Histological and histochemical examination of floral initiation was conducted to determine the pattern of flowering in Rudbeckia hirta, a long-day (LD) plant. Plants were grown under 8-hour short days (SDs) until they had 14 to 16 expanded leaves. Half of the group of plants was moved to LD conditions consisting of natural daylength plus a 4-hour night interruption. Rudbeckia hirta had a pattern of differentiation in flowering similar to that reported in species requiring one inductive day for initiation. Rudbeckia hirta required 8 LDs for evocation and 18 LDs for completion of initiation. Involucral bracts initiated after 18 LDs, after which the receptacle enlarged and was capped by a meristematic mantle of cells signaling the start of development. Floret primordia did not initiate, even after 20 LDs. Increases in pyronin staining were observed in actively dividing cells of the procambium, leaf primordium, and corpus of the vegetative meristems. After 8 LDs, the pith rib meristem stained darkly, a result indicating the arrival of the floral stimulus. An increase in pyronin staining was also observed in the meristematic mantle covering the receptacle after 18 LDs, a result indicating increased RNA levels.
Richard L. Harkess and Robert E. Lyons
Richard P. Buchner, William H Olson, Vito S. Polito, and Katherine Pinney
Walnut Blight caused by the bacteria Xanthomonas campestris pathovar juglandis is a very destructive disease for California walnut production. Streptomycin is an effective disease control material; however, Streptomycin sprays can result in significant nut drop 3 to 5 weeks after spray application. We investigated the basis for walnut drop following applications of Streptomycin (Agrimycin) for walnut blight control. Flowers and developing nuts were collected from four treatments, plus an unsprayed control. 200 ppm Streptomycim was applied at 1) budbreak; 2) pre, full, and post-bloom; 3) postbloom; 4) budbreak and postbloom; 5) untreated control. Samples were collected regularly beginning at the first budbreak spray and extending through the period of nut drop. Samples were fixed and prepared for histological examination. In treatments with a high incidence of nut drop, the embryo failed to develop. Examination of the stigma and style in flowers from these treatments showed inhibited pollen tube growth. Results indicate that Streptomycin inhibits pollen tube growth, which precludes fertilization. This pattern of development and timing of nut drop following Streptomycin application at full bloom is similar in all ways to unpollinated walnut flowers. Nut growth and development appear normal for 3 to 5 weeks; then nuts abort. If Streptomycin became available for walnut blight control, sprays timed to coincide with pistillate bloom and pistillate flower receptivity should be avoided.
L.G. Buckley, E.T. Graham, and R.N. Trigiano
Zygotic and somatic embryos are purported to follow similar developmental sequences, but few investigations have thoroughly compared the two processes. Developing pods of Cercis canadensis L. (redbud) were collected from trees on the Knoxville campus of the University of Tennessee once or twice per week from 28 March to 8 August 1991. At least 10 ovules/sample date were fixed in FAA to evaluate zygotic embryo ontogeny. A minimum of 40 ovules/sample date were aseptically excised and placed on SH medium supplemented with 9.0 μM 2,4-D and 5 mM ammonium ion to initate somatic embryogenesis. Zygotic and somatic embryos were prepared for histological examination using standard paraffin techniques. Somatic embryos developed primarily from cotyledons and epicotyls of zygotic embryos mat were cultured between 6 June and 19 July. Somatic and zygotic embryos were subtended by multiseriate suspensors and progressed through recognizable globular, cordate and cotyledonary stages of development. Cotyledon morphology was similar for both embryo types. However, many somatic embryos failed to differentiate dome-shaped shoot meristems exhibited by their zygotic counterparts.
Yong Cheong Koh and Fred T. Davies Jr.
The leaves of vegetative stolons of greenhouse grown Cryptanthus `Marian Oppenheimer' (wide leaf clone) were cultured in modified MS media to induce adventitious shoot formation via callus formation. The best callus induction medium was basal MS medium with 10 μM NAA, IBA and BA. Pure green (843), maroon (3), striped (2) and albino plantlets were obtained. Most of the albino plantlets were stunted, tightly clumped together and impossible to score. The medium which produced the highest average number of non-albino plantlets was basal MS medium with 0.3 μM NAA, IBA and BA All non-albino plantlets were rooted in MS medium with 5.4 μM NAA and transplanted ex vitro with a survival rate of 96.7%. The maroon plantlets became green two weeks after transplanting. Histological studies revealed that C. `Marian Oppenheimer' (wide leaf clone) has two tunicas (L1 and L2) and a corpus (L3). Callus on the leaf explant arose mainly from the L2 and L3. Apparently C. `Marian Oppenheimer' (wide leaf clone) is a GWG periclinal chimera.
Martin C. Goffinet, Mary Jean Welser, Alan N. Lakso, and Robert M. Pool
Northeastern U.S. grape growers have become more knowledgeable about many aspects of grape production, including pruning and training, canopy management, nutritional recommendations, pest and disease management strategies, vineyard floor management, etc. Important to all these aspects is a firm understanding of vine structure and development. Yet, there is no current publication on vine growth and development that growers and researchers can consult to gain an understanding of the organs, tissues, and developmental processes that contribute to growth and production of quality vines in the northeastern U.S. climate. A concerted effort is underway to secure enough information on how vines are constructed, grow, and develop in the northeast so that a publication useful to a wide audience can be produced. Our objective is to consolidate information already on hand that can help explain the internal and external structures of grapevines that are pertinent to the needs of northeast growers, to add information that is lacking by collecting and examining vine parts, and to work toward integrating vine structure with vine physiology and viticultural practices. Over the past decade, organs of various native American, French hybrid, and vinifera varieties have been collected from vineyards at Cornell's experiment stations and from growers' vineyards in the Finger Lakes and Lake Erie regions. Much quantitative data on vine development have been collected and interpreted. Lab work has included dissections of organs, histological and microscopic examination, microphotography, and the production of interpretive diagrams and charts. A list of the subject matter and examples of visual materials will be presented.
Michael Marcotrigiano and Susan P. McGlew
In an effort to accelerate breeding programs and to study somaclonal variation, a micropropagation system was devised for cranberries (Vaccinium macrocarpon). Using a factorial design, explants taken from greenhouse grown plants were placed on Anderson's medium containing different concentrations of 2ip' GA3, and IBA, with 4 cultivars tested over 3 subcultures. In other experiments, explant source, macro and micro salt formulations, and rooting treatments, were studied. Optimal multiplication and shoot quality occurred when single node explants taken from greenhouse grown plants were placed on Anderson's media containing 150 uM 2iP, 1.0 uM IBA and no GA3. Histological examinations indicate that initial response is axillary bud proliferation but upon subculture adventitious shoot formation may be possible. Proliferated shoots could be rooted ex vitro in plug trays under plastic tents and without hormone treatments. Optimal rooting occurred under high light conditions in a 1:1 (v:v) peat:sand mix. Plants were easily transplanted into the field in spring and will be evaluated by comparison to conventionally propagated material.
Maryke A. Cleland, Cynthia Jones, and Mark H. Brand
An interspecific hybridization program involving five species of Impatiens was initiated to delineate incompatibility barriers. With the exception of one cross, no viable hybrid seed was recovered. Fluorescence microscopy revealed foreign pollen tubes to reach ovules in all crosses, although not all ovules were approached. A histological study involving I. auricoma Baill. and I. walleriana Hook f. ensued to confirm the presence of hybrid embryos. Developing I. walleriana × I. auricoma and reciprocal hybrid embryos were compared to self embryos. Development of hybrid embryos was delayed as early as five days post-pollination. I. walleriana × I. auricoma embryos continued to develop for 8 days post-pollination, but did not reach a size greater than a 5-day self embryo. Excessive endosperm was observed in the hybrid. I. auricoma × I. walleriana embryos continued to enlarge up to ovary abortion but did not reach a size greater than a 7-day self embryo and little to no endosperm developed. Disintegration of ovules included disorganization and collapse of the endosperm, and vacuolization and loss of turgidity of the embryo.
William M. Walter Jr., Betsy Randall-Schadel, and William E. Schadel
Wound healing in cucumber fruit (Cucumis sativus L., cv. Calypso) was studied using histological and degradative techniques. A thick exudate appeared at the wounded surface shortly after wounding. This material retarded water loss and possibly aided in the formation of sclerified parenchyma observed 24 hours after wounding. The sclerified material was positive to a modified Weisner stain, indicating lignification was occurring. Wound periderm (cork) was initiated directly beneath the sclerified parenchyma cells within 48 hours after wounding. The cork layers were positive to Sudan IV stain, indicating suberin was being formed. The rate of phellem development decreased by 6 days after wounding. By day 7, younger phellem cells and sclerified parenchyma cells were stained by Sudan IV. Degradation of the wound tissue by chemical procedures demonstrated that relatively large amounts of lignin and suberin were deposited during healing. Fragments from the lignin degradation Indicated that lignin was composed mainly of gualacyl and p-hydroxyphenyl residues. Suberin was found to contain mainly 1,16-hexadecane and 1,18-osctadecene decarboxylic acids detected as the silylated diol derivatives.
X. Wang, J.T.A. Proctor, S. Krishna Raj, and P.K. Saxena
Ginseng is a very valuable agricultural species grown for its root, which contains pharmacologically active constituents. One limiting factor for expansion of ginseng production is an efficient method for mass propagation. Currently, seeding is the principal method of propagating ginseng, but the embryo of ginseng seeds at harvest is immature. A stratification schedule consisting of a cool-warm-cool temperature treatment over 18-22 months is required for embryo development and seed germination. An alternative for the efficient production of ginseng is mass propagation through the use of in vitro culture techniques. The objective of this work was to develop a highly efficient system for regeneration of ginseng. The efficacy of three auxins, viz. 2,4-D, NAA and dicamba, were compared for the induction of somatic embryogenesis in American ginseng. Somatic embryos formed on ginseng cotyledonary, zygotic embryo, and shoot explants after 8 weeks of induction by the auxins. Significantly more somatic embryos were induced by culture of any of the ginseng explants on media supplemented with 5 μmol·L-1 2,4-D than any other auxin treatment. Histological and SEM studies confirmed that the regenerants were somatic embryos. Somatic embryos germinated and developed into normal plants in 3-6 months. The development of a regeneration system for ginseng using somatic embryogenesis is a necessary first step for mass propagation and the improvement of American ginseng.
Tekalign Tsegaw, S. Hammes, and J. Robbertse
Potato (Solanum tuberosum L.) treatment with paclobutrazol resulted in short and compact plants having dark green and thicker leaves, and wider stem and root diameters. Investigating the underlying anatomical modifications in response to the treatment was the objective of the study. Plants of potato cultivar BP 1 were treated with 0, 45.0, 67.5, and 90.0 mg paclobutrazol per plant as a foliar spray. A month after treatment leaf, stem and root materials were taken from the control and plants treated with 67.5 mg paclobutrazol, and histological observations were made using light microscope. Leaves of treated plants showed an increased chlorophyll a and b contents, thicker epicuticular wax layer, elongated and thicker epidermal, palisade and spongy mesophyll cells. paclobutrazol increased stem diameter by about 58% due to induction of thicker cortex, larger vascular bundles, and wider pith diameter associated with larger pith cells. Widening the cortex and the induction of more secondary xylem vessels in response to paclobutrazol treatment increased the root diameter by about 52%. Paclobutrazol treatment remarkably increased the accumulation of starch granules in the stem pith cells and cortical cells of the stem and root. This study is similar to the other relevant studies in reporting an increased leaf thickness, and stem and root diameters; however, most of the underlying anatomical modifications described above have not been reported previously.