Photosynthetic characteristics of detached barley leaves during greening in the presence of SAN 9785

The effects of the pyridazinone compound SAN 9785 on the photosynthetic competence of leaves, on the photochemical activity of isolated thylakoids and on the formation and spectral properties of chlorophyll-protein complexes were studied during a 72-h greening period of detached etiolated leaves of barley (Hordeum vulgare L. cv. Horpácsi kétsoros). It was established that i) the photosynthetic capacity of the leaves decreased considerably (by 80 and 90%, as determined by¹⁴CO₂ fixation and fast fluorescence induction measurements, respectively); ii) the photochemical activity of isolated thylakoids from water to potassium ferricyanide and from dichlorophenol indophenol/ascorbate to methylviologen exhibited only slight reductions when expressed on a chlorophyll basis compared with the control; iii) the slow fluorescence induction curves of the treated leaves demonstrated the presence of a peculiar fluorescence component interrupting the quenching of fluorescence at around 1 min illumination; iv) a shortage of the chlorophyll-protein complex of photosystem I (CPI) occurred with a higher content of the monomer of the light harvesting complex in the thylakoids of treated leaves; and v) the fluorescence spectrum of the CPI band present in treated leaves indicates the destruction of the structural integrity of this complex during isolation from the membrane.Abbreviations Chl chlorophyll - CPI, CPII chlorophyll-protein complexes of the reaction centres of PSI and PSII - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DPIP 2,6-dichlorophenol indophenol - DPIPH₂ chemically reduced form of DPIP - F _o fluorescence of constant yield - F _v fluorescence of variable yield - F _i ,F _m mitial and maximum yield of fluorescence - LHCP³ monomer of the light-harvesting complex - LHCP² and LHCP¹ oligomers of the light-harvesting complex LHCP³ - PSI, PSII photosystems I, II - SAN 9785 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone, also known as BASF 13-338 - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis     

Hydrogen-peroxide-scavenging systems within pea chloroplasts

The subcellular distribution of ascorbate peroxidase and glutathione reductase (EC 1.6.4.2) in pea leaves was compared with that of organelle markers. Enzyme distribution was found to be similar to that of the chloroplast enzyme NADPH-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13). Isolated chloroplasts showed a close correlation between intactness and the percentage of enzyme activity recovered. Chloroplasts of 85% intactness were found to contain a high proportion of leaf dehydroascorbate reductase activity (EC 1.8.5.1), 10% of leaf glutathione and 30% of leaf ascorbate. These results are discussed in relation to the potential role of chloroplast antioxidant systems in plant resistance to environmental and other stress conditions.Abbreviations GSH reduced glutathione - GSSG oxidized glutathione - NADPH-GPD glyceraldehyde-3-phosphate dehydrogenase - SOD superoxide dismutase     

Tobacco-mosaic-virus-induced increase in abscisic-acid concentration in tobacco leaves:

The concentrations of free and bound abscisic acid (ABA and the presumed ABA glucose ester) increased three- to fourfold in leaves of White Burley tobacco (Nicotiana tabacum L.) systemically infected with tobacco mosaic virus. Infected leaves developed a distinct mosaic of light-green and dark-green areas. The largest increases in both free and bound ABA occurred in dark-green areas. In contrast, virus accumulated to a much higher concentration in light-green tissue. Free ABA in healthy leaves was contained predominantly within the chloroplasts while the majority of bound ABA was present in non-chloroplastic fractions. Chloroplasts from light-green or dark-green tissues were able to increase stromal pH on illumination by an amount similar to chloroplasts from healthy leaf. It is unlikely therefore that any virus-induced diminution of pH gradient is responsible for increased ABA accumulation. Tobacco mosaic virus infection had little effect on free ABA concentration in chloroplasts; the virus-induced increase in free ABA occurred predominantly out-side the chloroplast. The proportional distribution of bound ABA in the cell was not changed by infection. Treatment of healthy plants with ABA or water stress increased chlorophyll concentration by an amount similar to that induced by infection in dark-green areas of leaf. A role for increased ABA concentration in the development of mosaic symptoms is suggested.Abbreviations ABA abscisic acid - TMV tobacco mosaic virus     

Rates of synonymous substitution in plant nuclear genes

Summary The rate of synonymous nucleotide substitution in nuclear genes of higher plants has been estimated. The rate varies among genes by a factor of up to two, in a manner that is not immediately explicable in terms of base composition or codon usage bias. The average rate, in both monocots and dicots, is about four times higher than that in chloroplast genes. This leads to an estimated absolute silent substitution rate of 6 × 10^–9 substitutions per site per year that falls within the range of average rates (2–8 × 10^–9) seen in different mammalian nuclear genomes.     

Chloroplast DNA variation inAnemone s. lato (Ranunculaceae)

Chloroplast DNA of seven species belonging toAnemone (sectt.Omalocarpus, Anemonidium, andAnemonanthea),Hepatica, andPulsatilla have been analyzed by restriction enzymes. According to the dendrogram constructed, the sections ofAnemone and the generaHepatica andPulsatilla seem to be evolutionary approximately equidistant to each others. This supports the concept that these groups should be treated on a similar taxonomic level, either as genera or subgenera.     

Evolutionary analysis of Pinus densata (Masters), a putative Tertiary hybrid.

Summary Restriction fragment analysis and heterologous hybridization of chloroplast (cp) DNA was used to develop species-specific markers for P. tabulaeformis, P. yunnanensis and P. massoniana. Fragment patterns created by the BclI and DraI restriction enzymes and hybridization patterns to the psbC and psbD probes were distinctive among the three species. No intraspecific variation was detected with respect to any of the cpDNA markers developed in this study. The cpDNA markers obtained were subsequently used to examine the parentage of P. densata, a putative Tertiary hybrid between P. tabulaeformis and P. yunnanensis. The analysis demonstrated for the first time that P. densata populations accommodate chloroplast genomes of P. tabulaeformis and P. yunnanensis, which strongly supports earlier suggestions of the hybrid origin of this species. It appears that P. densata represents a stabilized natural hybrid that has become adapted to high mountain environments where neither of the parental species can normally grow.     

Chloroplast DNA in Pinus monticola

Summary Within-species variability of a restriction site in the chloroplast (cp) DNA in Pinus monticola has been surveyed. Frequencies of two variants of the cp genome are significantly different in interior versus coastal populations. Paternal inheritance of the cp genome predominates, though some individuals have both variants of the genome. The presence of heteroplasmic individuals indicates occasional biparental inheritance.     

High transmission of paternal plastid DNA in alfalfa plants demonstrated by restriction fragment polymorphic analysis

Summary A high frequency of paternal plastid transmission occurred in progeny from crosses among normal green alfalfa plants. Plastid transmission was analyzed by hybridization of radiolabeled alfalfa plastid DNA (cpDNA) probes to Southern blots of restriction digests of the progeny DNA. Each probe revealed a specific polymorphism differentiating the parental plastid genomes. Of 212 progeny, 34 were heteroplastidic, with their cpDNAs ranging from predominantly paternal to predominantly maternal. Regrowth of shoots from heteroplasmic plants following removal of top growth revealed the persistence of mixed plastids in a given plant. However, different shoots within a green heteroplasmic plant exhibited paternal, maternal, or mixed cpDNAs. Evidence of maternal nuclear genomic influence on the frequency of paternal plastid transmission was observed in some reciprocal crosses. A few tetraploid F₁ progeny were obtained from tetraploid (2n=4x=32) Medicago sativa ssp. sativa x diploid (2n=2x=16) M. sativa ssp. falcata crosses, and resulted from unreduced gametes. Here more than the maternal genome alone apparently functioned in controlling plastid transmission. Considering all crosses, only 5 of 212 progeny cpDNAs lacked evidence of a definitive paternal plastid fragment.Contribution No. 89-524-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan