Changes in esterase activity associated with peanut (Arachis hypogaea L.) seed deterioration

Rapid loss of peanut seed quality during storage is a common problem in seed production for which little information concerning the physiological mechanism(s) is known. This study examined changes in esterase activity of unimbibed and imbibed peanut seeds previously exposed to ambient storage conditions. A high quality (100% germination, 100% tetrazolium [TZ]) seed lot was divided into three subsamples. One was immediately placed into cool storage and classified high quality. The remaining two were exposed to ambient conditions until their seed quality declined to a medium (79% germination, 83% TZ) or low (58% germination, 61% TZ) quality level at which time they were also placed in cool storage. Total specific esterase activity of unimbibed seeds declined from 100% to 91% to 84% in the cotyledon and 100% to 92% to 87% in the axes of high, medium, and low quality seeds, respectively. After 3 days imbibition, total specific esterase activity for the low quality seed cotyledons and axes was 94% of the high quality seeds. Examination of the isoesterase profiles using isoelectric focussing demonstrated that these changes in esterase activity were not uniform among all isoesterase species. Seven isoenzymes increased and four decreased in the cotyledons and two isoenzymes increased in the axes following imbibition. These changes were not associated with damaged isoesterase species found in unimbibed seeds following seed storage. We conclude that specific isoesterases are prone to deterioration during ageing of peanut seeds and that other isoesterases associated with germination are preferentially synthesized in deteriorated peanut seeds during imbibition.