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American Journal of Botany, Vol 84, 308, Copyright © 1997 by Botanical Society of America, Inc.

PHYSIOLOGY AND DEVELOPMENT

Light perception for sun-tracking is on the lamina in Crotalaria pallida (Fabaceae)

JG Schmalstig

Trifoliolate leaves of Crotalaria pallida Aiton (Fabaceae) exhibit sun-tracking behavior in simulated days and in response to a fixed, oblique light. The site of light perception for sun-tracking is on the lamina, necessitating transport of a signal from the lamina to the site of response (the pulvinule at the base of the leaflet). Evidence for the site of light perception on the lamina includes the following: (1) leaflet movement in response to oblique light is not affected by shading the pulvinule or by illuminating the pulvinule with vertical light; (2) leaflet movement is stopped by shading the lamina while illuminating the pulvinule with oblique light. The proximal end of the leaflet is the most sensitive region for light perception. Light reaching the midveins is not necessary for leaflet reorientation. Presentation times of as little as 10 min followed by darkness resulted in partial leaflet movement in young leaves. This indicates that the signal was not inductive in nature. Estimates of the rate of signal transport range from 3 to 12 cm/h, within the range of phloem transport.




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Copyright © 1997 by the Botanical Society of America, Inc.