(75) Sugars and Flower Induction in Poinsettia

Abstract

During Fall 2004, poinsettia plants were grown in a greenhouse (Texcoco, Edo. Mexico, 19°29'N). The objectives were to: 1) evaluate which soluble carbohydrates (mono- and disaccharides) are present in the cultivars Supjibi and Peter Star and their concentrations; 2) study the relationship between sugar content and flower induction; and 3) analyze the relationship between starch content and phenology of the plant. Apical meristems were prepared for microscopy, soluble sugars, and sugars from starch hydrolysis were studied by HPLC. Flower induction in `Supjibi' took place about 99 days after transplant (DAT), with no artificial short photoperiod. In `Peter Star', flower induction took place about 137 DAT, 19 days after initiation of short-day photoperiod. Soluble sugars found were: sucrose, maltose, glucose, and fructose (in order of the highest to lowest concentration). Concentration varied from 0.5% to 2.1% for `Supjibi' and from 1.1% to 2.9% for `Peter Star', based on fresh weight. Sucrose content is reduced in root and mature leaf during flower induction, probably sent to young leaves. During flower induction, there is also an increase in glucose in young leaves. Sugars from starch hydrolysis were: fucose, (6-desoxi-L-galactose), fructose, and galactose. Soluble sugars content generated from starch varies in each organ from 2.0% to 32% for `Supjibi', and from 2.0% to 39% in `Peter Star'. During induction, starch content is reduced (between 6% and 9%). After flower induction, there is an increase in leaf area and in starch content (from 32% to 39%), during bract development starch seems to be utilized in this plant part.