Eustoma grandiflorum is a popular and important cut-flower crop as a result of its long, multiflowered inflorescence, and varying flower colors, sizes, and shapes. The vase life of Eustoma cut flowers can exceed 2 weeks under favorable conditions but is often cut short by early flower senescence or low opening rates of upper flower buds. Flower opening results from the rapid growth and enlargement of petal cells, which are in turn regulated by carbohydrate sources and the cell water potential (In et al., 2006; Pun and Ichimura, 2003). Flower senescence is accompanied by a drop in water uptake, petal wilting, flower abscission, and altogether lowered ornamental quality.
Sugars in vase solutions extend the vase life of many cut flowers including Eustoma (Cho et al., 2001; De la Riva et al., 2009; Ichimura and Korenaga, 1998; Islam et al., 2003). Carbohydrates are the main substrate for respiration, which is essential for all living cells, and they are also a major structural material used in cell growth and enlargement and a soluble component in petal tissues, and hence an important osmotic regulator of water potential (Mayak et al., 2001). Delaying climacteric ethylene production and reducing ethylene sensitivity are also reported to be beneficial effects of sugars, although the modes of action are not yet clear (Pun and Ichimura, 2003). In short, sugar enhances cut-flower quality by many different, interacting roles. A more thorough understanding of how sugars are translocated in cut flowers may greatly help in elucidating these roles.
In gladioluses (Gladiolus hybridus Hort.), opening florets have the highest sugar concentration, whereas senescent florets have lowered sugar concentrations (Waithaka et al., 2001). Total carbohydrates in the rose (Rosa hybrids L.) corolla decrease with time, but not as much as in the leaves; and the decrease in the corolla is more pronounced when leaves on cut flowers were removed, suggesting a source-sink relationship from leaves to petals (Marissen and La Brijn, 1995). Because cut flowers are isolated from the mother plant, sugars in cut flowers can only come from the leaves, stem, or vase solution during the vase life. Like gladioluses, Eustoma cut flowers contain florets of different development levels on the same stem; and like roses, leaves are usually retained on Eustoma cut flowers. Thus, sugar transport by Eustoma is more complex than that by the other two flowers, and more studies on Eustoma are needed. We tested the ability of Eustoma to take up and use different sugars in the vase solution and then investigated how the sugars were translocated by measuring sugar concentrations in different parts of Eustoma cut flowers with and without sugar-supplemented solutions.
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