Ginkgo biloba L. is a large tree native in China with evolutionary affinities to the conifers and cycads. However unlike conifers, the gymnosperm G. biloba is not able to synthesize chlorophyll (Chl) in the dark, in spite of the presence of genes encoding subunits of light-independent protochlorophyllide oxidoreductase (DPOR) in the plastid genome. The principal aims of the present study were to investigate the presence of DPOR protein subunits (ChlL, ChlN, ChlB) as well as the key regulatory step in Chl formation: aminolevulinic acid (ALA) synthesis and abundance of the key regulatory enzyme in its synthesis: glutamyl-tRNA reductase (GluTR). In addition, functional stage of photosynthetic apparatus and assembly of pigment-protein complexes were investigated. Dark-grown, illuminated and circadian-grown G. biloba seedlings were used in our experiments. Our results clearly showed that no protein subunits of DPOR were detected irrespective of light conditions, what is consistent with the absence of Chl and Chl-binding proteins (D1, LHCI, LHCIIb) in the dark. This correlates with low ALA-synthesizing capacity and low amount of GluTR. The concentration of protochlorophyllide (Pchlide) in the dark is low and non-photoactive form (Pchlide633) was predominant. Plastids were developed as typical etioplasts with prollamelar body and few prothylakoid membranes. Continual illumination (24 h) only slightly stimulated ALA and Chl synthesis, although Pchlide content was reduced. Prollamelar bodies disappeared, but no grana were formed, what was consistent with the absence of D1, LHCI, LHCIIb proteins. Lightinduced development of photosynthetic apparatus is extremely slow, as indicated by Chl fluorescence and gas exchange measurements. Even after 72 h of continuous illumination, the values of maximum (Fv/Fm) and effective quantum yield (ΦPSII) and rate of net photosynthesis (PN) did not reach the values comparable with circadian-grown plants. and A. Pavlovič ... [et al.].
Low temperature significantly influences chloroplast development and chlorophyll (Chl) biosynthesis, so effect of coldness on Chl content and Chl fluorescence characteristics was investigated in C. bungeana (Chorispora bungeana Fisch. & C.A. Mey). The levels of transcript and protein of an enzymatic step during Chl biosynthesis in response to chilling (4°C) and freezing (-4°C) were also examined in this work. Significant reduction in total Chl content was observed, but the reduction was much less at 4°C than that at -4°C. Moreover, the maximal quantum efficiency of photosystem II (PSII) photochemistry, indicated by Fv/Fm, decreased in the first 12 h, but then started to increase and reached higher levels than the control at 24 h and 48 h at 4°C, but decreased continuously at -4°C. Whereas quantum yield of PSII (ΦPSII) showed no significant difference between the chilling-stressed and the control seedlings, at -4°C, ΦPSII was markedly reduced with the prolonged treatment. In general, there were no significant responses of photochemical quenching (qP) and non-photochemical quenching (NPQ) to cold treatment. Meanwhile, the full-length cDNA of NADPH:protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) was isolated and termed CbPORB (GenBank Accession No. FJ390503). Its transcript and protein content only slightly declined at 4°C, but dramatically reduced at -4°C with the time. These results strongly suggest that CbPORB possesses certain resistant characteristics and is a major player in Chl biosynthesis process involved in plant growth and development of C. bungeana under cold environmental conditions. and Y. H. Li ... [et al.].
In the present studies, we have found a fragment of amino acid sequence, called TFT motif, both in light-dependent protochlorophyllide oxidoreductase (LPOR) and in the L subunit of dark-operative (light-independent) protochlorophyllide oxidoreductases (DPOR). Amino acid residues of this motif shared similar physicochemical properties in both types of the enzymes. In the present paper, physicochemical properties of amino acid residues of this common motif, its spatial arrangement and a possible physiological role are being discussed. This is the first report when similarity between LPOR and DPOR, phylogenetically unrelated, but functionally redundant enzymes, is described., M. Gabruk ... [et al.]., and Obsahuje bibliografii