Chlorophyliase (Chlase) is widely distributed in higher and lower plants and differs in activity. It occurs in various organs. In some plants the enzyme is synthesized in cytoplasm, in others in chloroplasts. Various Chlase forms are known. Participation, in the chlorophyll (Chl) degrading systém belongs to the main fimctions of Chlase. Moreover, it may catalyse Chl biosynthesis and takés part in photosynthesis. The Chlase activity is stimulated by radiant energy, sublethal freezing, heavy metals (Hg, Zn, Cu), Fe and Mn deficiency, and mosaic virus infection. The effect of water content on Chlase activity depends on individual plant organs. Osmotic and saline- osmotic stress decreases Chlase activity, but NaCl can stimulate the activity. The influence of plant age depends on plant genus. Some growth regulators (ethylene, heteroauxin, abscisic acid) increase Chlase activity, others (kinetin, dicarboxylic monoesters, gibberellic acid, gibbérellin A3) inhibit it. The mechanisms of Chlase action are also reviewed.
Chloroplasts utilize photons from solar radiation to synthesize energy-rich molecules of ATPs and NADPHs, which are further used in active cellular processes. Multiprotein complexes (MPCs), including photosystems (PSII and PSI), and the cellular architecture responsible for generation of the proton motive force and the subsequent photophosphorylation, mediate the task of ATP and NADPH synthesis. Both photosystems and other multiprotein assemblies are embedded in thylakoid membranes. Advances in techniques used to study structural biology, biophysics, and comparative genomics and proteomics have enabled us to gain insights of structure, function, and localization of each individual component of the photosynthetic apparatus. An efficient coordination among MPCs is essential for normal functioning of photosynthesis, but there are various stressors that might directly or indirectly interact with photosynthetic components and processes. Cadmium is one of the toxic heavy metals that interact with photosynthetic components and damage photosystems and other MPCs in thylakoids. In plants, iron deficiency shows similar symptoms as those caused by Cd. Our article provides a general overview of chloroplast structure and a critical account of Cd-induced changes in photosystems and other MPCs in thylakoids, and suggests the possible mechanisms involved in mediating these changes. The connection between Cd-induced Fe deficiency and the elevated Cd toxicity under the Fe-deficient condition was also discussed., H. Bashir, M. I. Qureshi, M. M. Ibrahim, M. Iqbal., and Obsahuje seznam literatury
A unified multibranched chlorophyll (Chl) biosynthetic pathway is proposed. The proposed pathway takes into account the following considerations: (a) that the earliest putative precursor of monovinyl Chl b that has been detected in higher plants is monovinyl protochlorophyllide b, (b) that in most cases, Chl b biosynthesis has its roots in the Chl a biosynthetic pathway, (c) that the Chl a biosynthetic pathway exhibits extensive biosynthetic heterogeneity, (d) that Chl biosynthesis may proceed differently at different stages of greening and in different greening groups of plants. Integration of the Chl a and b biosynthetic pathways into a unified multibranched pathway offers the functional flexibility to account for the structural and biosynthetic complexity of photosynthetic membranes. In this context, it is proposed that the unified, multibranched Chl a/b biosynthetic pathway represents the template of a Chl-protein biosynthesis center where photosystem (PS) 1, PS2, and light-harvesting Chl-protein complexes are assembled into functional photosynthetic units. The individual biosynthetic routes or groups of two to three adjacent biosynthetic routes may constitute Chl-protein biosynthesis subcenters, where specific Chl-protein complexes are assembled. and C. A. Rebeiz ... [et al.].
Recent experimental evidence (see part 80) suggests that the chlorophyll (Chl) b pathway is biosynthetically heterogeneous. The dissection of this biosynthetic heterogeneity requires the availability of a cell-free system capable of the net synthesis of Chl(ide) a and b. The development of such a system is described. and V. Kolossov ... [et al.].
a1_Photosynthesis is one of the most important processes in plant biology and in the development of new methodologies that allow a better understanding and characterization of the photosynthetic status of organisms, which is invaluable. Flow cytometry (FCM) is an excellent tool for measuring fluorescence and physical proprieties of particles but it has seldom been used in photosynthetic studies and thus the full extent of its potentialities, in this field of research, remains unknown. To determine the suitability of FCM in photosynthesis studies, pea plants were exposed to Paraquat and their status was analyzed during 24 h. FCM was used to evaluate the integrity (volume and internal complexity) and the relative fluorescence intensity (FL) of chloroplasts extracted from those plants. To elucidate which type of information the FL conveys, FL values were correlated with the minimum fluorescence level (F0), maximum fluorescence level (Fm) and maximum photochemical efficiency of PSII (Fv/Fm), obtained by using Pulse-Amplitude-Modulation (PAM) fluorometry. Results indicate that: (1) the biomarkers used to evaluate the structural integrity of the chloroplasts were more sensitive to Paraquat exposure than the ones related to fluorescence; (2) the variation of the chloroplast’s structure, as time progressed, pointed to a swelling and subsequent burst of the chloroplast which, in turn, compromised fluorescence emission; (3) FL presented a high and significant correlation with the Fv/Fm and to a lesser degree with Fm but not with F0; (4) pigment content did not reveal significant changes in response to Paraquat exposure and is in agreement with the proposed model, suggesting that the cause for fluorescence decrease is due to chloroplast disruption., a2_In sum, FCM proved to be an outstanding technique to evaluate chloroplastidal functional and structural status and therefore it should be regarded as a valuable asset in the field of photosynthetic research., E. Rodriguez ... [et al.]., and Obsahuje bibliografii
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