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Start Over Coverage 83-89

2. Contrasting effects of carbon dioxide and irradiance on the acclimation of photosynthesis in developing soybean leaves

Creator:
Bunce, J. A.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
dry matter accumulation, feed inhibition, Glycine max, protein, photosynthetic CO2 and O2 exchange, ribulose-1,5-bisphosphate carboxylase/oxygenase, and source-sing balance
Language:
Multiple languages
Description:
Leaves developed at high irradiance (I) often have higher photosynthetic capacity than those developed at low I, while leaves developed at elevated CO2 concentration [CO2] often have reduced photosynthetic capacity compared with leaves developed at lower [CO2]. Because both high I and elevated [CO2] stimulate photosynthesis of developing leaves, their contrasting effects on photosynthetic capacity at maturity suggest that the extra photosynthate may be utilized differently depending on whether I or [CO2] stimulates photosynthesis. These experiments were designed to test whether relationships between photosynthetic income and the net accumulation of soluble protein in developing leaves, or relationships between soluble protein and photosynthetic capacity at full expansion differed depending on whether I or [CO2] was varied during leaf development. Soybean plants were grown initially with a photosynthetic photon flux density (PPFD) of 950 µmol m-2 s-1 and 350 µmol [CO2] mol-1, then exposed to [CO2] ranging from 135 to 1400 µmol mol-1 for the last 3 d of expansion of third trifoliolate leaves. These results were compared with experiments in which I was varied at a constant [CO2] of 350 µmol mol-1 over the same developmental period. Increases in area and dry mass over the 3 d were determined along with daily photosynthesis and respiration. Photosynthetic CO2 exchange characteristics and soluble protein content of leaves were determined at the end of the treatment periods. The increase in leaflet mass was about 28 % of the dry mass income from photosynthesis minus respiration, regardless of whether [CO2] or I was varied, except that very low I or [CO2] increased this percentage. Leaflet soluble protein per unit of area at full expansion had the same positive linear relationship to photosynthetic income whether [CO2] or I was varied. For variation in I, photosynthetic capacity varied directly with soluble protein per unit area. This was not the case for variation in [CO2]. Increasing [CO2] reduced photosynthetic capacity per unit of soluble protein by up to a factor of 2.5, and photosynthetic capacity exhibited an optimum with respect to growth [CO2]. Thus CO2 did not alter the relationship between photosynthetic income and the utilization of photosynthate in the net accumulation of soluble protein, but did alter the relationship between soluble protein content and photosynthetic characteristics in this species.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

3. Critical buckling stress of patch loading

Creator:
Baláž, Ivan and Koleková, Yvona
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
patch loading, elastic critical stress, buckling coefficient, and parametrical study
Language:
English
Description:
Elastic critical buckling stress of the plate girder subjected to transverse force is calculated. The load is applied through the flange and resisted by shear forces in the web. Comparisons of values of buckling coefficient kσ,b = f (α, β) (Tab.2) obtained by 5 various authors: Petersen, von Berg, Ravinger, Kutzelnigg, Protte (Tab. 1) and calculated by computer program PLII (Tab. 2). Simply supported rectangular plate (a - length, b - width, t - thickness) without flanges and stiffeners is investigated for different aspect ratios α = a/b = 1; 2; 3; 4; 5; 8; 10; 20; 30; 40 when subjected to transverse uniformly distributed partial load having relative load lengths β = c/a = 0.005 (single concentrated force); 0.2; 0.4; 0.6; 0.7; 0.8; 1 (uniformly distributed load along a). The values of buckling coeffficient kσ,b = f (α, β, δ) calculated by program PLII (Tab. 3). Parametrical study of simply suppported rectangular plate without stiffeners with α = a/b = 4; 5; 8; 10; 20; 30; 40, β = c/a = 0.005 (single concentrated force); 0.01; 0.05; 0.1; 0.2; 0.3; 0.4 and different relative normal flange rigidity δ = Af / (b t) = 0 (without flange); 0.3; 0.5; 1; 1.5; 2; 3. Torsional rigidity of the flanges is not taken into account. and Obsahuje seznam literatury
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

4. Diurnal and seasonal changes in photosynthesis and photosystem 2 photochemical efficiency in Prosopis juliflora leaves subjected to natural environmental stress

Creator:
Shirke, P. A. and Pathre, U. V.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
chlorophyll fluorescence, diurnal courses, electron transport rate, irradiance, midday depression, non-photochemical quenching, photoinhibition, and photosystem 2 temperature
Language:
Multiple languages
Description:
The plants of Prosopis juliflora growing in northern India are exposed to large variations of temperature, vapour pressure deficits (VPD), and photosynthetic photon flux density (PPFD) throughout the year. Under these conditions P. juliflora had two short periods of leaf production, one after the winter season and second after summer, which resulted in two distinct even aged cohorts of leaves. In winter with cold nights (2-8 °C) and moderate temperatures during the day, the plants showed high rates of photosynthesis. In summer the midday temperatures often reached <45 °C and plants showed severe inhibition of photosynthesis. The leaves of second cohort appeared in July and showed typical midday depression of photosynthesis. An analysis of diurnal partitioning of the absorbed excitation energy into photochemistry showed that a smaller fraction of the energy was utilised for photochemistry and a greater fraction was dissipated thermally, further the photon utilisation for photochemistry and thermal dissipation is largely affected by the interaction of irradiance and temperature. The plants showed high photochemical efficiency of photosystem 2 (PS2) at predawn and very little photoinhibition in all seasons except in summer. The photoinhibition in summer was pronounced with very poor recovery during night. Since P. juliflora exhibited distinct pattern of senescence and production of new leaves after winter and summer stress period, it appeared that the ontogenic characteristic together with its ability for safe dissipation of excess radiant energy in P. juliflora contributes to its growth and survival. and P. A. Shirke, U. V. Pathre.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

5. Heterogeneous behaviour of subunits of the light-harvesting chlorophyll a/b-protein complex of photosystem 2 during cation-induccd aggregation

Creator:
Jackowski, G. and Kluck, E.
Format:
print
Type:
model:internalpart and TEXT
Language:
Multiple languages
Description:
Cation-induced aggrcgation of isolated LHC2 was ušed to compare the adliesion- promoting activities of individual LHCP2. Precipitated and waslied LHC2 of camation origin was aggregated in the presence of KCl. The polypeptide composition of the LHC2 sheets remaining in non-aggregated form after different tiine intervals was analysed by SDS-PAGE followed by scanning laser densitometiy. The LHC2 sheets enriched in a major camation LHC2-27 kDa polypeptide were shown to aggregate at a faster rate than the sheets enriched in minor LHCP2, i.e. 26 and 23 kDa polypeptides, although the finál degree of aggrcgation was similar for all types of LHC2 sheets.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

7. The spectrum of comet Arend-Roland

Creator:
Rajchl, J.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
spectrograms, microphotometers, and comets
Language:
Czech
Description:
Nine objective prism spectrograms by means of two cameras were achieved. It was impossible to point directly at the comet image by using the larger camera. The motions in α of both the camera and the comet were the same. The motion difference in δ was determined experimentally and introduced as correction. The photometrical tracings of the comet head and tail and of the stars were made by using a recording microphotometer. The computed dispersion curve was corrected by using the main comet head emissions. The identification of the emissions was done by a comparison with [2] and [3]. The spectrograms show strong CN and Na emissions. It was assumed, that the background below the emissions was due to continuous spectrum. Then its amplitude is nearly twice that of the emission lines. The amplitude ratio continuum/emission in the tail was 1 : 0·6. The spectrograms from the end of May show only weak C2 emissions. The tail directied towards the Sun was unobservable during our observations.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public