Temperature and flowers

Temperature Many annual plants (e.g., winter wheat) and biennial plants have their time of flowering delayed unless they have undergone a preceding period of wintertime cold. The change brought about by this prolonged exposure to the cold is called vernalization. In the "model" plant Arabidopsis thaliana, vernalization works like this. A gene designated Flowering Locus C (FLC) encodes a transcription factor that blocks the expression of the genes needed for flowering. The level of FLC mRNA is high in the fall. But with the onset of cold temperatures, production of an antisense transcript of FLC (called COOLAIR) increases as does, later, a sense transcript of part of the FLC gene. Both of these RNAs are non-coding; that is, they are not translated into protein. But they cooperate in suppressing the production of FLC mRNA and its translation into FLC protein. With the arrival of spring, there is no FLC protein remaining to suppress flowering so flowering can begin. The buds of many species of woody angiosperms found in temperate climates, such as apples and lilacs, also need a preceding period of cold weather before they can develop into flowers. So these plants cannot be grown successfully at lower latitudes because the winters never get cold enough (a few days at 0–10°C). This bud dormancy is localized. Prior chilling of one bud on a lilac stem enables it to flower while the other, nonchilled, buds on the stem remain dormant.