A POLYGALACTURONASE-INHIBITING PROTEIN IN THE FLOWERS OF PHASEOLUS-VULGARIS L

The localization of the endopolygalacturonase inhibiting protein (PGIP) has been studied in Phaseolus vulgaris L. by a simple infiltration-extraction procedure. Virtually all of the PGIP activity was recovered from the bean stem apoplast without significantly disturbing the symplastic component of the tissue. Activity of PGIP was determined in different parts and organs of developing bean seedlings. PGIP was present in all the tissues and organs tested (root, leaf, cotyledon, flower, stem, seed, embryo). Very low levels of PGIP were found in the roots. Higher specific activities were detected in all the other parts of the plant, the highest PGIP levels being detected in the vegetative apex and in the flower. PGIP levels in the stems increased during plant growth. At different stages of development a differential expression of PGIP along the stem was observed and an acropetal shift of the zone of maximum PGIP expression occurred. PGIP from Phaseolus vulgaris flowers was purified 32-fold by DEAE-cellulose chromatography followed by affinity chromatography through a Sepharose-endopolygalacturonase column. The purified PGIP, subjected to SDS-PAGE, showed a mobility similar but not identical to that of PGIP purified from hypocotyls. A molecular mass of 42 kDa was calculated for the flower PGIP, 1kDa larger than the molecular mass of the PGIP purified from stems. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.