Consuelo Monerri

Peroxidase activity and isoenzyme profile in buds and leaves in relation to flowering in satsuma mandarin (Citrus unshiu)

Abstract The changes in ionically bound cell-wall, and in soluble cationic and anionic peroxidase activities, have been determined in buds and leaves of flowering and non-flowering trees of satsuma mandarin ( Citrus unshiu Marc.) from September to February. At this time, the buds of the flowering trees become competent and are induced by the low winter temperatures. Both the anionic and the cationic soluble activities in the leaves were higher in flowering than in non-flowering trees. The activity of the cationic peroxidase further increased in the flowering trees during the acquisition of bud competence, at a time when its activity remained constant in the non-flowering trees. Ionically bound cell-wall peroxidase activity was also higher in the leaves of flowering as compared to non-flowering trees. The changes in this enzyme fraction did not show a consistent trend during the period studied. Soluble cationic peroxidase in the buds increased markedly with bud age. When buds of the same age were compared, the activity of every enzyme fraction was similar in flowering and in non-flowering trees. The same isoenzyme pattern was found in flowering and non-flowering trees, and the changes in enzyme activities were due to changes in the activity (intensity) of pre-existing isoenzymes but no change in the isoenzyme pattern was found. Although flowering trees had higher peroxidase (cationic, anionic and ionically bound cell-wall) activities in the leaves than non-flowering trees, neither the enzyme activities nor the isoenzyme pattern were useful markers for the developmental stage of the buds in relation to flowering. The differences in activity were already established before the buds became competent to respond to low temperature inductive conditions.