Polyamines and transglutaminase activity are involved in compatible and self-incompatible pollination of Citrus grandis

Pollination of pummelo (Citrus grandis L.Osbeck) pistils has been studied in planta by adding compatibleand self-incompatible (SI) pollen to the stigmasurface.The pollen germination has beenmonitored inside the pistil byfluorescent microscopy showing SI alteredmorphologieswithirregular depositions of callose in the tube walls, and heavycallose depositions in enlarged tips. The polyamine (PA)content as free, perchloric acid (PCA)-soluble and -insolublefractions and transglutaminase (TGase) activity have beenanalyzed in order to deepen their possible involvement in theprogamic phase of plant reproduction. The conjugated PAs inPCA-soluble fraction were definitely higher than the free andthePCA-insoluble forms, in both compatible and SI pollinatedpistils. In pistils, pollination caused an early decrease of freePAs and increase of the bound forms. The SI pollination,showed highest values of PCA-soluble and -insoluble PAswith a maximum in concomitance with the pollen tube arrest.As TGase mediates some of the effects of PAs by covalentlybinding them to proteins, its activity, never checked before inCitrus, was examined with two different assays. In addition,the presence of glutamyl-PAs confirmed the enzyme assaydata and excluded the possibility of a misinterpretation.The SIpollination caused an increase in TGase activity, whereas thecompatible pollination caused its decrease. Similarly to boundPAs, the glutamyl-PAs and the enzyme activity peaked in theSI pollinated pistils in concomitance with the observed block of the pollen tube growth, suggesting an involvement ofTGase in SI response.