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- Author or Editor: Yves Desjardins x
To identify the physiological and biochemical events leading to the negative effects of sucrose in culture medium on the photosynthetic capacity of plantlets cultivated in vitro, time-course changes in photosynthesis, metabolize pool sizes, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity were investigated in strawberry (Fragaria × ananassa Duch. cv. Kent) plantlets following their transfer to medium with or without sucrose. When the plantlets grown in medium without sucrose were transferred to a similar medium with 30 g sucrose/liter, their net photosynthesis decreased and their level of phosphorylated compounds increased with time. In addition, initial Kcat, total Kcat, and the activation state of Rubisco decreased in these plantlets. Conversely, when the plantlets grown in medium with 30 g sucrose/liter were transferred to a similar medium without sucrose, their net photosynthesis slowly increased with time and their level of phosphorylated compounds slowly decreased. A slow increase with time of initial Kcat, total Kcat, and the activation state of Rubisco was also observed in these plantlets. The results of the present research suggest that the reduced photosynthetic capacity of strawberry plantlets cultivated in vitro in the presence of sucrose was the consequence of reduced Rubisco efficiency due to its deactivation and the possible presence of a putative tight binding inhibitor.
Transient expression of electroporation-mediated DNA uptake was monitored in callus-derived protoplasts of two asparagus (Asparagus offcinalis L.) genotypes by measuring the GUS activity. The level of expression and the viability of the protoplasts were influenced by the voltage and duration of the electric pulse. An increased plasmid DNA concentration and the presence of polyethylene glycol (PEG) in the electroporation medium enhanced the transient expression level. A considerable increase in GUS activity was observed in the presence of both PEG and heat-shock treatments than with PEG treatment alone. An optimal level of GUS activity was obtained after electroporation with a capacitive discharge of 500 V/cm and 94 ms duration. The two genotypes differed in their responses in vitro and also showed variable levels of transient expression. The present technique was suitable to obtain transgenic plants, as histochemical GUS assay revealed GUS activity in the protoplast-derived microcolonies as well as in callus tissues.
At present, there is no herbicide registered for use in Canada to control annual bluegrass in sod production. Under serious infestations, aesthetic qualities are reduced and sod harvest becomes more complicated. The efficiency of propane burners to control annual bluegrass was tested in a trial initiated in Spring 1993. Specific objectives were to determine the appropriate period for treatment application and the heat intensity required for optimal control. Twenty-one plots (13 × 3 m) were treated with a conventional burner; a similar group was treated with a pipe burner. In addition to an untreated check, the combination of two tractor-burner speeds (3.6 and 5 km·h-1) and three gas pressures (20, 30, and 40 psi) made up the seven treatments. Randomized complete blocks were used and each treatment was replicated three times. The sod recovered well from all heat treatments. After 3 weeks, the best heat treatment reduced the annual bluegrass population by 70%. Unfortunately, this reduction lasted for about 1 month, after which the annual bluegrass population recovered. At best, weed population was reduced by 40% when evaluated in mid-September. Another trial is planned to identify environmental and edaphic factors that may reduce the effectiveness of heat treatments in controlling annual bluegrass in sod production.
Strawberry plantlets (Fragaria X ananassa Duch. cv. Kent) were submitted to a factorial arrangement of 2 photosynthetic photon fluxes (PPF) (80 and 150 μmol·m-2·s-1, PAR) and 2 CO2 concentrations (330 and 3000 ppm) during the in vitro rooting stage. Leaves were tagged and placed in a growth chamber tor acclimatization. Photosynthetic capability of leaves from different origins was determined by measuring the initial and total activity of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (rubisco), but the contribution of Phosphoenolpyruvate carboxylase (PEPCase) to fixation was also examined High CO2 concentration and PPF significantly increased fresh weight and surface area in vitro and after 4 weeks ex vitro. Improved growth was not the result of increased autotrophy in vitro since initial rubisco activity was 10 times lower than that of de novo formed leaves and declined under high CO2 and PPF. Carbon dioxide concentration and PPF had no effect on total activity of rubisco. Low activation state and total activity of rubisco in in vitro leaves is the cause of poor photosynthetic activity in vitro Persistent in vitro leaves after 4 weeks of acclimatization did not have higher total activity of rubisco, but the activation state was 4 times larger than the corresponding activity in vitro which might thus provide for non-negligible contribution to photosynthetic carbon assimilation. The possible inhibition of photosynthesis by the presence of sugar in the medium is discussed.
The effects of culture media, culture modes, and carbon sources on plating efficiencies of protoplasts of two genotypes of Asparagus officinalis L. were investigated. Protoplasts grew best in a semisolid culture system containing half-strength MS medium with 1 mg NAA/liter, 0.5 mg zeatin/liter, 0.6 M glucose, and 0.1% Gelrite. The plating efficiencies were 12.5% and 8.1% for genotypes G 203 and G 171, respectively. Embryogenic calli were produced from protoplast-derived microcalli after culturing on MS medium with 1 mg 2,4-D, 3% sucrose, and 0.2% Gelrite. The somatic embryos were initiated, matured, and then germinated to plantlets in MS medium containing 0.1 mg NAA/liter, 0.3 mg 2-iP/liter (EMM), and different levels of carbohydrates. Transfer of somatic embryos from EMM with 10% glucose to EMM containing 2% sucrose produced the highest number of bipolar embryos and plantlets. The plantlets regenerated shoots and roots in MS medium with 3% sucrose, 0.1 mg NAA/liter, 0.1 mg kinetin/liter, and 1.28 mg ancymidol/liter. Cytological analysis of these plants revealed 2n = 20 chromosomes.
Nitrogen and carbohydrate content of roots and the onset of crown cold hardiness were compared in `Tristar' day-neutral (DN) strawberries (Fragaria × ananassa Duch.) that were given various fruit removal treatments. Nontreated `Hecker' DN and `Redcoat' Junebearer were also used to determine genotypic variation. The removal of fruit after 15 or 30 Sept. promoted the accumulation of starch and increased cold tolerance of crowns as compared to fruiting plants. Nitrogen was increased only when fruit was removed after 15 Sept. DN cultivars were less hardy than Junebearing cultivars, but `Tristar' was almost as hardy as `Redcoat'. When compared to `Redcoat', DN cultivars had a less abrupt temperature-kill profile, perhaps because they were multicrowned.
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.
Asparagus (Asparagus officinalis L.) transplants and in vitro-cultured clones were grown and acclimatized under two photosynthetic photon flux (PPF) conditions (ambient and ambient + 80 μmol·s-1·m-2) and three atmospheric CO2 concentrations (330, 900, and 1500 ppm). Short- and long-term effects were measured in the greenhouse and after two seasons of growth in the field, respectively. In the greenhouse, CO2 enrichment (CE) and supplemental lighting (SL) increased root and fern dry weight by 196% and 336%, respectively, for transplants and by 335% and 229%, respectively, for clones. For these characteristics, a significant interaction was observed between SL and CE with tissue-cultured plantlets. In the absence of SL, CE did not significantly increase root or shoot dry weight. No interaction was observed between CE and SL for transplants, although these factors significantly improved growth. It was possible to reduce the nursery period by as much as 3 weeks with CE and SL and still obtain a plant size comparable to that of the control at the end of the experiment. Long-term effects of SL were observed after two seasons of growth in the field. Supplemental lighting improved survival of transplants and was particularly beneficial to in vitro plants. Clones grown under SL were of similar size as transplants after 2 years in the field.
Overseeding of tall fescue and perennial ryegrass into pre-existing stands of kentucky bluegrass is viewed as a strategy to enhance the quality and durability of turfgrass lawns. In a 3-year study, the authors investigated the winter survival and establishment of tall fescue (‘Bonsai 2000’), with or without Neotyphodium coenophialum, and perennial ryegrass (‘Palmer III’), with or without N. lolii, in the province of Quebec, Canada (≈lat., 54ºN), a region characterized by rigorous winter conditions. Grass species were overseeded in June 2003 at two different rates (90 and 180 kg·ha−1), in experimental plots from two bioclimatological conditions: Quebec City and Boucherville. Turfgrass establishment and endophyte infection were evaluated during the following two spring and fall periods. Both tall fescue and perennial ryegrass had the capacity to establish and survive winter conditions, but performed best when snow cover was thick and present throughout the winter. The proportion of overseeded plants in the turfgrass stand rarely reached 30% over the years. Although the proportion of tall fescue and perennial ryegrass plants was much reduced in the spring, some tillers survived and were able, later in the season, to compete with kentucky bluegrass as tall fescue and perennial ryegrass populations returned to initial establishment populations each summer in mixed stands. Overwinter endophyte survival was species specific, with N. lolii being able to survive the cold winter but not N. coenophialum, which had a low percent of infection. For the perennial ryegrass–N. lolii association, competition with kentucky bluegrass is a primary factor limiting the increase over time in the proportion of endophyte-infected plants in a turfgrass mixture. Seeding rates did not influence the establishment of either grass species.
Canadian environmental policies are aimed at reducing by 50%. the quantities of refuses intended for landfill by year 2000. In this perspective, landspreading and composting biosolids have been investigated as solutions. Paper sludges, wood wastes, and municipal solid wastes (MSW) are important components of landfill biosolids, but they are attractive by-products for agricultural use. Research projects were initiated to characterize the paper sludges produced by Daishowa Co. in Quebec City, wood wastes produced by Hydro-Quebec, and MSW composts produced from waste treatment at RITDM (Chertsey) and Conporec (Sorel). De-inked paper sludge and wood wastes have been landspreaded for growing potato and landscaping, whereas composted paper sludges have been evaluated as part of potting media for growing greenhouse plants and landspreaded for turfgrass production. The chemical and biological characteristics of these biosolids were investigated for their fertilization potential and their effect on plant growth.