Water status and carbohydrate pools in tulip bulbs during dormancy release

Changes in the physical state of cellular water and its interrelations with carbohydrate metabolism were studied during preplanting storage of tulip bulbs (Tulipa gesneriana 'Apeldoorn'). Magnetic resonance imaging, light and scanning electron microscopy and high-performance anion exchange chromatography with pulsed amperometric detection were used to follow time-dependent changes during bulb storage at 17 or 20degreesC (nonchilled) or 4degreesC (chilled). No visible differences in scale structure and central bud development were observed microscopically between chilled and nonchilled bulbs. However, the scales of the chilled bulbs exhibited higher water content, faster starch degradation and increased concentrations of sucrose and ethanol-soluble fructan. Quantitative measurements of magnetization transfer (MT) indicated a smaller fraction of a solid or a restricted-mobility proton pool in the scales of the chilled bulbs. By contrast, the MT effect was significantly higher in the central bud of the chilled than in the nonchilled bulbs. Degradation of storage polysaccharides to low-molecular-weight sugar molecules during release from dormancy could be accompanied by local release of water molecules tightly bound to the polysaccharide granules into the bulk water, or by an influx of free water molecules due to increased osmotic potential caused by the raised sugar concentration, or by a combination of both effects.