The Use of Papain in Clearing Plant Tissues for Whole Mounts

Materials killed and fixed in FAA (formalin-acetic acid-alcohol) and similar fixatives frequently are difficult to clear for whole mounts because the denatured proteins will not become soluble in NaOH and other clearing agents. If tissues are washed for 3 days in running water, then incubated at 40 C for 5-7 days in 2% papain buffered to pH 7.2 and activated with 15 ml of. 02 M Na2S, cell contents are partly digested. Normal clearing with 5-10% NaOH followed by chloral hydrate (sat. aq.) can then effect complete solublility of cell contents and their removal. Permanent slides can be made after staining (1% safranin O in 50% alcohol for 12 hr is successful), by dehydration through alcohols, clearing in xylene, and mounting in resin.