STATES OF WATER IN SUMMER-DORMANT APPLE BUDS DETERMINED BY PROTON MAGNETIC-RESONANCE-IMAGING

Magnetic resonance imaging was used to determine water states in parad ormant apple (Malus domestica Borkh.) buds and during early events whe n buds resumed growth. Proton density and states of water were determi ned by creating image maps of proton density and relaxation times (T2) . Summer-dormant (paradormant) buds had T2 relaxation times up to 30 m s. This water in bud tissues is considered relatively free compared to water that had T2 relaxation times of <1 ms in other parts of the ste m and bark. Buds were forced to grow either by pruning off the termina l bud or by starting the bud with thidiazuron (TDZ). Both treatments g ave essentially the same results. After treatment, buds started to gro w immediately and water moved into the stem and into the bud. As there was more free water in the bud, T2 values ranged up to 50 ms. There a ppeared to be an inhibitory gradient down on the shoot, which was remo ved temporarily by excising the top bud. However, between the 2nd and 10th day after removal of the top bud this dominance was reinstated by the highest bud on the stem, which eventually formed a shoot. TDZ tre atment overcame this inhibitory gradient effect. There was also a grow th potential gradient coinciding with the inhibitory gradient. The gro wth of lower buds was much slower than that of the upper buds. The gro wth potential gradient was not overcome by TDZ treatments.