Differential accumulation of plastid transcripts encoding photosystem II components in the mesophyll and bundle-sheath cells of monocotyledonous NADP-malic enzyme-type C4 plants.

As a first step in understanding the differential expression of the plastid-encoded photosystem II (PSII) genes in mesophyll and bundle-sheath cells, we have used RNA blotting techniques to investigate the transcript patterns of these genes in three NADP-malic enzymetype C4 species: Zea mays L., Sorghum bicolor (L.) Moench and Pennisetum americanum (L.) Leeke. Our comparison showed that in all three species the relative levels of transcripts encoding PSII proteins were diminished in bundle-sheath cells. No major differences, either in abundance or in the processing pathways, could be detected for transcripts encoding subunits of the PSI and ATP-synthase complexes. The transcript profiles of the psbB and psbD/C transcription units were particularly striking. These operons were of heterogeneous composition, i.e. they encode PSII subunits as well as proteins or RNAs which are involved in different functional entities. The transcript patterns of the psbB and psbD/C transcription units were complex and characterized by multiple, partially overlapping RNAs. Our analysis showed that the relative levels of the oligocistronic PSII transcripts derived from these transcription units with the exception of psbH were selectively reduced in bundlesheath cells. In contrast, RNAs carrying the non-PSII components were present in similar quantities in the two cell types. The data demonstrate that segmental RNAs within one single transcription unit can accumulate to different degrees. Regulatory mechanisms which may explain this expression behaviour are discussed.

Differential biogenesis of photosystem-II in mesophyll and bundle-sheath cells of 'malic' enzyme NADP(+)-type C4 plants. A comparative protein and RNA analysis.

We have investigated the photosystem-II organization in differentiating-bundle-sheath cells of the three malate dehydrogenase (oxaloacetate decarboxylating) (NADP+)-type C4 species maize, Sorghum and Pennisetum. Using a set of nine different antisera raised against individual subunits of photosystem-II, we demonstrate that photosystem-II components constitute a substantial part of the thylakoid membranes of young bundle-sheath chloroplasts. The abundance of subunits of the photosystem-II core, i.e. the 47-and 43-kDa chlorophyll-a-binding proteins, polypeptides D1 and D2, cytochrome b559, and the 34-kDa polypeptide, varies with the developmental state of the plant. However, the levels of the 23-kDa, 16-kDa and 10-kDa extrinsic polypeptides of the water-oxidation complex are drastically reduced in bundle-sheath chloroplasts of all three species analyzed, regardless of their state of differentiation. The reduction in protein abundance is also reflected at the transcript level: only traces of the nuclear-encoded mRNAs are found in differentiating bundle-sheath cells of Sorghum, suggesting that the transcription of these genes has been switched off. Our data are compatible with the idea that the water-oxidation complex is a prime site for initiating or maintaining the process leading to photosystem-II depletion during differentiation of bundle-sheath cells.

Chloramphenicol Stimulates the Accumulation of Light-Harvesting Chlorophyll a/b Protein II by Affecting Posttranscriptional Events in the Chlorina CD3 Mutant Wheat.

The levels of total chlorophyll (Chl), total carotenoids, light-harvesting Chl a/b apoprotein of photosystem II (LHCPII), and light-harvesting Chl a/b apoprotein (LHCP) mRNA were examined in the CD3 chlorina mutant wheat (Triticum aestivum, L.) after 18 hours greening at either a low (3 micromoles of photons per square meter per second) or moderate (200 micromoles of photons per square meter per second) irradiance. The Chl b and LHCPII deficient mutant wheat accumulated significantly greater levels of Chl and LHCPII when greened under low irradiance than when greened under a moderate irradiance level. The level of LHCP mRNA, as measured by dot-blot and Northern hybridization analyses to a cDNA probe, increased in response to the irradiance level in the wheat. Applications of chloramphenicol (CAP) to the mutant wheat increased total Chl, Chl b, and LHCPII accumulations at both irradiance levels. Even though the CAP-treated CD3 mutant wheat accumulated similar levels of plastid pigments as those of CAP-treated wild type, the LHCPII amounts were much higher in the wild type than in the CD3 mutant of wheat. CAP treatment did not significantly increase the LHCP mRNA level in either wheat. Applications of either benzyladenine or CAP to the mutant, greened under the moderate irradiance level for 72 hours, increased all plastid pigment levels except for beta-carotene. The benzyladenine plus CAP combination treatment had little effect on the LHCPII levels in the wild-type wheat. The combination treatment increased the LHCPII accumulation in the CD3 mutant of wheat by about twice that of the untreated mutant. Excess LHC pigment accumulation was promoted in each wheat line. We conclude that the regulation of LHCPII in the CD3 mutant of wheat is controlled by a posttranscriptional event. Furthermore, the accumulation of LHC bound pigments is not coupled with the accumulation of LHCPII in wheat thylakoid membranes.

Light Quality and Irradiance Level Interaction in the Control of Expression of Light-Harvesting Complex of Photosystem II: Pigments, Pigment-Proteins, and mRNA Accumulation.

Effects of red and blue light at irradiances from 1.6 to 28.3 micromolar per square meter per second on chloroplast pigments, light-harvesting pigment-proteins associated with photosystem II, and the corresponding mRNA were evaluated in maize (Zea mays L.) plants (OP Golden Bantum) grown for 14 days under 14 hours light/10 hours dark cycles. Accumulation of pigments, pigment-proteins, and mRNA was less in blue than in red light of equal irradiance. The difference between blue and red light, however, varied as a function of irradiance level, and the pattern of this variation suggests irradiance-controlled activation/deactivation (switching) of blue-light receptor. The maximum reduction in blue light of mRNA and proteins associated with light-harvesting complex occurs at lower irradiance levels than the maximum reduction of chlorophylls a and b.

Light quality effects on corn chloroplast development.

Corn was grown under greenhouse and controlled light quality conditions incluing full spectrum, red (R), and far-red (FR) sources. Young leaf samples were analyzed for pigments, pigment-proteins, membrane polypeptides, and ultrastructure. Chloroplast development in full spectrum white light was similar to that found in R but different from that found in FR plus low R. Compared to greenhouse and R, FR plus low R (670-760) repressed the formation of photosystem I reaction center protein (CP1 + CP1a) and enhanced those of photosystem II (CPa) in both bundle sheath and mesophyll cells. Photosystem II polypeptides were present in both cell types, with the 46 and 34 kilodalton proteins predominant in mesophyll cells. Bundle sheath cells contained relatively more of the 51 kilodalton and less of the 46 kilodalton proteins. However, they also contained measurable amounts of ribulose bisphosphate carboxylase which may interfere with estimates of the 51 kilodalton protein.

A Comparison of Pigment-Protein Complexes among Normal, Chlorophyll-Deficient and Senescent Soybean Genotypes.

Pigment-protein complexes were isolated from chloroplasts of normal green and several types of chlorophyll-deficient soybeans. The complexes were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and comparisons were made between normal and chlorophyll-deficient genotypes of the relative amounts of chlorophyll associated with Photosystem I (PSI), Photosystem II (PSII), light-harvesting, and free pigment complexes.Chlorophyll-deficient genotypes, compared to normal green genotypes, have fewer light-harvesting complexes and a higher ratio of PSII to PSI complexes. Chlorophyll associated with PSII in yellow genotypes is in relatively higher amounts in spite of the fact that these genotypes have much less grana stacking than normal green genotypes. Although PSII activity has been associated with appressed regions of grana in normal plants, our work shows that the association does not always hold true.

Pigment analysis of chloroplast pigment-protein complexes in wheat.

Pigment-protein complexes separated from wheat (Triticum aestivum L. selection ND96-25 by two gel electrophoresis techniques were analyzed by high-performance liquid chromatography for chlorophylls and carotenoids. The two techniques are compared, and pigment analyses are given for the major reaction centers and light-harvesting complexes. Reaction centers contain mostly chlorophyll a, carotene, and lutein, whereas light-harvesting complexes contain chlorophyll a, chlorophyll b, lutein, and neoxanthin. The amounts of violaxanthin are variable.

Genetic control of chloroplast pigment development in soybeans as a function of leaf and plant maturity.

Changes in the major chloroplast pigments of pigment-deficient genotypes of soybeans were studied as a function of leaf age and plant age. The trends of pigment development are plotted as a function of relative leaf age at two periods of plant development. Comparisons are made between aging leaves from different nodes and leaves of different ages from the same node. In addition, trends of pigment development are expressed as a ratio of pigment-deficient/normal genotypes for five different genotypes and seven sampling periods. Those genotypes that exhibit a lag in production of pigments during leaf development show a similar lag in overall plant pigment development.