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Open access

J. T. Watkins and D. J. Cantliffe

Abstract

The involvement of naphthaleneacetic acid (NAA), a synthetic auxin, and methyl-2-chloro-9-hydroxy-fluorene-9-carboxylate (chlorflurenol), an auxin transport inhibitor, in fruit set in cucumber (Cucumis sativus L.) was investigated. In the greenhouse, exogenously applied NAA and chlorflurenol enhanced fruit set depending on the position of application. In the growth chamber, when NAA was applied directly on the stigma, a small quantity moved into the ovary after 24 hours. However, when auxin was applied on the ovary, significant quantities of 14C NAA were detected in the ovary and other plant pieces. When NAA was placed on the peduncle, more accumulated in peduncle and stem sections than when NAA was placed on the stigma or ovary. Chlorflurenol applications to the peduncle inhibited movement of NAA out of the ovary and resulted in accumulation of auxin in that tissue. NAA movement in the intact plant was similar to that of excised sections: chlorflurenol applied to the peduncle reduced NAA movement out of the ovary. Thus, the regulation of fruit set by chlorflurenol may be through the restriction of auxin movement from the ovary. The increased auxin accumulation in the ovary may trigger fruit set and subsequent growth.

Open access

Walter J. Kender and Jean-Claude Desrochers

Abstract

Lowbush blueberry fruit, exhibiting the characteristic double sigmoid growth pattern, were analyzed for endogenous gibberellin-like substances, auxins, and inhibitors on 10 sampling dates throughout their ontogeny. During the initial berry enlargement period (stage I) from 0 to 26 days after anthesis, gibberellin content was high and auxin and inhibitor contents low. Gibberellin-like substances reached a peak of 2.1 GA3 equivalents (ug/g dry weight) 26 days after anthesis. At the onset of growth stage II, gibberellin activity declined sharply and remained at a low level throughout the developmental period. During the stage of retarded berry growth, 26 to 48 days after anthesis, auxin activity increased markedly followed by a decrease prior to the start of growth stage III.

All 3 growth substances were at non-active levels during the ripening period. However, inhibitor activity increased sharply as berries developed blue coloration, 61 and 69 days after anthesis. The growth promoting substances were associated with the premature phases of blueberry fruit development and the inhibiting substances with senescence. Auxins and inhibitors were low in flower buds and open flowers while gibberellin-like substances exhibited slight activity in these tissues.

Open access

E. M. Beyer Jr. and B. Quebedeaux

Abstract

A hypothesis is proposed and tested for the mechanism of action of parthenocarpy induction in cucumber (Cucumis sativus L. cv. ‘GY3’) by the potent inhibitors of auxin transport 3,3a-dihy dro-2-(p-methoxy phenyl)-8H-pyrazolo [5,1-a] isoindol-8-one (DPX1840), methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (morphactin), N-l-naphthylphthalamic acid (naptalam), and 2,3,5-triiodobenzoic acid (TIBA). The transport of NAA-l-14C in 5-mm peduncle sections was strongly polar in the basipetal direction (i.e., out of the ovary toward the stem) and was inhibited within 0.5 hr by each transport inhibitor when applied at 500 to 1000 mg/1 to intact plants. Ether extractions of ovary tissue from plants treated in a similar manner contained significantly greater auxin activity as determined by the Avena coleoptile straight growth bioassay.

These results are compatible with the hypothesis that auxin transport inhibitors induce parthenocarpy in cucumber by rapidly blocking the natural outward flow of auxin from the ovary thereby resulting in an accumulation of auxin within the ovary sufficient to trigger parthenocarpy.

Free access

Kathryn Keeley, John E. Preece, and Bradley H. Taylor

Hardwood and softwood cuttings of Vitis aestivalis Michx. 'Norton' were rooted under intermittent mist in a series of experiments using cuttings collected from two local vineyards. Hardwood cuttings treated in late March responded in a similar manner to KIBA and KNAA. Although there was little increase in the percentage rooting above 22.29 mm KIBA or 20.72 mm KNAA (5000 mg·L-1 of either auxin), root number (but not root length) increased linearly on cuttings treated with up to 44.58 mm KIBA or 41.44 mm KNAA (10000 mg·L-1 auxin). Cuttings treated with 10000 mg·L-1 auxin produced up to 4 times more roots than the nontreated controls. The gibberellin biosynthesis inhibitors CCC and PAC had little effect on either hardwood cuttings or softwood cuttings that were harvested, treated and placed in the propagation bench in June. However, when softwood cuttings were collected in August, the most roots were found on cuttings treated with 50.6 mm CCC or 0.85 μm PAC. Although all hardwood cuttings were collected at the same time and stored under refrigerated conditions, rooting percentage increased as storage time increased, especially on the nontreated control cuttings. When the cuttings were stored for the longest time (six weeks), KIBA no longer caused more roots per cutting. Chemical names used: potassium salt of indole-3-butyric acid (KIBA), potassium salt of α-naphthaleneacetic acid (KNAA), chlormequat chloride (CCC), paclobutrazol (PAC).

Open access

Bruno Quebedeaux and E. M. Beyer Jr.

Abstract

Parthenocarpy was induced in unfertilized pistillate flowers of cucumber, Cucumis sativus L., by the foliar application at early flowering of 10 to 1000 ppm of 3,3a-dihydro-2-(p-methoxyphenyl)-8H-pyrazolo[5,1-a]isoindol-8-one (DPX 1840) a new inhibitor of auxin transport. Treatment of a monoecious cultivar with ethylene or (2-chloroethyl)phosphonic acid (ethephon) increased the pistillate to staminate flower ratio and subsequent application of DPX 1840 increased the no. of fruit which developed parthenocarpically. Ethylene gas was just as effective as ethephon in altering sex expression. The threshold level of ethylene for this response was between 0.06 and 0.16 μl of ethylene per liter of air.

Free access

Rongcai Yuan, Walter J. Kender, and Jacqueline K. Burns

The effects of removal of young fruit and application of auxin transport inhibitors on endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) concentrations were examined in relation to the response of mature `Valencia' orange [Citrus sinensis (L.) Osb.] fruit to abscission materials. ABA concentrations were increased in the fruit abscission zone and pulp but not in the pedicel, peel, or seed of mature fruit by removal of young fruit during the period of reduced response of mature fruit to abscission materials in early May. However, removal of young fruit slightly decreased IAA concentrations in leaves and the abscission zone and pedicel of mature fruit but had no effect on the IAA concentrations in the peel, pulp, or seed of mature fruit. Young fruit had higher IAA concentrations in the abscission zone and pedicel than mature fruit. Application of 2,3,5-triiodobenzoic acid (TIBA), an IAA transport inhibitor, reduced IAA concentrations in the abscission zone of mature fruit but did not influence the IAA concentrations in the pedicel and peel when applied directly to an absorbent collar tied around the pedicel 2 cm above the fruit abscission zone during the less responsive period in early May. ABA concentrations were increased drastically in the fruit abscission zone and pedicel but not in peel by TIBA application. Applications of ABA, or IAA transport inhibitors such as naringenin, quercetin, or TIBA comparably increased the response of mature fruit to the abscission material 5-chloro-3-methyl-4-nitro-1 H-pyrazole (CMN-pyrazole) in early May. These data suggest that young fruit reduce the response of mature `Valencia' oranges to abscission materials through increasing IAA concentrations and decreasing ABA concentrations in the abscission zone of mature `Valencia' orangees.

Open access

Zachary D. Small, James D. McCurdy, Erick D. Begitschke, and Michael P. Richard

control of wild garlic was much slower to manifest when this trial was repeated in 2017 ( Table 2 ). All treatments with ALS-inhibiting active ingredients failed to control wild garlic greater than the nontreated check when assessed 20 DAA. Only the auxin

Free access

Bruce W. Wood

flowering the following “off” year and use of floral inhibitors [gibberellic acids (GA 3,4,7 ) ( Greene, 2000 ) and auxin analogs (e.g., NAA) in certain cases] in “off” years to decrease subsequent year flowering. It is unknown whether these promoters and

Free access

Masahumi Johkan, Tomoko Chiba, Kazuhiko Mitsukuri, Satoshi Yamasaki, Hideyuki Tanaka, Kei-ichiro Mishiba, Toshinobu Morikawa, Masayuki Oda, Chihiro Yamamoto, and Hiroshi Ohkawa

hormone levels in the ovary even in the absence of pollination and fertilization ( Gillaspy et al., 1993 ; Nitsch, 1970 ). Our hypothesis was that a high concentration of endogenous auxin in the parthenocarpic ovary may inhibit pollen tube growth in the

Open access

P. A. Domoto and A. A. Hewitt

Abstract

The wheat coleoptile straight-growth test was used to determine the effects of (2-chloroethyl)phosphonic acid (ethephon) on endogenous auxins and inhibitors in seeds of ‘Late Santa Rosa’ plum. Seeds of both developing and abscissing ethephon-treated fruits attained higher levels of auxin activity than did their respective controls suggesting an ethylene-induced inhibition of auxin transport. The level of growth inhibitors remained similar throughout.