The effect of different night conditions on the CO2 fixation in a lichen Xanthoria parietina

CO₂ fixation was studied in a lichen, Xanthoria parietina, kept in continuous light, and with cyclic changes in light intensity, dark period or temperature. The diurnal and seasonal courses of CO₂ exchange were followed. The rate of net photosynthesis was observed to fall from morning to evening, and this decline was more pronounced in winter than in summer. The maximal net photosynthetic rate, 223 ng CO₂g^-1dws^-1, occured in winter and the minimum, 94 ng CO₂g^-1dws^-1, late in spring. The light compensation point in summer was four times as high as in winter. In continuous light (180 or 90 mol photons m^-2s^-1, 15°C) net photosynthesis decreased noticeably during one week, falling below the level maintained in a 12 h light: 12 h dark cycle. Photosynthetic activity did not decrease, however, in lichens held in continuous light (90 mol photons m^-2s^-1) with cyclic changes of temperature (12 h 20 °C: 12 h 5 °C). Active photosynthesis was also maintained in light of cyclically changing intensity (12 h: 12 h, 15 °C) when night-time light was at least 75% lower than illumination by day. A dark period of 4 hours in a 24-h light:dark cycle was sufficient to keep CO₂ fixation at the control level. It seems that plants need an unproductive period during the day to survive and this can be induced by fluctuations in light and/or temperature.     

Electrooptical analysis of blue and of cation-regenerated bacteriorhodopsin

Blue bacteriorhodopsin was prepared by electrodialysis, cation-exchange chromatography and acidification. The electrooptical properties of these preparations compared to those of the native purple bacteriorhodopsin suggest that the blue bacteriorhodopsin has a smaller induced dipole moment than the native purple bacteriorhodopsin and that bound cations in the native bacteriorhodopsin stabilize the protein conformation in the membrane.Purple bacteriorhodopsin was regenerated by addition of potassium, magnesium or ferric ions to blue bacteriorhodopsin. Both spectrscopically and electrooptically the potassium- and ferric-regenerated samples are different from the native purple state. Although the magnesium-regenerated sample is spectroscopically similar to the native purple bacteriorhodopsin, the electrooptical properties are rather similar to those of the cation-depleted blue sample, suggesting that it is very difficult to re-stabilize protein structures once cations are depleted.     

The effect of canopy filtered light on the growth of white clover Trifolium repens

Summary Plants of white clover (Trifolium repens) were grown under canopies of clover leaves floating on shallow glass tanks of water and their growth was compared with that of plants under canopies of black polythene leaves. The experimental design allowed the growth of the clover plants in canopy filtered light to be compared with that in unfiltered light at different intensities of Photosynthetically Active Radiation (P.A.R.). The effect of canopy filtered light was to exaggerate the effects of reduced P.A.R. especially in promoting petiole extension and inhibiting stolon branching. Two clones of white clover differed in their responses to P.A.R. and to light quality and there were significant interactions between the effects of the intensity of P.A.R. and type of shade. It is argued that it may be important for both ecologists and plant breeders to recognise the role of radiation quality in regulating the dynamics of pasture.     

Inhibition and promotion by light of the accumulation of translatable mRNA of the light-harvesting chlorophyll a/b-binding protein of photosystem II

The amount of in-vitro translatable mRNA of the light-harvesting chlorophyll a/b-binding protein (LHCP) of photosystem II strongly increases in darkness (D) after a 5-min red-light pulse while continuous illumination of mustard seedlings with far-red (FR), red or white light leads only to a slight increase in the amount of translatable LHCP-mRNA. No increase can be observed after a long-wavelength FR (RG9-light) pulse. However, a FR pretreatment prior to the RG9-light pulse strongly increase LHCP-mRNA accumulation in subsequent D. This is not observed in the case of the mRNA for the small subunit of ribulose-1.5-bisphosphate carboxylase. The increase of LHCP-mRNA in D after a FR pretreatment can be inhibited by a reillumination of the seedlings with FR. The inhibition of LHCP-mRNA accumulation during continuous illumination with FR and the strong increase in D following a FR illumination was found to be independent of chlorophyll biosynthesis since no correlation between chlorophyll biosynthesis and translatable LHCP-mRNA levels could be detected. Even strong changes in the amount of intermediates of chlorophyll biosynthesis caused by application of levulinic acid or 5-aminolevulinic acid did not affect LHCP-mRNA levels. Therefore, we conclude that the appearance of LHCP-mRNA is inhibited during continuous illumination, even though illumination leads to a storage of a light singal which promotes accumulation of translatable LHCP-mRNA in D.Abbreviations c continuous - Chl chlorophyll - D darkness - FR far-red light (3.5 W·m^-2) - LHCP light-harvesting chlorophyll a/b-binding protein of photosystem II - NF Norfluration - PChl protochlorophyll(ide) - Pfr far-red absorbing form of phytochrome - Ptot total phytochrome - R red light (6.8 W·m^-2) - RG9-light long-wavelength FR (10 W·m^-2) - SSU small subunit of ribulose-1.5-bisphosphate carboxylase - WL white light - () Pfr/Ptot=wavelength-dependent photoequilibrium of the phytochrome system     

Internode length in Pisum. Action of gene lw

Jolly, C. J., Reid, J. B. and Ross, J. J. 1987. Internode length in Pisum. Action of gene lw.
Mutant K29 of Pisum sativum L. is shown to possess a recessive gene at a new locus, lw , which results in reduced internode length, delayed flowering and increased symptoms of water congestion compared with the parental cv. Torsdag. The interaction of gene lw with the internode length genes na, le, la and cry ⁵ is examined. Extracts from the shoots of Iw plants are shown to contain similar levels of gibberellin (GA)-like substances to comparable Lw plants, but Iw plants do not elongate to the same extent as Lw plants when treated with GA₁₉ GA₁₉, or GA₂₀. The effect of gene Iw is not graft-transmissible. Unlike essentially isogenic dwarf lines possessing the GA-synthesis genes le, Ih or Is, lw plants show a relative increase in elongation similar to Torsdag in response to photoperiod extensions from sources rich in far-red light. These results suggest that gene lw probably does not reduce elongation by influencing GA-synthesis and that the response to photoperiod extensions with far-red light may depend on the level of GA.     

Regulation of blue-green algal buoyancy and bloom formation by light,inorganic nitrogen,C02, and trophic level interactions

In highly eutrophic ponds, buoyancy of the gas-vacuolate blue-green alga Anabaenopsis Elenkinii (Miller) was regulated by complex interactions between chemical and physical parameters, as well as by biological interactions between various trophic levels. Algal buoyancy and surface bloom formation were enhanced markedly by decreased light intensity, and to a lesser extent by decreased CO₂ availability and increased availability of inorganic nitrogen. In the absence of dense populations of large-bodied Cladocera, early season blooms of diatoms and green algae reduced light availability in the ponds thus creating conditions favorable for increased buoyancy and bloom formation by A. Elenkinii. The appearance of blue-green algal blooms could be prevented by a reduced density of planktivorous fish, which allowed development of dense cladoceran populations. The cladocerans limited the growth of precursory blooms of diatoms and green algae, and given the resulting clear-water conditions, buoyancy of A. Elenkinii was reduced, and blue-green algal blooms never appeared.