Effects of Ca2+ chelators on plant resistance to bacteria and on plasma membrane NADH-DQR activity

The pretreatment of tobacco leaves with protein-lipopolysaccharide complexes purified from Pseudomonas syringae pv. aptata (Psa) prevents the hypersensitive response (HR) against heterologous bacteria (i.e. Psa) and delays disease symptoms induced by homologous bacteria (i.e. P. syringae pv. tabaci; Pst). That pretreatment also causes an increase of NADH-duroquinone reductase (NADH-DQR) located in the tobcco leaf plasma membrane. This enzyme may be involved in prLPS prevention of the HR by inhibiting superoxide radicals generation. According to this proposal, the protection induced by pr-LPS treatment may be partially due to chelation of Ca2+ ions. In fact calcium ions can act as secondary messengers in the plant-pathogen interaxtion. To test this hypothesis, the effect of some ca2+ chelators (EGTA, EDTA, oxalate) were studied in planta, on plant pathogen interaction, and on NADH-DQR activity in beet suspension cells.