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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.

The present study was conducted to determine the critical optimum and toxic concentrations of potassium (K) using segmented analysis and its relationship with some physiological, anatomical, and nutritional responses to increasing K in hydroponically grown Lilium sp. L. cv. Arcachon. Plants were fertigated with nutrient solutions containing K (K_ext) at 0, 2.5, 5.0, 7.5, 12.5, 17.5, 22.5, and 30 mmol·L⁻¹. Maximum flower diameter occurred when, on a dry mass basis, shoot K (K_int) ranged from 504 to 892 mmol·kg⁻¹; however, a lower K_int was required to obtain maximum biomass accumulation and shoot length (384 and 303 mmol·kg⁻¹, respectively). Potassium increased in all plant organs as K in the nutrient solution increased. Nitrogen increased in young leaves and magnesium (Mg) decreased as K_ext increased. Concentrations of K_ext from 5 to 17.5 mmol·L⁻¹ increased the size of chlorenchyma and occlusive cells; however, metaxylem vessels were unaffected. Net photosynthetic rate was higher in young leaves, whereas water potential increased in both young and mature leaves when K_ext was greater than 22.5 mmol·L⁻¹. Critical concentrations varied according to the growth parameter. Optimum K_int ranged from 303 to 384 mmol·kg⁻¹ for vegetative parts, whereas parameters related with flower growth ranged from 427 to 504 mmol·kg⁻¹. Concentration of 504 mmol·kg⁻¹ K_int was associated with optimum growth for all the parameters assessed, whereas a K_int greater than 864 mmol·kg⁻¹ was associated with a decline in growth; thus, these concentrations were considered as the critical optimum and critical toxicity levels, respectively. The optimum and toxicity critical K_int were estimated when K_ext in the nutrient solutions was 5.6 and 13.6 mmol·L⁻¹, respectively.