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  • Photosynthesis  (4)
  • δ15N  (2)
  • 1995-1999
  • 1990-1994  (6)
  • 1
    ISSN: 1432-2048
    Keywords: Nicotiana (transformed with antisense DNA) ; Photosynthesis ; Ribulose-1,5-bisphosphate carboxylase-oxygenase ; Transgenic plant (antisense)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Experiments were carried out to determine how decreased expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) affects photosynthetic metabolism in ambient growth conditions. In a series of tobacco (Nicotiana tabacum L.) plants containing progressively smaller amounts of Rubisco the rate of photosynthesis was measured under conditions similar to those in which the plants had been grown (310 μmol photons · m−2 · s−1, 350 μbar CO2, 22° C). (i) There was only a marginal inhibition (6%) of photosynthesis when Rubisco was decreased to about 60% of the amount in the wildtype. The reduced amount of Rubisco was compensated for by an increase in Rubisco activation (rising from 60 to 100%), with minor contributions from an increase of its substrates (ribulose-1,5-bisphosphate and the internal CO2 concentration) and a decrease of its product (glycerate-3-phosphate). (ii) The decreased amount of Rubisco was accompanied by an increased ATP/ADP ratio that may be causally linked to the increased activation of Rubisco. An increase of highenergy-state chlorophyll fluorescence shows that thylakoid membrane energisation and high-energy-state-dependent energy dissipation at photosystem two had also increased. (iii) A further decrease of Rubisco (in the range of 50–20% of the wildtype level) resulted in a strong and proportional inhibition of CO2 assimilation. This was accompanied by a decrease of fructose-1,6-bisphosphatase activity, coupling-factor 1 (CF1)-ATP-synthase protein, NADP-malate dehydrogenase protein, and chlorophyll. The chlorophyll a/b ratio did not change, and enolase and sucrose-phosphate synthase activity did not decrease. It is argued that other photosynthetic enzymes are also decreased once Rubisco decreases to the point at which it becomes strongly limiting for photosynthesis. (iv) It is proposed that the amount of Rubisco in the wildtype represents a balance between the demands of light, water and nitrogen utilisation. The wildtype overinvests about 15% more protein in Rubisco than is needed to avoid a strict Rubisco limitation of photosynthesis. However, this “excess” Rubisco allows the wildtype to operate with lower thylakoid energisation, and decreased high-energy-state-dependent energy dissipation, hence increasing light-use efficiency by about 6%. It also allows the wildtype to operate with a lower internal CO2 concentration in the leaf and a lower stomatal conductance at a given rate of photosynthesis, so that instantaneous water-use efficiency is marginally (8%) increased.
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  • 2
    ISSN: 1432-2048
    Keywords: Light climate ; Nicotiana (photosynthesis) ; Photosynthesis ; Ribulose 1,5-bisphosphate carboxylase-oxygenase ; Transgenic plant (tobacco, antisense DNA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tobacco (Nicotiana tabacum L.) plants transformed with ‘antisense’ rbcS to decrease the expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) have been used to investigate the contribution of Rubisco to the control of photosynthesis in plants growing at different irradiances. Tobacco plants were grown in controlled-climate chambers under ambient CO2 at 20°C at 100, 300 and 750 μmol·m−2·s−1 irradiance, and at 28°C at 100, 300 and 1000 μmol·m−2·s−1 irradiance. (i) Measurement of photosynthesis under ambient conditions showed that the flux control coefficient of Rubisco (C infRubisco supA ) was very low (0.01–0.03) at low growth irradiance, and still fairly low (0.24–0.27) at higher irradiance. (ii) Short-term changes in the irradiance used to measure photosynthesis showed that C infRubisco supA increases as incident irradiance rises, (iii) When low-light (100 μmol·m−2·s−1)-grown plants are exposed to high (750–1000 μmol·m−2·s−1) irradiance, Rubisco is almost totally limiting for photosynthesis in wild types. However, when high-light-grown leaves (750–1000 μmol·m−2·s−1) are suddenly exposed to high and saturating irradiance (1500–2000 μmol·m−2·s−1), C infRubisco supA remained relatively low (0.23–0.33), showing that in saturating light Rubisco only exerts partial control over the light-saturated rate of photosynthesis in “sun” leaves; apparently additional factors are co-limiting photosynthetic performance, (iv) Growth of plants at high irradiance led to a small decrease in the percentage of total protein found in the insoluble (thylakoid fraction), and a decrease of chlorophyll, relative to protein or structural leaf dry weight. As a consequence of this change, high-irradiance-grown leaves illuminated at growth irradiance avoided an inbalance between the “light” reactions and Rubisco; this was shown by the low value of C infRubisco supA (see above) and by measurements showing that non-photochemical quenching was low, photochemical quenching high, and NADP-malate dehydrogenase activation was low at the growth irradiance. In contrast, when a leaf adapted to low irradiance was illuminated at a higher irradiance, Rubisco exerted more control, non-photochemical quenching was higher, photochemical quenching was lower, and NADP-malate dehydrogenase activation was higher than in a leaf which had grown at that irradiance. We conclude that changes in leaf composition allow the leaf to avoid a one-sided limitation by Rubisco and, hence, overexcitation and overreduction of the thylakoids in high-irradiance growth conditions, (v) ‘Antisense’ plants with less Rubisco contained a higher content of insoluble (thylakoid) protein and chlorophyll, compared to total protein or structural leaf dry weight. They also showed a higher rate of photosynthesis than the wild type, when measured at an irradiance below that at which the plant had grown. We propose that N-allocation in low light is not optimal in tobacco and that genetic manipulation to decrease Rubisco may, in some circumstances, increase photosynthetic performance in low light.
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  • 3
    ISSN: 1432-2048
    Keywords: Biomass allocation ; Nicotiana ; Nitrogen nutrition ; Photosynthesis ; Relative growth rate ; Ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) ; Transgenic plant (tobacco antisense DNA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Wild-type tobacco (Nicotiana tabacum L.) plants and transgenic tobacco transformed with antisense rbcS to decrease expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) were grown at 300 mol-m−2 · s−1 irradiance and 20° C at either 0.1, 0.7 or 5 mM NH4NO3. In high nitrogen (N), growth was reduced in parallel with the inhibition of photosynthesis when Rubisco was decreased by genetic manipulation. In limiting N, photosynthesis was reduced strongly when Rubisco was decreased by genetic manipulation, but growth was hardly affected. At all N levels, decreased expression of Rubisco led to a decrease in the amount of starch accumulated in the leaves. There was a large increase of the specific leaf area (SLA; leaf area maintained per unit dry weight in the leaf) in plants with decreased Rubisco. Increased SLA was associated with an increased inorganic and a decreased carbon contribution to leaf structural dry weight. The increased SLA represents a more efficient investment of photosynthate with respect to maximisation of leaf area and light interception, and partly compensates for the decreased rate of photosynthesis in plants with decreased expression of Rubisco. The changes of starch content and SLA were particularly large in limiting N, when growth rate was effectively independent of the rate of photosynthesis. Increased N availability led to a large increase of the shoot/ root ratio, but only a small increase in SLA. It is argued that N availability and the availability of photosynthate both regulate storage and allocation of biomass to optimize resource utilization, but achieve this via different mechanisms.
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  • 4
    ISSN: 1573-5036
    Keywords: atmospheric deposition ; δ15N ; δ34S ; forest decline ; nitrogen ; Picea abies ; stable isotopes ; sulfur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Concentrations and natural isotope abundance of total sulfur and nitrogen as well as sulfate and nitrate concentrations were measured in needles of different age classes and in soil samples of different horizons from a healthy and a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), in order to study the fate of atmospheric depositions of sulfur and nitrogen compounds. The mean δ15N of the needles ranged between −3.7 and −2.1 ‰ and for δ34S a range between −0.4 and +0.9 ‰ was observed. δ34S and sulfur concentrations in the needles of both stands increased continuously with needle age and thus, were closely correlated. The δ15N values of the needles showed an initial decrease followed by an increase with needle age. The healthy stand showed more negative δ15N values in old needles than the declining stand. Nitrogen concentrations decreased with needle age. For soil samples at both sites the mean δ15N and δ34S values increased from −3 ‰ (δ15N) or +0.9 ‰ (δ34S) in the uppermost organic layer to about +4 ‰ (δ15N) or +4.5 ‰ (δ34S) in the mineral soil. This depth-dependent increase in abundance of 15N and 34S was accompanied by a decrease in total nitrogen and sulfur concentrations in the soil. δ15N values and nitrogen concentrations were closely correlated (slope −0.0061 ‰ δ15N per μmol eq N gdw −1), and δ34S values were linearly correlated with sulfur concentrations (slope −0.0576 ‰ δ34S per μmol eq S gdw −1). It follows that in the same soil samples sulfur concentrations were linearly correlated with the nitrogen concentrations (slope 0.0527), and δ34S values were linearly correlated with δ15N values (slope 0.459). A correlation of the sulfur and nitrogen isotope abundances on a Δ basis (which considers the different relative frequencies of 15N and 34S), however, revealed an isotope fractionation that was higher by a factor of 5 for sulfur than for nitrogen (slope 5.292). These correlations indicate a long term synchronous mineralization of organic nitrogen and sulfur compounds in the soil accompanied by element-specific isotope fractionations. Based on different sulfur isotope abundance of the soil (δ34S=0.9 ‰ for total sulfur of the organic layer was assumed to be equivalent to about −1.0 ‰ for soil sulfate) and of the atmospheric SO2 deposition (δ34S=2.0 ‰ at the healthy site and 2.3 ‰ at the declining site) the contribution of atmospheric SO2 to total sulfur of the needles was estimated. This contribution increased from about 20 % in current-year needles to more than 50 % in 3-year-old needles. The proportion of sulfur from atmospheric deposition was equivalent to the age dependent sulfate accumulation in the needles. In contrast to the accumulation of atmospheric sulfur compounds nitrogen compounds from atmospheric deposition were metabolized and were used for growth. The implications of both responses to atmospheric deposition are discussed.
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  • 5
    ISSN: 1432-1939
    Keywords: Air pollution ; Acid rain ; Photosynthesis ; Nutrition ; Picea abies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Photosynthetic rates and nutrient contents of spruce needles were measured in a region with high levels of air pollution in NE Bavaria, Germany (FRG), and compared to spruce grown under clean air conditions at Craigieburn, in the South Island of New Zealand (NZ). The absolute rates of CO2 uptake, the slope of the CO2 response curve at 240 μl l−1 internal CO2 concentration, and the change of photosynthetic rates with needle age at ambient and saturated CO2 concentrations were virtually identical at both measuring sites. These results confirm an earlier conclusion, that there is no long-term effect of atmospheric pollutants directly on photosynthetic CO2 uptake rates with persistent exposure at the FRG site to high levels of anthropogenic air pollution. Photosynthetic capacity at saturating CO2 concentration was three times higher in the NZ spruce. Needles with high photosynthetic capacity in NZ had lower nitrogen and higher calcium concentrations per unit dry weight but higher concentrations of nitrogen, phosphorus, potassium, magnesium and calcium per unit leaf area, and twice the specific leaf weight.
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  • 6
    ISSN: 1432-1939
    Keywords: δ13C ; δ15N ; Nitrogen assimilation ; Forest decline ; Picea abies ; Stable isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The δ13C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (δ13C between-25.3 and-27.8‰) were significantly less depleted in 13C than needles (δ13C between-27.3 and-29.1‰), and δ13C in twigs increased consistently with age. The δ15N values of needles ranged between-2.5 and-4.1‰ and varied according to stand and age. In young needles δ15N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in 15N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. δ15N values in twigs were more negative than in needles (-3.5 to-5.2‰) and showed age- and stand-dependent trends that were similar to the needles. δ15N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4‰ in the mineral soil. The δ15N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed.
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