Comparison of Photosynthetic and Photorespiratory Enzyme Activities between Green Leaves and Colorless Parts of Variegated Leaves of a C4 Plant, Stenotaphrum secundatum (Walt.) Kuntze

The activities of enzymes involved in C⁴ photosynthesis andphotorespiration in colorless parts of variegated leaves ofStenotaphrum secundatum (Walt.) Kuntze were compared with thosein green leaves. Chlorophyll content of the colorless part wasonly about 0.3–3% of that of the green leaves. The activities of chloroplastic enzymes, pyruvate, P_i dikinase,NADP⁺-malic enzyme and NADP⁺-glyceraldehyde 3-phosphate dehydrogenasewere considerably lower in colorless tissue on a fresh weightor protein basis (the ratios of the activities in the green/colorlesstissues ranging from 5 to 20). A cytoplasmic enzyme, UDP-glucosepyrophosphorylase as well as aspartate and alanine aminotransferasesshowed comparable activities in the two types of tissue, whereasPEP carboxylase in the colorless tissue had only the one-thirdactivity of that in green tissue. Differences in activitieswere also observed for the glycolate pathway enzymes (the ratiosranging from 2 to 7 for glycolate oxidase, hydroxypyruvate reductaseand serine hydroxymethyltransferase, and 7 to 15 for catalase),while cytochrome c oxidase showed comparable activity in thetwo types of tissue. The results suggest that the deficiency of thylakoid developmentin the colorless tissue influences enzyme activities not onlyin plastids but also in other cellular compartments. ¹Present address: Institute of Applied Microbiology, Universityof Tokyo, Tokyo 113, Japan. (Received March 26, 1986; Accepted June 17, 1986)     

Absence of Variable Fluorescence from Guard Cell Chloroplasts of Stenotaphrum secundatum

The lack of detectable variable fluorescence from guard cell chloroplasts in both the albino and green portions of variegated leaves of St. Augustine grass (Stenotaphrum secundatum var variegatum A.S. Hitchc.) is reported. Fluorescence was measured either with a highly sensitive, modified fluorescence microscope which was capable of recording fluorescence induction curves from single chloroplasts, or with a spectrofluorometer. Both fast and slow fluorescence transients from S. secundatum guard cells showed a rapid rise and then remained at a steady level. Neither variable fluorescence increase (induction) nor decrease (quenching), properties normally associated with photosystem II, was observed from these chloroplasts. These fluorescence kinetics did not change either with alterations of the specimen preparation procedure or with alterations of the excitation light intensities and wavelengths. These results indicate that guard cell chloroplasts in this variety of S. secundatum do not conduct normal photosystem II electron transport. Light regulation of stomatal conductance in intact leaves of this plant did occur, however, and was similar to light regulation observed in other species. The conductance of the green portion of the leaves was much greater in the light than in the dark, and was much greater than the conductance of the albino portion of the leaves. Stomata in the green portion of the leaves also showed greater opening in blue light than in red light. These results provide evidence that stomatal regulation in this variety of S. secundatum does not rely on photosystem II electron transport in guard cell chloroplasts.     

Enzymatic Activities for the Synthesis of Chlorophyll in Pigment-Deficient Variegated Leaves of Euonymus japonicus

The enzymes involved in the biosynthesis of chlorophyll (Chl)in pigment-deficient variegated leaves of Euonymus japonicuswere investigated. Each variegated leaf was composed of clearlydelineated green and white sectors. The white sectors containedalmost no Chls. The rate of synthesis of 5-aminolevulinic acid(ALA) in the white sectors in vivo was twice that in the greensectors. The level of glutamate 1-semialdehyde aminotransferasein the white sectors was much higher than that in the greensectors. Plastidic tRNA^Glu was also present at substantial levelsin the white sectors, indicating that the system for synthesisof ALA was very active in the white sectors. The activity of porphobilinogen (PBG) synthase in the whitesectors in vitro was twice that in the green sectors. In thewhite sectors the rate of porphyrin synthesis from PBG was 4-to 6-fold higher than in the green sectors. We measured Mg-chelataseactivity indirectly in both sectors by monitoring the accumulationof Mg-protoporphyrin IX in the presence of 2,2'-dipyridyl, whichinhibits isocyclic ring formation with the resultant accumulationof Mg-protoporphyrin IX. When sectors were incubated in darknesswith 2,2'-dipyridyl, large amounts of protoporphyrin IX accumulatedin the white sectors, whereas Mg-protoporphyrin IX mainly accumulatedin the green sectors. These results suggest that the enzymesfor the synthesis of porphyrin that catalyze conversion of ALAto protoporphyrin IX were very active and that the Mg-insertionstep might be blocked in the white sectors, with the resultantfailure to synthesize Chl. The deficiency is discussed in acomparison with that in other Chl-deficient plants. (Received November 15, 1995; Accepted March 21, 1996)     

C4 Pathway Enzymes in Soybean Leaves

High-yielding soybean ( Glycine max (L.) Merr.) variety, “Heinong 40”, and one control variety, “Heinong 37”, were used as experimental materials. The activities of C4 pathway enzymes, i.e. PEPCase (phosphoenolpyruvate carboxylase), NADP-ME (NADP-malic enzyme), NADP-MDH (NADP-malate dehydrogenase), PPDK (pyruvate phosphate dikinase) and RuBPCase (ribulose-1.5-bisphosphate carbozylase) were assayed at seedling, blooming, pod-bearing and pod-filling stage. The results indicated that C4 pathway enzymes were expressed differently at different developing stages in both varieties of soybean, but the ratio of PEPCase and RuBPCase showed that the expression of C4 pathway enzymes of “Heinong 40” was higher than those of “Heinong 37” at each stage. The results showed that C4 pathway enzymes were closely related to the crop yielding potential. Therefore, it is possible to select potentially high-yielding soybean variety by the expression of C4 pathway enzymes.     

A Comparison of the Growth of the C4 Grass Spartina anglica with the C3 Grass Lolium perenne at Different Temperatures

Dunn, R., Thomas, S. M., Keys, A. J. and Long, S. P. 1987. Acomparison of the growth of the C₄ grass Spartina anglica withthe C₃ grass Lolium perenne at different temperatures.—J.exp. Bot. 38: 433–441. S. anglica is one of the few C₄ species which occurs naturallyin cool temperate zones. It is known to attain photosyntheticrates which equal or exceed those of C₃ grasses over the temperaturerange typical of the spring and summer in cool temperate climates.This study examines whether S. anglica can also attain comparablegrowth rates at these temperatures. Seedlings of S. anglicaand L. perenne cv. S23 were grown in controlled environmentsat 10,15,20 and 25 °C. Quantitative growth analysis wasconducted by taking frequent harvests to determine the progressionsof leaf area and plant weight of individual plants with time.Quadratic regressions were found to describe these progressionswell. Instantaneous derived growth parameters were calculatedfrom the fitted regressions. Both absolute and relative growthrates of S. anglica were significantly lower than for L. perenne,this being largely attributable to a lower ratio of leaf areaproduction per unit of plant dry weight. Although the amountof dry matter invested into leaves was similar, the leaf areaper unit of leaf dry weight was lower in S. anglica. In comparisonto L. perenne, the rate of dry matter accumulation per unitof leaf area (ULR) was higher in S. anglica at 25 °C andinitially equal at 10 °C. Prolonged exposure to 10 °Csteadily reduced ULR in S. anglica which approached zero at80 d. Although growth in S. anglica is reduced more by low temperaturethan it is in L. perenne, by comparison to other C₄ speciesthe assimilatory capacity of S. anglica is more tolerant oflow temperature exposure. Key words: C4 photosynthesis, temperature, quantitative growth analysis     

Stomatal Responses to Light and Drought Stress in Variegated Leaves of Hedera helix

Direct and indirect mechanisms underlying the light response of stomata were studied in variegated leaves of the juvenile phase of Hedera helix L. Dose response curves of leaf conductance were measured with blue and red light in leaves kept in normal or in an inverted position. In the green portions of the leaves, the sensitivity to blue light was nearly 100 times higher than that to red light. No response to red light was observed in the white portions of the leaves up to 90 micromoles per square meter per second. Red light indirectly affected leaf conductance while blue light had a direct effect. Leaf conductance was found to be more sensitive to drought stress and showed a more persistent aftereffect in the white portions of the leaves. A differential effect of drought stress on the responses to blue and red light was also observed.     

Carbohydrate Metabolism in Photosynthetic and Nonphotosynthetic Tissues of Variegated Leaves of Coleus blumei Benth

Mature, variegated leaves of Coleus blumei Benth. contained stachyose and other raffinose series sugars in both green, photosynthetic and white, nonphotosynthetic tissues. However, unlike the green tissues, white tissues had no detectable level of galactinol synthase activity and a low level of sucrose phosphate synthase indicating that stachyose and possibly sucrose present in white tissues may have originated in green tissues. Uptake of exogenously supplied [¹⁴C]stachyose or [¹⁴C]sucrose into either tissue type showed conventional kinetic profiles indicating combined operation of linear first-order and saturable systems. Autoradiographs of white discs showed no detectable minor vein labelling with [¹⁴C]stachyose, but some degree of vein labeling with [¹⁴C]sucrose. Autoradiographs of green discs showed substantial vein loading with either sugar. In both tissues, p-chloromercuribenzenesulfonic acid had no effect on the linear component of sucrose or stachyose uptake but inhibited the saturable component. Both tissues contained high levels of invertase, sucrose synthase and α-galactosidase and extensively metabolized exogenously supplied ¹⁴C-sugars. In green tissues, label from exogenous sugars was recovered as raffinose-series sugars. In white tissues, exogenous sugars were hydrolysed and converted to amino acids and organic acids. The results indicate that variegated Coleus leaves may be useful for studies on both phloem loading and phloem unloading processes in stachyose-transporting species.     

Developmental Features of Cell Wall Formation in Sieve Elements of the Grass Aegilops comosa var. thessalica

In differentiating sieve elements of Aegilops comosa var. thessalicadictyosomes are abundant and they produce numerous smooth vesicles.Coated vesicles seem to bud from smooth ones. Since both kindsof vesicles appear both in the cytoplasm and in associationwith the plasmalemma, it is proposed that they move to and fusewith the plasmalemma transferring products for cell wall synthesis.During differentiation sub-plasmalemmal microtubules are initiallyscarce and randomly oriented but soon afterwards they becomenumerous and transversely oriented to the long axis. Cellulosemicrofibrils in the cell wall appear to run parallel to themicrotubules and the latter may regulate microfibril orientation. Root protophloem sieve elements develop wave-like wall thickenings,which are, during development, overlaid by microtubules perpendicularto the long axis. Just after maturation these thickenings progressivelybecome smooth and finally the walls appear uniform in thickness.The wave-like wall thickenings may function as stored wall material,utilized in later stages of development when wall material willbe needed and its synthesis will be impossible because of theabsence of a synthesizing mechanism in the highly degraded protoplastsof mature sieve elements. It is suggested that in this way thethickenings may enable root protophloem sieve elements to growand keep pace with the active clongation of the surroundingcells. Aegilops comosa var. thessalica, sieve elements. cell wall, microtubules, dictyosomes, coated vesicles, wave-like thickenings     

高凝状态对非小细胞肺癌患者深静脉血栓形成的影响

目的:探讨高凝状态对非小细胞肺癌患者深静脉血栓形成的影响,为临床治疗提供依据。方法:选择2010年5月至2013年6月在我院接受治疗的非小细胞肺癌患者195例,记录患者姓名、年龄、性别、病理类型、手术、临床分期、放化疗、伴随疾病、身体状况评分(eastern cooperative oncology group,ECOG评分)及是否发生血栓等指标。调查入选患者的高凝状态指标,包括血小板(platelet,PLT)、纤维蛋白原(fibrinogen,Fib)、血浆凝血酶原时间(plasma prothrombin time,PT)、凝血酶时间(thrombin time,TT)、活化部分凝血活酶时间(activated coagulation time of whole blood,APTT)和D-二聚体(D-dimer)。结果:195例非小细胞肺癌患者中,PLT高于正常上限的有42例(21.5%),FIB升高的有78例(40%),TT延长的有12例(6.2%),PT缩短的有45例(23.1%),D-D升高的有60例(30.8%),APTT缩短的有15例(7.7%)。两项指标异常的有62例(31.8%),FIB和D-D升高的有32例(16.4%);三项指标异常的有27例(13.8%),PLT、FIB及D-D升高的有15例(7.7%);四项指标异常的有5例(2.6%),PLT、FIB及D-D升高,而PT缩短的有5例(2.6%)。所有患者各凝血指标中位值PLT为219×109/L,FIB为3.6 g/L,TT为13.4 s,PT为10.8 s,D-D为0.341 mg/L,APTT为29.7 s。结论:高凝状态对非小细胞肺癌患者深静脉血栓形成具有重要的促进作用,应受到临床的重视。     

Cyanobacterial Cell Lineage Analysis of the Spatiotemporal hetR Expression Profile during Heterocyst Pattern Formation in Anabaena sp. PCC 7120

Diazotrophic heterocyst formation in the filamentous cyanobacterium, Anabaena sp. PCC 7120, is one of the simplest pattern formations known to occur in cell differentiation. Most previous studies on heterocyst patterning were based on statistical analysis using cells collected or observed at different times from a liquid culture, which would mask stochastic fluctuations affecting the process of pattern formation dynamics in a single bacterial filament. In order to analyze the spatiotemporal dynamics of heterocyst formation at the single filament level, here we developed a culture system to monitor simultaneously bacterial development, gene expression, and phycobilisome fluorescence. We also developed micro-liquid chamber arrays to analyze multiple Anabaena filaments at the same time. Cell lineage analyses demonstrated that the initial distributions of hetR::gfp and phycobilisome fluorescence signals at nitrogen step-down were not correlated with the resulting distribution of developed heterocysts. Time-lapse observations also revealed a dynamic hetR expression profile at the single-filament level, including transient upregulation accompanying cell division, which did not always lead to heterocyst development. In addition, some cells differentiated into heterocysts without cell division after nitrogen step-down, suggesting that cell division in the mother cells is not an essential requirement for heterocyst differentiation.     

Effects of Phosphorylation on Phosphoenolpyruvate Carboxykinase from the C4 Plant Guinea Grass

In the C4 plant Guinea grass (Panicum maximum), phosphoenolpyruvate carboxykinase (PEPCK) is phosphorylated in darkened leaves and dephosphorylated in illuminated leaves. To determine whether the properties of phosphorylated and non-phosphorylated PEPCK were different, PEPCK was purified to homogeneity from both illuminated and darkened leaves. The final step of the purification procedure, gel filtration chromatography, further separated phosphorylated and non-phosphorylated forms. In the presence of a high ratio of ATP to ADP, the non-phosphorylated enzyme had a higher affinity for its substrates, oxaloacetate and phosphoenolpyruvate. The activity of the non-phosphorylated form was up to 6-fold higher when measured at low substrate concentrations. Comparison of proteoloytically cleaved PEPCK from Guinea grass, which lacked its N-terminal extension, from yeast (Saccharomyces cerevisiae), which does not possess an N-terminal extension, and from the C4 plant Urochloa panicoides, which possesses an N-terminal extension but is not subject to phosphorylation, revealed similar properties to the non-phosphorylated full-length form from Guinea grass. Assay of PEPCK activity in crude extracts of Guinea grass leaves, showed a large difference between illuminated and darkened leaves when measured in a selective assay (a low concentration of phosphoenolpyruvate and a high ratio of ATP to ADP), but there was no difference under assay conditions used to estimate maximum activity. Immunoblots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels showed no difference in the abundance of PEPCK protein in illuminated and darkened leaves. There were no light/dark differences in activity detected in maize (Zea mays) leaves, in which PEPCK is not subject to phosphorylation.     

glide/gcmIs Expressed and Required in the Scavenger Cell Lineage

Glial cell differentiation inDrosophila melanogasterrequires the activity ofglide/gcm(glial cell deficient/glial cell missing). The role of this gene is to direct the cell fate switch between neurons and glial cells by activating the glial developmental program in multipotent precursor cells of the nervous system. In this paper, we show thatglide/gcmis also expressed and required in the lineage of hemocytes/macrophages, scavenger cells that phagocytose cells undergoing programmed cell death. In addition, we show that, as for glial cells,glide/gcmplays an instructive role in hemocyte differentiation. Interestingly, it has been shown that in the development of the fly adult nervous system the role of scavenger cells is played by glial cells. These data and our findings on the dual role ofglide/gcmindicate that glial cells and hemocytes/macrophages are functionally and molecularly related.     

Changes in Free Amino Acids in White and Green Tissues of Variegated Tobacco Leaves during Water Stress

Variegated tobacco leaves, white on one side of the midrib andgreen on the other, were detached from the stem and incubatedunder water stress or turgid conditions for 4 days to determineany changes in the levels of free amino acids. Drastic changes in the free amino acid composition occurredin the green tissue during the water stress period, but onlyvery small changes in the white tissue. During that time, themost striking difference between the two tissues was the largeamount of proline accumulated in the green tissue, but not inthe white. An exogenous supply of sucrose increased the prolinecontent in both tissues during water stress. An exogenous supplyof glutamic acid increased the proline and asparagine contentsin the green tissue, but it increased only the asparagine contentin the white tissue during water stress. (Received May 4, 1982; Accepted August 12, 1982)     

Notch-Mediated Suppression of TSC2 Expression Regulates Cell Differentiation in the Drosophila Intestinal Stem Cell Lineage

Epithelial homeostasis in the posterior midgut of Drosophila is maintained by multipotent intestinal stem cells (ISCs). ISCs self-renew and produce enteroblasts (EBs) that differentiate into either enterocytes (ECs) or enteroendocrine cells (EEs) in response to differential Notch (N) activation. Various environmental and growth signals dynamically regulate ISC activity, but their integration with differentiation cues in the ISC lineage remains unclear. Here we identify Notch-mediated repression of Tuberous Sclerosis Complex 2 (TSC2) in EBs as a required step in the commitment of EBs into the EC fate. The TSC1/2 complex inhibits TOR signaling, acting as a tumor suppressor in vertebrates and regulating cell growth. We find that TSC2 is expressed highly in ISCs, where it maintains stem cell identity, and that N-mediated repression of TSC2 in EBs is required and sufficient to promote EC differentiation. Regulation of TSC/TOR activity by N signaling thus emerges as critical for maintenance and differentiation in somatic stem cell lineages.