The role of exogenously added methyl jasmonate (MeJA), a lipid-derived signaling compound, in inducing oxidative stress in the marine red macroalga Gracilaria dura was investigated. MeJA at a concentration of 1-100 μM was a strong stimulant of reactive oxygen species (H2O2, HO· and O2·-) (P < 0.05) causing considerable oxidative stress in G. dura. This further led to lipid peroxidation and degradation of the pigments Chl a and phycocyanin, with a concomitant increase in phycoerythrin. The MeJA-induced oxidative burst also led to the induction of a fatty acid oxidation cascade, resulting in the synthesis of hydroxy-oxylipins and the up-regulation of the 13-lipoxygenase pathway. Electrospray ionization-mass spectrometry-based shotgun lipidomic analysis revealed that monogalactosyldiacylglycerol (a chloroplastic glycerolipid) and phosphatidylcholine (extrachloroplastidic phopholipid) were the most affected lipid classes. The degradation of 18:3-fatty acid-containing monogalactosyldiacylglycerol inferred that it provided fatty acyl chains for the biosynthesis of 13-hydroperoxylinolenic acid, which was further directed towards either the jasmonate pathway or other alternative pathways of the fatty acid oxidation cascade, analogous to higher plants. Also, G. dura modulated the lipid acyl chains in such a way that no significant change was observed in the fatty acid profile of the treated thalli as compared with those of the control, except for C16:0, C16:1 (n-9), C20:3 (n-6) and C20:4 (n-6) (P < 0.05). Furthermore, MeJA caused the accumulation of phenolic compounds and the up-regulation of enzymes involved in secondary metabolism such as polyphenol oxidase, shikimate dehydrogenase and phenylalanine ammonia-lyase, indicating a shift towards secondary metabolism as a defense strategy to combat the induced oxidative stress.
Bibliographical notePublisher Copyright:
© The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.
This study was supported by the Council of Scientific and Industrial Research (CSIR) [senior research fellowship (SRF) CSIR Award No. 31/028(0101)/2009-EMR-1 to P.K.]. Instrument acquisition and method development for lipid analysis at Kansas State Lipidomics Research Centre Analytical Laboratory were supported by the National Science Foundation [EPS 0236913, MCB 0455318 and 0920663, DBI 0521587]; Kansas Technology Enterprise Corporation; K-IDeA Networks of Biomedical Research Excellence (INBRE) of the National Institute of Health [P20RR16475]; Kansas State University.
We would like to thank the Kansas State Lipidomics Research Center (KLRC) for polar lipid analysis, and the Head, Analytical Sciences, CSIR-CSMCRI for permitting us to use the GC facility. We would also like to thank Profesor Jeff Leblond, Middle Tennessee State University, USA, and Professor Wendy Stirk, Research Centre for Plant Growth and Development, University of KwaZulu-Natal Pietermartizburg, South Africa for editing the manuscript for English language as well as for their valuable comments which helped in the improvement of the revised manuscript.
- Gracilaria dura
- Methyl jasmonate