EFFECTS OF ERWINIA-AMYLOVORA HARPIN ON TOBACCO LEAF CELL-MEMBRANES ARE RELATED TO LEAF NECROSIS AND ELECTROLYTE LEAKAGE AND DISTINCT FROM PERTURBATIONS CAUSED BY INOCULATED E-AMYLOVORA
Sm. Pike et al., EFFECTS OF ERWINIA-AMYLOVORA HARPIN ON TOBACCO LEAF CELL-MEMBRANES ARE RELATED TO LEAF NECROSIS AND ELECTROLYTE LEAKAGE AND DISTINCT FROM PERTURBATIONS CAUSED BY INOCULATED E-AMYLOVORA, Physiological and molecular plant pathology, 53(1), 1998, pp. 39-60
We have characterized the membrane potential response of cells in toba
cco leaves to externally applied or injected harpin from Erwinia amylo
vora (Ea321) and linked it to subsequent electrolyte leakage and event
ual necrosis. We similarly examined depolarization in response to inje
cted Ea321 cells, and mutant bacteria that are defective in harpin pro
duction. Injected and applied harpin depolarize only the H+-ATPase-dep
endent component of membrane potential, in contrast to injected wild-t
ype Ea321, which greatly depolarizes both pump and diffusion potential
s. The functional capacity of the H+-ATPase component is also much les
s impaired in harpin- than Ea321-injected leaves. Furthermore, harpin
production does not account for the entire set of differences in respo
nse to injected wild-type and mutant bacteria. Membrane depolarization
in response to applied harpin and necrosis induced by injected harpin
are similarly concentration-dependent and directly related. Parallel
inhibition of harpin-caused membrane depolarization, electrolyte leaka
ge and necrosis by the Ca2+ channel blocker, La3+, or the protein kina
se inhibitor, K252a, links these events and suggests that prolonged Ca
2+ entry and phosphorylation underlie them. Although harpin similarly
depolarizes leaf and suspension cell potentials, there is a substantia
l difference: leaf cell membranes are less sensitive and repolarize. I
ncreased repolarization upon harpin removal points to probable reversi
ble association with the plant cell. Dependence of repolarization upon
order of harpin/fusicoccin addition suggests separate modes or sites
of action. (C) 1998 Academic Press.