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Masahiro Toyoda, Yuko Yokota, Marni Barnes, and Midori Kaneko

.) and at the end of the intervention period (14 Feb.)]. As an indicator of physiological stress, participants’ pulse rates were recorded twice every working day (i.e., once in the morning and once in the afternoon) when the participants felt fatigue. The

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María del Carmen Vadillo-Pro, Luis Hernández-Sandoval, Guadalupe Malda-Barrera, María Luisa Osorio-Rosales, and Martín Mata-Rosas

eight replicates. Growth stage. After the induction period, the explants of either semisolid or pulse treatments, were subcultured every 30 d on semisolid MS medium without PGRs but with activated charcoal at 1 g·L −1 . After 3 months, survival rate and

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Juan Carlos Melgar, Arnold W. Schumann, and James P. Syvertsen

day applied in only one 30-s pulse per day at 0900 hr ; or 3) 45 mL applied every 3 d at 0900 hr . Two different N rates were applied in this experiment. Seedlings from the first two treatments (those with daily applications) were initially

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Fucheng Shan and Kevin Seaton

lignified cuttings are required for this method. This method provides a possibility to use immature cuttings for propagation; however, the multiplication rate could be improved if single-node immature cuttings could be used and if both the semimature

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Jiwoo Park and James E. Faust

Saigusa, 2002 ). Pulse fertilization refers to a one-time fertigation application performed before placing the plants in a postproduction environment and at a higher rate than the CLF rates applied during production. Both the CRF and PF methods have the

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Leonardo Lombardini, Moreno Toselli, and James A. Flore

Instrumentation to measure soil respiration is currently readily available. However, the relationship between soil respiration and root activity or root mass is not known. Herein we report on preliminary result using a 13CO2 pulse to the foliage to determine if 13C respiration can be related to either root activity or root mass. An experiment was performed in the field on a 5-year-old apple tree (cv. Jonagold on M7). The tree canopy was enclosed in a Mylar® balloon and 2.1 g 13CO2 were pulsed in the balloon for 1 hr. After the pulse, air emitted by the soil and selected roots was collected every 6 hr for 8 days, by bubbling it in 2 M NaOH. 13C/12C ratios were measured with the mass spectrometer. The emission of 13CO2 from the roots gradually increased after the pulse reaching a peak after 100 hr. The emission trend was not linear, but it seemed related to soil temperature. Leaves and fruit were also collected daily. 13C content in leaves was 1.15% right after the pulse, but it progressively decreased to 1.09% at the end of the experiment. The experiment was then repeated on 12 potted apple trees (cv. Redcort on M7) in greenhouse conditions. Six of them were maintained well-watered, whereas six plants were subjected to a mild water stress, by watering them with half of the volume of water used for well-watered plants. After the two soil moisture levels were achieved, the tree canopies of all the 12 trees were pulsed. Leaves, stems, and roots were ground and run in the mass spectrometer. The results of root emission rate were found to be similar to the field experiment. Results also indicated that, in our experiment, stress did not affect root respiration rate. Specific details of the physiology data will be presented.

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O. Monje, G.D. Goins, H.G. Levine, and G.W. Stutte

Tight control of growth media moisture content is needed when plant growth systems employ shallow root zones or for cultivating fast-growing plants (i.e., crops). Poor control of moisture can affect both growth rate and plant quality by either excessive watering (waterlogging) or drought events. We evaluated the performance of two types of moisture sensors: tensiometers and heat-pulse moisture sensors. The output from each sensor type was evaluated as a function of volumetric moisture content in 1 to 2 mm Turface. The tensiometers were more sensitive between 30% and 60% volumetric moisture content, and their output was nonlinear because they measure water potential directly. In contrast, both the sensitivity and the output of the heat-pulse moisture sensors, as a function of volumetric moisture content, were linear. The heat-pulse moisture sensors were used to control moisture content in a shallow root zone, whereby water was added or removed from the media through a porous tube using peristaltic pumps. Moisture content in the media could be maintained within ±2% of setpoint for moisture contents ranging from 20% to 100% volumetric moisture content. The heat-pulse sensors were better suited for controlling media moisture because of their linear output and because of their constant sensitivity as a function of volumetric moisture content.

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Jason R. Tutty, Peter R. Hicklenton, David N. Kristie, and Kenneth B. McRae

Stem elongation rate (SER) in Dendranthema grandiflorum (Ramat.) Kitamura was determined in light and in darkness under various temperature regimes. Stem growth as measured with linear voltage displacement transducers on plants in growth chambers. Under alternating 11-hour days and 13-hour nights, SER was strongly temperature dependent and showed patterns that were characteristic of the particular photoperiod-temperature regime under which the plants were grown. Total daily elongation was similar at constant 18.3C and at 11.5C days and 24C nights, but was much greater at 25.7C days and 12C nights. SER was rhythmic in continuous light with a period of slightly less than 24 hours. In continuous darkness, however, SER declined rapidly and the rhythm disappeared within 11 hours. Low-temperature pulses (a rapid decline from 18.3C to 8.3C) applied for 2, 4, 6, 8, or 11 hours during the day induced an immediate decline in SER followed by a slow recovery and peak shortly after the end of the pulse. Total diurnal stem growth declined with increasing pulse length, although short (2-hour) duration pulses apparently had little effect on growth. The results are discussed in relation to the influence of day and night temperature differentials (DIF) on stem growth in Dendranthema.

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Robyn McConchie and N.Suzanne Lang

A major postharvest problem of Protea neriifolia is premature leaf blackening. Carbohydrate stress, due to floral sink demand, may lead to cellular disorganization and leaf blackening. Leaf blackening, nonstructural carbohydrates, ethylene, carbon exchange rates, stomatal conductance and lipid peroxidation were measured on leaves of vegetative and floral stems preharvest, and during a 7 day dark postharvest period. Postharvest treatments were: 0 or 0.5% sucrose in the vase solution, 20% sucrose pulse, or floral decapitation. Leaf blackening was significantly reduced in vegetative stems and floral stems in the 20% pulse treatment, in comparison to all other treatments. Ethylene production and lipid peroxidation were not associated with leaf blackening in any treatment and leaf respiration rates declined for all treatments over time. The magnitude and rate of leaf blackening was inversely related to leaf starch concentrations, with greatest carbohydrate depletion occurring within 24 h of harvest (by 75-85%). Leaf starch from the 20% pulse treatment increased by 300%, in contrast to declining starch concentrations in all other treatments. The data suggest that the flowerhead functions as the major sink for carbohydrate depletion leading to subsequent leaf blackening.

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Robyn McConchie and N. Suzanne Lang

Abbreviations: AER, assimilate export rate; CER, carbon exchange rate; DNMR, Duncan's new multiple range test; GSH, reduced glutathione; GSSG, oxidized glutathione; MDA, malionaldehyde; POD, peroxidases; PPO, polyphenol oxidase. 1 Graduate Research