Differential effects of five types of antipathogenic plant peptides on model membranes

Abstract

The effects of five antipathogenic plant peptides, wheat a-thionin, potato PTH1 defensin, barley LTP2 lipid transfer protein, and potato tuber DL1 and DL2 defensins, have been tested against phospholipid vesicles (liposomes). Wheat thionin very actively induces aggregation and leakage of negatively charged vesicles. LTP2 displays the same activities, although to a limited extent. Under certain conditions PTH1 and DL2 induce vesicle aggregation, but not leakage. Potato defensin DL1 failed to show any effect on liposomes. The same peptides have been assayed against a plant pathogenic bacterium, both the membrane-active and -inactive compounds having efficient antibacterial action.

Specific, High Affinity Binding Sites for an Antifungal Plant Defensin on Neurospora crassa Hyphae and Microsomal Membranes

“…Such interaction has previously been shown to be dependent on the membrane potential in the case of insect defensins (8) and mammalian defensins (9,21). In contrast to insect and mammalian defensins, plant defensins are unable to influence the conduction of ion currents through artificial phospholipid membranes (7) or to cause release of fluorescent dyes entrapped in artificial phospholipid vesicles (10). Based on our binding data we propose that the membrane responses induced by plant defensins, including generation of ion fluxes, require the presence of specific receptors in the phospholipid membrane.…”

“…In contrast with insect (8) and mammalian defensins (9), plant defensins do not form ion-or dye-permeable pores in artificial membranes (7,10), nor do they exhibit substantial hyphal membrane permeabilization activity (7). Therefore, it seems likely that these membrane responses are initiated through interaction with a receptor that may either transduce a signal to endogenous ion channels in the membrane or, alternatively, facilitate insertion of the plant defensin into the membrane with subsequent ion channel formation (7).…”

Snakin-1, a Peptide from Potato That Is Active Against Plant Pathogens

“…The observed synergistic antimicrobial effect of combinations of SN1 and PTH1 is also in line with this hypothesis. No information is yet available concerning the mechanism of action of SN1, except that, in contrast to other plant antibiotic peptides tested, it does not medí-ate aggregation or leakage of artificial liposomes under low or high salt conditions (Caaveiro et al 1997). The rapid aggregation of SNl-treated gram-positive and gram-negative bacteria does not seem to be related to SN1 toxicity in vitro because, for example, R. solanacearum was not inhibited at SN1 concentrations that did cause aggregation.…”

Expression Cloning and Biochemical Characterization of a Rhizobium leguminosarum Lipid A 1-Phosphatase

“…Although not yet well characterized in terms of their ability to respond to lipid A, plants have recently been shown to possess systems of innate immunity (105,106) and to synthesize antibacterial peptides in a manner that is reminiscent of insects infected with bacteria or fungi (107,108). The unusual lipid A of R. leguminosarum might conceivably help bacteroids evade the innate immune response of plants during symbiosis in root cells while still allowing the plant to defend itself against Gram-negative pathogens containing a more typical, phosphorylated lipid A disaccharide.…”