Abstract
The cytokinin N-(3-methyl-2-butenyl)-1-4-purine-6-amine (2iP) has been used to proliferate explants of Ericaceous spp. in vitro (2, 3, 6); these explants often have a rhizomatous growth habit. (4, 6). The studies described here were designed to determine the effects of 2iP on rhizome development of lowbush blueberry (Vaccinium angustifolium Ait.) seedlings and rooted cuttings to aid in enhancing plant cover and yield (5, 7).
The main goal of this research was to develop Campanula glaumerata `Acaulis' plants transformed with the isopentenyl transferase (ipt) gene for increased growth of the axillary buds and en-hanced insect resistance. Isopentenyl transferase is a first enzyme in the cytokinin biosynthetic pathway. For Campanula transformation, leaf discs were co-cultivated with Agrobacterium tumefacience LBA4404, which harbored the binary vector pBC34 (A. Smigocki, Beltsville, Md.) that codes for the nos-nptII gene and the ipt gene controlled by the CaMV35S promoter. The transformation frequency was about three times higher when leaf blade explants were infected with LBA4404 containing pBC34 as compared to infection with pGUSINT, which contains the gusint gene instead of the ipt gene. This difference in transformation frequency was attributed to expression of cytokinin from the ipt gene. Transgenic plant lines containing the ipt gene were verified by southern hybridization and divided into three groups by phenotype following culture in vitro on MS medium: 1) yellow/large leaves, no rooting; 2) green/large leaves, no rooting; 3) green/normal leaf size, rooting. These different phenotypes could be due to different levels of cytokinin expression in the transgenic plants.
Two experiments were conducted to examine the effects of growth regulator application on cytokinin levels in developing apple leaves. In experiment 1, gibberellin GA4/7 (100 mg·liter-1) and benzyladenine (BA, 100 mg·liter-1) were applied alone or in combination as a foliar spray to `Golden Delicious' 7 days after full bloom. In experiment 2, BA was applied at 50 or 100 mg·liter-1 as a foliar spray to `Morespur McIntosh' 18 days after full bloom. Trans-zeatin ribosidelike (t-ZR) levels were determined by immunoassay. In experiment 1, GA1/7 had no effect and BA increased t-ZR-like levels. In experiment 2, BA increased t-ZR levels quadratically with application rate. The increase in endogenous cytokinin levels with BA treatment occured within 2 hours. Initially, t-ZR-like levels were 47 times higher in the BA (100 mg·liter-1) treated leaves as compared to check leaves. Over the next 8 days, t-ZR-like content in treated leaves decreased in a cubic manner.
≈12- to 14-d period following fertilization ( Olmstead et al., 2008 ), and this stage is therefore targeted for improving quality with exogenous PGRs. The applications of gibberellic acid, auxin, and cytokinins are responsible for growth at a certain
Treatment of cut carnation (Dianthus caryophyllus L. `White Sim') flowers with the synthetic cytokinin benzyladenine (BA) at concentrations >1.0 μm induced premature petal senescence. Flowers treated with 100 μm BA exhibited elevated ethylene production in styles and petals before untreated flowers. The gynoecia of BA-treated flowers accumulated 1-aminocyclopropane-l-carboxyllc acid (ACC) and enlarged before untreated flowers. Removal of the gynoecium (ovary and styles) or styles prevented BA-induced petal senescence and resulted in a substantial delay in petal senescence. In contrast, removal of the gynoecium had no effect on timing of petal senescence in flowers held in water. These results indicate BA stimulates petal senescence by inducing premature ACC accumulation and ethylene production in the gynoecium.
desiccation ( Fry and Huang, 2004 ). Plant adaptation to drought stress has been associated with the hormonal regulation of these processes. Changes in the level and proportion of endogenous phytohormones, such as cytokinins (CK) and abscisic acid (ABA
Leaf senescence is a natural process of leaf maturation, but it can be induced prematurely by environmental stresses. Cytokinins (CKs) have been well known for their function in delaying leaf senescence, and even in reversing the process of leaf
multiple carbohydrates on embryogenic callus initiation in rose. Cytokinin source plays a significant role in regeneration in rose. Some commonly used cytokinins for rose regeneration include zeatin ( Ludwig et al., 2000 ; Vergne et al., 2010
Cytokinins were first recognized as a class of phytohormones for their ability to promote cytokinesis in cultured plant cells and have since been shown to be involved in a wide range of physiological processes. Most recently, the availability of phytohorm one-specifying genes from Agrobacterium tumefaciens has allowed for direct in planta manipulation of cytokinin levels. Overexpression of the isopentenyl transferase (ipt) gene by constitutive promoters led to enhanced ability of plant cells to undergo shoot organogenesis but the high endogenous cytokinin levels almost completely suppressed root development. Transient overproduction of cytokinins using promoters regulated by environmental and/or developmental factors did not inhibit regeneration of rooted plants. Transgenic plants in which cytokinin levels can be modulated are being used to characterize the participation of cytokinins in fundamental regulatory mechanisms of morphogenesis, delayed senescence, disease resistance and directed nutrient transport. The potential for using reconstructed cytokinin biosynthesis genes in economically important crops is of tremendous agronomic significance.
Abstract
The growth of excised grape shoots in the absence of roots was investigated using asceptic culture. Sustained shoot development was observed only when cytokinins were present in the media. We used ‘Concord’ (Vitis labruscana Bailey) in most experiments, but the response was observed in other cultivars including those of Vitis vinifera L. Better response was obtained with cytokinin ribosides than with free bases. If roots developed, the requirement for an exogenous source of cytokinin was nullified.