TOXINS OF PSEUDOMONAS-SYRINGAE PV SYRINGAE AFFECT H-TRANSPORT ACROSS THE PLASMA-MEMBRANE OF MAIZE()

The activity of some phytotoxic metabolites of Pseudomonas syringae pv . syringae Van Hall strains B359 and B301 on in vivo and in vitro syst ems of H+-transport across the plasma membrane of maize (Zea mays L., hybrid Paolo) was investigated. Tn particular syringomycin, the first lipodepsinonapeptide isolated from Pas and already studied in plants a nd yeasts for its effects on several physiological systems, was compar ed with the recently described lipodepsipeptides with 22 or 25 amino a cid residues, so called syringopeptins. The in vivo activity of the ph ytotoxins was tested on fusicoccin-stimulated H+-extrusion from cuttin gs of maize roots, which was inhibited by both types of toxins, with s yringomycin more efficient than the syringopeptins. In vitro the H+-AT Pase activity of predominantly right-side-out plasma membrane vesicles purified by two-phase partitioning was stimulated by 10 mu M syringom ycin and inhibited by higher levels, in agreement with the results of others with preparations of dicotyledons. Also the inhibition of the p hosphohydrolytic activity of inside-out vesicles of mung bean plasma m embrane was confirmed for maize. In both types of vesicles the syringo peptins were better inhibitors than syringomycin. The pH gradient form ed on addition of ATP to predominantly (25% latency) inside-out vesicl es was immediately and completely collapsed by syringomycin and syring opeptins; H+-pumping was prevented if the toxins were added before ATP . The inhibition was concentration dependent, but at very low concentr ations the effect was inverted. The results of the present investigati on, carried out with maize preparations, confirm and extend the eviden ce so far obtained with dicotyledons in favour of the plasma membrane as an important site of interaction of syringomycin with the plant cel l. They also indicate that, except for some details, the effects of sy ringopeptins at the level of the plasma membrane are the same as those of syringomycin.