Analysis of growth rates during phototropism: modifications by separate light‐growth responses

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Abstract
The changes in growth rate during phototropism in light‐grown mustard (Sinapis alba L.) seedlings have been investigated to clarify the pattern of differential growth which causes curvature. It is shown that deliberately induced phytochrome‐mediated straight‐growth responses can modify the pattern of differential phototropic growth. A comparison of techniques used to analyse phototropic responses in mustard shows that separate light‐growth responses can explain the contradictory published data. When white light is moved from above to one side, straight‐growth responses not mediated directly by the blue photo‐receptor are induced by an increase in the amount of light within the hypocotyl, and these modify the pattern of differential growth. In the absence of such separate light‐growth responses, phototropism is caused by a redistribution of growth within the plant axis.