Formation Of Pigment-protein Complexes Research Articles

In vivo spectroscopy and internal optics of leaves as basis for remote sensing of vegetation

Abstract In vivo reflection spectra of intact bean leaves (Phaseolus vulgaris) were measured between 400 and 800 nm under remote sensing conditions (illumination with white light, detection of a narrow angle of the reflected light) using the VIRAF spectrometer. The leaves with colours from yellow to green were chosen at different times during light-induced greening. The colours of the leaves were characterized by the chromaticity coordinates according to CIE 1931 calculated from the reflection spectra. The influence of the absorption of chlorophyll—the main pigment of green leaves—on the reflection spectrum of leaves is outlined. The shape of the in vivo reflection spectra is interpreted taking into account (a)the formation of pigment-protein complexes, (b) the sieve effect and the detour effect, as well as (c) the reflection, refraction and scattering of light inside the leaf tissue. Reflection signals at several distinct wavelengths and their ratios as well as the inflection point of the reflection ris...

Oxygen tension regulated expression of the hemA gene of Rhodobacter capsulatus

The promoter of the Rhodobacter capsulatus hemA gene, coding for the enzyme δ-aminolevulinic acid synthase (ALAS), was identified by trans-complementation of a δ-aminolevulinic acid (ALA)-dependent mutant and found to be located within a 170 bp region proximal to the hemA gene. The activity of the hemA promoter was demonstrated by lacZ fusion and in vitro transcription-translation. An open reading frame (ORFX) was found downstream of hemA. The activity of the hemA promoter, but not that of the ORFX promoter, increased when oxygen tension was lowered in the culture. Deletions upstream of the hemA promoter region did not affect ALAS activity and formation of pigment-protein complexes in R. capsulatus.

Light and oxygen effects share a common regulatory DNA sequence in Rhodobacter capsulatus

External factors regulate the formation of pigment protein complexes in facultatively photosynthetic bacteria. The puf operon of Rhodobacter capsulatus encodes the pigment binding proteins of the reaction centre and light-harvesting I complex. Here we demonstrate that a single base-pair exchange within a sequence of dyad symmetry upstream of the puf promoter affects both the oxygen regulation and the light regulation of the formation of reaction-centre and light-harvesting I complexes in Rhodobacter capsulatus. Our results imply that effects of oxygen or light ultimately act on the same regulatory DNA sequence, although it is still unknown how these environmental signals are sensed and transmitted to a transcriptional regulator.

Endonucleolytic degradation of puf mRNA in Rhodobacter capsulatus is influenced by oxygen.

The formation of pigment-protein complexes in facultatively photosynthetic bacteria is regulated by the oxygen tension in the culture. It is shown that the degradation of some mRNA species encoding components of the photosynthetic apparatus is affected by oxygen. The puf mRNA segment, encoding the pigment-binding proteins of the reaction center, and the 0.5-kb puc mRNA species, encoding pigment-binding proteins of the light-harvesting LHII antenna complex of Rhodobacter capsulatus were degraded more rapidly under high oxygen tension than under low oxygen tension. Studies on strains having deletions or insertions in the puf operon indicate that rate-limiting endonucleolytic cleavage in the reaction center coding region of the polycistronic puf mRNA was influenced by growth conditions. However, other mRNA segments, for which exonucleolytic degradation was postulated to be rate-limiting, decayed with the same rate under either high or low oxygen tension. Likewise, the degradation of the puhA mRNA, the cycA mRNA, and the cytfbc mRNA was found to be independent of the oxygen tension in the culture. The data strongly suggest that specific mRNA sequences or structures are responsible for the observed oxygen effect on mRNA stability.

Herbicides which Inhibit Electron Transport or Produce Chlorosis and Their Effect on Chloroplast Development in Radish Seedlings II. Pigment Excitation, Chlorophyll Fluorescence and Pigment-Protein Complexes

Abstract DCMU, bentazon, amitrole and SAN 6706 affected the formation of the pigment-protein complexes and caused drastic alterations in the absorption of light and in the transfer of the absorbed energy in the antennae systems. Bentazon and DCMU, photosystem II inhibitors, did not change the pigment absorption and fluorescence excitation spectra. After application of both herbicides the long wavelength fluorescence emission band at 740 nm was reduced similar as in young developing leaves. Although DCMU and bentazon inhibit the photosynthetic electron transport at the same site, bentazon mainly suppressed the formation of the photosystem I complexes CP 1 a and CP 1 while DCMU mainly reduced the photosystem II complex CPa. Bentazon specifically enhanced the formation of LHCP3. This may be important for the increased grana stacking in plastids from bentazon treated plants. The bleaching herbicides amitrole and SAN 6706 inhibited the formation of carotenoids leading to an accumulation of lycopene, phytofluene and phytoene, while the accumulation of chlorophylls was suppressed. This bleaching effect was most pronounced during growth under higher intensities of light. In weak light (100 lux) amitrole reduced the long wavelength fluorescence maximum but the fluorescence excitation was not affected. With amitrole at 2000 lux and SAN 6706 at 100 lux the long wavelength emission band was further decreased and the fluorescence excitation spectra point to a less efficient energy transfer to chlorophyll a. The fluorescence spectra changed due to herbicide treatment resembled those of not yet fully developed leaves. In contrast to the photosystem II herbicides the bleaching herbicides amitrole and SAN 6706 had a similar effect on the formation of pigment-protein complexes. After growth at 2000 lux both herbicides suppressed the formation of the photosystem I complex CP 1 a and the photosystem II complex CPa. At 100 lux only the formation of CPla was affected. Except for DCMU all herbicides assayed primarily changed the formation of photosystem I.