Copper chelation of nitrosotyrosine has been found useful for histochemical localization for tyrosine in thick, fresh sections of large celled plant tissues. The nitrous acid reaction for ortho-dihydroxyphenolics also has been found useful for localization of chlorogenic acid, caffeic acid and dihydroxyphenylalanine in plant tissues. Application of these tests separately to serially adjacent sections demonstrated the distribution of tyrosine and chlorogenic acid in different plant tissues. Tests tube reactions on known substances verified specificity and also demonstrated that the presence of other amino acids and phenolics did not interfere with the positive test for tyrosine. The color reactions are sufficiently intense for stereoscopic microscopy and tested sections may be measured photometrically. Further adaptability of the nitrosotyrosine-metal chelate reaction to procedures for ultrastructural localization is suggested.
HISTOCHEMICAL DIFFERENTIATION BETWEEN TYROSINE AND CHLOROGENIC ACID IN PLANT TISSUES I. NITROUS ACID REACTIONS AND METAL CHELATION OF NITROSOTYROSINE
