Plant responses to photoperiod

Summary 517 I. The importance of photoperiod 517 II. The competence to respond to photoperiod 519 III. The photoperiodic response pathway 521 IV. Systemic signals 523 V. Moderating factors 524 VI. The flowering response to photoperiod in other species 525 VII. Tuberization in potato 526 VIII. Bud set and growth cessation in trees 527 References 528 Photoperiod controls many developmental responses in animals, plants and even fungi. The response to photoperiod has evolved because daylength is a reliable indicator of the time of year, enabling developmental events to be scheduled to coincide with particular environmental conditions. Much progress has been made towards understanding the molecular mechanisms involved in the response to photoperiod in plants. These mechanisms include the detection of the light signal in the leaves, the entrainment of circadian rhythms, and the production of a mobile signal which is transmitted throughout the plant. Flowering, tuberization and bud set are just a few of the many different responses in plants that are under photoperiodic control. Comparison of what is known of the molecular mechanisms controlling these responses shows that, whilst common components exist, significant differences in the regulatory mechanisms have evolved between these responses.