Programmed cell death in kiwifruit stigmatic arms and its relationship to the effective pollination period and the progamic phase.
OBJECTIVE
Kiwifruit is a crop with a highly successful reproductive performance, which is impaired by the short effective pollination period of female flowers. This study investigates whether the degenerative processes observed in both pollinated and non-pollinated flowers after anthesis may be considered to be programmed cell death (PCD).


METHODS
Features of PCD in kiwifruit, Actinidia chinensis var. deliciosa, were studied in both non-pollinated and pollinated stigmatic arms using transmission electron microscopy, DAPI (4',6-diamidino-2-phenylindole) staining, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling) assays, DNA gel electrophoresis and caspase-like activity assays.


RESULTS
In the secretory tissues of the stigmatic arms, cell organelles disintegrated sequentially while progressive vacuolization was detected. At the same time, chromatin condensation, nuclear deformation, and DNA fragmentation and degradation were observed. These features were detected in both non-pollinated and pollinated stigmatic arms; they were evident in the stigmas of pollinated flowers by the second day after anthesis but only by 4 d after anthesis in non-pollinated flowers. In addition, in pollinated stigmatic arms, these features were first initiated in the stigma and gradually progressed through the style, consistent with pollen tube growth. This timing of events was also observed in both non-pollinated and pollinated stigmatic arms for caspase-3-like activity.


CONCLUSIONS
The data provide evidence to support the hypothesis that PCD processes occurring in the secretory tissue of non-pollinated kiwifruit stigmatic arms could be the origin for the observed short effective pollination period. The results obtained in the secretory tissue of pollinated kiwifruit stigmatic arms upon pollination support the idea that PCD might be accelerated by pollination, pointing to the involvement of PCD during the progamic phase.
Departamento de Fisiología Vegetal, Facultad de Farmacia, Universidad de Santiago, Campus Sur, 15872 Santiago de Compostela, Spain.
Yolanda
Y
Ferradás
Departamento de Fisiología Vegetal, Facultad de Farmacia, Universidad de Santiago, Campus Sur, 15872 Santiago de Compostela, Spain.
Marián
M
López
Departamento de Biología Vegetal y Ciencia del Suelo, Facultad de Biología, Universidad de Vigo, 36310 Vigo, Spain.
Manuel
M
Rey
Departamento de Fisiología Vegetal, Facultad de Farmacia, Universidad de Santiago, Campus Sur, 15872 Santiago de Compostela, Spain mvictoria.gonzalez@usc.es.
Ma Victoria
MV
González
D029042:Actinidia / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics; D002843:Chromatin / Q000235:genetics; D053837:DNA Cleavage; D053938:DNA Fragmentation; D018744:DNA, Plant / Q000235:genetics; D035264:Flowers / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure; D020287:In Situ Nick-End Labeling; D046529:Microscopy, Electron, Transmission; D010940:Plant Proteins / Q000378:metabolism; D054817:Pollination / Q000502:physiology*; D012098:Reproduction
D002843:Chromatin; D018744:DNA, Plant; D010940:Plant Proteins; D053148:Caspase 3
Actinidia chinensis var. deliciosa; DAPI staining; EPP; PCD; TEM; TUNEL assay; caspase-like activity; effective pollination period; pollen–pistil interaction; programmed cell death; reproductive biology