THE MECHANOSENSORY CALCIUM-SELECTIVE ION-CHANNEL - KEY COMPONENT OF APLASMALEMMAL CONTROL CENTER

Mechanosensory calcium-selective ion channels probably serve to detect not only mechanical stress but also electrical, thermal, and diverse chemical stimuli. Because all stimuli result in a common output, most notably a shift in second messenger calcium concentration, the channel s are presumed to serve as signal integrators. Further, insofar as sec ond messenger calcium in turn gives rise to mechanical, electrical, an d diverse chemical changes, the channels are postulated to initiate re gulatory feedbacks. It is proposed that the channels and the feedback loops play a wide range of roles in regulating normal plant function, as well as in mediating disturbance of normal function by environmenta l stressors and various pathogens. In developing evidence for the phys iological performance of the channel, a model for a cluster of regulat ory plasmalemmal proteins and cytoskeletal elements grouped around a s et of wall-to-membrane and transmembrane linkers has proved useful. An illustration of how the model might operate is presented. It is found ed on the demonstration that several xenobiotics interfere both with n ormal channel behaviour and with gravitropic reception. Accordingly, t he first part of the illustration deals with how the channels and the control system within which they putatively operate might initiate gra vitropism. Assuming that gravitropism is an asymmetric expression of g rowth, the activities of the channels and the plasmalemmal control sys tem are extrapolated to account for regulation of both rate and allome try of cell expansion. Finally, it is discussed how light, hormones, r edox agents and herbicides could in principle affect growth via the pu tative plasmalemmal control cluster or centre.