Apical dominance

Most plants exhibit "apical dominance" which means that the presence of a terminal (distal) meristem tends to suppress lateral shoot initiation (11). Since lateral shoot production is an important characteristic to assess in hydrilla, the frequency of shoot production was determined in sequentially cut (distal to proximal) explants (Table VI). Even though the 4 cm apical meristem contained several nodes, almost none of these produced new shoots. However, nearly half the 2-node explants subtending the cut apical meristem produced new shoots. There was no apparent difference in percent of new shoots produced once the apical meristem was removed. 

Acetylcholine 254 receptor, 256 Actinomycin D, 225 Action potential, 260 Active transport, 249 ATP requirement, 254, 257, 258 Activin, 100 Actinomycetes, 211 Allelic exclusion, 2, 34-38, 64 Allosterism, 273 Animal cap assay, 99, 100 Animal pole, 99 Antibody diversity, 1-66 Apical dominance, 226 Apical ridge, 100, 103-105 Aptamers, 177... 

The root tip with apical meristem showed length enhancement with lateral root formation. However, the center root tip formed lateral roots without length enhancement of the original root tip (Fig. 3). Some researchers have reported the effect of the apical dominance on growth, which was observed as an increase in specific growth rate for inocula formed by branched roots (12,14). 

Some suggest the concept that diversity of the hairy root tip—cell division, elongation, and maturation regions—is necessary for optimal growth rate (15). The best growth of root tips is consistent with the formation of new branches in maturation zones and enhancement of apical dominance (14). 

Auxin, cytokinin, and other unknown substances are thought to regulate apical dominance.482 Application of cytokinin or overexpression of the 1PTgene shows a phenotype with a reduction in apical dominance.404 483 484 Arabidopsis mutants with increased levels of cytokinin also show reduced apical dominance 485-487 These results suggest that cytokinins play a role in the promotion of bud outgrowth. 

A root-derived suppressor negatively regulating the formation of roots has been hypothesized.497 This proposed mechanism, termed root apical dominance, is analogous to the means for apical dominance in shoots. The cytokinin, tZR, in root xylem sap is hypothesized to play the role of the main suppressor, and tZR transported from roots to shoots via the transpiration stream negatively regulates the formation of adventitious roots.365... 

A transgenic reduction in MIPS activity has also been reported. Antisense suppression of MIPS in transgenic potato resulted in a sevenfold reduction in inositol, and resulted in reduced apical dominance, altered leaf morphology, precocious leaf senescence and a decrease in overall tuber yield. The altered leaf morphology was found to be due to cell enlargement in the leaves. The authors of this study found that in addition to inositol, galactinol, and raffinose levels were reduced. In contrast, increases were observed for hexose phosphates, sucrose, and starch. The authors further concluded that many different inositol metabolites may have contributed to the development of the phenotypes observed (Keller et al., 1998). 

Abscission and dehiscence Seed and bud dormancy release Apical dominance release... 

It is generally known that the equilibrium between auxin and cytokinin concentrations is determinative for the type of organ regenerated from callus tissue in vitro. High cytokinin to auxin ratio leads to the shoot Ibrmation, whereas the change in the ratio on behalf of auxin eventuates mostly in root proliferation [253]. Concerning apical dominance and... 

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