title: Molecular and physiological evidence suggests the existence of a system II-like pathway of ethylene production in non-climacteric Citrus fruit.
abstract: Mature citrus fruits, which are classified as non-climacteric, evolve very low amounts of ethylene during ripening but respond to exogenous ethylene by ripening-related pigment changes and accelerated respiration. In the present study we show that young citrus fruitlets attached to the tree produce high levels of ethylene, which decrease dramatically towards maturation. Upon harvest, fruitlets exhibited a climacteric-like rise in ethylene production, preceded by induction of the genes for 1-aminocyclopropane-1-carboxylate (ACC) synthase 1 (CsACS1), ACC oxidase 1 (CsACO1) and the ethylene receptor CsERS1. This induction was advanced and augmented by exogenous ethylene or propylene, indicating an autocatalytic system II-like ethylene biosynthesis. In mature, detached fruit, very low rates of ethylene production were associated with constitutive expression of the ACC synthase 2 (CsACS2) and ethylene receptor CsETR1 genes (system I). CsACS1 gene expression was undetectable at this stage, even following ethylene or propylene treatment, and CsERS1 gene expression remained constant, indicating that no autocatalytic response had occurred. The transition from system II-like behavior of young fruitlets to system I behavior appears to be under developmental control.
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, 76100 Rehovot, Israel.
authors.forename: Ehud
authors.initials: E
authors.lastname: Katz
authors.forename: Paulino Martinez
authors.initials: PM
authors.lastname: Lagunes
authors.forename: Joseph
authors.initials: J
authors.lastname: Riov
authors.forename: David
authors.initials: D
authors.lastname: Weiss
authors.forename: Eliezer E
authors.initials: EE
authors.lastname: Goldschmidt
mesh_terms: D005075:Biological Evolution; D032084:Citrus sinensis / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D005030:Ethylenes / Q000096:biosynthesis*; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008190:Lyases / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: D005030:Ethylenes; C036216:ethylene; D008190:Lyases; C021773:1-aminocyclopropanecarboxylate synthase