The main transport form of sugar in plants is sucrose. It is a disaccharide made from one glucose molecule and one fructose molecule.
During photosynthesis, leaves produce carbohydrates from carbon dioxide and water. Plants commonly convert some of that newly made sugar into sucrose, which dissolves readily in water and can be loaded into the phloem. The phloem then distributes it from sources such as mature leaves to sinks such as roots, fruits, seeds, flowers, and growing shoots.
Sucrose is not the same as glucose, although glucose is one of its components. Fructose is the other component, while maltose consists of two glucose units and is not the principal long-distance transport sugar in most plants. Plants may store carbohydrates as starch, but starch is insoluble and is not the usual form carried through the vascular system.
The same molecule is familiar as table sugar. Commercial sucrose is refined mainly from sugarcane and sugar beet, and plants also use it as an energy-storage and signaling molecule.