Profiling membrane glycerolipids during γ-ray-induced membrane injury

Zheng and Li BMC Plant Biology (2017) 17:203 DOI 10.1186/s12870-017-1153-9 RESEARCH ARTICLE Open Access Profiling membrane glycerolipids during γray-induced membrane injury Guowei Zheng1,2 and Weiqi Li1,2* Abstract Background: γ-rays are high-energy radiation that cause a range of random injuries to plant cells. Most studies on this issue have focused on γ-ray-induced nucleotide damage and the production of reactive oxygen species in cells, so little is known about the glycerolipid metabolism during γ-rays induced membrane injury. Using an ESI-MS/MSbased lipidomic method, we analysed the lipidome changes in wild-type and phospholipase D (PLD)δ- and α1deficient Arabidopsis after γ-ray treatment. The aim of this study was to investigate the role of PLD-mediated glycerolipid metabolism in γ-ray-induced membrane injury. Results: The ion leakage of Arabidopsis leaves after 2885-Gy γ-ray treatment was less than 10%. High does γ-ray treatment could induce the accumulation of intracellular reactive oxygen species (ROS). Inhibition of PLDα1 caused severe lipid degradation under γ-ray treatment. γ-ray-induced glycerolipid degradation mostly happened in chloroplastidic lipids, rather than extraplastidic ones. The levels of lysophosphatidylcholine (lysoPC) and lysophosphatidylethanolamine (lysoPE) were maintained in the WS ecotypes during γ-ray treatments, while increased significantly in the Col ecotype treated with 1100 Gy. After 210- and 1100-Gy γ-ray treatments, the level of lysophosphatidylglycerol (lysoPG) decreased significantly in the four genotypes of Arabidopsis. Conclusions: γ-ray-induced membrane injury may occur via an indirect mechanism. The degradation of distinct lipids is not synchronous, and that interconversions among lipids can occur. During γ-ray-induced membrane injury, the degradation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) may be mediated by PLDζ1 or phospholipase A1. The degradation of phosphatidylglycerol was not mediated by PLA, PLDδ or PLDα1, but by phospholipase C or other PLDs. γ-rays can decrease the double-bond index and increase the acyl chain length in membrane lipids, which may make membranes more rigid and further cause injury in membranes. Keywords: Gamma irradiation, Membrane injury, Phospholipase D, Lipidomics, Plastidic lipids, Extraplastidic lipids Background Gamma irradiation (γ-rays) from 60Co involves exposure to high-energy photons and is widely used to induce mutations in crops and flowers [1–3]. It is also extensively applied to extend the shelf life of food by altering its biochemical metabolism and destroying microorganisms [4–6]. The targeting of γ-rays to plant cells is completely non-specific and the response of the plant is random [7]. γ-rays can directly induce DNA damage and influence genome structure due to their high energy [8, 9]. They can * Correspondence: 1 Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, People’s Republic of China 2 Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, People’s Republic of China also induce the production of free radicals and reactive oxygen species (ROS), which indirectly disturb the physiological and biochemical properties of cells and have deleterious effects on the plant [10–13]. Membranes are sensitive to environmental changes, and abiotic stresses directly affect membrane properties. Glycerolipids are the main constituents of membranes; adjustments of the composition, unsaturation and acyl chain length, enables plant to keep the integrity and fluidity of their membranes under environmental stresses [14–16]. During freezing treatment, plants tend to synthesise glycerolipids with a larger head group to maintain the integrity of their membranes [17]. In addition, the level of galactolipids and the degree of unsaturation were found to decline in the alpine plant Meconopsis racemosa after its introduction to a lowland region [18], © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Zheng and Li BMC Plant Biology (2017) 17:203 and abscisic acid (ABA)-promoted leaf senescence in Arabidopsis was shown to be retarded by attenuating lipid degradation [19]. However, little is known about how membrane glycerolipids respond to γ-rays. Phospholipase D (PLD) is one of the most important enzymes regulating phospholipid metabolism. The PLD family in plants comprises 12 members, which are classified into six types: PLDα (3), β (2), γ (3), δ, ε and ζ (2). PLD and its hydrolysate, phosphatidic acid (PA), play important roles in plant responses to drought, cold and salinity [20–24]. Different PLD isoforms might play different regulatory roles in plants [25]. PLDα1 and δ are the most abundant PLDs [26], and they play complex roles during plant responses to stress. An Arabidopsis mutant with suppressed PLDα1 was found to be tolerant to cold, while a PLDδ antisense mutant was sensitive to it [22, 27]. In addition, suppression of both PLDα1 and PLDδ was found to retard ABA- and ethylene-promoted senescence of detached leaves in Arabidopsis [19, 28]. It is reported that γ-rays could induce microsomal membranes deterioration in cauliflower florets [29]. However, little is known about the involvement of PLDα1 and PLDδ during γ-ray-induced membrane injury. In the present study, we treated wild-type (Columbia and Wassilewskija) and PLD-deficient mutant (PLDδ-def and PLDα1-def ) Arabidopsis with γ-rays at doses of 46, 210 and 1100 Gy. The two higher doses were previously reported to cause growth retardation and inhibition of bolting in Arabidopsis, respectively [30]. Using an lipidomic analysis based on electrospray tandem mass spectrometry (ESI-MS/MS) [31], we investigated the changes of membrane glycerolipid profiles after these different γray treatments. The following two questions were addressed in this work: (i) How do membrane lipids respond to abiotic stresses of γ-rays? (ii) Do PLDs participate in plant responses to γ-rays? Results γ-ray-induced membrane injury may occur via an indirect mechanism γ-rays are high-energy ion radiation that may damage membranes. Ion leakage monitored by the relative conductivity is an effective method to detect such damage. We thus investigated the ion leakage of Arabidopsis irradiated with γ-rays at 1918 and 2885 Gy, two higher doses t (...truncated)