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

摘要

Senescence is a natural, energy-dependent, style="font-family:""> style="font-family:Verdana;">physiological, developmental and an ecological process that is controlled by the plant’s own genetic program, allowing maximum recovery of nutrients from older organs for the survival of the plant, as such; it is classified as essential component of the growth and development of plants. In some cases, under one or many environmental stresses, senescence is triggered in plants. Despite m style="font-family:Verdana;">any style="font-family:Verdana;"> stud style="font-family:Verdana;">ies style="font-family:Verdana;"> in the area, less consideration has been given to plant secondary metabolites, especially the role of VTCs on plant senescence. This review seeks to capture style="font-family:""> style="font-family:Verdana;">the biosynthesis style="font-family:""> style="font-family:Verdana;">and signal transduction of VTCs, the physiology of VTCs in plant development and how that is linked to some phytohormones to induce senescence. style="font-family:""> style="font-family:Verdana;">Much progress has 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, lead style="font-family:Verdana;">s style="font-family:""> style="font-family:Verdana;"> to the biosynthesis of isoprenoid precursors, isopentenyl diphosphate and dimethyl allyl diphosphate. VTCs synthesis and emission are 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 CO _{style="font-family:Verdana;">2} style="font-family:Verdana;"> that directly affect stomatal conductance and ultimately biochemical limitation to photosynthesis, style="font-family:""> style="font-family:Verdana;">there has been observed induction of VTC synthesis and emissions, reflecting the elicitation of MEP pathway. This reveals the possibility of important function(s) of VTCs in plant defense against stress by mobilizing resources from components of plants and therefore, senescence. style="font-family:""> style="font-family:Verdana;">Our current understanding of the relationship between environmental responses and senescence mostly come style="font-family:Verdana;">s style="font-family:Verdana;"> 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 style="font-family:""> style="font-family:Verdana;">phytohormones to eventually trigger expression of stress-responsive genes, which in turn appears to affect leaf senescence. Comparison of plant response to stresses in relation to patterns of VTCs and phytohormones style="font-family:""> style="font-family:Verdana;">biosynthesis indicate style="font-family:Verdana;">s style="font-family:Verdana;"> a considerable crosstalk between these metabolic processes and their signal to plant senescence.