CHARACTERIZATION OF PECTINASES AND PECTIN METHYLESTERASE CDNAS IN PODS OF GREEN BEANS (PHASEOLUS-VULGARIS L)

Tomato fruit maturation is accompanied by a depolymerization of cell w all pectins which is due to the action of endopolygalacturonase (endoP G) preceded by pectin methylesterase (PE) activity. To investigate the role of endoPG and PE in determining the structure of green bean (Pha seolus vulgaris I,.) pectins, these pectinases were studied during pod development. Early developmental stages displayed low endoPG or exoPG activities while PE activities were measurable during all stages of p od and seed development. These results do not favour a possible synerg istic action of PE and PG. For seeds, the relatively high PE activitie s concurred with relatively low levels of pectin methyl esterification . At a molecular level, one partial chromosomal clone of 210 bp (PE1V) , two partial PE cDNA clones of 660 bp (PE2V and PE3V) from cv, verona and one full-length PE cDNA clone of 1990 bp (PE3M), from cv. Masai w ere isolated. The identity of the CDNA clones was confirmed by express ion in Escherichia coli and immunodetection with antibodies directed t owards a tomato fruit PE. Transcripts corresponding with the genomic c lone PE1V were not detected but both PE2 and PE3 cDNAs corresponded wi th mRNAs 1.8 kb in length. In contrast to PE2, PE3 gene expression lev els varied significantly in pods from different cultivars suggesting a n involvement in determining pod morphology.