Student Sheet 4 - Pollen Tube Growth

When a pollen grain is released from an anther, it is partially dehydrated. If it lands on the surface of a stigma of the same flower (self-compatible) or of a different flower of the same species (self-incompatible), it rehydrates. Some species have ‘dry’ stigmas, and it is thought that lipids in the surface coat of the pollen grain bring about a concentration gradient of water that directs the growth of the pollen tube. If the humidity is very high, the pollen will rehydrate anyway. Other plants have ‘wet’ stigmas and the stigma exudate hydrates the pollen grain itself, so surface lipids in the pollen are not so important.

The growth of pollen tubes is easily observed under medium power of a microscope, and this practical suggests some ways in which this can be done.

The attached ZIP file shows the growth of pollen tubes under the microscope over the course of 75 minutes.

Pollen tubes from birch (at 75 min)

Pollen tubes from chestnut (at 40 min).