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  • Journal of the American Society for Horticultural Science x
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The use of abscisic acid (ABA) as an in vitro prehardening treatment to enhance ex vitro acclimatization of Stage III Aronia arbutifolia plantlets was explored. Effects of ABA (0-4 mg·liter-1) pretreatment on ex vitro shoot growth, leaf carbon assimilation (LCA) and nonstructural carbohydrate content were evaluated during plantlet acclimatization under two photosynthetic photon flux (PPF) levels (450 and 650 μmol·m-2·s-1). Stage III plantlets rooted in the presence of ABA exhibited both shoot growth inhibition and transient negative LCA rates at time of transfer ex vitro. Regardless of treatment, maximum LCA rates were achieved by day 20 post-transplant. Pretreatment with ABA had no effect on stem or leaf starch content at time of transplant, however, leaf and stem soluble sugar content was higher in ABA treated plantlets than controls. Further suppression of shoot growth and alteration in the pattern of stem starch utilization occurred at the higher irradiance level. These results indicate that ABA pretreatments provide no physiological advantage that would facilitate ex vitro acclimatization of Aronia plantlets.

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Abstract

The effect of CO2 enrichment (CE) and supplemental lighting (SL) on the growth of ex vitro strawberry (Fragaria × ananassa Duch.) plantlets was studied during acclimatization. Three different concentrations of CO2 [330, 900, and 1500 ppm (v/v)] and two SL treatments (0 and 150 μmol·s–1·m–2) were applied. There was no significant interaction between light and CO2 for root and leaf dry weight and leaf area. CE had no effect on these parameters in the early period following transfer but resulted in significant increases at days 20 and 30. CE had no significant influence on leaf and root relative growth rate (RGR) over the three sampling periods, but had a significant effect on net assimilation rate at a 20- to 30-day period. At the end of the experiment, 900- and 1500-ppm treatments had a significantly higher root and shoot dry weight than the 300-ppm treatment. SL resulted in increased dry weight at 10 days and even greater increases at days 20 and 30. CE was more effective than SL in stimulating root growth, whereas SL increased shoot growth significantly. There was a synergistic effect between CE and SL. The period needed to obtain plants of a similar size to an acclimatized plantlet was shortened by 15 days with 900 ppm CO2 and SL. At the end of the experiment, SL and CE at 1500 and 900 ppm increased leaf and root dry weight by a factor of 3 and 5 for ‘Honeyoye’ and ‘Kent’, respectively. These increases were less important for SL or CE used alone.

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One-node explants and one-node stem cuttings of Asian jasmine [Trachelospermum asiaticum (Siebold & Zucc.) Nakai] were rooted, respectively, in vitro [tissue culture (TC)] or by conventional macropropagation (MACRO). The TC and MACRO stem bases were then analyzed for differences in the time-course sequence of 1) root primordia initiation and development and 2) adventitious root xylem development and root-to-shoot xylem connections. Early root primordia were observed at Day 3, and, by Day 7, root-to-shoot xylem connections were equally developed in TC and MACRO systems. Continued development and emergence of adventitious roots were observed at Days 8 to 10. At Days 13 and 18, when viewed using scanning electron microscopy, TC root hairs were morphologically thicker and one-third to one-half the length of MACRO root hairs. There was no apparent difference in root-hair density. Inferior TC root-hair length may be a factor in the acclimation of TC-generated plantlets.

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In vitro tissue-cultured (TC) and macropropagated (MACRO) 18-day old adventitious roots of Asian jasmine [Trachelospermum asiaticum (Siebold & Zucc.) Nakai] were compared for their ability to absorb and translocate radiolabelled P from a nutrient solution. Samples were taken at 1, 2, 4, 8, 12, and 24 hours after the initial dosage of the nutrient solution with 7.4 × 10-2 MBq KH 32 2PO4/liter. TC roots were capable of absorbing P, but at significantly lower levels than MACRO roots. Greater P absorption occurred in MACRO roots within the first hour and continued for the duration of the experiment. However, there was no significant difference in the rate of P translocation from roots to shoots between treatments. Root systems formed in vitro survived acclimation and had developed into well-branched root systems after 13 weeks. Reduced P absorption by TC roots did not limit either P translocation or survivability during and after acclimation.

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Abstract

CO2 uptake and various leaf parameters were examined including photosynthetic pigment content (chlorophyll a, b, and total carotenoids), fresh/dry weight, percentage of water content, gram dry weight/area, and total plantlet leaf areas of an aseptically cultured clone of red raspberry (Rubus idaeus L.) incubated at 5 light intensities, from 2 to 6 klx. Cultured plantlets demonstrated relatively low levels of CO2 uptake, averaging 2.5 mg CO2 dm–2hr–1 and rarely exceeding 4 mg CO2 dm–2 hr–1 at saturating light intensities. Pigment content was higher in plantlets incubated at lower light intensities (2 to 4 klx). Cultures incubated at 3 klx were evaluated both at the time of transfer to soil and 1 month later. Plantlet leaves retained from culture could be distinguished from new leaves by tagging all plantlet leaves prior to soil transfer; both were assessed separately 1 month after transplantation. Leaves retained from culture, 30% of the total leaf area of transplants, contributed less than 10% of the CO2 uptake at 3 klx. These leaves accounted for 10% to 30% of the total leaf area at higher light intensities but were net respirers. There was an increase in dry matter accumulation at 6 and 9 klx in these tagged leaves, but not at 3 klx. Continued accumulation of dry matter by the tagged leaves can be only at the expense of photosynthetic activity of the newly formed leaves. New leaves of transplants had a greater dry matter accumulation at 9 klx and a pigment content greater than the tagged leaves. Their pigment content was similar to that of young, control plant leaves. Transplants were capable of uptake rates of 5–7 mg CO2 dm–2 hr–1 or 50% of field control rates. The photosynthetic contribution of the leaves from culture was small or negative. The first new leaves formed in soil were transitional with intermediate capability. Acclimatization to the soil environment was time dependent and required the production of new leaves initiated in the new environment.

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Chimeral `Thornless Evergreen' (CTE), (Rubus laciniatus Willd.) somaclones selected in 1983 and field planted in 1985 were reexamined in 1992 for various vegetative and reproductive characteristics. Two major types of thornless (prickle-free) plants, intermediate-sized (`UI 6-6' = `Everthornless') and dwarf (`UI 6-4'), originally selected from a chimeral thornless parent plant, were compared with thorny plants. The intermediate and dwarf somaclones have maintained their distinctive habits over 7 years' growth in the field, indicating that their growth habits are stable and not a transient effect of tissue culture. Although the thornless somaclones remained thornless, the degree and type of prickle-like structures varies considerably, indicating that the thornless gene (S te) does not entirely suppress the production of prickles, but apparently alters their development. Increasing suppression was directly related to increasing dwarfism, suggesting a link between thornlessness and internode length.

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Photosynthesis and growth of in vitro-cultured strawberry plantlets (Fragaria × ananassa Duch. cv Kent) were investigated during a 4-week in vitro culture in a rooting medium and a 4-week ex vitro period. The leaves formed in vitro on a medium containing sucrose developed a positive photosynthetic capacity. At transplanting to the ex vitro environment, their photosynthetic rate was 12.76 μmol CO2/m2 per second, which was as high as that of leaves generated and grown in the greenhouse. During the ex vitro period, photosynthetic rates of in vitro-generated leaves decreased and dark respiration rates increased. However, in vitro leaves were photosynthetically active throughout the 4 weeks ex vitro. In the first 2 weeks of the ex vitro period, in vitro-generated leaves had an important contribution to the overall plantlets' photosynthetic capacity.

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The effects of natural ventilation and CO2 enrichment during the rooting stage on the growth and the rates of photosynthesis and transpiration of in vitro cauliflower (Brassica oleracea L.) plantlets were investigated. In vitro plantlets were established in airtight or ventilated vessels with or without CO2 supplied (≈1200 μg·L-1) through gas permeable films attached to the vessel's cap for 15 days before transplanting ex vitro. Leaves generated in vitro in ventilated vessels had a higher photosynthetic rate than those produced in airtight vessels, which lead to greater leaf expansion and shoot and root dry matter accumulation during in vitro culture and acclimatization. Enhanced photosynthesis in leaves of ventilated plantlets was positively correlated with chlorophyll content. Increasing photosynthetically active radiation from 70 to 200 μmol·m-2·s-1 enhanced the growth of in vitro plantlets under ventilated conditions but it depressed photosynthesis of the leaves grown photomixotrophically with sugar and CO2 enrichment which might be due to the feedback inhibition caused by marked accumulations of sucrose and starch. Higher CO2 levels during in vitro culture enhanced photosynthesis under photoautotrophic conditions, but inhibited it under photomixotrophic conditions. Fifteen days after transplanting ex vitro, high photosynthetic ability and stomatal resistance to transpiratory water loss of ventilated plantlets in vitro had important contributions to rooting and acclimatization. Our findings show that the ventilated culture is effective for accelerating photoautotrophic growth of plantlets by increasing photosynthesis, suggesting that, especially for plantlets growing in vitro without sugar, CO2 enrichment may be necessary to enhance photosynthetic ability.

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A two-stage micropropagation system was devised for cranberries (Vaccinium macrocarpon Ait.). Shoot-tip explants taken from four cultivars of greenhouse-grown plants were placed on media composed of Anderson's major salts, Murashige and Skoog's (MS) minor salts and organics, plus various concentrations of 2iP, IBA, and GA3. In other experiments, explant source, salt formulations for media, and rooting treatments were studied. Optimal multiplication and shoot quality occurred when nodal explants taken from greenhouse-grown or micropropagated plants were placed on medium containing 150 μm 2iP, 1.0 μm IBA, and no GA3. Histological examination revealed that the initial response of nodes to culture is axillary bud proliferation, but adventitious shoot formation occurred after 4 to 6 weeks. Cultures that contained only axillary shoots were not evident unless low levels of 2iP were used, at which point only axillary buds present on the explants were released. Proliferated shoots could be rooted ex vitro without auxin treatment. Optimal rooting occurred under high-light conditions. Plants were transplanted to the field for comparison to conventionally propagated material. Chemical names used: gibberellic acid (GA3), N-(3-methyl-2-butenyl)-1H-purin-6-amine (2iP), 1H-indole-3-butanoic acid (IBA).

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Presently, there are no standards for producing Phalaenopsis Blume (the moth orchids) as a flowering, potted crop. Determining optimal irradiance for in vitro and greenhouse production will help optimize growth and flowering. Four-month-old, aseptically propagated Phalaenopsis Atien Kaala seedlings with 1.0 cm leaf spread were transferred to a sterile agar medium in November 1995. They were placed under 10, 20, 40, or 80 μmol·m-2·s-1 photosynthetic photon flux (PPF) from cool-white fluorescent lamps. In June 1996, plants grown under 40 or 80 μmol·m-2·s-1 in vitro PPF had 38% greater fresh weight (FW), wider leaves, and more roots than those under the two lower PPF levels. Plants from each in vitro PPF were then transplanted and grown ex vitro in a greenhouse (GH) under high, medium, or low PPF, representing 12.0%, 5.4%, or 2.6% of full sunlight, respectively. Full sunlight at this location was 2300 and 1700 μmol·m-2·s-1 in August 1996 and January 1997, respectively. In November 1996 and June 1997, plants that had received 40 μmol·m-2·s-1 in vitro PPF and then grown under the high or medium GH PPF had the greatest FWs. Overall, plants under the high, medium, or low GH PPF had average FWs of 61, 36, or 17 g, respectively, in June 1997. By mid-September 1997, plants had increasingly larger leaves and higher concentrations of malic acid, sucrose, and starch as GH PPF increased. Leaf glucose and fructose concentrations remained constant as GH PPF increased; however, sucrose level doubled and malic acid concentration increased by nearly 50% from the low to high GH PPF. Each doubling in GH PPF more than doubled plant FW. Plants grown under the high, medium, or low GH PPF had 98%, 77%, or 2% flowering, respectively, in Spring 1998. Anthesis occurred 2 weeks earlier under the high GH PPF. Plants grown under the high GH PPF had twice as many flowers and larger flowers than those grown under the medium PPF.

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