Chemotropism

[5] The ovary releases chemicals that stimulates a positive chemotropic response from the developing pollen tube.

[5] The steep calcium gradient is localized in the tip and promotes elongation and orientation of the growth.

[8][9] In more complex organisms an example of chemotropic movement includes the growth of individual neuronal cell axons in response to extracellular signals.

[11] The neuronal growth cones are guided by gradients of chemoattractant molecules released from their intermediate or final targets.

[16] By secreting these factors a chemical gradient is formed that attracts the other type of yeast cell during mating.

In order for the yeast to sense the gradient they have to have proper receptors that bind a- or α-factor: Ste3 and Ste2 respectively.

PSM V77 D352 The course of the pollen tube in a rock rose
Chemotropism seen in Yeast. Haploid Yeast cells release a- and α-factors that bind to the receptors of another haploid Yeast cell. The two Yeast cells fuse together to form an a/α diploid zygote.