Formation of functionally active chloroplasts is determined at a limited stage of leaf development in virescent mutants of rice

The ability to form functionally active chloroplasts is determined at a certain early stage of leaf development in three non-allelic temperature-sensitive virescent mutants of rice. Temperature-shift analysis, together with anatomical observations, indicates that the intrinsic developmental signals of the virescent genes are expressed at the stage immediately following the formation of basic leaf structure, but just before the onset of leaf elongation. These signals control the expression of chloroplast-encoded genes but do not affect the subsequent morphological development of the leaf or the photo-regulation of the expression of nuclear genes encoding chloroplast proteins.     

Sequence,proposed secondary structure,and phylogenetic analysis of the chloroplast 5S rRNA gene of the brown alga Pylaiella littoralis (L.) Kjellm

Summary The chloroplast 5S rRNA gene of the brown alga Pylaiella littoralis (L.) Kjellm has been cloned and sequenced. The gene is located 23 bp downstream from the 3 end of the 23S rRNA gene. The sequence of the gene is as follows: GGTCTTG GTGTTTAAAGGATAGTGGAACCACATTGAT CCATATCGAACTCAATGGTGAAACATTATT ACAGTAACAATACTTAAGGAGGAGTCCTTT GGGAAGATAGCTTATGCCTAAGAC. A secondary structure model is proposed, and compared to those for the chloroplast 5S rRNAs of spinach and the red alga Porphyra umbilicalis. Cladograms based on chloroplast and bacterial 5S rRNA and rRNA gene sequences were constructed using the MacClade program with a user-defined character transformation in which transitions and transversions were assigned unequal step values. The topology of the resulting cladogram indicates a polyphyletic origin for photosynthetic organelles.Offprint requests to: S. Loiseaux-de Goër     

Light dependence of protoplasmic streaming in Nitella flexilis L. as measured by means of laser-velocimetry

Laser-velocimetry was applied in order to study the effect of light on the velocity of protoplasmic streaming (pps) in Characean cells. A change from dark to light (= 6 W · m^–2) leads to an acceleration of streaming by about 15–30% with a time-constant of approx. 300 s. The transition from light to dark causes a transient decrease of velocity below the original dark level. This response occurs with a time constant of about 500 s. It returns to its initial value with a time-constant of about 2000 s. This may indicate that a control loop of cytosolic homeostasis takes a decrease in pCa more seriously than an increase. A possible involvement of temperature effects caused by illumination was excluded by measuring the influence of temperature. Steady-state velocity of streaming changed by 5% per 1° C. Irradiation with infra-red light ( > 780 nm) did not cause a change in velocity. The absence of a light effect on streaming velocity in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) shows that photosynthesis and not phytochrome is involved. The role of light-induced changes of pCa is discussed, especially with respect to the hypothesis of Vanselow and Hansen (1989, J. Membr. Biol. 110, 175–187) that photosynthesis acts on the plasmalemma K⁺-channel via light-induced uptake of Ca²⁺ into the chloroplasts.Abbreviations and Symbols ASF auto structure function - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - pps protoplasmic streaming - _L, _D, _C time-constants of the light and dark responses, and of a putative Ca-control system Financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged. The first author was granted a scholarship by the state of Schleswig-Holstein. We are indebted to Prof. Dr. G. Pfister for technical advice and helpful discussions and to Mrs. E. Götting for drawing the figures.     

Photoinduction of formation of circular structures by microfilaments on chloroplasts during intracellular orientation in protonemal cells of the fernAdiantum capillus-veneris

Summary Changes in the organization of cortical actin microfilaments during phytochrome-mediated and blue light-induced photoorientation of chloroplasts were investigated by rhodamine-phalloidin staining in protonemal cells of the fernAdiantum capillusveneris. Low- and high-fluence rate responses were induced by partial irradiation of individual cells with a microbeam of 20 m in width. In the low-fluence rate responses to red and blue light, a circular structure composed of microfilaments was induced on the chloroplast concentrated in the irradiated region, on the side facing the plasma membrane, as already reported in the case of the low-fluence rate response induced by polarized red or blue light. Such a structure was not observed on the chloroplasts located far from the microbeam. Time-course studies revealed that the structure was induced after the chloroplasts gathered in the illuminated region and that the structure disappeared before chloroplasts moved out of this region when the microbeam was turned off. In the high-fluence rate response to blue light, chloroplasts avoided the irradiated site but accumulated in the shaded area adjacent the edges of microbeam. The circular structure made of microfilaments was also observed on the chloroplasts gathered in the area and it showed the same behavior with respect to its appearance and disappearance during a light/dark regime as in the case of the low-fluence rate response. However, no such circular structure was observed in the high-fluence rate response to red light, in which case the chloroplasts also avoided the illuminated region but no accumulation in the adjacent areas was induced. These results indicate that the circular structure composed of microfilaments may play a role in the anchorage of the chloroplast during intracellular photo-orientation.     

中国大麦叶绿体DNA和核糖体RNA基因限制性片段长度多型性

本文报道了我们对我国不同大麦区80份大麦品种叶绿体DNA和核糖体RNA基因限制性片段长度多型性的研究。结果表明:rDNA间隔序列长度存在丰富的多样性,80份材料中出现了8种长度变异炎型共组成8种表现型。长度变异类型及其表现型在地理分布上存在着明显的区域性。推测这种分布上的地区性与植物对环境的适应性有关。所用的两个叶绿体DNA克隆片段未检测到限制性片段长度多型性,说明栽培大麦叶绿体DNA变异程度低。     

Mode of action of Photosystem II herbicides studied by thermoluminescence

The mode of action of chemically different herbicides (ureas, pyridazinones, phenylcarbamates, triazines, hydroxyquinolines, hydroxybenzonitriles and dinitrophenols) on photosynthetic electron transport was investigated by measurements of oxygen evolution and thermoluminescence. Depending on the particular herbicide used the thermoluminescence band related to Q (the primary acceptor of Photosystem II) appears at +5, 0 or −14°C. It was shown that these three different peak positions can be ascribed to various redox states of Q, the shifts being due to the binding of herbicides to the chloroplast membrane. Both displacement experiments and additive inhibition of herbicide pairs measured by thermoluminescence and oxygen evolution suggested that the sites of action of these herbicides are on the same protein. However, herbicide treatment of trypsinized chloroplasts showed that there were three different binding sites on the same protein, in agreement with the classification of herbicides into three groups based on thermoluminescence measurements. Our results suggest that the primary and secondary acceptors of Photosystem II (Q and B, respectively) are in close proximity and form a common complex with the herbicide-binding protein within the chloroplast membrane.     

Proton-induced grana formation in chloroplasts. Distribution of chlorophyll-protein complexes and Photosystem II photochemistry

Lowering the pH of the incubation medium to pH 5.4 leads to grana formation morphologically similar to that induced by metal cations. The same phenomenon is observed in EDTA-washed chloroplasts, indicating that it is not due in part to electrostatic ‘masking’ by residual cations associated with the membranes. Digitonin fractionation studies have indicated that the distribution of the major chlorophyll-protein complexes between granal and stromal membrane regions is similar at pH 5.4 in the absence of Mg²⁺, and at pH 7.4 in the presence of Mg²⁺. Chlorophyll fluorescence induction studies have indicated that the primary photochemistry of Photosystem II (PS II) is stimulated by lowering the pH to 5.4, just as it is upon metal cation addition at higher pH values. The failure to observe such an increase at pH 5.4 by measuring electron transport to ferricyanide is attributed to a combination of an inhibition by this pH of electron transport at a site after Q reduction and an increase in the number of PS II centres detached from the plastoquinone pool. We conclude that the stacked configuration of chloroplast membranes leads to increased PS II primary photochemistry, which is most simply explained in terms of a redistribution of excitation energy towards PS II.     

Mg2+ restores membrane potential in rat liver mitochondria deenergized by Ca2+ and phosphate movements

Cellular ornithine biosynthesis could be expected to play a significant role in putrescine formation and hence in growth. Two enzymes are involved in ornithine biosynthesis: arginase and transamidinase. These enzyme activities were studied in two human melanoma cell lines differing in their K_m of diamine oxidase for putrescine and in their tumorigenicity in nude mice. Arginase activity accounts for the majority of ornithine formed in the highly tumorigenic cell line, while the majority of ornithine is derived from transamidinase action in the poorly tumorigenic cell line, with concomitant formation of methyl guanidine, a potent inhibitor of diamine oxidase.