title: Cellular and Pectin Dynamics during Abscission Zone Development and Ripe Fruit Abscission of the Monocot Oil Palm.
abstract: The oil palm (Elaeis guineensis Jacq.) fruit primary abscission zone (AZ) is a multi-cell layered boundary region between the pedicel (P) and mesocarp (M) tissues. To examine the cellular processes that occur during the development and function of the AZ cell layers, we employed multiple histological and immunohistochemical methods combined with confocal, electron and Fourier-transform infrared (FT-IR) microspectroscopy approaches. During early fruit development and differentiation of the AZ, the orientation of cell divisions in the AZ was periclinal compared with anticlinal divisions in the P and M. AZ cell wall width increased earlier during development suggesting cell wall assembly occurred more rapidly in the AZ than the adjacent P and M tissues. The developing fruit AZ contain numerous intra-AZ cell layer plasmodesmata (PD), but very few inter-AZ cell layer PD. In the AZ of ripening fruit, PD were less frequent, wider, and mainly intra-AZ cell layer localized. Furthermore, DAPI staining revealed nuclei are located adjacent to PD and are remarkably aligned within AZ layer cells, and remain aligned and intact after cell separation. The polarized accumulation of ribosomes, rough endoplasmic reticulum, mitochondria, and vesicles suggested active secretion at the tip of AZ cells occurred during development which may contribute to the striated cell wall patterns in the AZ cell layers. AZ cells accumulated intracellular pectin during development, which appear to be released and/or degraded during cell separation. The signal for the JIM5 epitope, that recognizes low methylesterified and un-methylesterified homogalacturonan (HG), increased in the AZ layer cell walls prior to separation and dramatically increased on the separated AZ cell surfaces. Finally, FT-IR microspectroscopy analysis indicated a decrease in methylesterified HG occurred in AZ cell walls during separation, which may partially explain an increase in the JIM5 epitope signal. The results obtained through a multi-imaging approach allow an integrated view of the dynamic developmental processes that occur in a multi-layered boundary AZ and provide evidence for distinct regulatory mechanisms that underlie oil palm fruit AZ development and function.
authors.affiliation: UMR DIADE, Institut de Recherche pour le Développement Montpellier, France.
authors.forename: Peerapat
authors.initials: P
authors.lastname: Roongsattham
authors.affiliation: UMR DIADE, CIRAD Montpellier, France.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Morcillo
authors.affiliation: UMR DIADE, Institut de Recherche pour le Développement Montpellier, France.
authors.forename: Kim
authors.initials: K
authors.lastname: Fooyontphanich
authors.affiliation: Department of Genetics, Kasetsart University Bangkok, Thailand.
authors.forename: Chatchawan
authors.initials: C
authors.lastname: Jantasuriyarat
authors.affiliation: National Center for Genetic Engineering and Biotechnology, Genome Institute Pathum Thani, Thailand.
authors.forename: Somvong
authors.initials: S
authors.lastname: Tragoonrung
authors.affiliation: PalmElit SAS Montferrier-sur-Lez, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Amblard
authors.affiliation: UMR DIADE, Institut de Recherche pour le Développement Montpellier, France.
authors.forename: Myriam
authors.initials: M
authors.lastname: Collin
authors.affiliation: Institut Jean-Pierre Bourgin, UMR1318 Institut National de la Recherche Agronomique -AgroParisTech ERL3559 Centre National de la Recherche Scientifique, France.
authors.forename: Gregory
authors.initials: G
authors.lastname: Mouille
authors.affiliation: UMR AGAP, PHIV-MRI CIRAD Montpellier, France.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Verdeil
authors.affiliation: UMR DIADE, Institut de Recherche pour le Développement Montpellier, France.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Tranbarger
keywords: abscission zone; cell wall; fruit abscission; oil palm; pectin