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 cells of the parasitic angiosperm Orobanche into host root tissues was studied using cytochemical and immunocytochemical methods. Pectin methyl esterase (PME) was detected, with specific antibodies, in the cytoplasm and cell walls of Orobanche intrusive cells and in adjacent host apoplast. Depletion and chemical changes of pectins in host cell walls were shown by histochemical staining with PATAg, which detects carbohydrates that are sensitive to periodic acid, especially pectins, and with the monoclonal antibodies JIM 5 and JIM 7 that label pectins with low and high rates of esterification, respectively. Galacturonic sequences with low rates of esterification were more abundant in host cell walls adjacent to the parasite, which is consistent with pectin de-methylation by PME release from the parasite. Pectins were absent in middle lamellae and in host cell walls neighbouring mature intrusive cells of the parasite, consistent with further degradation of pectins by other enzymes. These results provide the first direct evidence for the presence and activity of a pectolytic enzyme in the infection zone of the haustorium of a parasitic angiosperm in situ. (C) 1998 Annals of Botany Company.