Early histological, hormonal, and molecular changes during pineapple (Ananas comosus (L.) Merrill) artificial flowering induction.

Natural flowering can cause serious scheduling problems in the pineapple (Ananas comosus) industry and increase harvest costs. Pineapple flowering is thought to be triggered by increased ethylene levels and artificial forcing of pineapple flowering is a common practice to promote flowering synchronisation. However, little is known about the early hormonal and molecular changes of pineapple flowering induction and development. Here, we aimed to analyse the molecular, hormonal, and histological changes during artificial pineapple flowering by Ethrel48 treatment. Histological analyses of the shoot apical meristem, leaf gibberellic acid (GA), and ethylene quantification were carried out during the first 72h after Ethrel48 treatment. Expression profiles from ethylene biosynthesis (AcACS2 and AcACO1), gibberellin metabolism (AcGA2-ox1 and AcDELLA1), and flower development (FT-like gene (AcFT), LFY-like gene (AcLFY), and a PISTILLATA-like gene (AcPI)) genes were analysed during the first 24h after Ethrel48 treatment. Differentiation processes of the shoot apical meristem into flower buds were already present in the first 72h after Ethrel48 treatment. Ethrel48 lead to a reduction in GA levels, probably triggered by elevated ethylene levels and the positive regulation AcGA2-ox1. AcLFY activation upon Ethrel48 may also have contributed to the reduction of GA levels and, along with the up-regulation of AcPI, are probably associated with the flower induction activation. AcFT and AcDELLA1 do not seem to be regulated by GA and ethylene. Decreased GA and increased ethylene levels suggest an accumulation of AcDELLA1, which may display an important role in pineapple flowering induction. Thus, this study shows that molecular, hormonal, and histological changes are present right after Ethrel48 treatment, providing new insights into how pineapple flowering occurs under natural conditions.