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Yue Wen, Shu-chai Su, Ting-ting Jia, and Xiang-nan Wang

.244 g) > slow growth stage (4 h after 13 C labeling; 0.219 g) > maturation stage (0.213 g). In addition, there were significant differences in dry matter accumulations in the leaf, flower bud, and leaf bud at different leaf nodes during each fruit

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Junhuo Cai, Junjun Fan, Xuying Wei, and Lu Zhang

, flower bud predifferentiation, and leaf maturation ( Fig. 2 ). Before flower bud differentiation, a short period of low temperatures (6 to 12 °C) was necessary. Plants required high temperatures (26 to 30 °C) before flowering initiation, but only required

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Namiko Yamori, Yoriko Matsushima, and Wataru Yamori

growth and flower bud maturation are generally suppressed ( Corbesier et al., 1998 ; King et al., 2008 ; Sheldon et al., 2000 ). Therefore, the use of supplemental lighting is critical to enhancing both production and quality under low light

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Nancy W. Callan

Exposure of `Meteor' tart cherry (Prunus cerasus L.) flower buds to deacclimating conditions resulted in an increase in the temperature of the low-temperature exotherms (LTEs) produced by the flower primordia during controlled freezing. Primordium supercooling temperature was related to chill unit accumulation, an indicator of depth of flower bud endodormancy. LTEs ceased to be detected after deacclimation earlier in 1986-87, a season of more rapid chill unit accumulation, than in 1987-88. Before deacclimation, the range of primordium LTE temperatures within a flower bud was normally ≤1C, but in deacclimated buds considerable variability in LTE temperatures was observed. However, primordia within a flower bud lost the ability to supercool simultaneously. This change was generally concurrent with the appearance of mature xylem vessel elements (XVE) in the upper bud axis and in the flower primordium but did not entirely depend on vessel element maturation.

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Karen E. Burr, Stephen J. Wanner, and Richard W. Tinus

It is not known when changes in primary direct heat stress tolerance of conifer seedlings occur in relation to other seasonally changing physiological parameters. This information should be incorporated into nursery practices and the matching of genotypes to landscape sites. Greenhouse-cultured, container-grown Douglas-fir, Engelmann spruce, and ponderosa pine. were cold acclimated and reacclimated in growth chambers over 19 weeks. Direct heat stress tolerance of needles, cold hardiness, and bud dormancy were measured weekly. Douglas-fir and Engelmann spruce heat stress tolerance increased with the development of new growth through one complete growth cycle, i.e., bud break, maturation, cold hardening, dehardening, and bud break the following growing season. Ponderosa pine differed in that new needles had intermediate tolerance, and fully cold hardy needles were the most intolerant. In none of the species did the timing of changes in heat stress tolerance coincide consistently with changes in cold hardiness or bud dormancy.

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Frederick C. Felker and Henry A. Robitaille

Abstract

The response of ‘Montmorency’ sour cherry (Prunus cerasus L.) flower buds to controlled chilling was determined using both cut shoots and intact trees. Chilling hours accumulated quantitatively when shoots were held at 5°C. Heat unit accumulation also occurred at 5°, whereas at 15° chilling was either nullified or buds accumulated sufficient heat units to break, depending on how many chilling hours were accumulated previously. Chilling nullification at 15° was reversible, as chilling could be reaccumulated at 5°. A daily cycle of 5°/15° for 16/8 hr, respectively, chilled buds as efficiently as did continuous 5° for the same number of total hours. Buds on entire trees in pots, and on shoots cut from the orchard immediately before forcing, responded identically to buds on control-chilled cut shoots. Differences in bud response to controlled chilling with collection date suggested that bud maturation, chilling, and heat unit accumulation overlap. Gibberellic acid was the only chemical among various putative rest-breaking agents tested that accelerated break of partially chilled buds.

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L.L. Creasy and M. Coffee

Abstract

The capacity to synthesize the stilbene resveratrol in response to UV irradiation is used as a measure of the phytoalexin production potential of grape berry skin. Greenhouse-grown berries after set, but before maturation, had high phytoalexin potential, whereas buds, flowers, and mature fruits had low potential. Stilbenes were not synthesized in the fleshly part of fruit and were found erratically in small amounts in noninduced berry skin. In field samples, ‘Concord’, ‘Cabernet Sauvigon’, and ‘Catawba’ had high resveratrol production potential whereas ‘White Riesling’, ‘Chancellor’, and ‘Cayuga White’ had low potential. The phytoalexin production potential decreased in all cultivars after late August, independent of their maturity.

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Barbara D. Webster, Steven P. Lynch, and C. L. Tucker

Abstract

Lima bean, Phaseolus lunatus cv. Early Thorogreen, is primarily self-pollinated. Morphological characteristics of reproductive structures which facilitate self-pollination include the stage of floral development at the time of anther dehiscence and the relative positions of anthers and stigma within the keel at the time of pollen shedding. Coincidental maturation of pollen and receptivity of the stigmatic surface also enhance the capacity for self-pollination. The varying degrees of cross-pollination frequently reported may be facilitated by extrusion of the stigma from the keel, which occurs in connection with insect visitation at an thesis, and also by the prolonged period of stigma receptivity, which extends from the white bud stage through anthesis.

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Anne Fennell and Michael J. Line

Physiological and biophysical changes were monitored during shoot maturation and bud endodormancy induction in grape (Vitis riparia Michx.) under controlled environments. Growth, dry weight (DW), periderm development, bud endodormancy, and nuclear magnetic resonance imaging (MRI) T2 relaxation times were monitored at 2, 4, or 6 weeks of long-photoperiod [long day (LD), 15 h, endodormancy inhibition] or short-photoperiod [short day (SD), 8 h, endodormancy induction] treatments at 15/9 h day/night thermoperiod of 25/20 ± 3 °C. Shoots on LD plants grew throughout the entire study period, although the rate of growth decreased slightly during the 6th week. Shoot growth slowed significantly after 2 weeks of SD, was minimal by the 4th week of SD and most of the shoot tip meristems had abscised after 6 weeks of SD. Endodormancy was induced after 4 weeks of SD. DW of the stem and buds increased with increasing duration of LD and SD. While bud DW increased more under SD than LD, stem DW increased more under LD than SD. T2 relaxation times were calculated from images of transverse sections of the grape node. There was a slight decrease in the T2 times in the node tissues with increased duration of LD treatment, whereas SD induced a significant decrease in T2 times during endodormancy induction. T2 values for the node decreased after 4 weeks of SD, coinciding with endodormancy induction. Separation of node tissues into bud, leaf gap, and the remainder of the stem and analysis of the proportion of short and long T2 times within those tissues indicated differential tissue response. A greater proportion of short T2 times were observed in the 2-week SD leaf gap tissue than in the LD and the proportion of short T2 times continued to increase with subsequent SD treatment. Bud and all other stem tissues had a greater proportion of short T2 times after 4 weeks of SD, coinciding with bud endodormancy induction. The proportion of short and long T2 times in a tissue was a better indicator of endodormancy than the averaged T2 time for the tissue. Thus, MRI allows nondestructive identification of differential tissue response to photoperiod treatments and makes it possible to separate normal vegetative maturation responses from endodormancy induction.

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John L. Maas and Michael J. Line

Nuclear magnetic resonance (NMR) can be used to examine tissue structure and developmental changes during growth and maturation of plant organs nondestructively. Spin-lattice, relaxation time (T1)-weighted, inversion recovery, spin-echo images of strawberry (Fragaria×ananassa Duch.) flower buds were acquired at 3 and 1 day before anthesis and receptacles at 4, 10, 15, and 25 days after anthesis (DAA). The central pith and ovules of flower buds imaged intensely with inversion echo times between 0.1 and 0.5 seconds. Achenes and the vascular cylinder, composed of vascular bundles surrounding the pith, were prominent in receptacles at 4 and 10 DAA. Vascular bundles leading to achene positions, cortex and pith tissues, and the vascular cylinder were evident in receptacles at all developmental stages. A general trend to homogeneity of structure was observed in images of receptacles nearing full maturity (25 DAA). Inversion recovery, spin-echo NMR microimaging may be useful for studying internal physicochemical changes in flower buds and fruit of strawberry and of other fruit crops.