Pistil strategies controlling pollen tube growth

The progamic phase appears especially well suited for pollen-pistil interaction. During this phase the pistil supports pollen germination and tube growth, and provides an adequate environment, nutrition and directional cues. However, this support does not occur indiscriminantly and some mechanisms operating in the pistil constrain pollen tube growth. An active, regulated constraint is the self-incompatibility reaction, but moderate restrictions of pollen tube growth also occur in compatible matings. These moderate restrictions involve reduced support by the pistil and they operate through two main strategies; one is by decreasing the amount of support and the other is by varying the time at which this support is provided. In this minireview, we examine the evidence that is accumulating for both support and constraint of pollen tube growth by the pistil and discuss the benefits of this dual system.