INVOLVEMENT OF POLYAMINES, DIAMINE OXIDASE AND PEROXIDASE IN RESISTANCE OF CHICKPEA TO ASCOCHYTA-RABIEI

Peroxidase (POD, EC 1.11.1.7), diamine oxidase (DAO, EC 1.4.3.6) activities and polyamine levels have been investigated in stems, untreated or inoculated with conidia of Ascochyta rabiei, obtained from chickpea cultivars, respectively susceptible (<Calla>) and resistant (<Sultano>) to an isolate of the fungus. DAO activity and cadaverine content are constitutively higher in the fourth internode of resistant cultivar Sultano as compared with the cultivar Calia. Germination of conidia, development of hyphae and formation of appressoria were found to be similar in the two cultivars. POD and DAO activities and putrescine level increased markedly after infection in both cultivars as compared with control plants, with a greater enhancement of both enzyme activities and diamine level in <Sultano>. Apparent histochemical activities of both DAO and POD were detected in the lignosuberized barriers set up by cortical and pith parenchyma cells in response to pathogen invasion. The barriers are thicker and wider in resistant plants. In addition to these responses, the two cultivars showed different histological features. The resistant cultivar Sultano has a higher number of xylem elements and xylem parenchyma cells as compared with <Calia>. Results obtained suggest that the structural organization of xylem tissues, polyamine metabolism and peroxidase activity may have a role in the resistance of the cultivar Sultano to A. rabiei.