ヒゲカビ（Phycomyces）は重力刺激にどのように反応するか

―重力屈性の研究の現状と問題点―

抄録

　Gravity is one of the factors guiding growth in fungi. We summarize what is known about gravitropism in Phycomyces sporangiophore―one of the most developed model systems considering "stimulus perception―stimulus transduction―response" system in fungi.

　Compared with response to light, gravitropism in Phycomyces appears to be less effective in respect to the latency period and the speed of response. Maybe this is the reason why studies on gravitropism have been less intensive, resulting in obscure and sometimes contradictory information on receptors and involved mechanisms.

　There are several parameters influencing the gravitropic response: developmental stage and diameter of the sporangiophore, absolute growth rate, ratio of differential growth. The interplay between gravity and light is expressed in two ways: influence of light on gravisensitivity and tropic equilibrium when both stimuli are present simultaneously.

　Attempts to dissect the mechanism of gravitropic response and to model its kinetics involve experiments in a microgravity environment as well as application of centrifugal force. The gravireceptor is suspected to be localized in the growth zone but has not yet been identified. Further progress in the gravitropic studies could be achieved using mutants with impaired or enhanced perception of gravitational stimuli.