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Abstract

Ethylene evolution from excised plant parts was tested as an indicator of stage of seasonal development in red-osier dogwood (Cornus sericea L., syn. C. stolonifera Michx.). A reduction in ethylene production occurs several weeks prior to the time when defoliation can be safely accomplished. This reduction occurs synchronously over the length of the plant, although ethylene production by basipetal tissues prior to the decrease was lower than that by more acropetal tissues. The pattern of change in ethylene production by nodal tissue, which included the axillary buds and about 5 mm of petiole, seemed to be least affected by environmental growing conditions. Ethylene could be used as a predictor for vegetative maturity stage in red-osier dogwood.

Abstract

Electrical impedance ratios and water contents were measured during the development of vegetative maturity and dormancy in a clone of red-osier dogwood Cornus sericea L.) on plants exposed to 16 hour and 12 hour photoperiods in growth chambers to selectively prevent or induce dormancy. Vegetative maturity was designated as the point at which buds were no longer stimulated to grow following artificial defoliation. After this time the ratio of impedance values obtained from the frequencies 10 kHz:100kHz increased and tissue water decreased. Electrical impedance ratios were more easily measured and showed less variation between plants. We conclude that electrical impedance ratios are a means of identifying the onset of vegetative maturity and dormancy in woody deciduous species.

Abstract

Aseptically cultured Malus domestica (Borkh.) cv. Mac 9 plants were exposed to 30–40% relative humidity (RH) for 0 to 6 days. The relative water content (RWC) and percent stomatal closure were measured on leaves excised from plants exposed to low humidity and from greenhouse acclimatized controls. Both RWC and percent stomatal closure successfully monitored acclimatization. The RWC of excised leaves exposed to low RH for 0 or 1 day was significantly higher than that of leaves exposed for 4.5 days or of greenhouse-acclimatized plants. Speed of stomatal closure upon leaf excision increased with the duration of plant exposure to low humidity. The rate of water loss from excised apple leaves was linearly related to the stomatal closure. Aseptically cultured plant (ACP) leaves consistently lost more water than greenhouse leaves at corresponding percentages of stomatal closure. These results indicated that ACP leaves can be acclimatized to low humidity within 4 to 5 days of exposure to 30 to 40% RH and that low humidity acclimatization involved development of an accelerated stomatal response.

Abstract

Ethylene and ethane production of freeze-stressed rhododendron (Rhododendron sp. ‘Sappho’) leaf disks were compared to visual rating, TTC reduction, and electrolyte leakage as possible means of measuring tissue viability. Ethane production, as caused by freezing temperatures, was highly correlated with visual rating, TTC reduction, and electrical conductivity (r = 0.96, r = −0.81, and r = 0.96, respectively). Ethylene production peaked concurrently with initial stages of visual tissue damage, then decreased as the temperature was lowered until complete death occured. Ethane production and electrolyte leakage peaked coincidentally with the decrease of ethylene. Ethylene:ethane ratios are suggested as a measurement of freeze-induced tissue damage. This study supports the view that ethylene production is related to stress and ethane production to cell death. Chemical names used: 2,3,5-triphenyltetrazolium chloride (TTC).

Abstract

Rooted cuttings of a clonal selection of Salix purpurea L. were grown in perlite, in a warm greenhouse at natural daylengths and irrigated daily with one of 10 different mineral nutrient solutions. Plants from each of the nutrient treatments were hand defoliated at weekly intervals beginning in August to assess the effects of mineral nutrients on vegetative maturity development. Vegetative maturity was quantified the following spring by measuring stem dieback. Plants in some nutrient treatments ceased growing 9 weeks earlier in the autumn, and became vegetatively mature several weeks sooner than plants in other treatments. Specifically, treatments such as the distilled water control and Hoagland solution -N,-P, and -S induced early growth cessation, resulted in less stem growth, and induced early onset of vegetative maturity as evidenced by reduced stem dieback the following spring. Development of vegetative maturity was slower in plants irrigated with complete Hoagland solution or Hoagland solution -Ca, -Mg, and -K, which continued growing until October when natural defoliation and growth cessation occurred on control plants treated with complete Hoagland solution. The study demonstrates that vegetative maturity in S. purpurea can be hastened by witholding N, P, and S.

Abstract

The title and byline of the paper, The Relationship between Vegetative Maturity and the First Stage of Cold Acclimation by P. C. Nissila and L. H. Fuchigami (J. Amer. Soc. Hort. Sci. 103(6):710-711. 1978), was inadvertently omitted from the table of contents.

Ethylene production in stem tissues of red-osier dogwood (Cornus sericea L.) following heat treatment was determined at several growth stages. Ethylene production of heat-stressed stem tissue depended on the stage of development and was a function of the degree of stress. During active growth and early endodormancy, heat stress of stem tissues stimulated ethylene production, reaching a peak at 40C, followed by a steady decrease at higher temperatures. Highest ethylene levels from stressed tissues occurred in May, July, September, and March. Only a trace amount of ethylene was produced during endodormancy to ecodormancy (late October to January) from stressed and nonstressed stem tissues. Applying ACC to stem segments at late endodormancy (December) or applying methionine and IAA to stem segments at maximum endodormancy (November) enhanced ethylene production of both nonstressed and heat-stressed stem tissues. Chemical names used: 1 H- indole-3-acetic acid (IAA); 1-aminocyclopropane-1-carboxylic acid (ACC).

Antitranspirant N-2001 (10%), Great Lakes Chemical Corporation, was applied as a soil drench to `Fuji'/EMLA7' apple plants growing in 15 cm pots in a 25/22±3°C (D/N) greenhouse. After bringing pots to field capacity, chemical application was made and water was withheld thereafter. One hour after chemical application, stomatal conductance of treated and control plants was 0.25 and 0.70 cm/sec, respectively. Stomatal conductance of treated plants was maintained at approximately 0.25 cm/sec throughout the test period (28 days). Stomatal conductance of the control plants decreased to 0.25 cm/sec 13 days after treatment due to desiccation. The stem xylem water potential of the treated and control plants was -2.0 and -5.5 MPa, respectively, 28 days after treatment. The relative water content of leaves of treated plants was 45% greater than controls. The average loss of water via transpiration of treated plants was 32% less than the control plants.

Potted apple trees (Malus domestica L. `Gala') were drenched with either water or an antitranspirant (N-2001). After treatment, no additional water was applied to the plants. Abscisic acid (ABA) content of immature and mature leaves was determined by radioimmunoassay after 0, 1, 3, and 5 h and 1, 2, 4, 7, 8, and 9 days after treatment. ABA content of mature and immature leaves of antitranspirant-treated plants peaked 1 and 4 days after treatment, respectively, and remained constant thereafter. In contrast, with increasing water stress, the ABA content of mature and immature leaves of control plants without antitranspirant peaked at 7 and 8 days, respectively. The overall level of ABA in mature leaves of both treatment groups was significantly greater than in immature leaves. The water saturation deficit increased, water and turgor potentials of leaves decreased, and stomatal conductance decreased in response to antitranspirant application. The changes in water relations parameters and stomatal conductance were highly correlated with changes in leaf ABA content.

Abstract

Rhododendron leaf disks (Rhododendron L., cv. Jean Marie de Montague) release water-soluble phenolic compounds when subjected to lethal freezing stress. Following low-temperature exposure, the levels of phenolic compounds leached from the disks are assessed by spectrophotometric measurement (260 nm). The increase in phenolics is highly correlated with other viability tests—electrolyte leakage, visual browning, ethane production, and TTC reduction have r values of 0.99, 0.99, 0.95, and −0.88, respectively. Chemical names used: Trichloroacetic acid (TCA), polyvinylpolypyrrolidone (PVPP), 2,3,5-triphenyl tetrazolium chloride (TTC).