THE REFLECTANCE PROPERTIES OF PLANT INTERNODES MODIFY ELONGATION RESPONSES TO LATERAL FAR-RED RADIATION

The quality and quantity of light reflected from Nicotinia tabacum L. internodes was monitored as the angle of incidence was varied, Reflect ance of incident light, which was either normal or longitudinal to the internode asis, was investigated. Increasing the angle of incidence c aused a greater proportion of incident light to be reflected, Light st riking N. tabacum internodes was always modified prior to reflection, and smaller incident angles produced greater modification of the refle cted light quality, At larger angles, interactions with the internode were reduced, As a parallel investigation, the extension growth rate o f light-grown Sinapis alba L. seedlings was monitored continuously usi ng sensitive linear displacement transducers, When the angle of illumi nation by fibre-optic probes, presenting far-red light to the growing internode, was changed from 0 degrees to 45 degrees, an increase was o bserved in stem extension rate, There is a possibility that this rate increase was the result of a fall in the red:far-red ratio (R:FR) pres ent inside the plant internode as the angle of incidence was altered, However, it is more likely that it was due to the larger surface area of stem being illuminated, The consequences of these observations are discussed in relation to the potential influence of such modified refl ections on canopy light environments and resultant shade responses,whi ch ma occur when light of known R:FR impinges on plant internodes at a ngles other than 0 degrees, The possibility is discussed that plants m ag perceive the quality of reflected radiation from neighbouring plant s to be substantially different dependent upon the angle at which it i s reflected.