ISSN:
1365-3040
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Abstract The present study was prompted by the question as to whether the strong effect of red and far-red light treatments on blue-light-mediated phototropism in the sesame (Sesamum indicum L.) hypocotyl (Woitzik & Mohr, 1988) should be attributed in part to changes initialed by light in the gravitropic counter-response. Light treatments, operating through phytochrome, do indeed strongly affect the gravitropic response. However, the direction of the light effect is the same in gravitropism, as in phototropism. Thus, the gravitropic counter-response leads to an underestimate, rather than an overestimate, of the importance of phytochrome action on phototropic responsiveness. The effect of red and far-red light, operating via phytochrome, on the gravitropic response of the sesame hypocotyl could be studied in the present paper without any interference due to phototropism or light control of longitudinal growth. It was found that the effects of red and far-red pretreatments (given prior to the onset of the stimulus) as well as the action of simultaneously applied red or far-red light (simultaneous to the phototropic or gravitropic stimulus) are very similar in both phototropism and gravitropism. In particular, the seedling is capable of superimposing information about the actual light conditions during bending on the ‘memory’ it has about the light conditions prior to the onset of phototropism or gravitropic stimulation, This striking similarity between the phototropic and gravitropic responses possibly indicates that phytochrome affects the signal-response-chain at a relatively late stage, after the phototropic and the gravitropic signal-response chains have merged. From a teleonomic point of view the action of red and far-red light on phototropic, as well as gravitropic, responsiveness can be conceived as part of a shade escape strategy.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-3040.1988.tb01809.x
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