Lipid changes after leaf wounding in Arabidopsis thaliana: expanded lipidomic data form the basis for lipid co‐occurrence analysis

Abstract

SUMMARYA direct-infusion electrospray ionization triple-quadrupole mass spectrometry method with multiple reaction monitoring (MRM) was employed to measure 264 lipid analytes extracted from leaves of Arabidopsis thaliana subjected to mechanical wounding. The method provided precise measurements with an average coefficient of variation of 6.1%. Lipid classes analyzed comprised galactolipids and phospholipids (including monoacyl molecular species, molecular species with oxidized acyl chains, phosphatidic acids (PAs)), tri-and tetra-galactosyldiacylglycerols (TrGDGs and TeGDGs), head-group-acylated galactolipids, and headgroup-acylated phosphatidylglycerol (acPG), sulfoquinovosyldiacylglycerols (SQDGs), sphingolipids, di-and tri-acylglycerols (DAGs and TAGs), and sterol derivatives. Of the 264 lipid analytes, 254 changed significantly in response to wounding. In general, levels of structural lipids decreased, whereas monoacyl molecular species, galactolipids and phosphatidylglycerols (PGs) with oxidized fatty acyl chains, PAs, TrGDGs, TeGDGs, TAGs, head-group-acylated galactolipids, acPG, and some sterol derivatives increased, many transiently. The observed changes are consistent with activation of lipid oxidizing, hydrolyzing, glycosylating, and acylating activities in the wounding response. Correlation analysis of the levels of lipid analytes across individual control and treated plants was used to construct a lipid dendrogram and to define clusters and sub-clusters of lipid analytes, each composed of a group of lipids which occurred in a coordinated manner. Current knowledge of metabolism supports the notion that observed sub-clusters comprise lipids generated by a common enzyme and/or metabolically downstream of a common enzyme. This work demonstrates that co-occurrence analysis, based on correlation of lipid levels among plants, is a powerful approach to defining lipids generated in vivo by a common enzymatic pathway.

Chloroplast Membrane Remodeling during Freezing Stress Is Accompanied by Cytoplasmic Acidification Activating SENSITIVE TO FREEZING2

“…As the cells chill and the membranes become partially damaged, leakage of small ions including protons and Mg 2+ could provide a convenient mechanism for rapidly activating the membrane protective machinery, beginning with the activation of SFR2 at the outer chloroplast envelope membrane. Consistent with this hypothesis, wounding by a crushing force was observed to cause SFR2 activity (Vu et al, 2014b(Vu et al, , 2015. Wounded tissue allows cytoplasmic mixing with acidic apoplastic fluid and, possibly through this simple mechanism, SFR2 activation.…”

Modifications of membrane lipids in response to wounding of Arabidopsis thaliana leaves

“…Vu et al 5 found that, after wounding, the total levels of membrane and membrane-derived lipids dropped. The mass spectral intensity of all measured leaf lipids fell 6% from the level in unwounded plants at 45 min after wounding and a further 22% at 6 h after wounding (Fig.…”

“…1C and D). 5,8,[11][12][13] Additionally phosphatidylglycerol (PG) with an acyl chain on the terminal glycerol and small amounts of head-group acylated DGDGs are also produced in Arabidopsis leaves when they are wounded (Fig. 1C).…”

“…1C). 5,11,13 DGMG may also be produced by the acylhydrolases, such as DAD1 and DAD1-like enzymes, localized in chloroplasts and capable of acting on galactolipids. 14 In addition to DGMG, mono-acyl glycerolipids produced in response to wounding include lysophosphatidylcholines, which increase more than 2 fold at 45 min after wounding, and lysophosphatidylethanolamines (Fig.…”

“…[1][2][3][4] . In a recent study, 5 complex lipids were analyzed in leaves of unwounded plants and mechanically wounded plants, sampled 45 min and 6 h after wounding, with each treatment replicated 31 times. The levels of 254 out of the total of 264 complex lipids detected changed significantly in response to mechanical wounding.…”