Studies on peroxidases and vascular discoloration in cassava root tissue

Abstract

Abstract Extracts from discoloured cassava root tissue contained peroxidase activity in the soluble, covalently‐bound and ionically‐bound fractions. Extracts from non‐discoloured tissue lacked activity in the latter fraction and showed reduced activity in the other two fractions. Fractions from discoloured tissue showed nine soluble, two ionically‐bound and three covalently‐bound activity bands. Eight soluble peroxidase bands and one covalently‐bound band were detected by electrophoresis in fractions from non‐discoloured tissue. Some bands were less intensely stained than the corresponding bands detected in discoloured tissue extracts. Polyphenol oxidase showed increased activity only in the covalently‐bound fraction from discoloured tissue. Cassava roots produced ethylene in response to mechanical damage. Production commenced 6 h after injury and was only slightly affected by the accumulation of carbon dioxide. Neither the presence of carbon dioxide nor of exogenous ethylene had much effect on the electrophoretic pattern of soluble peroxidases.