The Movement of Coiled Bodies Visualized in Living Plant Cells by the Green Fluorescent Protein

Coiled bodies are nuclear organelles that contain components of at least three RNA-processing pathways: pre-mRNA splicing, histone mRNA 3'- maturation, and pre-rRNA processing. Their function remains unknown. However, it has been speculated that coiled bodies may be sites of splicing factor assembly and/or recycling, play a role in histone mRNA 3'-processing, or act as nuclear transport or sorting structures. To study the dynamics of coiled bodies in living cells, we have stably expressed a U2B"-green fluorescent protein fusion in tobacco BY-2 cells and in Arabidopsis plants. Time-lapse confocal microscopy has shown that coiled bodies are mobile organelles in plant cells. We have observed movements of coiled bodies in the nucleolus, in the nucleoplasm, and from the periphery of the nucleus into the nucleolus, which suggests a transport function for coiled bodies. Furthermore, we have observed coalescence of coiled bodies, which suggests a mechanism for the decrease in coiled body number during the cell cycle. Deletion analysis of the U2B" gene construct has shown that the first RNP-80 motif is sufficient for localization to the coiled body.     

Enzymic Mechanism of Starch Breakdown in Germinating Rice Seeds II. Scutellum as the Site of Sucrose Synthesis

In a close parallel to the developmental pattern of α-amylase activity, a rapid increase of maltase activity occurred in the endosperm tissue of germinating rice seeds after about 4 days of the seed imbibition. The overall pattern of the 2 hydrolytic enzyme activities strongly suggest that amylolytic breakdown is the major metabolic route of starch utilization in the germinating rice seeds. Results of the chemical analyses of sugar constituents as well as the measurements of sucrose synthetase activity show that the scutellum is the site of sucrose synthesis in the germinating rice seeds. It is thus supported that glucose derived from the reserve starch in endosperm is transported to scutellum, where it is converted to sucrose. Sucrose is further mobilized to the growing tissues, shoots and roots.     

The Repertoire of Plant Cells

Cryptic (camouflaged) prey often seek out backgrounds that match their coloration, and when at rest adopt an attitude that makes their crypsis most effective. We suggest a simple method for investigating the adaptive significance of such orientation. We used flat discs of pastry as the ‘prey’, either plain white or painted with a central black stripe, and wild garden birds as the predators. In the eight main experiments the backgrounds were white wooden boards painted with black parallel stripes of the same width as the stripes on the prey. In each experiment we presented equal numbers of two (of seven) ‘treatments’ of prey. The selection resulting from the combined predation by the birds confirmed the advantages of resting on a matching background and in the ‘correct’ orientation. We suggest that the technique can be developed further to explore the adaptive significance of background matching     

植物体内蔗糖转运蛋白的功能和调控

蔗糖转运蛋白（sucrose transporter,SUT）负责蔗糖的跨膜运输,在韧皮部介导的源-库蔗糖运输和为库组织供应蔗糖的生理活动中起关键作用。本文介绍植物体内蔗糖转运蛋白基因家族、细胞定位与功能调节以及高等植物的蔗糖感受机制的研究进展。     

小麦开花后旗叶中蔗糖合成与籽粒中蔗糖降解

在小麦开花后,旗叶中蔗糖磷酸合成酶（SPS）活性在开花后14d内一直维持较高水平,蔗糖合成酶（SS）的活性在开花后14-28d较高,蔗糖的含量与SPS活性呈显著正相关,籽粒中蔗糖合成酶（SS）在开花后28d内一直维持较高的活性;与此相对应,籽粒蔗糖的含量在开花后28d内呈明显的下降趋势。而旗叶和籽粒中SS活性均与籽粒淀粉的积累速率呈极显著正相关。     

Synthesis of Arabinose-Containing Cell Wall Precursors in Suspension-Cultured Tobacco Cells I. Intracellular Site of Synthesis and Transport

The distribution of arabinose-containing macromolecules in suspension-culturedtobacco cells was examined using sucrose density gradients.Exogenously applied ¹⁴Carabinose was scarcely converted intoother sugars, and concentrated in the Golgi-rich fraction (1.15g/cm³) and then secreted to the cell wall. ¹⁴C-Arabinose wasalso incorporated in a lower sucrose density fraction (1.11g/cm³), which contains small vesicles presumably originatedfrom the Golgi apparatus. The arabinose-containing macromoleculesin this fraction was more easily solubilized in water than thosein the Golgi-rich fraction. Alkaline hydrolysis of the macromoleculesindicated that cell-wall glycoprotein is a major component ofthe macromolecules and that the degree of glycosylation is slightlygreater in the lower density fractions than in the Golgi-richfraction. Based on these results, a scheme is suggested in whichthe glycoproteins and polysaccharides are glycosylated in theGolgi apparatus and secreted to the cell wall via secretionvesicles in the low density fraction. The possibility of ¹⁴C-arabinose-containingmacromolecules, in the early phase of synthesis, being a markerof the plant Golgi apparatus is also proposed. (Received September 21, 1980; Accepted January 27, 1981)     

Sucrose Phosphate Synthetase from Various Plant Origins

Some properties of sucrose-P synthetases obtained from various plant tissues, including sweet potato roots, potato tubers and leaves of barley, rape and ladino clover were studied. The specific enzyme activity of the sucrose-P synthetase from sweet potato roots was much lower than that of the sucrose synthetase of the other tissues. The enzyme activity decreased gradually as the roots developed. The optimum pH did not differ between enzyme preparations from sweet potato roots and barley leaves. Manganese chloride exhibited a marked stimulative effect on the sucrose-P synthetase from sweet potato roots and potato tubers, whereas it was inhibited the barley leaf enzyme.

Kinetic studies of sucrose-P synthetase showed that the behavior of the enzyme to the substrates did not differ in the enzyme sources examined. The substrate saturation curve of the enzyme with respect to fructose-6-P was sigmodal in shape, giving a straight line with a slope of 1.35~1.5 (n value) in a plot of the data using the empirical Hill equation. On the other hand, enzymes from all the various tissues exhibited a hyperbolic substrate saturation curve for UDP-glucose, obeying the ordinary Michaelis-Menten type reaction. Manganese chloride had no effect on the Km for UDP-glucose, the S_0.5 for fructose-6-P and the n value of the enzyme from potato tuber tissues.     

植物细胞内钙信号的特异性

文章对植物细胞内钙信号特异性的形式、特异性钙信号的产生以及解读等方面的研究结果进行了评述。     

The Cost of Maintenance Processes in Plant Cells

The most important maintenance processes in plants are proteinturnover and active transport processes to maintain certainion concentrations in the cells. In this paper an attempt ismade to calculate the total energy cost of these processes fromwhat is known about their specific costs and what has been observedabout their rates. Because of insufficient reliable data aboutrates of individual maintenance processes, only approximatevalues can be obtained. The average turnover rate of leaf proteins may be about 100mg protein per g proteins per day at normal temperature in leavesassimilating at moderate light intensities. This process consumes28–53 mg glucose per g protein per day, which equals 7–13mg glucose per g dry weight per day in leaves. It is likelythat the rates of protein turnover and of CO₂-assimilation arerelated. The cost of maintaining ion concentrations is estimatedto be about 6–10 mg glucose per g dry weight per day inleaves. The sum of these figures is lower than is indicatedby measurements of maintenance respiration. One reason for theunderestimation may be that the protein turnover rates usedin the calculations apply to plants with lower photosyntheticrates than the plants in which the maintenance respiration wasmeasured. Effects of water stress and salinity, temperatureand other environmental factors on the rate of maintenance processesare discussed. The consumption of assimilates for maintenance of plant cellsis a significant, negative factor in plant productivity. A betterunderstanding of the maintenance processes may give a clue howto manipulate plant characteristics or the environment to reducethe amount of assimilates consumed in these processes. It issuggested that reduction in protein turnover rates may be onesuch manipulation.     

Autophagy in Tobacco Suspension-Cultured Cells in Response to Sucrose Starvation

The response of tobacco (Nicotiana tabacum) suspension-cultured cells (BY-2) to nutrient starvation was investigated. When the cells that were grown in Murashige-Skoog medium containing 3% (w/v) sucrose were transferred to the same medium without sucrose, 30 to 45% of the intracellular proteins were degraded in 2 d. An analysis with sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that proteins were degraded nonselectively. With the same treatment, protease activity in the cell, which was measured at pH 5.0 using fluorescein thiocarbamoyl-casein as a substrate, increased 3- to 7-fold after 1 d. When the cysteine protease inhibitor (2S,3S)-trans-epoxysuccinyl-L-leucylamido-3-methyl-butane (10 [mu]M) was present in the starvation medium, both the protein degradation and the increase in the protease activity were effectively inhibited. Light microscopy analysis showed that many small spherical bodies accumulated in the perinuclear region of the cytosol 8 h after the start of the inhibitor treatment. These bodies were shown to be membrane-bound vesicles of 1 to 6 [mu]m in diameter that contained several particles. Quinacrine stained these vesicles and the central vacuole; thus, both organelles are acidic compartments. Cytochemical enzyme analysis using 1-naphthylphosphate and [beta]-glycerophosphate as substrates showed that these vesicles contained an acid phosphatase(s). We suggest that these vesicles contribute to cellular protein degradation stimulated under sucrose starvation conditions.     

Sucrose Synthesis in Cereal Grains under Oxygen Deprivation

Received 24 May 1999/ Accepted in revised form 21 June 1999     

植物细胞中的前纤维蛋白

肌动蛋白组成的微丝骨架是真核细胞中的重要结构,在体内处于高度动态变化之中,受多种肌动蛋白结合蛋白（actin-binding proteins）的调节。前纤维蛋白（profilin）是一种单体肌动蛋白结合蛋白,存在于所有的真核细胞中,在植物细胞中也得到较多的研究。前纤维蛋白除可以结合单体肌动蛋白之外,还可以与磷脂酰肌醇及富含多聚脯氨酸的蛋白质等多种分子结合,在细胞信号转导中行使着重要的功能。本文结合本实验室的研究结果,概述了前纤维蛋白的最新研究进展。     

绿色荧光蛋白在植物细胞生物学中的应用

克隆于海洋动物水母 (Ａｅｑｕｏｒｅａｖｉｃｔｏｒｉ ａ)的绿色荧光蛋白 (ｇｒｅｅｎｆｌｕｏｒｅｓｃｅｎｔｐｒｏｔｅｉｎ ,ＧＦＰ)作为一种新型的非酶性报告基因具有检测简便 ,结果真实可靠 ,不需要任何外源底物或辅助因子的特点 ,自出现以来它已引起人们的广泛兴趣 ,目前已经应用于烟草、柑橘、拟南芥、玉米、水稻、大豆、苜蓿等多种植物材料的研究中。ＧＦＰ含有特殊的六肽生色团结构 ,用蓝紫光激发即能发出肉眼清晰可见的绿色荧光 ,而无需任何底物或辅助因子。ＧＦＰ能与多种不同蛋白质的Ｎ端或Ｃ端融合而保持与天然蛋白质相似的荧…     

植物细胞中的膜联蛋白（annexin）

膜联蛋白（annexin）是存在于动植物细胞中的钙依赖性磷脂结合蛋白,广泛参与受钙离子调控的生命活动,如囊泡运输、膜融合、信号转导、钙离子通道的形成、细胞分化和细胞骨架蛋白间的相互作用等。本文就植物细胞中annexin的研究进展进行了介绍。     

A Modified Procedure for the Synthesis of Sucrose

A modified procedure for synthesis of sucrose was carried out by using purified crystalline 1,3,4,6-tetra-O-benzoyl-d-fructofuranose in place of 1,3,4,6-tetra-O-acetyl-d-fructofuranose; namely, reaction of 1,2-anhydro-3,4,6-tri-O-acetyl-α-d-glucopyranose with tetrabenzoyl-d-fructose at 110~118°C for 3 hr followed by deacylation, and by chromatographic separation of the deacylated product afforded crude sucrose. Acetylation of the synthetic product gave octaacetate sucrose in the yield of 5.0%.     

Plant Stem Cells

Molecular Biology - A brief review of current data on the molecular biology of stem cells forming meristems and differentiating into various organs of angiosperms is presented. Different primary...     

植物蔗糖转运蛋白及其功能调节研究进展

综述了高等植物蔗糖转运蛋白基因家族的分类,蔗糖转运蛋白的细胞定位,蔗糖转运蛋白的功能调节,以及果实中糖运转的特性等方面的研究进展,并提出了深入研究果实蔗糖运转蛋白的展望。     

The Effect of Low Temperature upon Starch, Sucrose and Fructan Synthesis in Leaves

Measurements on plants in a temperature gradient tunnel showthat diurnal accumulation of starch in illuminated leaves wasgreatly reduced at temperatures below 8 °C, whereas sucrosesynthesis was less affected under similar conditions. High chillingsensitivity for leaf starch accumulation was observed in a numberof chilling resistant temperate species. Enzymes of sucroseand fructan metabolism from mature leaves of Lolium temulentumwere less strongly inhibited at low temperatures than enzymesinvolved in starch synthesis. These results are discussed inrelation to carbon partitioning in species which grow and aremetabolically active at chilling temperatures. Lolium temulentum, starch, sucrose, fructan, temperature, enzyme activity, carbon partitioning