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

1 To whom reprint requests should be addressed. The helpful suggestions and guidance in microscopy technique of Valerie Lynch-Holm and Christine Davitt are gratefully acknowledged, as is the partial financial support of the Washington Tree Fruit

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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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Yin Xu, Yizhou Ma, Nicholas P. Howard, Changbin Chen, Cindy B.S. Tong, Gail Celio, Jennifer R. DeEll and Renae E. Moran

Maine, Ontario, and Wisconsin were shipped overnight to Minnesota, where 10 fruit were processed immediately for light microscopy, and the remaining fruit were stored at 0 ± 1 °C. In Minnesota, at least 10 fruit per harvest were processed immediately for

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Bhaskar Bondada and Markus Keller

microscopy. To examine the gross external and internal morphological features of berries and seeds, berries were excised from healthy and afflicted clusters. Berries were then sectioned longitudinally through the center to examine the internal morphology of

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Maurus V. Brown, James N. Moore, William M. Harris and Patrick Fenn

Calcofluor and berberine were used to determine the potential of epifluorescence microscopy to observe the interaction between grape leaves and P. viticola. Leaf disks (10 mm in diameter) were inoculated and incubated for 2, 4, and 7 days. Disks were stained with berberine at 0.1% for 1 h, rinsed, placed in 0.1 M Tris (pH 5.8) for 15 min, stained in calcofluor at 0.1% for 25 min, and rinsed. Disks were mounted abaxial side up in 30% glycerin and viewed with an epifluorescence microscope. Various leaf features (e.g., trichomes, stomates) were distinguishable from the fungal structures (e.g., hyphae, sporangiophores). Leaf surface colors were red, orange, brown, green, and yellow, and fungal structures were light to dark blue. Epifluorescence microscopy was a useful means of differentiating leaf and fungal structures.

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Ro-Na Bae, Ki-Woo Kim, Tae-Choon Kim and Seung-Koo Lee

Anatomical observations of anthocyanin rich cells in `Fuji' apple skins were carried out by light microscopy and electron microscopy. Apple skins with fully developed red color had more layers of anthocyanin-containing epidermal cells than those of green skins. The density of anthocyanin was high in cells of the outer layer of the fruit skins and gradually decreased inward to the flesh. Anthocyanins were frequently found in clusters or in agglomerations that were round in the epidermal cells of the red skins. They accumulated in the inner side of developed vacuoles. Transmission and scanning electron microscopy revealed that the shapes of anthocyanins were cluster style, indeterminable forms, or complete spheres. Anthocyanin seemed to be synthesized around the tonoplast and condensed on the inward side of the vacuole. There was no distinct envelope membrane on the anthocyanin granule in the vacuoles of apple skin cells.

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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.

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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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E. Marroquin, J.L. Silva, J. Magee, J. Braswell and J. Spiers

Rabbiteye (Vaccinium ashei) blueberries were harvested in Mississippi and highbush (V. corymbosum) blueberries were harvested in Michigan. The berries were rapidly cooled to 5C after harvest and kept at this temperature for 48 h before being analyzed as fresh fruit or freezing for later analyses. Microstructural (light and scanning/transmission electron microscopy) and chemical (pectins, cellulose, hemicellulose, lignin, and fiber) evaluations were performed to evaluate differences between the two types of blueberries. Scanning electron micrographs showed that rabbiteye spp. have thicker epidermal and subepidermal cells than highbush spp. Transmission electron micrographs also showed that rabbiteye spp. have a thicker, more uniform cuticle layer than highbush spp. Rabbiteye spp. contained higher fiber and complex polysaccharides than highbush spp. Although, there were no differences in total pectins, rabbiteye berries had lower water soluble pectins and oxalate soluble pectins than highbush blueberries. Differences in polysaccharides and pectins between highbush and rabbiteye berries indicate that their cell wall components differ. These differences, along with the variation in subepidermal, epidermal and cuticle layers of the skin, provide valuable information to explain the textural differences between rabbiteye and highbush blueberries.

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Darrell Sparks, William Reid, I.E. Yates, Michael W. Smith and Thomas G. Stevenson

The influence of fruiting stress on shuck decline, nut quality, and premature germinaiton was evaluated on trees of pecan [Carya illinoensis (Wangenh.) C. Koch]. Fruit at the liquid endosperm state were removed from trees with a mechanical shaker to reduce crop load by 0%, 25%, 41%, 56%, or 77%. Shuck decline and premature germination decreased and kernel quality increased with a reduction in crop load. An excessive fruit load or fruit stress elevated the incidence of shuck decline, previously referred to as shuck disease, tulip disease, shuck die-back, or late season shuck disorder; decreased kernel development; and increased premature germinaiton. Shucks were dissected from fruit ranging from healthy to those with premature shuck opening and examined by scanning electron, transmission electron, and light microscopy. Fungal growth was detectable, but only after tissue degeneration had occurred. Thus, results indicate the onset of shuck decline is caused by stress associated with an excessive crop load and not a pathological disorder. Fungal growth is a secondary, not a primary, factor in deterioration of shucks with decline.