Ethylene, ACC, Soluble Polyuronide, and Cell Wall Noncellulosic Neutral Sugar Content in ‘Eldorado’ Pears during Cold Storage and Ripening

Abstract

Abstract The capacity of ‘Eldorado’ pears to ripen increased dramatically after 4 weeks of exposure to 0°C and was associated with the synthesis of ethylene by pear tissue. Endogenous levels of ACC and internal ethylene were low after harvest, but increased rapidly after 4 weeks at 0°. Exposure to 0° for 4 weeks also resulted in an increase in soluble polyuronide during subsequent ripening at 20°. In contrast, after 9 months at 0°, soluble polyuronide content showed little increase when pears were transferred to 20°, and fruit failed to soften normally even though ACC content, internal ethylene concentration, ethylene evolution, and respiration remained relatively high. The content of arabinose, galactose, and rhamnose residues in cell walls decreased substantially during the ripening period after 4 weeks or longer at 0°. These cell wall neutral sugars decreased during ripening, even after 9 months of storage at 0°, while firmness and soluble polyuronide showed little change after fruit were transferred to 20°. These data indicate that the failure of pears to soften normally at 20° after prolonged storage at 0° is not related to ethylene synthesis or to changes in cell wall noncellulosic neutral sugar content, but is probably associated with mechanisms of polyuronide solubilization. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).