Plant Senescence: The Role of Volatile Terpene Compounds (VTCs)

Plant senescence is deemed as a complex, highly regulated, developmental phase in the life of a plant with a consequence of a coordinated degradation of macromolecules and a subsequent benefit of component mobilization from other parts of the plant. In some cases, under one or many environmental stresses, senescence is triggered in plants. Despite many studies in the area, less consideration has been given to plant secondary metabolites, especially the role of volatile terpene compounds (VTCs) on plant senescence. Actually, Not only does VTCs serve as a feeding deterrent to insects and some herbivores, it is now well accepted that VTCs play a major role in plant senescence by keeping the plant healthy and also protecting it against environmental stresses that are known to cause plant death.

This review sought to capture the biosynthesis and signal transduction of VTCs, the physiology of VTCs in plant development and how that was linked to some phytohormones to induce senescence. And much progress had been made in the elucidation of metabolic pathways leading to the biosynthesis of VTCs. In addition to the classical cytosolic mevalonic acid (MVA) pathway from acetyl-CoA, the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, originating from glyceraldehyde-3-phosphate (GAP) and pyruvate, led to the biosynthesis of isoprenoid precursors, isopentenyl diphosphate and dimethyl allyl diphosphate. VTCs synthesis and emission were believed to be tightly regulated by photosynthetic carbon supply into MEP pathway. Thus, under abiotic stresses such as drought, high salinity, high and low temperature, and low CO₂ that directly affected stomatal conductance and ultimately biochemical limitation to photosynthesis, there had been observed induction of VTC synthesis and emissions, reflecting the elicitation of MEP pathway. This revealed the possibility of important function(s) of VTCs in plant defense against stress by mobilizing resources from components of plants and therefore, senescence.

In short, the current understanding of the relationship between environmental responses and senescence mostly comes from the study of senescence response to phytohormones such as abscisic acid, jasmonic acid, ethylene and salicylic acid, which are extensively involved in response to various abiotic and biotic stresses. These stresses affect synthesis and/or signaling pathways of phytohormones to eventually trigger expression of stress-responsive genes, which in turn appears to affect leaf senescence. Future molecular studies to profile expressed genes in plants during senescence and abscission will help indicate the induced transcripts that encode for VTCs and phytohormones.

Article by Ernest Asante Korankye, et al, from Dalhousie University, Halifax, Canada.

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Image by Katie Howell, from Flickr-cc.