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To investigate the mechanisms of sucrose transport and its accumulation into `Murcott' mandarin (Citrus reticulata Blanco) fruit, developmental changes in determinants of sink strength such as sucrose metabolizing enzymes, and sucrose transport across both plasmalemma and tonoplast were analyzed. Concurrently with sucrose levels, sucrose synthase, sucrose phosphate synthase and sucrose phosphate phosphatase increased throughout fruit development. Plasmalemma and tonoplast vesicles isolated from fruit collected at different developmental stages were analyzed for their transport capabilities. Sucrose uptake into energized plasmalemma vesicles was abolished by gramicidin, which is in accordance with the presence of an active symport mechanism of sucrose transport from the apoplast into the cytosol. Unexpectedly, tonoplast vesicles were shown to lack active transport mechanism of sucrose into the vacuole. More importantly, however, and in conformity with recent findings showing the occurrence of an endocytic mechanism of ion uptake in maize (Zea mays L.) root cells, citrus (Citrus L.) juice cells were shown to incorporate membrane impermeable dyes into their vacuoles in the presence of sucrose. High definition confocal microscopy revealed the co-localization of membrane impermeable markers in cytoplasmic vesicles and the formation of vesicles at the plasmalemma. The data provide evidence for an endocytic system of transport that allows direct incorporation of sucrose from the apoplast to the vacuole bypassing both the plasmalemma and tonoplast.

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Abstract

We investigated the areas of water penetration and the anatomical structures of hilar regions of permeable and impermeable seed coats of lima beans (Phaseolus lunatus L.). Results indicate that water can enter permeable seeds through the hilum, raphe, and micropyle. In impermeable seeds water cannot pass through any of these areas. Anatomical data confirm that there were no structural differences in the testae of permeable and impermeable seeds, but a noticeable difference was apparent in the hilar region. In permeable seeds the palisade layer did not connect evenly in the hilar canal. By contrast, the hilar canals of impermeable seeds had connected palisade layers that were uniformly coated with a cuticular layer. Micropylar openings were clearly visible in permeable seeds, but these openings were occluded and well covered with cuticle in impermeable seeds. Visible differences were evident in the raphe.

Open Access

This investigation documents the key anatomical features in embryo development of Cypripedium formosanum Hayata, in association with the ability of embryos to germinate in vitro, and examines the effects of culture media and seed pretreatments on seed germination. A better understanding of zygotic embryogenesis for the Cypripedium L. species would provide insights into subsequent germination events and aid in the in vitro propagation of these endangered species. In seeds collected at 60 days after pollination (DAP), soon after fertilization, no germination was recorded. The best overall germination was found at 90 DAP (≈70%), at which time early globular to globular embryos with a single-celled suspensors can be observed. After 135 DAP, the seeds germinated poorly. At this time the inner integument shrinks and forms a tight layer, which encloses the embryo, the so-called “carapace.” Using Nile red stain, a cuticular substance was detected in the carapace, which may play a role in the impermeability of the mature seed and may help the seeds survive in the stringent environment. At maturity (after 210 DAP), the embryo proper has an average size of eight cells along its length and six cells across the width. Lipids and proteins are the main storage products within the embryo. To improve seed germination, experiments were conducted to test the suitability of various media and pretreatments of seeds. When different media were used, except for the Harvais medium at 120 DAP, there was no significant difference in seed germination at three different developmental stages tested. Soaking mature seeds in 1% NaOCl or treating them with ultrasound may slightly increase the germination percentage. For seed germination, our results indicate that the timing of seed collection outweighs the composition of medium and the seed pretreatments.

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One of the proposed alternative chemicals for methyl bromide is 1,3-D. The most common forms of 1,3-D products are cis- or trans-isomers of 1,3-D with the fungicidal agent, chloropicrin, containing such mixtures as 65% 1,3-D and 35% chloropicrin (C-35). Soil fumigants are commonly applied under a polyethylene film in Florida raised bed vegetable production. Much of the research regarding cropping system effects of alternative fumigants to methyl bromide has focused primarily on plant growth parameters, with little regard to the atmospheric fate of these chemicals. The objective of this research was to determine both the atmospheric emission of 1,3-D under different plastic film treatments and to evaluate effects of application rates of 1,3-D and C-35 on plant pests, growth, and yield of Sunex 9602 summer squash (Cucurbita pepo L.). Results showed that use of a high barrier polyethylene film (or virtually impermeable film - VIF) greatly reduced fumigant emission compared to ground cover with conventional polyethylene films or uncovered soil. Summer squash seedling survival was a severe problem in several of the 1,3-D alone treatments where no fungicidal agent was added, whereas C-35 resulted in excellent disease control at both full and one-half of the recommended application rates for this chemical. Both 1,3-D and C-35 provided good plant stands and higher yields when applied at their recommended application rates. However, all squash yields were lower than typical squash production levels due to late planting and early winter frost kill. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitropropene (chloropicrin).

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molecular weight ≥6000, PEG6000 molecules are inert, nonionic, and cell-impermeable. They are small enough to influence osmotic pressure, but large enough to avoid being absorbed by plants ( van den Berg and Zeng, 2006 ). Here, three kinds of rootstocks were

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apertures become neatly tucked inside the impermeable exine ( Chaffey, 2010 ; Couturier et al., 2013 ). Despite the early recognition of the importance of the pollen-wall structure in folding, the process remains obscure ( Katifori et al., 2010 ). Just

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.H. Paul, R.N. Vaughn, K.C. Duke, S.O. 1983 Role of peroxidase in the development of water impermeable seed coats in Sida spinosa L Planta 157 224 232 10.1007/BF00405186 Elings, A. Kempkes, F.L.K. Kaarsemaker, R.C. Ruijs, M.N.A. Van de Braak, N.J. Dueck

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Abstract

During imbibition, water always follows the same pattern when entering the seed testa in semihard seeds (SHS) of snap bean (Phaseolus vulgaris L.). Water first enters the raphe and the chalazal region of the testa (R-CT), then migrates circumferentially along the midline of the seed, leaving the lateral faces the last to be fully imbibed. The R-CT region is the main site of primary uptake of both water vapor and liquid water by SHS. The hilum, micropyle, and strophiole play only a minor role in water uptake in SHS. In comparison to the readily permeable seeds of ‘Bush Blue Lake 47’, SHS have more total phenols in the osteosclereid cells and more pectic substances in the palisade cells of the CT. The presence of these compounds may account for the impermeable nature of SHS. Measurements made of palisade cell length and width in the R-CT region revealed that cell length increased and width decreased in the chalazal testa region (CT) as seed moisture content increased from 6% to 12%. It is proposed that semihardening of bean seeds is mainly a result of the reversible physical changes in the length and width of the palisade cells in the R-CT region. Seeds imbibe at high moisture content (12%) because the palisade cells have stretched, which allows water uptake. Seeds are impermeable at low moisture content (6%) because the palisade cells change in size and form a physical barrier to water movement.

Open Access

Abstract

Germination of Cycas revoluta seed is slow and erratic when planted immediately after collection, and most lose viability in a few months. In a 2 × 4 × 4 factorial experiment, seeds were stored at 5° and 22°C for 24 weeks and subsequently treated with H2SO4 (18 M) for 0, 1, 2, or 3 hr followed by GA3 (1000 ppm) for 0, 24, 48, or 72 hr. Morphophysiological complex dormancy contributes to the lengthy germination process. Removal of the fleshy, water-repellant sarcotesta (containing inhibitors), scarification of the thick water-impermeable sclerotesta, and maturation of the embryo, which is in very early stages of development at the time of seed abscission, all enhance germination. At 5°, 92% of the seeds survived, but only 42% of the seeds stored at 22° were viable after 24 weeks, the result of desiccation. Under all but 72 hr of GA3 exposure time, response surface shapes lead to the expectation that germination will be better without H2SO4 or with higher levels of H2SO4 than with intermediate levels. The response to GA3 at any given exposure to H2SO4 is similar in both cold- and warm-stored seeds: for a given GA, level, one optimum H2SO4 exposure gives the best germination percentage, peak value (PV), or germination value (GV). Optimal GV results when seeds are stored at 5° for 24 weeks to allow embryo maturation followed by removal of the sarcotesta, 1 hr of H2SO4 exposure, and 36 hr of GA3 exposure.

Open Access

Abstract

Each of 8 antitranspirants reduced transpiration of 2 species of woody plants. Dow Silicone and CS 6432 were the most effective compounds on Fraxinus americana and Dow Silicone was effective on Pinus resinosa. Keykote, Folicote and Improved Wilt Pruf showed an increased effect on plant water loss and net photosynthesis (measured by net CO2 uptake) of P. resinosa up to 8 days after compound application. Thereafter there was no significant change in the effect of any compound on transpiration or photosynthesis. Effects on F. americana of all compounds except Improved Wilt Pruf decreased with time after application. Scanning electron micrographs of treated leaves suggested that antitranspirant films on F. americana leaves cracked over the guard cell pore, accounting for the decrease in compound effect with time. Antitranspirants apparently reduced water loss of P. resinosa by combining with wax in the stomatal pore and forming an impermeable plug. The compounds tested were toxic to F. americana seedlings and photosynthesis of treated plants decreased with time, even when direct physical effect of a compound had worn off. Pinus resinosa seedlings showed no decrease in photosynthesis with time. F. americana plants treated with Keykote exhibited low rates of water loss and transpiration/photosynthesis ratios that were not significantly different from those of control plants. Folicote was toxic, and Clear Spray increased water loss of F. americana seedlings. Dow Silicone reduced water loss of Pinus seedlings by about 80%, and plants treated with Dow Silicone, Improved Wilt Pruf, Keykote, or Folicote had favorable transpiration/photosynthesis ratios. The effects of antitranspirants on transpiration and photosynthesis were greatly influenced by environmental regimes and by species.

Open Access