Chilling effects for normal growth of tulip bulbs estimated by MRI

Changes in the distribution of free water by chilling treatment was non-destructively traced in tulip 'Oxford' bulb tissues using ¹H-NMR imaging (MRI). A strong water signal was observed in bulb scales stored initially at 15°C for 3 weeks and subsequently at 5°C for 9 weeks (chilling treatment), while a weak water signal was observed in non-chilled bulb scales held at 20°C throughout the storage period (non-chilling treatment). Starch granules, which characterize cortex parenchyma cells, were degraded by the chilling treatment from the vicinal cells to epidermal tissues. The degraded products of starch and water from out layers seem to migrate and accumulate temporarily in inner cortex parenchyma cells. Respiratory activity of the chilled bulbs was three times higher than the non-chilled bulbs, when the bulbs were transferred to 20 °C. The accumulation of low-molecular compounds from the starch breakdown and the accelerated metabolism of cortex parenchyma cells, during chilling treatment, are considered to sustain rapid growth of a shoot after planting.