PHYSIOLOGICAL-RESPONSES OF DOWNY BROME (BROMUS-TECTORUM) ROOTS TO PSEUDOMONAS-FLUORESCENS STRAIN D7 PHYTOTOXIN

Effects of a crude preparation of a phytotoxin from Pseudomonas fluore scens strain D7 (D7) on various physiological processes were evaluated in roots of downy brome seedlings. Cell division, respiration, and sy nthesis of protein, RNA, and DNA were not inhibited or only slightly i nhibited under treatment conditions that caused substantial inhibition of root elongation. Significant inhibition of each of these processes was detected by known inhibitors included in each study to verify sen sitivity of the procedures used. Disruption of lipid synthesis and mem brane integrity by the crude phytotoxin preparation was significant an d might account for inhibition of root elongation. Additional studies on these two possible target sites were conducted with partially purif ied phytotoxin. In intact roots, incorporation of [C-14]acetate and [C -14]malonic acid into lipophilic fractions was reduced by 50% or great er during a 1-h treatment with concentrations between 10 and 100 mug m l-1 of the partially purified phytotoxin preparation. In a membrane in tegrity study, a similar treatment increased radioactivity efflux 250% from seedlings preloaded with scyllo-[R-H-3]inositol. Additionally, d isruption of lipid synthesis and membrane integrity by the partially p urified phytotoxin was dose dependent. Collectively, these findings in dicate that the D7 phytotoxin may inhibit downy brome root elongation through its effects on lipid synthesis and membrane integrity.