Figure 8.

A putative molecular model of the self-incompatibility (SI) response in sheepgrass. Interaction of a stigma S-determinant with its cognate pollen S-determinant rapidly triggered the SI signaling network. Solid segments and arrows show SI-induced reactions at cytological and molecular levels. Dotted segments and arrows show possible SI triggered events. Cytological observation revealed that the self-pollinated pollens can normally germinate at 5 min. However, the elongation of pollen tubes was inhibited from 10 to 30 min, and subsequently, the pollen tube growth stopped. Many SI-related signaling genes and pathways were induced, including genes related to calcium (Ca²⁺) signaling, protein phosphorylation, plant hormone, reactive oxygen species (ROS), nitric oxide (NO), actin depolymerization, microtubule depolymerization, and programmed cell death (PCD). Thus, SI may trigger a comprehensive calcium- and phytohormone-dominated signaling cascade and activate PCD, which may explain the rapid inhibition of self-pollen tube growth as observed by cytological analyses.