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I. Gergely, R. F. Korcak, and M. Faust

Abstract

Polyethylene glycol (PEG)-induced water stress in nutrient solutions decreased both water consumption and 45Ca uptake by apple seedlings (Malus domestica Borkh.) The decrease in water uptake was more severe than the decrease in 45Ca uptake. When 45Ca uptake was calculated on the basis of water consumption, it was found that 45Ca uptake was not dependent on water uptake although water was necessary for movement of 45Ca. In split-root experiments, PEG and 45Ca were either applied to the same half of the root or to separate halves. Calcium uptake decreased in plants subjected to water stress. The results indicated that the site of this decrease was at the root, not the aerial portion of the plant which, indirectly, may affect root function and thus 45Ca uptake. Split-root experiments also indicated that the unstressed half of the root cannot fully compensate for the stressed half of the root in either water or 45Ca uptake. Water use of plants with half of their root under a −5.0 bar water stress was decreased by 30%. Urea-nitrogen pretreatment did not modify the effect of osmotic stress on leaf Ca, Mg and K concentrations, water use or dry matter production during the period of applied water stress. All these parameters decreased with increasing solution osmotic stress.

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Carlos A. Parera, Daniel J. Cantliffe, D.R. McCarty, and L. Curtis Hannah

The shrunken-2 (sh2) mutant of maize (Zea mays L.) increases sucrose and reduces starch in developing endosperm. An associated trait is poor seed and seedling vigor in seeds containing the mutation. The specific effects of sh2 mutant endosperm on embryo and seedling vigor were determined by analyzing seeds that contained either concordant wild-type or nonconcordant combinations of mutant and wild-type embryo and endosperm genotypes. The nonconcordant seed types that contained a wild-type embryo in association with a sh2 mutant endosperm or a sh2 mutant embryo in association with a wild-type endosperm were generated using the TB-3La translocation chromosome in which a wild-type Sh2 gene is attached to the centromeric portion of a B chromosome. Under stress conditions (complex stress vigor test), the seeds with mutant endosperm had lower germination, seedling fresh and dry weight, and index of conductivity than seeds with wild-type endosperm. Mutant endosperm and embryos excised from mutant endosperm imbibed more water than wild-type endosperm or embryos excised from wild-type endosperm. Because of the high concentration of osmotic solutes in the mutant endosperm, a rapid water uptake may induce a membrane disorganization. Leachate conductivities of seeds with mutant endosperm were higher than seeds with wild-type endosperm. In addition, a higher sucrose content and a lower raffinose to sucrose ratio were measured in the wild-type embryos associated with mutant endosperms than in the normal embryos excised from concordant wild-type seeds. These results suggest that a high rate of water uptake caused by the elevated concentration of osmotic solutes in seeds with mutant endosperms may affect membrane integrity during imbibition. Alternatively, the lower raffinose to sucrose ratio present in the mutant endosperm class might affect stabilization of cell membranes during seed desiccation. Embryos cultured in media containing 10% starch or no carbohydrate produced smaller seedlings than embryos cultured in 5% or 10% sucrose. Wild-type embryos excised from mutant endosperms exhibited lower germination in 0% and 5% sucrose media than embryos from concordant seed, indicating that reduced water uptake rates associated with lower external osmotic potential (10% sucrose) can improve vigor of embryos associated with sh2 mutant endosperm. The reduced vigor of embryos and seedlings that develop in association with sh2 mutant endosperm can be traced to the physiological and biochemical effects of the elevated sucrose levels present during seed formation and imbibition.

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Juan C. Díaz, Kenneth Shackel, and Ellen Sutter

The contribution of in vitro-formed roots to the water status of tissue culture plants was studied by observing the stomatal responses of rooted and unrooted apple shoots. Stomatal conductance was measured on whole plants with a modified steady state porometer in a temperature-controlled room. The porometer was maintained at a steady 90% RH and conductance was measured every 30 seconds. Plants were kept in the gas exchange system for about 28 h. Steady state values of stomatal conductance for rooted and unrooted shoots were 220 (S.E= 19) and 163 (S.E=23) mmol m-2 s-1, respectively. When the plants were exposed to a light stimulus (1200 μmol m-2 s-1), rooted shoots showed an increase of about 64% in stomatal conductance. In the absence of roots, no response to light was observed. These results suggest that the presence of the roots improved, at least partially, water uptake and plant water status.

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Mayuko Otsubo and Mari Iwaya-Inoue

Florets of cut gladiolus (Gladiolus ×grandiflora hort. cv. Fujinoyuki) spikes kept at 25 °C under 14 h light/10 h dark condition showed severe wilting 4 days after flower opening. Treatment with 0.1 m trehalose prolonged vase-life 2 days, whereas inhibitors and other sugars had no effect. The upper florets also opened properly in trehalose-treated spikes, but not in cycloheximide-treated ones. After 4 days, the first florets of trehalose-treated spikes maintained water content more effectively than did controls or spikes treated with other sugars. The parenchyma adjacent to vascular bundles in the petals of trehalose-treated spikes maintained viability for 4 days. These results suggest that trehalose preserves cell viability in gladiolus spikes, thereby enhancing water uptake into petal tissues.

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Leon H. Allen Jr., Mary P. Brakke, and James W. Jones

A water flow model was developed which uses irradiance, leaf-to-air vapor concentration difference, and soil water potential to establish stomatal conductance. Water flow to the roots was computed using a linear approximation of radial flow through the soil toward the axis of the roots across concentric shells. Root length density and soil rooting volume within four separate layers or compartments were included in the model. The simulation was executed in small time step iterations. A small increment of transpiration was translated to a water content deficit at the root and then sequentially through the concentric shells to simulate water uptake and change of soil water potential. The change in soil water potential was used to increment changes in stomatal conductance and transpiration. The output of the model simulated the pattern of diurnal stomatal behavior observed in other types of experiments, as well as the total soil water extraction patterns of young potted citrus trees.

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Caroline H. Pearson-Mims and Virginia I. Lohr

Cut `Samantha' roses (Rosa hybrida L.) were placed in deionized water or a 20-mm Ca(NO3)2 pulsing solution for 72 hours. Flowers then were held in preservative solutions containing 0 or 4 mg fluoride/liter. Fresh weight gain, solution uptake, degree of flower opening, and flower longevity were reduced in the presence of fluoride in the holding solution. Visual symptoms of injury and reduced flower quality also were noted in treatments with fluoride. Pulsing improved fresh weight gain and degree of opening of flowers held in solutions containing fluoride. Pulsing also delayed the onset of visual symptoms of fluoride injury. Water uptake for flowers that were pulsed and exposed to fluoride was not different from uptake for flowers exposed to fluoride alone. Flower longevity for roses in all treatments was increased by using the calcium nitrate pulse, but pulsed flowers in fluoride did not survive as long as the control flowers.

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Theo J. Blom and Brian D. Piott

Low volume drip (2 l/h) was compared with 2 subirrigation ('trough' and `ebb and flo') systems for production of poinsettias and chrysanthemums in 15 cm diameter (1.6 l) `azalea' pots. Irrigation frequency as well as fertilizer rates were the same for all systems. The drip system received 280 ml per watering.

Two plantings of poinsettias (fall) as well as two plantings of chrysanthemums (spring and summer) showed no differences in plant growth between the drip and the subirrigation systems. Water uptake by the medium was similar for all irrigation systems, but water and fertilizer application was 70% higher for the drip system. Nutrients, measured at 4 depths within the pot at monthly intervals, increased with time and was markedly more concentrated in the top layer, regardless of the irrigation system.

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Mayuko Otsubo and Mari Iwaya-Inoue

Florets of cut gladiolus (Gladiolus ×grandiflora hort. cv. Fujinoyuki) spikes kept at 25 °C under 14 h light/10 h dark condition showed severe wilting 4 days after flower opening. Treatment with 0.1 m trehalose prolonged vase-life 2 days, whereas inhibitors and other sugars had no effect. The upper florets also opened properly in trehalose-treated spikes, but not in cycloheximide-treated ones. After 4 days, the first florets of trehalose-treated spikes maintained water content more effectively than did controls or spikes treated with other sugars. The parenchyma adjacent to vascular bundles in the petals of trehalose-treated spikes maintained viability for 4 days. These results suggest that trehalose preserves cell viability in gladiolus spikes, thereby enhancing water uptake into petal tissues.

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Fisun G. Çelikel and Michael S. Reid

The respiration of flowers of stock [Matthiola incana (L.) R. Br.] had a Q10 of 6.9 between 0 and 10 °C. Simulated transport for 5 days resulted in marked reduction in the vase life of flowers transported at 10 °C and above. Flower opening, water uptake, and vase life of the flowers increased somewhat in a vase solution containing 50 ppm NaOCl, and considerably in a commercial preservative containing glucose and a bactericide. Exposure to exogenous ethylene resulted in rapid desiccation and abscission of the petals, effects that were prevented by pretreatment with 1-methylcyclopropene (1-MCP). Even in the absence of exogenous ethylene, the life of the flowers was significantly increased by inhibiting ethylene action using pretreatment with silver thiosulfate (STS) or 1-MCP. STS was more effective than 1-MCP in maintaining flower quality.

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Carlos A. Parera and Daniel J. Cantliffe

Generally, sweet corn cultivars (Zea mays L.) carrying the shrunken-2 (sh2) gene have lower germination and seedling vigor than normal or sugary (su) cultivars. Seeds of sh2 `How Sweet It Is' (HSII) and `Crisp N'Sweet 711' (CNS-711) were imbibed for 6 hours. Rapid water uptake, higher seed leakage, and fungal infection were found in HSII, the lower germinating cultivar. Imbibition rate and leakage conductivity were reduced in both cultivars during the first 5 hours at 5C as compared with 25C. Sodium hypochlorite was an effective seed disinfectant. When the seeds were primed with sodium hypochlorite via solid matrix priming (SMP), germination under stressful conditions (soilcold test) was significantly improved in both cultivars. Primed seeds had significantly lower imbibitional rates and leakage conductivity than nonprimed seeds. The superior germination measured in primed and disinfected seeds was possibly due to the lower imbibitional rate and reduced seed fungal infection.