Electrolyte Leakage and Evolution of Ethylene and Ethane from Pepper Leaf Disks Following Temperature Stress and Fatty Acid Infiltration

Abstract

Electrolyte leakage (EL) and ethane: ethylene ratio (EER) responses of pepper (Capsicum annuum L. `Early Calwonder') leaf disks to temperature stresses were in close agreement. Midpoints of sigmoidal response curves following freezing stress were -4.6 and -4.4C for EL and EER, respectively, and 49.0 and 48.7C following high-temperature stress. Leaf disks exposed to temperatures below -4C in freezing experiments were induced to freeze while disks held at -4C and higher avoided freezing by supercooling. Evolution of ethane and EL were measured from disks infiltrated with a saturation series of 18-C fatty acids ranging from 0 to 3 double bonds. Only cis-9,12,15 linolenic acid (18:3 n-3) stimulated ethane production and EL. In a second fatty acid experiment with 18 and 20-C acids with a double bond 3 (n-3) or 6 (n-6) carbons from the nonpolar end of the molecule, n-3 fatty acids stimulated more ethane than n-6 acids with the same number of carbons. Trienoic 18-C fatty acids stimulated more ethane than trienoic 20-C acids. Both 18-C trienoic acids yielded significantly greater EL, while values from 20-C fatty acids were only slightly higher than those of controls. Propyl gallate, a free radical scavenger, reduced ethane production without decreasing EL or K + leakage.