Ethylene is involved in the autochemotropism of Phycomyces.

The sporangiophore of the fungus Phycomyces blakesleeanus has the property of growing away from a barrier which is few mm from the growing zone of the sporangiophore (avoidance or autochemotropic response). A model has been published (Cohen, R.J., Jan, N.Y., Matricon, J., Delbrück, M.: J. Gen. Physiol. 66, 67-95 (1975)). To explain the avoidance response which postulates that the sporangiophore emits and readsorbs a volatile growth-promoting effector (gas X) and that the barrier modifies the effector distribution by acting as an aerodynamic obstacle, causing a higher concentration of gas X on the side of the sporangiophore closer to the barrier. From this model we deduced three properties of the gas X. Of the several gases tested (N2, CO2, CH4, C2H2, C2H4, C2H6) only ethylene (C2H4) had all these three properties, a finding which suggests that it has a role in the avoidance response (autochemotropism).