Effect of Organ Removal on Vegetative Growth and Regeneration

The pattern of regeneration of flowering plants depends on the type of treatment. Plants cut to ground level regenerate from the stem base, while those with a stem or part of a stem left, mostly branch and produce new flowering shoots from leaf nodes between petioles and the stem (Tiley and Philp, 1997, 2000; Otte and Franke, 1998).

The only study that measured the ability of H. mantegazzianum to compensate for removal of leaves (Pysek et al., 1995) found that on average 12.4% of the leaf area removed at flowering time was regenerated by the end of the growing period (corresponding to 2752 cm2/plant). In August, at the time of fruit ripening, plants that had their leaves removed in June had three times more leaf area than control plants, which at that time had lost most of their leaf area due to senescence (Pysek et al., 1995).

Plants in the experiment reported in the previous section did not survive to the next year but differed widely in the level of regeneration effort. Those cut when the flowering stem appeared produced an average of 7.6 ± 4.0 regenerating branches (mean ± sd, n = 10), while those cut after the terminal bud had opened produced 5.1 ± 3.6 (Fig. 7.1 A). The difference was

Fig. 7.1. (A) Vigorous plants are likely to regenerate better than weak plants. Ten plants were cut at ground level shortly after the flowering stem appeared (diamonds, dotted line), another ten when the terminal bud opened and the inflorescence emerged from sheathed bracts (solid square, solid line). The number of branches plants had at the time of the treatment is used as a proxy for plant vigour. Regeneration is measured as the number of branches that a plant produced under continuous branch removal. Branches were removed immediately as they developed. (B) Measures of regeneration effort are correlated. Plants that made many regeneration attempts over a long period regenerated more branches. This is indicated by a significant correlation between these measures (r = 0.492, P < 0.05). Note that the slopes are not significantly different and hence not distinguished in the plot. Symbols for the two treatments as in (A). Based on original data.

Fig. 7.1. (A) Vigorous plants are likely to regenerate better than weak plants. Ten plants were cut at ground level shortly after the flowering stem appeared (diamonds, dotted line), another ten when the terminal bud opened and the inflorescence emerged from sheathed bracts (solid square, solid line). The number of branches plants had at the time of the treatment is used as a proxy for plant vigour. Regeneration is measured as the number of branches that a plant produced under continuous branch removal. Branches were removed immediately as they developed. (B) Measures of regeneration effort are correlated. Plants that made many regeneration attempts over a long period regenerated more branches. This is indicated by a significant correlation between these measures (r = 0.492, P < 0.05). Note that the slopes are not significantly different and hence not distinguished in the plot. Symbols for the two treatments as in (A). Based on original data.

significant (t = 2.36; df = 18, P = 0.03), indicating that early treated plants have more resources that could be mobilized and allocated to regeneration. In addition, the regeneration effort in terms of the number of branches produced marginally significantly depended on plant vigour at the time of treatment (t = 2.02, df = 18, P = 0.06). Strong plants produced more regenerating branches than plants that were less vigorous at the time of tissue removal (Fig. 7.1A). The period over which regeneration occurred did not depend on the timing of the treatment (t = 0.94, df = 18, P = 0.36); plants produced new branches over 38.2 ± 14.0 days (mean ± sd, n = 20). Neither was the length of this period affected by plant vigour (t = 0.51, df = 18, P = 0.62). Nevertheless, both measures of regeneration effort are significantly correlated, which indicates that there might be an advantage of being large, manifested both in the period of time over which and extent to which regeneration occurs (Fig. 7.1B).

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