount specimens, however, often prevents accurate determin ation of sites of expression within specific tissues. Although post-hybridi zation embedding and sectioning is a solution to this problem, the precipit ate formed following the common colorimetric detection procedure is soluble in the organic solvents used for dehydration prior to embedding. We have d eveloped a dehydration and embedding procedure that takes advantage of the compatibility of L.R. White(R) resin containing 10% (v/v) polyethylene glyc ol 400, and heat polymerized. The addition of the plasticizer allows L.R. W hite(R) embedded tissues to be sectioned at 10 mum providing excellent sign al contrast.