Effects of high irradiance (HI) treatment on chloroplast pigment bleaching and on low temperature excitation and emission fluorescence spectra were studied in thylakoids isolated from 3- or 24-h greening cucumber cotyledons of etiolated seedlings. Irradiation of thylakoids isolated from 3-h greening seedlings with HI (approx. 3500 pmol m'^ s'*) caused chlorophyll (Chl) and carotenoid (Car) breakdown with the initial rates 3.0 and 4.2 mg m’^ s'*, respectively, whereas these values were 1.3 and 0.8 mg m-^ s'^ respectively, in thylakoids isolated from 24-h greening cotyledons. The photosusceptibility decreased in the sequence: protochlorophyll(ide), P-carotene, xanthophylls, Chl a, Chl b. In control seedlings the ratio E472/E437 or E486/E437 was 1.7-1.8-fold higher at the later phase than at the early phase of greening whereas the ratio F730/F684 reached approx. 0.40 or approx. 1.65 after 3- or 24-h greemng, respectively. Treatment of isolated thylakoids with high photon flux density caused a relative increase of the 472 and 486 nm band intensities in the excitation fluorescence spectrum of Chl, whereas the ratio F730/F684 increased only at the later phase investigated.
Little data on the role played in vivo by chloroplast protein AtDeg2 as a chaperone is available. Therefore, we sought for chloroplast proteins protected from high irradiance-induced interprotein aggregation via disulphide bridges by AtDeg2 acting as a holdase. To reach this goal, we performed analyses which involved comparative diagonal electrophoreses of lysates of chloroplasts isolated from wild type (WT) plants and transgenic plants 35S:AtDEG2ΔPDZ1-GFP which expressed AtDeg2 lacking its chaperone activity but retaining the protease activity. The results of the analyses indicate that AtDeg2 acting as a holdase prevents a single chloroplast protein, i.e., the γ1 subunit of ATP synthase from long-term high irradiance-induced homodimerization mediated by disuplhide bridges and this allows us to better understand a complexity of physiological significance of AtDeg2 - the chloroplast protein of dual protease/chaperone activity.
Many RNA recognition motif (RRM)-containing proteins are known to exist in chloroplasts. Major members of the RRM protein family, which are chloroplast ribonucleoproteins (cpRNPs), have been investigated in seed plants, including tobacco and Arabidopsis thaliana, but never in early land plants, such as bryophytes. In this study, we surveyed RRM proteins encoded in the moss Physcomitrella patens genome and predicted 25 putative chloroplast RRM proteins. Among them, two RRM-containing proteins, PpRBP2a and PpRBP2b, resembled cpRNPs and were thus referred to as cpRNP-like proteins. However, knockout mutants of either one or two PpRBP2 genes exhibited a wild type-like phenotype. Unlike Arabidopsis cpRNPs, the levels of mRNA accumulation in chloroplasts were not affected in the PpRBP2 knockout mutants. In addition, the efficiency of RNA editing was also not altered in the mutants. This suggests that PpRBP2a and 2b may be functionally distinct from Arabidopsis cpRNPs., H. Uchiyama, M. Ichinose, M. Sugita., and Obsahuje bibliografické odkazy
Development of mesophyll cell chloroplasts during ontogeny of second wheat (Triticum aestivum L.) leaf was compared in plants grown in Ml nutrient solution (+N) and in nutrient solution without nitrogen (-N). Chloroplast size and ultrastructure were evaluated quantitatively by means of transmission electron microscopy and stereology. In -N plants compared to +N ones, the life spán of the second leaf was shortened and chloroplast development modified; the most striking feature was the accumulation of starch. Moreover, mature chloroplasts of -N plants were smaller and had smaller relative partial volume of thylakoids and larger relative partial volume of plastoglobules than those of +N plants.
Glechoma longituba (Nakai) Kupr. is a perennial shade plant with pharmaceutical importance. The aim of this study was to investigate the effects of light intensity on the growth, photosynthesis, and accumulation of secondary metabolites in G. longituba grown under six different light environments. The high light intensity decreased the leaf size, specific leaf area, and aboveground dry mass, the number of grana per chloroplast, the number of lamella per granum, the thickness of the grana, the apparent quantum efficiency, the chlorophyll (Chl) content, the concentrations of ursolic and oleanolic acid. The high light increased the stomatal density, the stoma size, the number of chloroplast per a cell, the chloroplast size, the dark respiration rate, the light saturation point, the light compensation point, and the Chl a/b ratio. With the reduction in the light intensity, the light-saturated net photosynthetic rate, the aerial dry mass per plant, and the yields of ursolic and oleanolic acid decreased after an initial increase, peaking at 16 and 33% of sunlight levels. Overall, the 16 and 33% irradiance levels were the most efficient in improving the yields and qualities of the medicinal plant. The lower light demand and growth characteristics suggest that G. longituba is an extremely
shade-tolerant plant and that appropriate light intensity management might be feasible to obtain higher yields of secondary metabolites in agricultural management., L. X. Zhang, Q. S. Guo, Q. S. Chang, Z. B. Zhu, L. Liu, Y. H. Chen., and Obsahuje bibliografii
Differences between sun (E) and shaded (S) foliage were studied in a Norway spruce (Picea abies [L.] Karst.) stand. Response curves describing the dependence of the CO2 assimilation rate (PN) on the CO2 concentration at the catalytic site of ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO (PN-Cc) were estimated using the simultaneous measurements of chlorophyll fluorescence and leaf gas exchange. Higher PN, higher electron transport (Ja), higher carboxylation capacity (Vc), and higher RuBPCO activity (τ) for sun acclimated needles was found. The S-needles had higher portion of internal limitation and higher CO2 compensation concentration (Γ) than the E-needles. Because higher degree of limitation of photosynthesis by carboxylation was ascertained, it can be assumed that photosynthesis in shade foliage is limited mainly by lower carboxylation capacity and by low chloroplastic CO2 concentration. and I. Priwitzer ... [et al.].
Changes in chloroplastidic pigments, gas exchange and carbohydrate concentrations were assessed during the rapid initial expansion of C. guianensis leaflet. Leaves at metaphyll stage were tagged and assessments were carried out 14, 17, 20, 23, 27, and 31 days later. Pigments synthesis, distribution and accumulation were uniform among leaflet sections (basal, median and apical). Chlorophyll (Chl) a, Chl b, Chl (a+b), and total carotenoids (Car) concentrations were significantly increased after 27 days from metaphyll, and the most expressive increases were parallel to lower specific leaflet area. Chl a/b was lower on day 14 and it was increased on subsequent days. Negative net photosynthesis rate (PN), and the lowest stomatal conductance (gs) and transpiration (E) were registered on day 14, following significant increases on subsequent days. The Chl (a+b) and Chl a effects on PN were more expressive until day 20. Intercellular to ambient CO2 concentration ratio (Ci/Ca) was higher on day 14 and lower on subsequent days, and no stomatal limitation to CO2 influx inside leaflets was observed. Leaflet temperature was almost constant (ca. 35°C) during leaflet development. Sucrose and starch concentrations were increased in parallel to increases in PN. Altogether, these results highlight the main physiological changes during C. guianensis leaflet expansion and they should be considered in future experiments focusing on factors affecting PN in this species. and F. K. C. Moraes ... [et al.].
The addition of chymostatin (100 mg m'^) to the extraction and desalting media for phosphoenolpyruvate carboxylase (EC 4.1.1.31) from Zea mays L. and Setaria verticillata (L.) Beauv. (C4-plants) affected profoundly the kinetics of the enzymic activity, the rate curve became considerably more sigmoid than that of the control and, therefore, the activity at low phosphoenolpyruvate levels was much reduced. Also, the sensitivity towards malate inhibition was substantially increased in both the day and night forms of the enzyme. The above effects were observed at pH 7.0, but not at pH 8.0. Glucose-6-phosphate (5 mM in extraction and desalting media) partly counteracted the effect of chymostatin on malate sensitivity. Hence chymostatin affected directly or indirectly the enzymic dimer/tetramer equilibrium in favour of the dimer.The addition of chymostatin (100 mg m'^) to the extraction and desalting media for phosphoenolpyruvate carboxylase (EC 4.1.1.31) from Zea mays L. and Setaria verticillata (L.) Beauv. (C4-plants) affected profoundly the kinetics of the enzymic activity, the rate curve became considerably more sigmoid than that of the control and, therefore, the activity at low phosphoenolpyruvate levels was much reduced. Also, the sensitivity towards malate inhibition was substantially increased in both the day and night forms of the enzyme. The above effects were observed at pH 7.0, but not at pH 8.0. Glucose-6-phosphate (5 mM in extraction and desalting media) partly counteracted the effect of chymostatin on malate sensitivity. Hence chymostatin affected directly or indirectly the enzymic dimer/tetramer equilibrium in favour of the dimer.