Histological and Histochemical Changes in Developing and Ripening Peaches Iii. Catechol Tannin Content Per Cell

R eeve , R. M. (Western Regional Res. Lab., U. S. Dept. of Agriculture, Albany, Calif.) Histological and histochemical changes in developing and ripening peaches. III. Catechol tannin content per cell. Amer. Jour. Bot, 46(9): 645–650. Illus. 1959.—Photometric measurements were made of the densities of catechol tannin test colors histochemically developed with a nitrous acid reaction in fresh sections of fruits. The measured values showed a linear relationship with both section thickness and tannin concentration. When average cell size, section thickness. and the volume of tissue photometrically illuminated are known, it is possible to calculate an amount of phenolic substance per cell. Such values calculated for the naturally occurring catechol tannins in developing and ripening peaches revealed very large changes in these substances per cell. Catechol tannins so estimated increased about 90‐fold from the beginning of cell enlargement until the fruit was slightly over half its mature size, a period of about 16‐fold increase in volume of the average cell. After a maximum tannin content had been reached, a decrease of about 8‐fold per cell was found as the fruit matured and ripened. The early changes in tannin content, when expressed on a unit volume basis, were much less pronounced (about 5‐fold increases) and agreed in general with published chemical data for increases in chlorogenic acid on a weight basis during a comparable growth period in a sweet cherry. The semiquantitative, percell expressions of these histochemical results show relation to established phenomena of growth.