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Alyssa H. Cho, Carlene A. Chase, Danielle D. Treadwell, Rosalie L. Koenig, John Bradley Morris, and Jose Pablo Morales-Payan

cultivars with growth habits that reduce light penetration to the soil surface and reduce weed seed germination. Branching in sunn hemp depends on the planting density and apical dominance of the plant. Planting density can influence the height and formation

Open access

Julian C. Crane and Ben T. Iwakiri

Abstract

Pronounced vegetative apical dominance in pistachio was exhibited by sparse lateral branching and by response to conventional pruning. This dominance necessitates a pruning procedure different from other deciduous fruit and nut species. Marked apical dominance also occurred both in the patterns of fruit set in the inflorescence as a whole and in the individual branches composing it. The percentage of fruit set was highest in the apical portion of the inflorescence and generally decreased to the proximal portion. Similarly, although only 8% of the flowers on the branches of the inflorescence occupied a terminal position, 60% of the total fruit produced were terminal.

Open access

M. L. Brenner, D. J. Wolley, V. Sjut, and D. Salerno

Abstract

Correlative inhibition of axillary shoot growth is one aspect of apical dominance that has been extensively investigated, but we still have a limited understanding of how this interesting process is controlled (2). Substantial evidence indicates that auxin, especially IAA synthesized in the apical portion of the plant, can inhibit axillary shoot growth (see refs. 2, 14, and 15) and that the inhibitory effect of IAA is most likely exerted indirectly (see ref. 10). In general, when apical dominance is released by surgical removal of the apical portion of a young plant, release of suppressed growth of axillary buds is detectable within 6 to 12 hr. There are three phases of growth, an initial slow phase, a second accelerated growth phase (see ref. 2) and a subsequent slow phase. There is also considerable information indicating that factors from roots, especially cytokinins, may be important for promotion of axillary shoot growth (12).

Open access

George C. Martin

Abstract

None of the physiological events in plant growth and development is truly independent. Photosynthesis, flowering, and mineral transport are sharply focused areas of research; yet these phenomena are not separable from other metabolic events in the plant. This feature of interdependence may be called correlations (26) or growth correlations (49, 50). The control exerted by the growth zone emanates from a meristem; these meristems include the root or shoot apex, cambium, flowers, fruit, pollen on stigma, and the ovule or seed in a fruit.

Open access

M. Tran-Thanh-Van

Abstract

Lateral buds situated along the stem axis of a Cymbidium pseudobulb show a gradient in their degree of differentiation. It is shown that buds situated on the swollen upper part of the pseudobulb, normally inhibited in their growth and development by apical dominance, are capable of evolving either into floral shoots or into protocorms and vegetative shoots. A new method, both simple and rapid, of clonal multiplication of Cymbidium is described.

Free access

Rodomiro Ortiz and Dirk R. Vuylsteke

Apical dominance, i.e., the inhibition of lateral bud growth due to growth substances released by the terminal bud, has been considered as a limiting factor for the perennial productivity of plantains (Musa spp., AAB group). Segregation ratios in F1 and F2 plantain-banana hybrids suggest that inheritance of apical dominance is controlled by a major recessive gene, ad. The dominant Ad allele improved the suckering of plantain-banana hybrids, as measured by the height of the tallest sucker at flowering and harvest. At harvest, the ratoon crop of the diploid and tetraploid hybrids had completed 70% to 100% of its vegetative development, whereas the ratoon of the plantain parents, due to high apical dominance, was only at 50% of total pseudostem growth. Sucker growth rates are generally the result of gibberellic acid (GA3) levels, and it is suggested that the Ad gene regulates GA3 production. However, the Ad gene has incomplete penetrance, genetic specificity, and variable expressivity. Increased frequency of the Ad gene and a commensurate improvement in the suckering behavior of the diploid populations may be achieved by phenotypic recurrent selection.

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Senay Ozgen, James S. Busse, and Jiwan P. Palta

; Sha et al., 1985 ). This condition is typified by browning and death of the shoot tip, loss of apical dominance, and axillary shoot development in an in vitro shoot culture. Transpiration is limited during in vitro culture by the high humidity that

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Shiow Y. Wang, Miklos Faust, and Michael J. Line

The effect of IAA on apical dominance in apple buds was examined in relation to changes in proton density (free water) and membrane lipid composition in lateral buds. Decapitation induced budbreak and enhanced lateral bud growth. IAA replaced apical control of lateral buds and maintained paradormancy. Maximal inhibition was obtained when IAA was applied immediately after the apical bud was removed; delaying application reduced the effect of IAA. An increase in proton density in lateral buds was observed 2 days after decapitation, whereas the change in membrane lipid composition occurred 4 days later. Removing the terminal bud increased membrane galacto- and phospholipids and the ratio of unsaturated to corresponding saturated fatty acids. Decapitation also decreased the ratio of free sterols to phospholipids in lateral buds. Applying thidiazuron to lateral buds of decapitated shoots enhanced these effects, whereas applying IAA to the terminal end of decapitated shoots inhibited the increase of proton density and prevented changes in membrane lipid composition in lateral buds. These results suggest that change in water movement alters membrane lipid composition and then induces lateral bud growth. IAA, presumably produced by the terminal bud, restricts the movement of water to lateral buds and inhibits their growth in apple.

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Bradley Dotson*, Camila Rey, Joonyup Kim, and Sara Patterson

Cell separation regulates basic developmental processes such as abscission and dehiscence and is one of the horticultural traits first to be selected by mankind. Abscission is characterized by an active cell separation process where organs are detached from the main body of the plant through the dissolution of the middle lamella. Crops with early abscission can have significant reduction in yield. For example, canola, Brassica napus, loses 5% to 10% of crop due to early pod shatter. By screening T-DNA mutagenized populations of A. thaliana for delayed abscission, we have identified several genes that regulate cell separation, slm1-1 (slender lasting inflorescence and meristem) is one such genes. During our investigation of slm1-1 we have employed phenotypic, physiological, genetic, and molecular assays. Phenotypically, slm1-1 displays traits such as delayed abscission of floral organs, lack of anther pollen dehiscence (making slm1-1 functionally male sterile), delayed meristem arrest, and strong apical dominance. Phenotypic characterization includes scanning electron microscopy, bright field microscopy, and stereoscope microscopy. Physiological assays include reporter gene expression and break strength analyses. Genetically, slm1-1 is regulated by a single recessive gene. Molecular assays characterizing slm1-1 include TAIL-PCR, RT-PCR, and preliminary microarray of abscission zones. We have also begun to map based cloning of slm1-1. We believe that understanding genes that regulate cell separation in A. thaliana will contribute to crop improvement. Applications could include reducing loss during harvesting, regulation of pollination, changes in branching patterns, and longevity of flowering.

Open access

Jung M. Lee and N. E. Looney

Abstract

Regrowth of decapitated seedlings of apple (Malus domestica Borkh.) of a compact phenotype revealed stronger apical dominance and narrower branching angle than normal seedlings. Normal and compact seedlings were also found to differ in their phyllotaxy at lower nodes. Spraying with 2,3,5-triiodobenzoic acid (TIBA) before and/or after decapitation increased apparent apical dominance in compact seedlings; reduced shoot thickness in normal seedlings; and reduced shoot length and increased branching angle of both phenotypes. Gibberellic acid (GA3) increased shoot length and reversed the TIBA effect on branch angle in the compact seedlings. These differing growth regulator effects are thought to relate to differences in endogenous growth substance levels. Shoot tips of normal seedlings were higher in abscisic acid (ABA) but the dwarf pea bioassay indicated the presence of another acidic inhibitor present only in the compact seedlings. Normal seedlings exhibited higher levels of gibberellin-like growth promoters.