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  • Author or Editor: Ji Li x
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This study was undertaken to critically analyze the effects of reduced phosphorus (P) on shoot and root growth, partitioning, and phosphorus utilization efficiency (PUtE) in lantana (Lantana camara ‘New Gold’). Plants were grown in a 1:1 mixture of perlite and vermiculite with complete nutrient solutions containing a range of P concentrations considered to be deficient (1 mg·L−1), low (3 and 5 mg·L−1), adequate (10 mg·L−1), and high (20 and 30 mg·L−1). Higher P supply had most dramatic effect on increasing the number of leaves and leaf surface area, subsequently leading to a disproportionate increase in shoot biomass than root biomass. Increasing P from 1 to 30 mg·L−1 linearly (P < 0.0001) increased shoot dry weight (DW) during vegetative growth, and logarithmically (P < 0.0001) during reproductive growth. Regardless of plant growth stage, biomass of roots and flowers (inflorescences) logarithmically increased (P < 0.0001) with increasing P concentrations. Plants grown with lower P allocated more biomass to roots than shoots, resulting in a higher root-to-shoot ratio. Increasing P concentration to 20 mg·L−1 increased the accumulation of P in all plant parts, but predominantly in shoots, whereas further increasing the concentration increased the accumulation primarily in roots and flowers. Higher P accumulation in plant tissues did not strongly contribute to the biomass production. Phosphorus utilization efficiency was higher with lower P supply in all plant tissues. P-deficient roots had the highest PUtE and specific root length (SRL), and retained higher proportion of P compared with nondeficient roots. Our results indicate that P concentration at 20 mg·L−1 is sufficient to maintain optimal vegetative growth while reproductive growth does not require P concentrations over 10 mg·L−1 as it stimulates greater level of P accumulation in plant parts with little or no effect on growth and flowering, and biomass accumulation in lantana.

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Seasonal alteration of the cytosolic and nuclear Ca2+ concentrations of spruce (Picea engelmannii Parry) and brome grass (Bromus inermis Leyss) was investigated by the antimonate precipitation cytochemical technique. Electron microscopic (EM) observations revealed that electron-dense Ca2+ antimonate deposits, an indication of Ca2+ localization, were seen mainly in the vacuole, the cell wall and the intercellular space in samples of both species, collected on 14 July 1997. Few deposits were found in the cytosol and nuclei, showing a low resting level during summer months. On 8 Aug. 1997 following a decrease in daylength of 1 hour and 12 minutes, Ca2+ accumulation was initiated in spruce with increased cytosolic and nuclear Ca2+ deposits, but not in brome grass. On 8 Sept. 1997, Ca2+ accumulation occurred in the cytosol of brome grass. This followed a drop in ambient temperature to 12 °C. Cytosolic and nuclear Ca2+ deposits continued to increase in spruce. Controlled experiments confirmed that it was the low temperature, not shortening daylength, that triggered Ca2+ accumulation in brome grass. High cytosolic and nuclear Ca2+ concentrations lasted about three months in spruce from early August to early November. However, the high cytosolic and nuclear Ca2+ concentrations in brome grass lasted only about 20 days from early September to the end of the month. During winter and spring, both species had low resting cytosolic and nuclear Ca2+ concentrations. The relationship between the duration of the high cytosolic and nuclear Ca2+ concentrations and the status of the developed dormancy/cold hardiness is discussed in light of current findings.

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The most obvious effects of a low leaf:fruit (LF) ratio [two leaves for one cluster per shoot (LF2)] on grape (Vitis vinifera) berries are suppressed anthocyanin biosynthesis in the berry skin, decreased berry weight and soluble solids concentration, and increased titratable acidity. In this study, proteins isolated from berry skins grown under low and high LF ratio conditions, LF2 and LF12, respectively, were characterized by two-dimensional gel electrophoresis coupled to mass spectrometry. A survey of ≈600 to 700 spots from berry skin yielded 77 proteins with differential expression between LF12 and LF2 treatments. Of these, the 59 proteins that were identified consisted of 47 proteins that were down-regulated and 12 that were up-regulated under LF2 conditions compared with LF12 conditions. Most proteins involved in metabolism, energy, transcription, protein synthesis, binding function, signal transduction, and cell defense were down-regulated in LF2 berries, whereas two important enzymes of anthocyanin biosynthesis, chalcone synthase and dihydroflavonol reductase, were not detected. Only a few proteins (e.g., two heat shock proteins related to protein fate and nutrient reservoir storage protein) were found to be up-regulated in LF2 berries. This suggested that, with the exception of secondary metabolism, many proteomic events may have an effect on anthocyanin synthesis in the skins responding to LF.

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The physiological role of arginase in nitrogen remobilization processes from protein degradation during seed germination has well been described in several species. However, very little is known about its possible roles in plant stress responses. Treatment of tomato fruit (Solanum lycopersicum L.) with 0.05 mm methyl jasmonate (MeJA) enhanced transcription levels of arginase genes, especially LeARG2. Chilling injury (CI) of fruit treated with 0.05 mm MeJA for 12 hours was also effectively alleviated, as manifested by decreases in CI index, electrolyte leakage, and malondialdehyde (MDA) content. To investigate the potential role of arginase in MeJA-induced chilling tolerance, fruit were treated with MeJA or the arginase inhibitor Nω-hydroxy-nor-l-arginine (nor-NOHA) combined with MeJA and then stored at 2 °C for 28 days. MeJA-induced arginase activity was strongly inhibited and the reduction of CI by MeJA was nearly abolished by the inhibitor. In addition, MeJA treatment increased the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX); inhibited peroxidase (POD) activities; and promoted proline and polyamines accumulation. These effects were partially counteracted by nor-NOHA; putrescine accumulation, however, was unaffected by the inhibitor. Our results indicate that arginase may be involved in MeJA-induced chilling tolerance, possibly by ameliorating the antioxidant enzyme system of fruit and increasing proline levels.

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Heat treatment induces resistance to low temperature in horticultural crops. Changes in soluble protein and heat-stable protein (HSP) contents, the total soluble solids (TSS), titratable acidity (TA), reducing sugar, weight loss and firmness of honey peach (cv. Hujingmilu) during heat treatment and refrigerated storage were investigated. Low-temperature storage alone led to decreasing of TA and reducing sugar and caused severe fresh mealiness. The hot-air treatment before low temperature combined with the use of a plastic bag (thickness of 0.03 mm) could counteract this effect. Heat treatment before refrigerated storage increased both soluble protein and HSP contents, and the ratio of heat-stable to soluble protein. The most favorable effect was obtained with 46 °C for 30 minutes. In addition, heat treatment before storage retarded the increase in fruit firmness, maintained the highest contents of the TSS and reducing sugar and inhibited the decline of TA during refrigerated storage. Treatment for 30 minutes at 46 °C before low-temperature storage in combination with a 0.03-mm plastic bag might be a useful technique to alleviate chilling injury (CI) and maintain honey peach fruit quality during cold storage.

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This study examined the ability to vegetatively propagate 1-year-old pecan (Carya illinoinensis) through the rooting of hardwood cuttings. Cuttings were treated with varying concentrations of different auxins and different combinations of media and ambient temperatures. Under different temperature conditions, all auxin treatments induced the rooting of cuttings but did not promote sprouting. The effectiveness of the induction of adventitious roots was as follows: 1-naphthalene acetic acid (NAA) > indole 3-butyric acid > indole 3-acetic acid. The base of the parent shoot treated by NAA at a concentration of 0.09%, planted in substrate with bottom heat was the most effective, with 82% rooting, 8.3 roots/cutting and root lengths of 7.3 cm. These findings suggested that auxin and substrate/air temperature differences are both indispensable in the process of adventitious roots formation in pecan. This study revealed that the propagation of hardwood cuttings derived from branches of 1-year-old pecan is possible.

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Anthocyanins are protective pigments that accumulate in plant organs such as fruits and leaves, and are nutritionally valuable components of the human diet. There is thus considerable interest in the factors that regulate synthesis. Malus crabapple leaves are rich sources of these compounds, and in this study we analyzed leaf coloration, anthocyanin levels, and the expression levels of anthocyanin biosynthetic and regulatory genes in three crabapple cultivars (Royalty, Prairifire, and Flame) following various temperature treatments. We found that low temperatures (LTs) promoted anthocyanin accumulation in ‘Royalty’ and ‘Prairifire’, leading to red leaves, but not in ‘Flame’, which accumulated abundant colorless flavonols and retained green colored leaves. Quantitative reverse transcript PCR (RT-PCR) analyses indicated that the expression of several anthocyanin biosynthetic genes was induced by LTs, as were members of the R2R3-MYB, basic helix–loop–helix (bHLH) and WD40 transcription factor families that are thought to act in a complex. We propose that anthocyanin biosynthesis is differentially regulated in the three cultivars by LTs via the expression of members of this anthocyanin regulatory complex.

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