PECTOLYTIC ACTIVITY BY THE HAUSTORIUM OF THE PARASITIC PLANT OROBANCHE L. (OROBANCHACEAE) IN HOST ROOTS

The possible involvement of enzymes in the penetration of intrusive ce lls of the parasitic angiosperm Orobanche into host root tissues was s tudied using cytochemical and immunocytochemical methods. Pectin methy l esterase (PME) was detected, with specific antibodies, in the cytopl asm and cell walls of Orobanche intrusive cells and in adjacent host a poplast. Depletion and chemical changes of pectins in host cell walls were shown by histochemical staining with PATAg, which detects carbohy drates that are sensitive to periodic acid, especially pectins, and wi th the monoclonal antibodies JIM 5 and JIM 7 that label pectins with l ow and high rates of esterification, respectively. Galacturonic sequen ces with low rates of esterification were more abundant in host cell w alls adjacent to the parasite, which is consistent with pectin de-meth ylation by PME release from the parasite. Pectins were absent in middl e lamellae and in host cell walls neighbouring mature intrusive cells of the parasite, consistent with further degradation of pectins by oth er enzymes. These results provide the first direct evidence for the pr esence and activity of a pectolytic enzyme in the infection zone of th e haustorium of a parasitic angiosperm in situ. (C) 1998 Annals of Bot any Company.