SERRATE coordinates shoot meristem function and leaf axial patterning in Arabidopsis

Leaves of flowering plants are determinate organs produced by pluripotent structures termed shoot apical meristems. Once specified, leaves differentiate an adaxial (upper) side specialized for light capture, and an abaxial (lower) side specialized for gas exchange. A functional relationship between meristem activity and the differentiation of adaxial leaf fate has been recognized for over fifty years, but the molecular basis of this interaction is unclear. In Arabidopsis thaliana, activity of the class I KNOX (KNOTTED1-like homeobox) genes SHOOTMERISTEMLESS (STM) and BREVIPEDICELLUS (BP) is required for meristem function but excluded from leaves, whereas members of the HD-Zip III (class III homeodomain leucine zipper) protein family function to promote both meristem activity and adaxial leaf fate. Here we show that the zinc-finger protein SERRATE acts in a microRNA (miRNA) gene-silencing pathway to regulate expression of the HD-Zip III gene PHABULOSA (PHB) while also limiting the competence of shoot tissue to respond to KNOX expression. Thus, SERRATE acts to coordinately regulate meristem activity and leaf axial patterning.     

Direct control of paralysed muscles by cortical neurons

A potential treatment for paralysis resulting from spinal cord injury is to route control signals from the brain around the injury by artificial connections. Such signals could then control electrical stimulation of muscles, thereby restoring volitional movement to paralysed limbs. In previously separate experiments, activity of motor cortex neurons related to actual or imagined movements has been used to control computer cursors and robotic arms, and paralysed muscles have been activated by functional electrical stimulation. Here we show that Macaca nemestrina monkeys can directly control stimulation of muscles using the activity of neurons in the motor cortex, thereby restoring goal-directed movements to a transiently paralysed arm. Moreover, neurons could control functional stimulation equally well regardless of any previous association to movement, a finding that considerably expands the source of control signals for brain-machine interfaces. Monkeys learned to use these artificial connections from cortical cells to muscles to generate bidirectional wrist torques, and controlled multiple neuron-muscle pairs simultaneously. Such direct transforms from cortical activity to muscle stimulation could be implemented by autonomous electronic circuitry, creating a relatively natural neuroprosthesis. These results are the first demonstration that direct artificial connections between cortical cells and muscles can compensate for interrupted physiological pathways and restore volitional control of movement to paralysed limbs.     

Direct enzyme transfer from lymphocytes is specific

Lymphocytes are known to interact directly with other cells in vivo and in vitro, and have recently been shown to transfer the lysosomal enzyme, beta-glucuronidase, to fibroblasts from patients with an inherited deficiency of the enzyme. This process requires cell-cell contact, is unaffected by inhibitors of 'classical' receptor-mediated endocytosis and is abolished by inhibitors of protein synthesis. Although it is not yet known to what extent the transfer of enzymes by direct cellular interaction is a general phenomenon, a similar mechanism could possibly be involved in the transfer of other lysosomal enzymes in vivo and in the exchange of protein in vitro. We show here that the direct transfer of enzymes from lymphocytes to fibroblasts is restricted to only certain lysosomal enzymes.     

Inhibition by chloroquine of a novel haem polymerase enzyme activity in malaria trophozoites.

The incidence of human malaria has increased during the past 20 years; 270 million people are now estimated to be infected with the parasite. An important contribution to this increase has been the appearance of malaria organisms resistant to quinoline-containing antimalarials such as chloroquine and quinine. These drugs accumulate in the acid food vacuoles of the intraerythrocytic-stage malaria parasite, although the mechanism of their specific toxicity in this organelle is uncertain. The primary function of the food vacuole is the proteolysis of ingested red cell haemoglobin to provide the growing parasite with essential amino acids. Haemoglobin breakdown in the food vacuole releases haem, which if soluble can damage biological membranes and inhibit a variety of enzymes. Rather than degrading or excreting the haem, the parasite has evolved a novel pathway for its detoxification by incorporating it into an insoluble crystalline material called haemozoin or malaria pigment. These crystals form in the food vacuole of the parasite concomitant with haemoglobin degradation, where they remain until the infected red cell bursts. The structure of haemozoin comprises a polymer of haems linked between the central ferric ion of one haem and a carboxylate side-group oxygen of another. This structure does not form spontaneously from either free haem or haemoglobin under physiological conditions, and the biochemistry of its formation is unclear. Here we report the identification and characterization of a haem polymerase enzyme activity from extracts of Plasmodium falciparum trophozoites, and show that this enzyme is inhibited by quinoline-containing drugs such as chloroquine and quinine. This provides a possible explanation for the highly stage-specific antimalarial properties of these drugs.     

一类不确定非线性系统的直接自适应模糊控制

针对一类具有未知函数增益的不确定非线性系统,基于监督控制方法并利用第二类模糊系统的通用逼近能力,提出一种新的直接自适应模糊控制设计方案.该方案通过引入最优逼近误差的自适应补偿项和新的鲁棒项,削减建模误差和参数估计误差的影响,从而在稳定性分析中取消了要求逼近误差平方可积或逼近误差的上确界已知的条件.理论分析证明了闭环系统状态有界,跟踪误差收敛到零.仿真结果表明了该方法的有效性.     

基于自适应补偿低通滤波器的直接转矩控制系统的研究

传统的异步电动机直接转矩控制在低速段由于纯积分环节中定子电阻的影响对磁链的观测不稳定,将造成磁链和转矩脉动过大,限制了实用范围.针对这一不足,本文引进新的磁链观测方法,即带自适应补偿低通滤波器模型,对其进行仿真实验.结果表明,该模型能够较好地改善磁链轨迹,转矩、电流脉动均得到有效控制,能够保证系统的控制品质,具有工程实用价值.     

基于径向基神经网络的精馏塔产品质量自适应控制

对精馏塔全阶模型进行了分析 ,设计了基于RBF神经网络的直接自适应控制器。采用双端控制 ,克服了单端控制的不足。网络权值的调整算法基于所选择的Lyapunov函数 ,这样可保证闭环系统的稳定性和权值参数的收敛性。仿真结果表明所设计闭环系统具有良好的跟踪性和鲁棒性。     

基于径向基神经网络的精馏塔产品质量自适应控制

对精馏塔全阶模型进行了分析。设计了基于RBF神经网络的直接自适应控制器。采用双端控制，克服了单端控制的不足。网络权值的调整算法基于所选择的Lyapunov函数，这样可保证闭环系统的稳定性和权值参数的收敛性。仿真结果表明所设计闭环系统具有良好的跟踪性和鲁棒性。     

四轮转向车辆的直接横摆力矩控制

将横摆力矩控制(DYC)与四轮转向(4WS)系统相结合,建立侧偏角和横摆角速度具有最佳输出响应的车辆理想模型.采用前馈和反馈控制相结合跟踪理想模型的控制策略,设计出最优控制器,并分别在低速和高速下进行仿真分析.结果表明:四轮转向模型与横摆力矩控制相结合,采用跟踪理想模型的控制策略能够有效地同时控制汽车转向侧偏角和横摆角速度,得到较好的瞬态及稳态响应,有效地减轻驾驶员操纵负担,提高了车辆操纵稳定性.尤其在高速行驶时,仍能获得较好的输出响应,利于提高行车安全性.     

车用轮毂电动机直接转矩控制特性建模

以某型号车用轮毂电动机为研究对象,针对矢量控制存在的转矩响应慢、动态性能不佳等问题,提出了轮毂电动机直接转矩控制方法.在分析轮毂电动机直接转矩控制数学模型的基础上,利用Matlab/Simulink仿真软件建立了轮毂电动机直接转矩控制仿真模型,进行了轮毂电动机动态性能仿真分析.设计了基于实时仿真系统dSPACE的轮毂电...     

Oncogenic lncRNA LINC00973 promotes Warburg effect by enhancing LDHA enzyme activity

Aerobic glycolysis,also known as the Warburg effect,is a hallmark of cancer and essential for metabolism in malignancies,but its regulation and modulation in ca...     

Inhibition of shoot branching by new terpenoid plant hormones

Shoot branching is a major determinant of plant architecture and is highly regulated by endogenous and environmental cues. Two classes of hormones, auxin and cytokinin, have long been known to have an important involvement in controlling shoot branching. Previous studies using a series of mutants with enhanced shoot branching suggested the existence of a third class of hormone(s) that is derived from carotenoids, but its chemical identity has been unknown. Here we show that levels of strigolactones, a group of terpenoid lactones, are significantly reduced in some of the branching mutants. Furthermore, application of strigolactones inhibits shoot branching in these mutants. Strigolactones were previously found in root exudates acting as communication chemicals with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Thus, we propose that strigolactones act as a new hormone class-or their biosynthetic precursors-in regulating above-ground plant architecture, and also have a function in underground communication with other neighbouring organisms.     

Sequence, structure and activity of phosphoglycerate kinase: a possible hinge-bending enzyme.

The fitting of sequenced peptides to a high-resolution X-ray map of phosphoglycerate kinase has yielded the complete sequence and structure of the horse muscle enzyme. Metal ADP and ATP substrates are bound to one of the two widely separated domains in an environment that seems unsuitable for phosphoglycerate binding. The most plausible binding site for the phosphoglycerate substrate is on the other domain about 10 A from the ATP, which implies the possibility of a large scale hinge-bending of the domains to bring the two substrates together in a water-free environment for catalysis.     

Structure-based activity prediction for an enzyme of unknown function

With many genomes sequenced, a pressing challenge in biology is predicting the function of the proteins that the genes encode. When proteins are unrelated to others of known activity, bioinformatics inference for function becomes problematic. It would thus be useful to interrogate protein structures for function directly. Here, we predict the function of an enzyme of unknown activity, Tm0936 from Thermotoga maritima, by docking high-energy intermediate forms of thousands of candidate metabolites. The docking hit list was dominated by adenine analogues, which appeared to undergo C6-deamination. Four of these, including 5-methylthioadenosine and S-adenosylhomocysteine (SAH), were tested as substrates, and three had substantial catalytic rate constants (10(5) M(-1 )s(-1)). The X-ray crystal structure of the complex between Tm0936 and the product resulting from the deamination of SAH, S-inosylhomocysteine, was determined, and it corresponded closely to the predicted structure. The deaminated products can be further metabolized by T. maritima in a previously uncharacterized SAH degradation pathway. Structure-based docking with high-energy forms of potential substrates may be a useful tool to annotate enzymes for function.     

永磁同步电机直接转矩模糊控制系统

结合永磁同步电机(PMSM)的数学模型和经典直接转矩控制理论,采用空间矢量控制方法,以定子磁链角增量为控制目标,将模糊控制器作为转速与转矩调节器和定子磁链优化控制器.运用MATLAB/Simulink软件对该控制系统建模和仿真.结果表明:与经典DTC控制系统相比,该控制方式能够减小转矩脉动,降低系统损耗,从而提高了效率.