Redbud seeds have intermediate physiological dormancy. Embryos displaying this type of dormancy show an increased growth potential following chilling stratification (Hartmann et al., 2002). Geneve (1991) showed that isolated redbud embryos from chilled seeds grew faster than non-chilled ones. However, these measurements were performed by hand and made every 24 h. In contrast, using the computer-aided imaging system, radicle length could be measured every hour and a precise growth rate calculated with little researcher investment in time. As predicted, radicles of
Fig. 33.3. Germination time course of ctg144-D (o) and Columbia wild-type (•) Arabidopsis thaliana seeds at 10°C after 6 months dry after-ripening (AR) at 25°C. Each symbol represents the mean of four replicates of 50 seeds and the bars represent the standard error. An asterisk above a symbol depicts statistically significant differences in percentage germination determined by a single degree of freedom F-test (P < 0.05). HAI = hours after imbibition.
non-chilled redbud embryos took 90 h to reach 10 mm in length, while embryos chilled for 4 weeks reached a radicle length of 10 mm in only 45 h (Fig. 33.4; P < 0.01). If the data was evaluated on a 24 h basis, as has been done earlier (Geneve, 1991), a clear quadratic increase in seedling size was seen (Fig. 33.4a). However, using a shorter interval image analysis, redbud embryos showed three distinct phases of growth (Fig. 33.4b). Following removal from the testa, there was a lag period prior to initiation of a slow increase in radicle size. This was followed by a rapid linear increase in size. In non-chilled embryos, growth did not begin until 50 h after removal from the testa. The subsequent slow growth phase required an additional 30 h before embryos entered the rapid linear phase of growth. In contrast, embryos from chilled seeds required only 15 h to initiate growth and began the rapid linear phase only 25 h later. These results show that the major difference between embryos isolated from non-chilled and chilled seeds was the time to initiate radicle growth. After growth was initiated the growth patterns were comparable.
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