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Michael A. Creller and Dennis J. Werner

mini-grant for the Center for Electron Microscopy. Use of trade names in this publication does not imply endorsement by the NCARS of products named nor criticism of similar ones not mentioned. The technical assistance of Valerie Knowlton and Eleanor

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Charlotte M. Guimond, Preston K. Andrews, and Gregory A. Lang

Flower initiation and development in `Bing' sweet cherry (Prunus avium L.) was examined using scanning electron microscopy. There was a 1- to 2-week difference in the time of initiation of flower buds on summer pruned current season shoots (P) compared to buds borne on unpruned shoots (U) or spurs (S). By late July, this difference was obvious in morphological development. The P buds had already formed floral primordia, while the S and U buds showed little differentiation in the meristem until early August. In general, buds from unpruned shoots were similar developmentally to spur buds. By late August, primordial differentiation was similar in the buds from all the wood types; however, buds from pruned shoots were significantly larger (838 μm) than buds from spurs (535 μm) and unpruned shoots (663 μm). Early summer pruning may shift allocation of resources from terminal shoot elongation to reproductive meristem development at the base of current season shoots. The similarity in reproductive bud development between spurs and unpruned shoots, given the difference in active terminal growth, might suggest that developmental resources are inherently more limiting in reproductive buds on spurs.

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Jacqueline A. Ricotta and John B. Masiunas

In the past few years, leaf trichomes of tomato (Lycopersicon esculentum) and related wild species have received considerable attention due to their potential role in insect resistance. However, the last complete characterization of all 7 trichome types was by Luckwill in 1943, before the advent of scanning electron microscopy (SEM). Since that time, the taxonomic designations of the genus have been modified, expanding from 6 species to 9. The purpose of this work was to use SEM to observe and record trichome types from the presently accepted Lycopersicon species, and determin etheir species specific distribution. Studies have shown variation within trichome type due to number of cells per trichome, and base and surface characteristics.

Open access

Archana Khadgi and Courtney A. Weber

Caneberry crops (raspberry and blackberry) are globally commercialized specialty crops with a high fresh market value. Field management of canes and harvesting of fruits can be complicated by the presence of prickles (the botanically accurate term rather than spines or thorns) on the stems, petioles, and underside of the leaves. Both field management and fruit harvesting could be simplified by the development of cultivars with prickle-free canes. Scanning electron microscopy (SEM) was used to analyze and compare prickle development in different Rubus species. Comparisons were made between prickled vs. prickle-free red raspberry (Rubus idaeus L.), black raspberry (Rubus occidentalis L.), blackberry (Rubus hybrid), complex hybrid with purple fruit (R. occidentalis × R. idaeus), and the hairy and prickled wineberry (Rubus phoenicolasius Maxim). Samples from stems and leaves with petioles attached were used for imaging. There were distinct differences between prickled vs. prickle-free phenotypes in each species. The images of prickle development suggest that prickles either develop directly from glandular trichomes (in red raspberry and wineberry) or that the signal originates from glandular trichomes (in blackberry). Black raspberry prickle development was similar to that of blackberry, suggesting that prickles developed after a developmental signal from glandular trichomes rather than as a direct development from glandular trichomes. The prickle development in the purple hybrid was unique in the presence of one-sided lumps in the trichomes, which has not been seen in any other Rubus species to date; however, both prickled and prickle-free plants exhibited simple nonglandular trichomes. Unlike previous studies, an increase in the number of simple trichomes was not specific to prickle-free plants, but rather variability among the different genotypes was observed. This study adds to the basic understanding of prickle development in the genus Rubus as a first step in the development of prickle-free versions of important cultivars through gene-editing procedures for improving the ease of field management and harvesting.

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Uday K. Tirlapur, Guglielmo Costa, Carlo Malossini, Giannina Vizzotto, and Mauro Cresti

`Redhaven' peach (Prunus persica L. Batsch) fruit abscission has been investigated using scanning electron microscopy, computer-assisted video-image analysis, and confocal laser scanning microscopy in conjunction with chlorotetracycline and ethidium bromide as fluorescent probes for membrane Ca2+ and nuclear DNA. This enabled us to document the morphological changes of the cells, distribution patterns of membrane Ca2+ in the constituent cells of the abscission zone, and the nuclear morphology with accompanying changes in nuclear DNA. The digitized images of CTC-fluorescence emissions revealed that the membrane Ca2+ levels in the pre-abscission zone (control) is uniform and similar to that present in the cells of the spongy proximal region of the peduncle and that of the fruit parenchyma. However, with the induction of abscission, 2 days after embryoctomy, there was a significant increase in membrane Ca2+ in the cells of the abscission zone compared to the neighboring cells of the fruit and the peduncle. Thereafter, with the gradual separation of the cells and the concomitant vacuolation, the membrane Ca2+ level decreased substantially. Confocal imaging of EB labeled cells of the abscission zone before induction invariably revealed a well-organized nucleus. However, during cell separation, significant changes in the cellular and nuclear morphology occured, including 1) rounding of cells, 2) reduction in the nuclear volume, and 3) concomitant fragmentation of nuclear DNA. The possible role of Ca2+ during the process of peach fruit abscission and nuclear DNA fragmentation leading to cell death is discussed. Chemical names used: chlorotetracycline (CTC), ethidium bromide (EB).

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Y. Manakasem and P.B. Goodwin

Field surveys were conducted on cultivated strawberries (Fragaria ×ananassa Duch.) to determine the time of flower initiation and its relation to maximum and minimum temperatures and daylength. Stereomicroscopy and scanning electron microscopy (SEM) were compared. Flower initiation in `Torrey' strawberry was more dependent on minimum temperature than on daylength or maximum temperature. Flower initiation in the day-neutral `Aptos' occurred regardless of daylength or temperature during sampling. For the study of flower initiation and inflorescence development, SEM gave more detail than stereomicroscopy.

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Ludwika Kawa and August A. De Hertogh

Shoot apical meristems of Freesia ×hybrida Klatt `Rossini' reached the reproductive state after 3 weeks of precooling at 9C. Meristems isolated after 6 and 7 weeks of precooling showed the development of the initial four florets of the inflorescence.

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Stéphane Roy, Alley E. Watada, William S. Conway, Eric F. Erbe, and William P. Wergin

Frozen hydrated buds and epicarp of `Golden Delicious' apple (Malus domestica Borkh.) were observed with a low-temperature, field emission scanning electron microscope (SEM). In addition to observing surface features of these specimens, holders were modified to observe fractured specimens. A modified hinged holder retained both halves of a fractured specimen for examination of the complementary faces of frozen hydrated tissues. Low-temperature SEM avoided artifacts, such as extraction, solubilization, and shrinkage, which are normally encountered with chemical fixation, dehydration, and drying, respectively. The technique allowed observations of well-preserved frozen hydrated structures, such as the platelets of epicuticular wax; loosely associated organisms on plant surfaces, such as spider-mite eggs; delicate structures, such as fungal hyphae; and partially hydrated tissues, such as fruit epicarp and winter bud scales.

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B.R. Bondada, C.E. Sams, D.E. Deyton, and J.C. Cummins

preparation and scanning electron microscopy. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.

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Jose Lopez-Medina, James N. Moore, and Kyung-S. Kim

Scanning electron microscopy (SEM) and light microscopy (LM) were used to study the transition of meristems from vegetative to floral phase in erect primocane-fruiting (PF) blackberries [Rubus (Tourn.) L. subgenus Rubus] developed at the Univ. of Arkansas. Dormant root cuttings of A-1836 and APF-13 blackberries were dug from the field and planted on 28 Dec. 1996 and 1 Mar. 1997 to produce plants for use in a greenhouse study. In a field study, terminal buds of field-grown A-1836, APF-13, NC194, and summer-fruiting `Arapaho' were sampled on 21 Mar 1997 (before shoot emergence from soil), and then weekly from 14 to 28 May 1997. Flower bud primordia were first observed at five and six nodes of growth in greenhouse-grown A-1836 and APF-13 plants, respectively, 35 to 42 days after root cuttings were planted (DAP). Under field conditions, floral primordia were not observed until 21 May when A-1836 and APF-13 had at least 20 nodes of growth; NC194 did not differentiate floral structures until 10 July. The developmental patterns of the vegetative apical meristem in the PF selections, both field- and greenhouse-grown plants, were similar to those of `Arapaho'. Opening of the terminal flower of the inflorescence occurred 32 to 35 days after floral initiation in APF-13, and 8 to 10 days later on A-1836. Field-grown NC194 bloomed in late August. The first fruits of greenhouse-grown APF-13 were harvested 120 DAP. These findings demonstrate that PF blackberries form flower buds after a short period of vegetative growth.