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Lívia Lopes Coelho, Amalia Fkiara, Kathryn Kuligowska Mackenzie, Renate Müller, and Henrik Lütken

many plants, the flowering response is closely linked to endogenous hormonal levels, which is directly or indirectly associated with their developmental stage ( Bratzel and Turck, 2015 ). Gibberellins are a class of hormones that play multiple roles in

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Steven McArtney, Dick Unrath, J.D. Obermiller, and Ann Green

vegetative, could result in more consistent cropping. Various gibberellins can inhibit flower bud formation in apple ( Bertelsen and Tustin, 2002 ; Dennis and Edgerton, 1966 ; Li et al., 1995 ; Marino and Greene, 1981 ; McArtney, 1994 ; McArtney and Li

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Stephen S. Miller

cracking, but also reduced fruit weight and yield. A single spray of 1000 ppm daminozide applied on 27 July reduced the percentage of cracked ‘Stayman’ apples from 58% to 35% ( Byers et al., 1990 ). In the same study, four weekly sprays of gibberellins A4

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Yuval Eshed, Joseph Riov, and Nir Atzmon

Rooting of Quercus ithaburensis Deche. cuttings decreased significantly with increasing stock plant age. Gibberellin (GA3) applied as bark treatment on leafless pruned stems of 3-year-old stock plants improved rooting percentage 6- to 7-fold. GA3 application also enhanced bud release and particularly shoot growth, thus increasing the number of cuttings per stock plant.

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Robert Fritts Jr. and Daniel L. Ward

Release LC (Abbott Laboratories), a commercial formulation of gibberellins, was applied to apricot, cling peach, freestone peach, nectarine, and plum varieties. Application was by commercial airblast sprayer. Fruit firmness was increased in the season of application in all crops. Meta analysis of the data indicated a maximum response for each crop differed over the rate range of 16 to 48 g a.i./acre. Changes in fruit soluble solids were slight. No differences in fruit color were observed. Reduction in flower bud density (thinning) was observed the following season. The reduction in bud density reduced the time required to hand-thin to a commercially acceptable level. A difference in thinning sensitivity to gibberellin was evident between crops.

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Jack D. Early Jr. and George C. Martin

Photoperiod is an important environmental signal for regulating developmental patterns in many plant species. In several species, photoperiodic regulation of gibberellin A1 biosynthesis has been implicated as the mechanism by which photoperiod may alter development. To examine this phenomenon in strawberry, Fragaria virginiana plants grown under long day (LD) and short day (SD) conditions with equivalent total PAR were examined to determine changes in vegetative growth and GA1 biosynthesis.

LD conditions (16 hr) promoted vegetative growth. Runner production, total leaf area, area of individual leaves, and petiole lengths, all increased under LD conditions. No runner production occurred under SD conditions (8 hr); however, the number of branch crowns increased.

Gibberellins A44, A19, A20, and A1, all from the GA1 biosynthetic pathway, were identified in plants under both LD and SD conditions. However, SD conditions appeared to affect the 2β-hydroxylation of GA20 to GA1. Whereas levels of most GAs decreased under SD conditions, levels of GA20 increased, and only trace amounts of GA1 were found, indicating a possible blockage of the pathway at this point. As GA1 is considered the active component of the pathway, blockage of GA20 conversion under SD conditions may explain the concomitant reduction in vegetative growth.

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Sonja L. Maki and Nihal C. Rajapakse

Endogenous gibberellins of chrysanthemum [Dendrathema×grandiflorum (Ramat) cv. Bright Golden Anne] were characterized in preparation for quantification of endogenous gibberellins in apices under control and CuSO4 spectral filters. Expanding shoots were separated into young expanding leaves and apices. Methanolic extracts of young expanding leaves were purified by solvent partitioning, PVPP column chromatography, and reversed-phase high performance liquid chromatography. Two bioactive regions corresponding to the HPLC retention times of GA and GA19 standards were detected in fractions using the recently developed non-dwarf rice bioassay. Dideuterated internal standards of GA12, GA53, GA19, GA20, and GA1 were added to similar extracts of shoot apices. The presence of endogenous GA53, GA19, GA20, and GA1 in chrysanthemum apices was confirmed by isotope dilution using gas chromatography–mass spectrometry-selected ion monitoring and Kovats retention indices. Ions for the deuterated internal standard of GA12 were detected, but not for endogenous GA12. The above results demonstrate that the early 13-hydroxylation pathway operates in chrysanthemum.

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Sorua L. Maki, Melissa B. Riley, and Nihal C. Rajapakse

Endogenous gibberellins of chrysanthemum [Dendranthema ×grandiflorum (Ramat)] cv. Bright Golden Anne were characterized in apices from plants grown under control and CuSO4 spectral filters. Expanding shoots were separated into young expanding leaves and apices. Methanolic extracts of young expanding leaves were purified by solvent partitioning, PVPP column chromatography and reversed-phase high performance liquid chromatography. Two bioactive regions corresponding to the HPLC retention times of GA1 and GA19 standards were detected in fractions using the recently-developed non-dwarf rice bioassay. Di-deuterated internal standards of GA12, GA53, GA19, GA20, and GA1 were added to similar extracts of shoot apices. The presence of endogenous GA53, GA19, GA20, and GA1 in chrysanthemum apices was confirmed by isotope dilution using gas chromatography-mass spectrometry-selected ion monitoring and Kovats retention indices. In a preliminary quantification study, GA20 and GA1 levels were found to be higher in apices from plants grown under control filters while GA19 levels were higher in apices grown under CuSO4 filters. The possibility that light transmitted through CuSO4 filters alters gibberellin levels in shoot apices is discussed.

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Iftikhar Ahmad, John M. Dole, and Bruno T. Favero

, cultivars vary in exhibiting leaf chlorosis symptoms ( Leonard et al., 1998 ). Use of gibberellins and cytokinins effectively controlled leaf chlorosis of calla lily [ Zantedeschia aethiopica ( Skutnik et al., 2001 )], narcissus [ Narcissus tazetta

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Michael R. Evans, Harold F. Wilkins, and Wesley P. Hackett

Exogenous foliar spray applications of gibberellic acid (GA3) applied at 7- or 14-day intervals providing 50 or 125 μg per plant inhibited long-day (LD) floral initiation in poinsettia [Euphorbia pulcherrima (Willd. ex. Klotzsch)]. Periodic application of GA3 resulted in an additional number of nodes being produced by the plant before floral initiation equivalent to the number of nodes over which GA3 was applied. Further, GA, application eliminated the nodal position dependence of the long-day node number (LDNN) of axillary meristems observed in control plants. It was concluded that GA3 application inhibited the inclusion of nodes into the LDNN count and thus inhibited ontogenetic aging of the meristem. Exogenous application of GA, also inhibited LD floral initiation, while application of GA4 had no effect. Application of GA7 delayed LD floral initiation, but plants did initiate cyathia by the termination of the experiment. All gibberellins increased the average internode lengths similarly. The gibberllin-biosynthesis inhibitors chlormequat and paclobutrazol had no effect on LD floral initiation when applied as single or multiple foliar sprays or as soil drenches, although heights and internode lengths were reduced by application of the inhibitors. The LDNN of plants grown at 31C was significantly higher than of plants grown at 16, 21, or 26C. All plants eventually initiated cyathia regardless of temperature. When plants were grown under a range of day/night temperatures, an increase in the LDNN occurred only when plants were grown at 31C during the day. Chemical names used: 2-chloroethyl-trimethyl-ammonium chloride (chlormequat); (+/-)-(R*,R*)-β -(4-chlorophenyl)methyl-α -(1,1-dimethylethyl)-1-H-1,2,4-triazole-1-ethanol (paclobutrazol).