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921.
Chlorophyll a Fluorescence Predicts Total Photosynthetic Electron Flow to CO(2) or NO(3)/NO(2) under Transient Conditions
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A model which predicts total photosynthetic electron flow from a linear regression of the relationship between corrected steady-state quantum yield and nonphotochemical quenching (E Weis, JA Berry [1987] Biochem Biophys Acta 894: 198-208) was formulated for N-limited cells of the green alga Selenastrum minutum. Unlike other models based on net CO2 fixation, our model is based on total photosynthetic electron flow measured as gross O2 evolution. This allowed for the prediction of total photosynthetic electron flow from water to both CO2 fixation and NO3−/NO2− reduction. The linear regression equation predicting electron flow is of the form: J = I · Qq[0.4777-0.3282 QNP] (where J = gross photosynthetic electron flow, I = incident PAR, Qq = photochemical quenching, QNP = nonphotochemical quenching). During steady-state photosynthesis, over a range of irradiance, the model predicted a photosynthetic light saturation curve which was well correlated with that observed. Although developed under steady-state conditions, the model was tested during nonsteady-state photosynthesis induced by transient nitrogen assimilation. The model predicted transient rates of gross O2 evolution which were in excellent agreement with the rates observed under a variety of conditions regardless of whether CO2 or NO3−/NO2− served as the physiological electron acceptor. The fluorescence transients resulting from ammonium and nitrate assimilation are discussed with respect to metabolic demands for reductant and ATP. 相似文献
922.
Two isoforms of dihydroxyacetone phosphate reductase were present in Dunaliella tertiolecta. The major form was located in the chloroplast and the minor form in the cytosol. The chloroplastic reductase eluted first from a DEAE cellulose column followed immediately by the cytosolic form. Both forms were unstable and cold labile. Addition of 5 millimolar dithiothreitol helped to stabilize the enzymes. The cytosolic isoform of DHAP reductase was detected only if the cells were in an active log phase of growth. Then its activity was 20 to 30% of the total reductase activity. When cell cultures entered late log phase of growth the activity of the cytosolic form of the enzyme disappeared, but the chloroplastic form remained. The cytosolic DHAP reductase from Dunaliella has some properties similar to the cytosolic isoform from spinach leaves. Detergents inhibited both enzymes. However, neither form of the algal dihydroxyacetone phosphate reductase was stimulated by fructose 2,6-bisphosphate. In Dunaliella the properties of the chloroplastic form were those expected for glycerol production for osmoregulation, whereas the cytosolic form, like the reductases in leaves, is more likely involved in glycerol phosphate formation for lipid synthesis. 相似文献
923.
Gibberellins in Embryo-Suspensor of Phaseolus coccineus Seeds at the Heart Stage of Embryo Development 总被引:2,自引:1,他引:1
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Gibberellins (GAs) in suspensors and embryos of Phaseolus coccineus seeds at the heart stage of embryo development were analyzed by combined gas chromatography-mass spectrometry (GC-MS). From the suspensor four C19-GAs, GA1, GA4, GA5, GA6, and one C20 GA, GA44, were identified. From the embryo, five C19-GAs GA1, GA4, GA5, GA6, GA60 and two C20 GAs, GA19 and GA44 were identified. The data, in relation to previous results, suggest a dependence of the embryo on the suspensor during early stages of development. 相似文献
924.
Dynamics of Imbibition in Phaseolus vulgaris L. in Relation to Initial Seed Moisture Content 总被引:1,自引:1,他引:0
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The seed moisture level marking the onset of imbibitional injury (breakpoint) was determined for two cultivars of Phaseolus vulgaris L. cvs `Tendercrop' (TC) and `Kinghorn Wax' (KW). At 20°C the breakpoints were 0.15 gram H2O/gram dry weight (gram per gram) for TC and 0.11 gram per gram for KW. When seeds were imbibed at 5°C, the breakpoints were 0.19 gram per gram (TC) and 0.16 gram per gram (KW). Below the breakpoint germination changed 4.6%/0.01 gram per gram for all treatments. Imbibition rates were maximal at 0.07 gram per gram and 0.33 gram per gram after 20 minutes imbibition. Rates of electrolyte leakage were correlated with the imbibition rate maximum at 0.07 gram per gram but were unaffected by the maximum at 0.33 gram per gram. The transition from tightly bound to semibound water occurred at 0.09 gram per gram and 0.11 gram per gram for KW and TC, respectively. T1 values increased exponentially as seed moisture decreased from 0.47 gram per gram to 0.05 gram per gram. 13C-NMR sugar signals increased at moisture levels above 0.14 gram per gram and plateaued at approximately 0.33 gram per gram seed moisture. These results suggest that the breakpoint moisture level for imbibitional damage is a function of temperature while the injury process is similar at both 5 and 20°C. Imbibition and leakage rate maxima reflect transitions in the states of seed water. NMR data support the application of the Water Replacement Hypothesis to seeds. Thus, imbibitional injury may be related to specific, temperature dependent moisture levels that are determined by water binding characteristics in the seed tissue. 相似文献
925.
A lipoxygenase preparation was obtained from green algae Oscillatoria sp. and was shown to differ from previous described lipoxygenases in the positional specificity and pH characteristics of the dioxygenation reaction. The enzyme had a pH optimum at 8.8 and was inactive at pH 6. Oscillatoria lipoxygenase converted linoleic acid into two products: 13-hydroperoxylinoleic acid (52%) and 9-hydroperoxylinoleic acid (48%). The molecular weight of the enzyme was estimated at 124,000. Esculetin was found to be the best inhibitor of the enzyme activity. 相似文献
926.
Water relations of turgor recovery and restiffening of wilted cabbage leaves in the absence of water uptake 总被引:4,自引:3,他引:1
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A novel phenomenon in which wilted cabbage leaves appeared to regain positive turgor pressures without additional water uptake has been previously reported (J Levitt [1986] Plant Physiol 82: 147-153). These experiments were replicated and the biophysical nature of turgor recovery characterized. Leaf water potential and its components were assayed in hydrated, wilted, and desiccated leaves which appeared to regain turgor after wilting. The hypotheses that turgor recovery was due to an increased volumetric elastic modulus (ε), or alternatively the result of solute redistribution were tested. Quantitative evidence that turgor recovery occurs in excised leaves was found. Leaf turgor pressure in hydrated leaves (~0.6 megapascal) decreased to zero upon wilting. After continued desiccation, turgor pressure returned to approximately 0.3 megapascal even though leaf relative water content declined. The ε of hydrated leaves was large and there was no evidence of an increased ε in the turgor-recovered leaves. Solute mobilization occurred during desiccation. The apoplastic osmotic potential decreased from −0.15 to −0.44 megapascal in hydrated and turgor-recovered leaves, respectively, and solutes were transported from the lamina to the midrib tissue. Solute redistribution coupled with the high ε may have resulted in localized turgor recovery in specific cells in the desiccated leaves. 相似文献
927.
Methods used to estimate the (nonosmotic) bound water fraction (BWF) (i.e. apoplast water) of spinach (Spinacia oleracea L.) leaves were evaluated. Studies using three different methods of pressure/volume (P/V) curve construction all resulted in a similar calculation of BWF; approximately 40%. The theoretically derived BWF, and the water potential (Ψw)/relative water content relationship established from P/V curves were used to establish the relationship between protoplast (i.e. symplast) volume and Ψw. Another method of establishing the protoplast volume/Ψw relationship in spinach leaves was compared with the results from P/V curve experiments. This second technique involved the vacuum infiltration of solutions at a range of osmotic potentials into discs cut from spinach leaves. These solutions contained radioactively labeled H2O and sorbitol. This dual label infiltration technique allowed for simultaneous measurement of the total and apoplast volumes in leaf tissue; the difference yielded the protoplast volume. The dual label infiltration experiments and the P/V curve constructions both showed that below −1 megapascals, protoplast volume decreases sharply with decreasing water potential; with 50% reduction in protoplast volume occurring at −1.8 megapascals leaf water potential. 相似文献
928.
The effect of gibberellic acid (GA) on light-induced greening of etiolated pea plants (Pisum sativum [L.] cultivars Alaska and Progress) was characterized. Progress, a GA-deficient dwarf of Alaska, was found to accumulate chlorophyll and light harvesting chlorophyll protein associated with photosystem II (LHC-II) more rapidly than Alaska, Alaska treated with GA, or Progress treated with GA. A slightly lower chlorophyll content was noted after 24 hours of light induced greening for Alaska treated with GA relative to untreated Alaska. GA-treated Progress, Alaska, and GA-treated Alaska all gave essentially identical patterns for LHC-II accumulation. Similar patterns of LHC-II mRNA induction were found in all four treatments indicating that differences in mRNA induction did not cause differences in LHC-II accumulation. Chlorophyll and LHC-II accumulation in each treatment followed the same patterns of accumulation and a significant correlation (at the 0.01 level of significance) was found between chlorophyll and LHC-II content. Since Progress treated with GA accumulated LHC-II and chlorophyll in a manner similar to that of Alaska, it is clear that GA alters the process of greening either directly or indirectly. 相似文献
929.
New ways to look at the architecture of plant cell walls : localization of polygalacturonate blocks in plant tissues 总被引:5,自引:3,他引:2
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We report the use of Ni2+ and Co2+ on free-hand sections of soybean (Glycine max L.) and Bidens sp to localize polygalacturonates. In soybean only the hourglass cells of the seedcoat stain intensely. In the pod the epidermis of the outer pod wall and a few layers of subepidermal cells stain lightly, while that part of the funiculus adjacent to the seedcoat palisade epidermal cells stains heavily and the neck of the funiculus close to the pod also stains. In Bidens stem sections, the walls of the collenchyma stain most intensely. 相似文献
930.
Hydroxycinnamoyl-CoA:Putrescine Hydroxycinnamoyltransferase in Tobacco Cell Cultures with High and Low Levels of Caffeoylputrescine 总被引:1,自引:0,他引:1
A new hydroxycinnamoyl-CoA:putrescine hydroxycinnamoyltransferase (PHT) was detected in two variant lines of Nicotiana tabacum L. (TX1, TX4) accumulating markedly different levels of caffeoylputrescine. The enzyme accepted only the aliphatic diamines putrescine, cadaverine and 1,3-diaminopropane at a ratio of 100:33:8. Caffeoyl- and feruloyl-CoAs were the best acyl donors. The apparent Km-values for caffeoyl-CoA and putrescine were near 3 and 10 micromolar, respectively, at the pH-optimum of 10.0. PHT activity was quite similar in low producing TX1 and high producing TX4 cells, while some other biosynthetic enzymes (phenylalanine ammonia-lyase, ornithine decarboxylase) were greatly enhanced in TX4 cells, suggesting that PHT does not catalyze the rate-limiting step in hydroxycinnamoylputrescine formation. 相似文献