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  • Author or Editor: L. H. Fuchigami x
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New roots of Malus domestica Borkh MM106 apple rootstock were divided into two categories, 1) feeder roots and 2) extension roots based on morphology and their ability to take up NH4 +, were studied. The roots were harvested in August from 1-year-old potted plants growing under natural conditions in Corvallis, Ore. Extension roots were thicker and longer than feeder roots. Average diameter and length were 0.89 and 45.29 mm for extension roots and 0.27 and 5.36 mm for feeder roots. Root special length (cm/g FW) and surface area (cm2/g FW) were 11.94 and 33.17 for extension roots and 108.97 and 93.38 for feeder roots. Maximum uptake rate, Imax, Km, and root absorption power, α (α = Imax•1/Km), for NH4 + absorption were 6.875, 0.721, and 9.48 for extension roots and 4.32, 0.276, and 15.63 for feeder roots. Feeder roots had stronger affinity to NH4 + (low Km) and higher NH4 + absorption power (high α value) than extension roots. The feeder roots were better able to uptake NH4 + at lower external solution concentrations than extension roots according to the nutrient depletion curve, which indicates feeder roots being more efficient than extension roots in nutrient absorption when NH4 + availability was low.

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The nutrient uptake kinetics by new roots of 1-year-old potted clonal apple rootstocks (M7, M9, M26, M27, MM106, and MM111) were determined by the ion depletion technique at the stable development stage of trees in August. The total roots of five of the rootstocks (except MM111) consisted of more than 60% feeder roots and less than 12% extension roots. MM111, the most vigorous rootstocks tested, had 60.7% feeder roots and 24.5% extension roots. Root: top ratio was negatively related to the growth inhibiting character of the rootstock. Nutrient uptake by excised new roots was found to fit into Michaelis-Menton kinetic model for all rootstocks tested. The kinetic characteristics (maximum uptake rate, Imax, apparent Michaelis-Menton constant, Km, and root absorption power, (α = Imax•1/Km) between rootstocks differed significantly. MM111 had the highest Imax for NH4 + absorption and M9 for NO3 -. Root affinity to ions was highest with MM106 for NH4 + and with M26 for NO3 -. Root absorption power (α = Imax•1/Km) was greatest in MM106 for NH4 + and M9 for NO3 -. At this developmental stage the data suggest no relationship between nutrient uptake and dwarfing character of the rootstocks.

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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.

Open Access

Abstract

Potted plants of red-osier dogwood (Cornus sericea L., syn. C. stolonifera Michx) were grown under 3 different dormancy-inducing regimes. Each week 5 plants per group were defoliated and placed in a warm greenhouse. Plants were checked daily for regrowth and new leaves were removed. When defoliation ceased to induce bud break, the plants were considered to be in a state of winter dormancy. Plants were observed for damage the following spring to determine when they had reached vegetative maturity, and it was found that vegetative maturity corresponded to winter dormancy development in all 3 growing conditions.

Open Access

Abstract

Xylem water potential (XWP) and electrical impedance ratios were used to determine the time of vegetative maturity in red-osier dogwood (Cornus stolonifera Michx.) grown under 2 temperature and a short-day dormancy inducing regime in growth chambers and a lathhouse under natural conditions. The decline in XWP correlated with the development of vegetative maturity as measured by tip dieback after defoliation. Under growth chamber conditions, average XWP values reached a minimum at the time of vegetative maturity. In all cases, however, variability within samples was so large as to preclude the use of XWP as an accurate, reliable index of vegetative maturity. A change in electrical impedance ratios at and after vegetative maturity caused the impedance meter to go “off scale.” Compared with XWP values, changes in electrical impedance ratios were more consistent and show promise in predicting vegetative maturity.

Open Access

Abstract

Red-osier dogwood (Cornus stolonifera Michx.) plants were grown outdoors in a lathhouse to study the relationship between vegetative maturity and the first stage of cold acclimation. Both microscopic observations and electrical impedance ratios used to measure damage of frozen stem sections verified the close association of the onset of the first stage of cold acclimation and vegetative maturity. The relationship of these processes to dormancy development is discussed.

Open Access

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.

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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.

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Abstract

Ethephon at 120 mg·liter−1 applied to hand-defoliated or nondefoliated trees in late Oct. 1984 delayed ‘Redhaven’ [Prunus persica (L.) Batsch.] full bloom by ≈5 days in 1985. The same treatment applied on 1 Nov. 1985 delayed full bloom by 9 days in 1986. Hand-defoliation alone was ineffective in delaying bloom in either season. Ethephon treatments increased abscisic acid (ABA) and ethylene levels in dormant buds collected throughout the 1985–86 dormant season. Starch and reducing sugar contents and total chilling requirement were not affected by the ethephon and hand-defoliation. Flower primordia were delayed in differentiation and growth during late fall following a 1986 spray of ethephon. A delay in flower development and growth may be caused by increased levels of ethylene and ABA. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon); aminoethoxyvinylglycine (AVG).

Open Access

Buds, leaves, or stems of red-osier dogwood (Cornus sericea L). plants were covered with aluminum foil and placed in a warm greenhouse under long day condition to determine the perceptor site for overcoming the early stage of endodormancy. The following categories with treatments were studied; Category A, foliated plants: A1) not covered, A2) buds covered, A3) stem covered, A4) stem and bud covered. Category B, foliated-covered plants: B1) leaves covered, B2) leaves and buds covered, B3) leaves and stem covered, B4) leaves, stem and buds covered. Category C, defoliated plants: C1) not covered, C2) buds covered, C3) stem covered, C4) stem and buds covered. These studies indicate the bud as the long day (LD) perceptor site for overcoming the early stage of endodormancy. However, the presence of leaves (Category A) stimulated terminal budbreak only in bud covered (A2) and stem and bud covered (A4) treatments. In addition, etiolation treatments (Stem covered, A3, A4 and C3) resulted in significant root initiation on stem internodes within 2 weeks. The rate of presence of roots in stem-covered treatment promoted shoot growth.

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