Cytosolic aldolase is a ripening related enzyme in strawberry fruits (Fragaria x ananassa)

Two aldolase isoenzymes have been isolated from ripe strawberry fruits (Fra garia x ananassa cv. Camarosa and Elsanta) and partially purified by DEAE a nion exchange and Sephacryl size exclusion chromatography. The isoenzymes w ere identified as class I cytosol and plastid aldolase on the basis of thei r chromatographic behavior on DEAL-cellulose columns, native molecular weig ht, pH optimum pattern, K-m value for D-fructose-1,6-bisphosphate, tendency to be inactivated by lower pH values and SDS-PAGE subunit determination of 40 and 38 kDa, respectively. Total aldolase activity and distribution of b oth aldolase isoenzymes was also investigated at different stages of strawb erry fruit ripening. Strawberries in the green and white ripening stage sho wed the same ratio of the two isoenzymes as green leaves with 15 and 8% cyt osol aldolase activity, respectively. During strawberry fruit development t he overall total aldolase activity decreased until the pink ripening stage and then increased due to a rise of cytosol aldolase yielding up to 75% in red strawberries. A cDNA putatively encoding the cytosolic form of aldolase in strawberry was cloned during the course of this study. Both microarray and RNA gel blot analyses showed that the cytosolic aldolase gene expressio n is induced during ripening as detected for the cytosolic aldolase enzyme. We suggest that induction of the cytosolic aldolase both at the levels of transcription and translation might be part of a ripening related stress re sponse in the receptacle tissue. (C) 2001 Elsevier Science Ltd. All rights reserved.