Molecular mechanisms that trigger flowering...( The appearance of flowers in spring is ...)

The appearance of flowers in spring is one of the surest signs that winter is over, but how do plants follow the changing seasons, and use this information to trigger the formation of flowers? That plants contain internal clocks enabling them to measure day length was proposed 80 years ago and was initially controversial, but now the mechanisms by which plants measure time are being explained by the isolation of genes and proteins that play central roles in this process. In the recent issue of Science (Science,13th February 2004) a group at the Max Planck Institute for Zchtungsforschung in Cologne describes how a molecular circuit around the protein CONSTANS induces flowering. This protein accumulates in the nuclei of plants exposed to long days of spring, but is rapidly degraded if the plant is exposed to short winter days. This molecular circuit is widely conserved in the plant Kingdom and knowledge of how it initiates the formation of flowers in spring could help increase the yield of crop plants.

Around 80 years ago, tobacco plants were shown to distinguish summer and winter by measuring the length of the day and night. This process, called photoperiodism, was later shown to be widespread in the plant Kingdom, and to occur in mammals, insects and birds. In addition to flowering, other seasonal responses in plants are controlled by day length, including the formation of potato tubers and the dormancy of buds in trees.

The first breakthrough in explaining the mechanism of photoperiodism was proposed in the 1930s by Erwin Bnning (1906 - 1990), who worked in Jena, Koenigsberg, and since 1946 Tuebingen. Many aspects of plant behaviour show daily rhythms, such as the movement of leaves to optimise exposure to sun light, or the opening and closing of pores on the leaves to reduce water loss during the day. These behaviours are controlled by the circadian clock, an internal timer that takes 24 hours to complete one cycle. Bnning proposed t
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Contact: Prof. George Coupland
coupland@mpiz-koeln.mpg.de
49-221-5062-205
Max-Planck-Gesellschaft
13-Feb-2004

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