Search Results

You are looking at 21 - 30 of 206 items for :

  • "electron transport" x
Clear All
Authors: , , and

Abstract

A cyanide-resistant alternative pathway was found to exist in root tissue of apple (Malus domestica Borkh.). In the absence of potassium cyanide (KCN), an inhibitor of cytochrome electron transport, the alternative pathway did not contribute to overall root respiration. However, in the presence of KCN or carbonyl cyanide m-chlorophenyl hydrazone (CCCP), an uncoupler, active participation of the alternative pathway was detected. Inhibition of O2 uptake by salicylhydroxamic acid (SHAM) was observed in the presence of antimycin A (AA) or sodium azide (NaN3), but to a lesser degree than when KCN was present. The degree of inhibition by SHAM was greatest in the presence of KCN, followed by AA and then NaN3. The antioxidant n-Propyl gallate (PG) was found to be an effective inhibitor of the alternative pathway. The site of inhibition in apple root tissue by PG is very similar to that of SHAM. Sodium benzoate, another antioxidant and free radical scavenger, and tetraethylthiuram disulfide (disulfiram), a copper chelator, did not inhibit the alternative pathway in apple root tissue.

Open Access

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

Free access

Yellow vine symptoms are often observed in cranberry bogs. To explore the mechanisms of the formation of yellow vine syndrome in cranberry leaves, the shade effect on the chlorophyll (Chl) content and photosynthetic activities in cranberry bogs were investigated by spectrometric, high-performance liquid chromatography (HPLC), and in vivo Chl fluorescence kinetics. Spectrometric and HPLC analyses revealed that the yellow vine leaves were associated with a 11% ± 5% and 14% ± 5% increase in Chl a/Chl b ratio after shading, respectively. The Chl a/Chl b ratio was the same in both types of leaves, suggesting the photosystem (PS) II organization remains invariant. The rise in chlorophyll content suggested that the number of reaction sites on PS II is increased in the shaded yellow vine leaves. The results of in vivo chlorophyll fluorescence analysis also indicated that the electron transport chain in the PS II is enhanced and that the size of the quinone pool is increased. In addition, the overall photosynthesis index is drastically improved by shading. These three lines of evidence imply that the shading of cranberry plants appeared to reduce the syndrome by improving the photosynthetic activity and increasing the chlorophyll content. The techniques presented here may be valuable for characterizing variations of plants by stress or disease.

Free access

Sorgoleone, the oxidized quinone form of a hydrophobic p-benzoquinone was first isolated from Sorghum root exudates. Sorgoleone is a potent inhibitor of growth in several annual weed species and causes tissue bleaching at concentrations of <25 μ M. These investigations were designed to determine if soreoleone's allelopathic activity was related to an inhibition of photosynthetic electron transport. The effect of sorgoleone versus DCMU (diuron) on inhibition of O2 evolution by broken wheat thylakoids, and in oxygenevolving PSII membranes containing QA and QB primary and secondary electron acceptors in PSII was determined. Sorgoleone was a potent inhibitor of O2 evolution in this system with ∼ 0.04 and 0.78 μ M concentrations required for 50 and 100% inhibition as compared to -0.11 and 2.0 μ M DCMU, respectively. Sorgoleone caused no significant inhibition of PSI mediated photooxidation of ascorbate/dichlorophenolindophenol, establishing that the locus of inhibition by sorgoleone was within the PSII complex. The effect of trypsin treatment of chloroplasts and PSII membranes on sensitivity to inhibition by DCMU and sorgoleone was examined. The comparison of DCMU and sorgoleone upon the formation and decay of flash-induced chlorophyll a variable fluorescence indicates that sorgoleone specifically inhibited the oxidation of QA by QB.

Free access

Evaluation of thermostability of photosynthetic apparatus of intact leaves and isolated thylakoids of five cultivars of wine grapes (Vitis vinifera) was conducted. Four- week- old plants of Semillon, Chenin Blnac, Pinot Noir, Chardonnay, and White Riesling, were placed into a control environment chamber held at 20/15° 30/25°, and 40/35 °C day/night temperature for 14 days. Induced (F0), variable (Fv), and maximum fluorescence (Fm) and the quantum yield of net photosynthesis (Fv/Fm) were measured after 1-14 days exposure. All fluorescence parameters were not affected by 20/15° and 30/25°C. However, high temperature (40/35°C) increased F0 and decreased Fm, Fv, and Fv/Fm. These changes were severe in Semillon and Chenin Blanc, moderate in Chardonnay and White Riesling and scarce in Pinot Noir. Average high temperature data that are experienced in Yakima Valley area will be presented. Isolated thylakoid membranes from the cultivars were heated at 20-40°C. and uncoupled electron transport was determined. Thylakoid stability to heating varied similarly to whole-plant response to high temperature.

Free access

A process-based whole-tree simulation model was used to simulate crown transpiration in several species and cultivars of nursery crops. To validate estimates, we measured transpiration in cultivars of red maple (Acer rubrum L.) to determine if there were differences in intraspecific variation that could affect estimates of whole tree water use. We used a combination of field and published data to parameterize additional species and cultivar differences in response to environment and/or management. The different water use estimates of the species and cultivars were related to their genetic variability in leaf biochemical limitations, where the relationship between stomatal conductance and photosynthetic rate may be so closely matched that stomatal conductance appears to adjust itself to the photosynthetic capacity of the species or cultivar. Model predictions indicated that species and cultivars that had higher biochemical limitation regulated transpiration by down regulation of the rate of carboxylation (Vcmax) and coupled photosynthetic electron transport (Jmax), whereas the reverse occurred as Vcmax and Jmax increased. Our model simulations show significant variation in transpiration due to both inter and intraspecific variation in biochemical limitations. These results suggest that models that do not account for inter and intraspecific variation, to reflect genetic variation in physiology, may over or under estimate transpiration. Therefore, physiology-based species and cultivar variation should be part of process-based simulations that assess nursery water use. Results also suggest that effects of leaf dark respiration adaptation interactions can concurrently reduce variation in water use estimates.

Free access

Wasabi japonica plantlets were acclimatized in a hydroponic system to determine effective procedures. The plantlets were cultured on solid Murashige-Skoog medium with 3% sucrose. Shoots that formed roots were transplanted into hydroponic systems: 1) acclimatization in ebb-and-flow (EBB) for subirrigation (medium: granulated rockwool and coir); and 2) acclimatization in deep flow technique (DFT). The plantlets were acclimatized for 5 weeks under two irradiance treatments, 50 and 300 mmol·m-2·s-1. Photosynthetic capacity in high PPF was higher than that in low PPF during acclimatization. Electron transport rate from PS II (ETR) and biomass production increased significantly with increased light availability. The fresh weight, dry weight, and leaf area of plantlets in high PPF were higher than those in low PPF. In particular, the dry weight and ETR of the plantlets grown in high PPF increased more than twice as much as those in low PPF. At 50 mmol·m-2·s-1 PPF, growth indexes, such as number of leaves, leaf length, leaf width, leaf area, fresh weight, and dry weight, were higher in EBB (granulated rockwool) > EBB (coir culture) > DFT. At 300 mmol·m-2·s-1 PPF, those indexes were higher in DFT > EBB (granulated rockwool) > EBB (coir). The Wasabi japonica plantlets acclimatized in a hydroponic system also had a superior performance when they were transferred to the field.

Free access

The application of ultraviolet light on fruit and vegetables is a promising new method to control storage diseases and to delay the onset of senescence. In this investigation, we studied the effects of hormic dose (1,4 Merg•cm-2) of UV-radiation on the ripening of tomato pericarp discs by measuring different characteristics of ripening and senescence during storage. We observed that UV-treatment induced significant delays of the red color development, chlorophyll degradation, and lycopene production compared to control discs. UV-treatment also retarded the decline of the chlorophyll-a fluorescence ratios Fv: Fm and *F : Fm′, two characteristics related, respectively, to the maximum and operational quantum yield of photosystem II electron transport. Furthermore, the climacteric ethylene peak was delayed in the treated discs. However, UV-treatment did not alter textural changes, and the respiratory climacteric peaks were observed concomitantly for both treated and untreated tomato discs. However, the respiratory rate was consistently higher in treated discs. These results indicate that UV irradiation of tomato pericarp discs delays some processes of ripening associated with chloroplast to chromoplast transition whereas other ripening processes seem unaffected.

Free access

Effect of crop load on tree growth, leaf characteristics, photosynthesis, and fruit quality of 5-year-old `Braeburn' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees on Malling 26 (M.26) rootstock was examined during the 1994-95 growing season. Crop loads ranged from 0 to 57 kg/tree [0 to 1.6 kg fruit/cm2 trunk cross sectional area (TCA) or 0 to 8.7 fruit/cm2 TCA]. Fruit maturity as indicated by background color, starch/iodine score, and soluble solids was advanced significantly on low-cropping trees compared to high-cropping trees. Whole-canopy leaf area and percentage tree light interception increased linearly with a significant trend as crop load decreased. From midseason until fruit harvest, leaf photosynthesis decreased significantly on lighter cropping trees and similarly, a positive linear trend was found between whole-canopy gas exchange per unit area of leaf and crop load. Leaf starch concentration in midseason increased linearly as crop load decreased, providing some explanation for the increased down-regulation of photosynthesis on trees with lower crop loads. After fruit harvest, the previous crop loads had no effect on leaf photosynthesis and preharvest differences in whole-canopy gas exchange per unit area of leaf were less pronounced. At each measurement date, daily whole-canopy net carbon exchange and transpiration closely followed the diurnal pattern of incident photosynthetic photon flux. The photochemical yield and electron transport capacity depended on crop load. This was due mostly to reaction center closure before harvest and an increased nonphotochemical quenching after harvest.

Free access

To determine the cause of a characteristic zonal chlorosis of `Honeycrisp' apple (Malus ×domestica Borkh.) leaves, we compared CO2 assimilation, carbohydrate metabolism, the xanthophyll cycle and the antioxidant system between chlorotic leaves and normal leaves. Chlorotic leaves accumulated higher levels of nonstructural carbohydrates, particularly starch, sorbitol, sucrose, and fructose at both dusk and predawn, and no difference was found in total nonstructural carbohydrates between predawn and dusk. This indicates that carbon export was inhibited in chlorotic leaves. CO2 assimilation and the key enzymes in the Calvin cycle, ribulose 1,5-bisphosphate carboxylase/oxygenase, NADP-glyceraldehyde-3-phosphate dehydrogenase, phosphoribulokinase, stromal fructose-1,6-bisphosphatase, and the key enzymes in starch and sorbitol synthesis, ADP-glucose pyrophosphorylase, cytosolic fructose-1,6-bisphosphatase, and aldose 6-phosphate reductase were significantly lower in chlorotic leaves than in normal leaves. However, sucrose phosphate synthase activity was higher in chlorotic leaves. In response to a reduced demand for photosynthetic electron transport, thermal dissipation of excitation energy (measured as nonphotochemical quenching of chlorophyll fluorescence) was enhanced in chlorotic leaves under full sun, lowering the efficiency of excitation energy transfer to PSII reaction centers. This was accompanied by a corresponding increase in both xanthophyll cycle pool size (on a chlorophyll basis) and conversion of violaxanthin to antheraxanthin and zeaxanthin. The antioxidant system, including superoxide dismutase and ascorbate peroxidase and the ascorbate pool and glutathione pool, was up-regulated in chlorotic leaves in response to the increased generation of reactive oxygen species via photoreduction of oxygen. These findings support the hypothesis that phloem loading and/or transport is partially or completely blocked in chlorotic leaves, and that excessive accumulation of nonstructural carbohydrates may cause feedback suppression of CO2 assimilation via direct interference with chloroplast function and/or indirect repression of photosynthetic enzymes.

Free access