1. Flowering HORT 301 – Plant Physiology November 30, 2009 Taiz and Zeiger Chapter 25 Web Topics 1.2, 25.7 Web Essay 25.2 paul.m.hasegawa.1@purdue.edu A flower is composed of several organs Flowering is due to a shoot meristem transition from a vegetative to a reproductive structure

2. Primary and secondary inflorescences, and flowers Vegetative and reproductive meristems

3. Floral organs are initiated from the floral meristem in concentric whorls Arabidopsis Meristem identity genes → floral organ identity genes → cadastral genes

4. Floral organ identity genes are responsible for formation of reproductive organs No sepals/petals No petals/stamens No stamens/pistils

5. Flowering is regulated by internal and external stimuli Juvenile to adult phase transition is characterized by morphological and physiological characteristics English Ivy (Hedera helix)

6. Juvenile to adult transition requires competence (adult vegetative phase), determination and expression

7. Photoperiodism is an external stimulus of flowering Short-day, long-day and day-neutral plants Night break inhibits flowering Night break of sufficient duration induces flowering

8. Plants are adapted to day-length at different latitudes Phytochromes and cryptochromes are the photoreceptors that regulate flowering

9. Circadian biological clock is how plants track time Periodic rhythm of plant processes that is regulated by an internal timepiece

10. CO (CONSTANS) and FT (FLOWERING LOCUS T ) are regulators of flowering in Arabidopsis (long-day plants) CO expression is clock controlled CO protein accumulation is regulated by proteolysis

11. Similar homologs Regulate flowering in short-day plants Rice (short-day plant) - Heading-date1 (Hd1) = CO and Heading-date3 (Hd3) = FT However, Hd1 inhibits Hd3 activation of flowering

12. Vernalization is required before some plants are responsive to photoperiodic-induced floral transition FLC negatively regulates flowering

13. Plant Biology (2010) Smith et al. Florigen is the biochemical signal for flowering

14. Zeevart (2007) Taiz and Zeiger Web Essay 25.2 FLOWERING LOCUS T is florigen A model for flowering

15. Plant Biology (2010) Smith et al. Integration of flowering stimuli