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  • Author or Editor: Stephen J. Wallner x
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Abstract

The topic of this symposium, “Basic Research Ideas and Opportunities for Horticulturists in Stress Physiology”, relates to the activities of most horticultural scientists. Plant response to environmental stresses connects many disciplines and is important to all commodities. Even a cursory review of the symposium papers reveals that molecular genetics, biochemistry, cell biology, plant anatomy, etc. receive major emphasis in consideration of physiological response to unfavorable environments. The broad relevance of this topic is also reflected in the joint sponsorship of the symposium by five working groups: Climatology and Meteorology, Cropping Efficiency and Photosynthesis, Developmental Physiology, Environmental Stress Physiology, and Postharvest.

Open Access

Abstract

Fruit softening of apple (Malus domestica Borkh.) and the activity of β-galactosidase in 0.5 m citrate extracts of fruit cortex were compared for ‘Lodi’, ‘McIntosh’, ‘Golden Delicious’, and ‘York Imperial’ during storage at 0° or 3.3°, 10.0°, and 18.3°C. Enzyme activity per g fresh weight increased as fruits softened, but specific activity did not change. Cell wall galactose content also decreased during softening. The decrease in wall galactose was least in ‘Lodi’ which contained the lowest β-galactosidase activity. ‘York Imperial’ which softened most slowly showed the highest β-galactosidase activity at harvest and throughout storage. Concentrated enzyme preparations did not release measurable amounts of reducing sugar, uronic acid, or neutral hexose from isolated cell walls.

Open Access

Abstract

Explants of apple (Malus domestica Borkh.) fruit cortex were used to establish tissue cultures of ‘Lodi’, ‘Golden Delicious’, and ‘York Imperial’ harvested at various stages of maturity. Cell division and initial callus formation occurred in all cases and was not affected by fruit age. However, the capacity to produce callus which survived subculture declined in later stages of development, especially for ‘Golden Delicious’. Although somewhat variable, callus of ‘Lodi’ and ‘York Imperial’ was generally soft and that derived from ‘Golden Delicious’ tended to be friable or hard. The texture of the callus was not related to the age of the fruit from which it was obtained. The degree of cell separation in suspension culture was not entirely consistent with the textural characteristics exhibited on solid medium. There was no striking change in the extent of cell separation during development in suspension culture.

Open Access

Abstract

Freezing woody stem segments of supercooling and non-supercooling species resulted in acoustic emissions in characteristic reproducible patterns. In the supercooling species examined (Fraxinus americana, Malus × ‘Dolgo’, Pyrus communis, and Fraxinus pennsylvanica), many acoustic emissions began after extracellular freezing, but before freezing of the supercooled fraction, and ended near −40°C. Acoustic emissions also occurred in species that did not supercool (Pinus edulis, Pinus ponderosa, and Cornus sericea), but to a much lesser extent. Cavitation of water within the cells during freezing is discussed as a source of acoustic emissions and possible cause of freezing injury.

Open Access

Abstract

Heat resistance of aspen (Populus tremuloides) leaves was assessed by stressing leaf discs in vitro and measuring electrolyte leakage. Leaves were obtained from trees growing at elevations of 1960, 2195, and 2454 m. Heat tolerance was greatest in leaf samples from trees growing at the lowest site. Trees propagated from these sites and grown at 1520 m for 2 years showed some increase in heat tolerance, but apparent ecotypic differences persisted.

Open Access

Abstract

Suspension-cultured pear (Pyrus communis ‘Bartlett’) cells cold-acclimated during exposure to 2°C. Cold acclimation was accompanied by changes in soluble extracellular polysaccharides and in the deposition of callose in the cell wall. Release of a relatively small neutral polysaccharide into culture medium was increased at 2°. However, low temperature decreased the extracellular accumulation of a larger molecular weight (M r) pectic polysaccharide. The reduced amount of pectic polysaccharide may have been the result of both a low-temperature-enhanced degradation of existing polysaccharide and an inhibition of new synthesis or secretion. The effect of low temperature on callose deposition was observed using an aniline blue fluorescent staining procedure. Pear cells held at 2° showed far more intense staining than those at 22°, indicating increased deposition of callose or other β-1,3-glucans at the cell surface during cold acclimation.

Open Access

As the landscape design/build industry continues to develop, opportunities for providing baccalaureate degree programs in landscape contracting increase. Employers seek individuals with competencies that are not adequately addressed by traditional horticulture or landscape architecture curricula. The Department of Horticulture at Penn State has developed a Bachelor of Science in Landscape Contracting degree. The program, now entering its fourth year of resident instruction, has experienced rapid growth and a high degree of success. Annual increases in student interest and demand have necessitated caps on the number of students entering the major. An emphasis on design process and on construction technology, and a requirement for successful completion of courses in Horticulture and allied departments contribute to an education which instructs students in the art, science, and management of a professional design/build business. Integration of computer-aided design into Landscape Contracting courses positions graduates to carry current technology to the industry. Students obtain skills on the use of AutoCAD, LandCADD, and New Image software.

Free access

Greenhouse-cultured, container-grown seedlings of interior Douglas fir [Pseudotsuga menziesii var. glauca (Beissn.) France], Engelmann spruce [Picea engelmannii (Parry) Engelm.], and ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) were acclimated and deacclimated to cold in growth chambers over 19 weeks. Heat tolerance and cold hardiness of needles, and bud dormancy, were measured weekly. Heat tolerance of Douglas fir and Engelmann spruce needles increased with development through the first complete annual cycle: new needles on actively growing plants; mature needles, not cold-hardy, on dormant plants; cold-hardy needles on dormant and quiescent plants; and mature, needles, not cold-hardy, on actively growing plants. Heat tolerance of ponderosa pine needles differed in two respects. New needles had an intermediate tolerance level to heat, and fully cold-hardy needles were the least tolerant. Thus, the physiological changes that conferred cold hardiness were not associated with greater heat tolerance in all the conifers tested. In none of these species did the timing of changes in heat tolerance coincide consistently with changes in cold hardiness or bud dormancy.

Free access