Dormancy Interferes with Flowering in Perennial Plants with Short Day Regulation of Both Processes: A Mini-Review

In many perennial woody plants growing in the temperate and cold regions, regulation of seasonal growth cessation and floral initiation are closely integrated, both taking place in photoperiods shorter than a critical length. In the temperate shrub black currant (Ribes nigrum L.), the two processes proceed harmoniously in parallel under naturally decreasing autumn photoperiods, whereas an abrupt shift to photoperiods well below the critical length results in an immediate growth cessation and premature dormancy. As a result, floral initiation is suppressed and arrested. Other perennial plants such as hop (Humulus lupulus), which have the same dual short day responses, behave in the same way. In such plants, optimal flowering takes place at near-critical photoperiods, which are short enough to induce flowering and still long enough to prevent premature dormancy. These responses deviate from the situation in annual plants, which have predominated in studies on photoperiodic control of flowering. Another example of linkage between flowering and dormancy responses is the well-known dual effects of chilling temperature on vernalization and its relation to dormancy. Elucidation and disentangling of these networks of integrated processes are now awaiting joint research efforts in the areas of molecular genetics and experimental plant physiology.