Partial floral evocation by high irradiance in the long‐day plant Sinapis alba

Abstract

Previous work has shown that increased irradiance promotes flower initiation in the long‐day plant Sinapis alba when given during the first half of a single, suboptimal long day. It is without flower‐promoting effect, however, when given during a single short day. In the present work it is shown that, in the apex of plants exposed to a single short day at high irradiance, some changes occur that are normally observed during the transition to flowering (full evocation), e.g., elevated soluble sugar and starch levels, increased numbers of mitochondria and changed nucleolus structure. These changes are of similar magnitude and follow the same sequence as the corresponding changes during full evocation. Other changes, normally associated with full evocation, e.g., increased mitotic activity, are not caused by one short day at high irradiance. This treatment thus produces only what we call “partial evocation”.