ABSTRACT
BACKGROUND: Ginkgo biloba (Ginkgoaceae) is one of the most ancient living seed plants and is regarded as a living fossil. G. biloba has a broad spectrum of resistance or tolerance to many pathogens and herbivores because of the presence of toxic leaf compounds. Little is known about early and late events occurring in G. biloba upon herbivory. The aim of this study was to assess whether herbivory by the generalist Spodoptera littoralis was able to induce early signaling and direct defense in G. biloba by evaluating early and late responses. METHODOLOGY/PRINCIPAL FINDINGS: Early and late responses in mechanically wounded leaves and in leaves damaged by S. littoralis included plasma transmembrane potential (Vm) variations, time-course changes in both cytosolic calcium concentration ([Ca(2+)](cyt)) and H(2)O(2) production, the regulation of genes correlated to terpenoid and flavonoid biosynthesis, the induction of direct defense compounds, and the release of volatile organic compounds (VOCs). The results show that G. biloba responded to hebivory with a significant Vm depolarization which was associated to significant increases in both [Ca(2+)](cyt) and H(2)O(2). Several defense genes were regulated by herbivory, including those coding for ROS scavenging enzymes and the synthesis of terpenoids and flavonoids. Metabolomic analyses revealed the herbivore-induced production of several flavonoids and VOCs. Surprisingly, no significant induction by herbivory was found for two of the most characteristic G. biloba classes of bioactive compounds; ginkgolides and bilobalides. CONCLUSIONS/SIGNIFICANCE: By studying early and late responses of G. biloba to herbivory, we provided the first evidence that this "living fossil" plant responds to herbivory with the same defense mechanisms adopted by the most recent angiosperms.
Subject(s)
Feeding Behavior , Genes, Plant , Ginkgo biloba/metabolism , Plant Leaves/metabolism , Plant Leaves/parasitology , Signal Transduction , Spodoptera/physiology , Animals , Biomarkers/metabolism , Calcium/metabolism , Cytosol/metabolism , Flavonoids/metabolism , Gene Expression Profiling , Hydrogen Peroxide/metabolism , Membrane Potentials , Oligonucleotide Array Sequence Analysis , Plant Extracts/pharmacology , RNA, Messenger/genetics , RNA, Plant/genetics , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Volatile Organic Compounds/metabolismABSTRACT
Interactions between herbivorous insects and plants storing terpenoids are poorly understood. This study describes the ability of Chrysolina herbacea to use volatiles emitted by undamaged Mentha aquatica plants as attractants and the plant's response to herbivory, which involves the production of deterrent molecules. Emitted plant volatiles were analyzed by GC-MS. The insect's response to plant volatiles was tested by Y-tube olfactometer bioassays. Total RNA was extracted from control plants, mechanically damaged leaves, and leaves damaged by herbivores. The terpenoid quantitative gene expressions (qPCR) were then assayed. Upon herbivory, M. aquatica synthesizes and emits (+)-menthofuran, which acts as a deterrent to C. herbacea. Herbivory was found to up-regulate the expression of genes involved in terpenoid biosynthesis. The increased emission of (+)-menthofuran was correlated with the upregulation of (+)-menthofuran synthase.
