INFLORESCENCE INDUCTION AND INITIATION IN HEDERA HELIX

Abstract

ABSTRACT At 16°C Hedera helix L. is an obligatory short-long day (SLD) plant as regards inflorescence initiation (12-h photoperiod for short days (SD). 16-h photoperiod for long days (LD)). The presence of a developing terminal inflorescence (for at least 24 days after initiation) can substitute for SD and allow inflorescence initiation on a pruning-induced branch of a flowering shoot under LD only. The temperature at which exposure to LD occurs is critical, such that the inflorescence initiation response obtained is saturating at 16°C, only very marginal at 21°C, and absent at 24°C. A partial evocation (a prefloral stage) tends to occur under environmental conditions in which inflorescence initiation and development do not occur. At 16°C this is expressed as a production of bracts (scales), a change in apical meristem morphology, and an activation of the axillary meristems near the apical one. At the end of this process, the partially evoked meristem can either reduce in size or entirely cease its activi...