Abstract
For the characterization of BOA-OH insensitive plants, we studied the time-dependent effects of the benzoxazolinone-4/5/6/7-OH isomers on maize roots. Exposure of Zea mays seedlings to 0.5 mM BOA-OH elicits root zone-specific reactions by the formation of dark rings and spots in the zone of lateral roots, high catalase activity on root hairs, and no visible defense reaction at the root tip. We studied BOA-6-OH- short-term effects on membrane lipids and fatty acids in maize root tips in comparison to the benzoxazinone-free species Abutilon theophrasti Medik. Decreased contents of phosphatidylinositol in A. theophrasti and phosphatidylcholine in maize were found after 10–30 min. In the youngest tissue, α-linoleic acid (18:2), decreased considerably in both species and recovered within one hr. Disturbances in membrane phospholipid contents were balanced in both species within 30–60 min. Triacylglycerols (TAGs) were also affected, but levels of maize diacylglycerols (DAGs) were almost unchanged, suggesting a release of fatty acids for membrane lipid regeneration from TAGs while resulting DAGs are buildings blocks for phospholipid reconstitution, concomitant with BOA-6-OH glucosylation. Expression of superoxide dismutase (SOD2) and of ER-bound oleoyl desaturase (FAD2-2) genes were contemporaneously up regulated in contrast to the catalase CAT1, while CAT3 was arguably involved at a later stage of the detoxification process. Immuno-responses were not elicited in short-terms, since the expression of NPR1, POX12 were barely affected, PR4 after 6 h with BOA-4/7-OH and PR1 after 24 h with BOA-5/6-OH. The rapid membrane recovery, reactive oxygen species, and allelochemical detoxification may be characteristic for BOA-OH insensitive plants.
Highlights
An increase of reactive oxygen species (ROS) is a characteristic feature when plants are exposed to their own allelochemicals or those from other plants (Gniazdowska and Bogatek 2005; Lara-Nuñez et al 2006; Huang et al 2020). H2O2 and the superoxide anion radical (O2·−) are key compounds in signaling and cell wall loosening reactions (Baxter et al 2014; Marino et al 2012; Liszkay et al 2004)
We describe the synthesis of four BOA-OH isomers as compounds causing oxidative stress in maize root tips, and time-dependent differentiated reactions of the root zones faced with these compounds
We looked for early impacts of BOA-6-OH on root membrane lipids of maize in comparison to the weed A. theophrasti and on membrane recovery by determination of total fatty acids and structural PLs, TAGs, and DAGs in maize and Abutilon seedlings
Summary
An increase of reactive oxygen species (ROS) is a characteristic feature when plants are exposed to their own allelochemicals or those from other plants (Gniazdowska and Bogatek 2005; Lara-Nuñez et al 2006; Huang et al 2020). H2O2 and the superoxide anion radical (O2·−) are key compounds in signaling and cell wall loosening reactions (Baxter et al 2014; Marino et al 2012; Liszkay et al 2004). An increase of reactive oxygen species (ROS) is a characteristic feature when plants are exposed to their own allelochemicals or those from other plants (Gniazdowska and Bogatek 2005; Lara-Nuñez et al 2006; Huang et al 2020). Cinnamaldehyde interacts with membrane receptors, whereas allelopathic concentrations of citronellal and citronellol disorganize membrane lipids (Lins et al 2019), some allelochemicals change the membrane potential (Maffei et al 2001). The allelochemical benzoxazolinone (BOA), for instance, induces oxidative stress in lettuce, mung bean, or maize, resulting in enhanced malondialdehyde (MDA) levels (Sanchez-Moreiras and Reigosa 2005; Batish et al 2006; Schulz et al 2013). The loss of membrane functions is a consequence of lipid peroxidation and damaged enzymes anchored therein or otherwise attached (Stark 2005)
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