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.
Charlotte M. Guimond, Preston K. Andrews, and Gregory A. Lang
Michael A. Creller and Dennis J. Werner
Scanning electron microscopy (SEM) was used to compare the novel surface morphology of `Marina' peach [plant introduction (PI) 133984] to a normal peach (`Contender') and a nectarine (`Sunglo'). Samples were collected before, during, and after anthesis. Compared to `Contender', `Marina' showed different trichome structure, lower trichome density, and delayed initiation of trichomes on the gynoecium. No pubescence was observed on `Sunglo' nectarine at any sampling date. Trichomes were present on the flower bud scales of all three cultivars. Arrangement and structure of trichomes on flower bud scales of `Marina' differed from those on `Contender' and `Sunglo'.
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.
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).
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.
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.
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.
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.
G.L. Roberts, M.J. Tsujita, and J. Gerrath
Sisyrinchium bemudiana L. plants were grown in growth chambers under lo-hour short-day regimes. Scanning electron microscopy of shoot apices collected at biweekly intervals showed that the transition from vegetative to floral status occurs after 10 weeks of short days. Stamens and tepals develop first as common stamentepal primordia that then bifurcate to form outer tepals with stamens opposite. Subsequently, the inner tepals are initiated in an alternate pattern.
K.I. Theron and G. Jacobs
We thank A. Doorduin and S. Oudhuis, Oak Valley Flowers, for facilities, plant material, and supervision, P. van der Merwe and D. Janse van Rensburg for scanning electron microscopy assistance, and S.A. le Grange for editorial assistance. The cost