Characterization and hydrodynamic behaviour of modified gelatin: I. Light scattering and viscometry studies

Commercial samples of gelatin modified by succinylation and currently used as plasma substitutes and fractionated samples obtained by diafiltration have been studied by viscometry, light scattering and osmometry. Viscometric results show that the aqueous medium containing potassium phosphate (0.1 ) and NaCl (0.12 ) at pH 3.3 behaves nearly like a theta solvent (a=0.48) for these modified gelatins. The Stockmayer-Fixman diagram reveals a negative slope attributed to a swelling of the macromolecules which decreases as the molecular weight _w increases. The Stokes radius R_H determined by quasielastic light scattering is independent of the pH of the medium in a range 7-3.3. The conformation of gelatins in solution has been characterized through the ratio _G· _H⁻¹, the radius of gyration _G being determined by viscometry. This ratio decreases as the molecular weight increases. The low molecular weight fractions have a more compact structure than the Gaussian chains in theta conditions. For high molecuar weight fractions, the values of _G· _H⁻¹ tend to those of an hard sphere.     

Recycling of CO2 via Crassulacean acid metabolism in the rock outcrop succulent Sedum pulchellum Michx. (Crassulaceae)

Under well-watered conditions in the laboratory, Sedum pulchellum assimilated CO₂ only during the day, yet exhibited small nocturnal increases in tissue acid content followed by deacidification in the light (CAM-cycling). When drought-stressed, little CO₂ was fixed in the day and none at night, yet even greater acid fluctuations were observed (CAM-idling). Calculations indicate that water savings associated with CAM-cycling when water is available are small. Water saving is more likely to be significant during CAM-idling when water supply is limited and stomata are closed day and night. Thus, in this species, CAM-idling may be of greater benefit to the plant, relative to CAM-cycling, in surviving habitats prone to frequent drought stress.Abbreviations A CO₂ exchange rate - CAM Crassulacean acid metabolism - c_i shoot internal CO₂ concentration - g_c shoot conductance to CO₂ - PPFD photosynthetic photon flux density - WUE water-use efficiency Supported by National Science Foundation Grant No. DMB 8506093.     

Effect of chloramphenicol and lincomycin on chloroplast DNA amplification in greening pea leaves

The light-induced increase in chloroplast DNA was not inhibited by two inhibitors of protein synthesis on 70S polysomes, chloramphenicol and lincomycin, in greening pea leaves. The changes in chloroplast DNA were observed by fluorescence microscopy and measured by hybridization to specific cloned probes. The results suggest that the light-induced increase in chloroplast DNA proceeds without de novo protein synthesis in the chloroplast, in agreement with those with mutants and cultured leaf tissue.     

Effect of adaptation to high light intensity on the kinetics of energy transfer from phycobilisomes to photosystem II in Anabaena cylindrica

Transfer efficiencies between phycobilisomes and photosystem II antenna chlorophylls were determined on membrane fragments isolated from low and high light adapted Anabaena cells. The observed increase in energy transfer in high light adapted cells is a consequence of shorter interchromophore distances and a decrease in the number of jumps of the exciting photons. Calculation of the rates of energy transfer and the coupling energies indicate that the weak interaction inferred for energy transfer between phycobilisome and photosystem II in low light adapted cells is replaced by an intermediate interaction in high light adapted cells.Abbreviations LLA low light adapted - HLA high light adapted - PBS phycobilisome - PS photosystem     

The efficiency of pitfall trapping for polyphagous predatory Carabidae

ABSTRACT.

• 1 The efficiency of pitfall trapping was investigated for seven carabid species, using time-lapse video recording equipment, in the laboratory.
• 2 The effects of differing substrates, trap designs and seasons of collection on the capture rates of the carabids was also investigated.
• 3 Capture rate differed significantly between the species studied. The differences in capture rates between the species were unrelated to beetle size, speed of movement and diurnal behaviour.
• 4 Few differences arose in the capture rates when type of substrate or trap or season of capture were changed.

     

The effect of grasses on the quality of transmitted radiation and its influence on the growth of white clover Trifolium repens

Summary Plants of white clover Trifolium repens were grown under the canopies of three grass species, Lolium perenne, Agrostis tenuis and Holcus lanatus, and under simulated canopies of black polythene and controls were exposed to unfiltered natural radiation. The canopies were adjusted so that they transmitted equal intensities of Photosynthetically Active Radiation (P.A.R.). The ratio of red to far red radiation () was unchanged under the black polythene canopies but was reduced under canopies of Lolium and Agrostis and even more so under Holcus. The effect of canopy filtered radiation on the growth of clover was greatly to reduced internode length, mean number of nodes, the number of branched nodes and the number of rooted nodes and greatly to increase petiole length. The effect of canopies of Holcus was greater than that of the other grass species both in its effect on and on the responses of the clover plant to its shade.     

Relation of light and nitrogen source to growth, nitrate reductase and glutamine synthetase activity of jack pine seedlings

Two-month-old jack pine ( Pinus banksiana Lamb.) seedlings were placed in a greenhouse where both nitrogen source and light level were varied. After 4 months, whole seedling biomass, leaf biomass and relative growth rate were greatest in seedlings grown with NH⁺₄/NO/NO⁻₃-N and full light (FL) and least in seedlings grown with NO ⁻₃-N and low light (LL). NO ⁻₃-seedlings grown under full light and NH⁺₄/NO⁻₃-seedlings grown under low light were approximately equal. This indicates that the extra carbon costs of assimilating only NO⁻₃-N were similar to the reduction of carbon fixation resulting from a 50% decrease in photon flux density. Percentage and total nitrogen content of needles were greater in seedlings grown under low light independent of nitrogen fertilization. Percentage and total nitrogen content of roots were higher under low light and lower when fertilized with NO⁻₃.
Nitrate reductase (NR) activity was higher in roots than in needles, while glutamine synthetase (GS) activity was higher in needles than in roots. Low light resulted in decreased NR activity (mg N)⁻¹ in needles, but not in roots. However, no nitrate was detected in the needles in any treatment. GS activity, on the other hand, was greater under low light in both needles and roots. GS activity in needles is most likely involved with the reassimilation rather than the initial assimilation of ammonium. Some implications of these shifts in enzymatic activity for ecological phenomena in forests are discussed.     

Phytochrome is not involved in the red-light-enhancement of the stomatal blue-light-response in wheat seedlings

The stomatal response to blue light (BL) in wheat seedlings ( Triticum aestivum L. cv. Starke II, Weibull) was enhanced by background red light (R). This enhancement was only slightly affected by the addition of background far-red light (FR). Under similar light treatments, the addition of FR induced a 43% transformation from the far-red-absorbing form towards the red-absorbing form of phytochrome from etiolated oat ( Avena sativa L. cv. Sol II), immobilized on phenyl-sepharose. Furthermore, the enhancement of the stomatal BL-response by 15 min R was not reversed by a subsequent irradiation with 5 min FR. It is concluded that the red-light-enhancement of the stomatal blue-light-response in wheat seedlings does not involve a change in the photostationary state of phytochrome.