Survival of Plants During Short-Term Boa-Oh Exposure: Ros Related Gene Expression and Detoxification Reactions are Accompaniedwithfast Membrane Lipid Repair in Root Tips

Abstract

Exposure of Zea maysseedlings to 0.5µM benzoxazolinone-4/5/6/7-OH allelochemicals elicits root zone specific reactions by formation of dark rings and spots in the zone of lateral roots,high catalase activity at root hairsand no visible defense reaction at the root tip. We studied short term effects on membrane lipids and fatty acids in maize root tips in comparison to those of Abutilontheophrastiafter BOA-6-OH incubations. We found a decrease mainly of phosphatidylinositol in Abutilon and phosphatidylcholinein maize after 10-30 min of exposure. In the youngest tissue, α-linoleic acid (18:2), decreased considerably in both species but amounts recovered within one hour.Disturbances in membrane phospholipid contents were balanced in both species within 30-60 min. The findings that triacylglycerols(TAGs) were also affected, but levels of maize diacylglycerols (DAG) were almost unchanged, suggestedthat fatty acids for membrane lipid regeneration are released from TAGs while resulting DAGs are buildings blocks for phospholipid reconstitution,concomitant with BOA-6-OH glucosylation. Theexpression of superoxide dismutase (SOD2)and of ER-bound oleoyldesaturase (FAD2-2) genes were contemporaneously up regulated in contrast to the catalase gene CAT1,while CAT3was arguably integrated at a later stage of the detoxification process. Major catalase activity seems to be attributed to root colonizing microorganisms. Immuno-responses were not elicited in short-terms, since expression of NPR1, POX12were rather affected,PR4 after 6h with BOA-4/7-OH and PR1 after 24hwith BOA-5/6-OH.The rapid membrane recovery, reactive oxygen species and allelochemical detoxification may be characteristic forBOA-OH insensitive plants.