The dyad gene is required for progression through female meiosis in Arabidopsis

In higher plants the gametophyte consists of a gamete in association with a small number of haploid cells, specialized for sexual reproduction. The female gametophyte or embryo sac, is contained within the ovule and develops from a single cell, the megaspore which is formed by meiosis of the megaspore mother cell. The dyad mutant of Arabidopsis, described herein, represents a novel class among female sterile mutants in plants, dyad ovules contain two large cells in place of an embryo sac. The two cells represent the products of a single division of the megaspore mother cell followed by an arrest in further development of the megaspore. We addressed the question of whether the division of the megaspore mother cell in the mutant was meiotic or mitotic by examining the expression of two markers that are normally expressed in the megaspore mother cell during meiosis. Our observations indicate that in dyad the megaspore mother cell enters but fails to complete meiosis, arresting at the end of meiosis 1 in the majority of ovules, This was corroborated by a direct observation of chromosome segregation during division of the megaspore mother cell, showing that the division is a reductional and not an equational one. In a minority of dqad ovules, the megaspore mother cell does not divide. Pollen development and male fertility in the mutant is normal, as is the rest of the ovule that surrounds the female gametophyte. The embryo sac is also shown to have an influence on the nucellus in wild type. The dyad mutation therefore specifically affects a function that is required in the female germ cell precursor for meiosis. The identification and analysis of mutants specifically affecting female meiosis is an initial step in understanding the molecular mechanisms underlying early events in the pathway of female reproductive development

Production, optimization and characterisation of chitosanase of Bacillus sp. and its applications in nanotechnology

Chitosanases is a class of enzymes which hydrolyse chitosan, a natural biopolymer consisting of d-glucosamine in various degrees. In this study, chitosanase producing Bacillus sp. was isolated from soil sample. Chitosanase production was optimized using response surface methodology and the produced chitosanase was characterized. The crude enzyme was found to possess antibacterial and antifungal activity. Chitosanase enzyme was used for trimming chitosan based polymeric nanoparticles produced using sodium trimetaphosphate chelator. Chitosanase enzyme was also utilized for synthesis of silver nanoparticles which were then characterized by UV–Vis, FTIR, SEM, TEM and AFM. The produced nanoparticles were checked for antibacterial and antifungal activity

On the Nonlinear Stability of Inviscid Homogeneous Shear Flows in Sea Straits of Arbitrary Cross Sections

In this paper we study the nonlinear stability of steady flows of inviscid homogeneous fluids in sea straits of arbitrary cross sections. We use the method of Arnol'd [1] to obtain two general stability theorems for steady basic flows with respect to finite amplitude disturbances. For the special case of plane parallel shear flows we find a finite amplitude extension of the linear stability result of Deng et al [2]. We also present some examples of basic flows which are stable to finite amplitude disturbances

The 'checkmate' for iron between human host and invading bacteria: chess game analogy

Iron is an essential nutrient for all living organisms with critical roles in many biological processes. The mammalian host maintains the iron requirements by dietary intake, while the invading pathogenic bacteria compete with the host to obtain those absorbed irons. In order to limit the iron uptake by the bacteria, the human host employs numerous iron binding proteins and withholding defense mechanisms that capture iron from the microbial invaders. To counteract, the bacteria cope with the iron limitation imposed by the host by expressing various iron acquisition systems, allowing them to achieve effective iron homeostasis. The armamentarium used by the human host and invading bacteria, leads to the dilemma of who wins the ultimate war for iron

Differential Evolution Based IDWNN Controller for Fault Ride-Through of Grid-Connected Doubly Fed Induction Wind Generators

The key objective of wind turbine development is to ensure that output power is continuously increased. It is authenticated that wind turbines (WTs) supply the necessary reactive power to the grid at the time of fault and after fault to aid the flowing grid voltage. At this juncture, this paper introduces a novel heuristic based controller module employing differential evolution and neural network architecture to improve the low-voltage ride-through rate of grid-connected wind turbines, which are connected along with doubly fed induction generators (DFIGs). The traditional crowbar-based systems were basically applied to secure the rotor-side converter during the occurrence of grid faults. This traditional controller is found not to satisfy the desired requirement, since DFIG during the connection of crowbar acts like a squirrel cage module and absorbs the reactive power from the grid. This limitation is taken care of in this paper by introducing heuristic controllers that remove the usage of crowbar and ensure that wind turbines supply necessary reactive power to the grid during faults. The controller is designed in this paper to enhance the DFIG converter during the grid fault and this controller takes care of the ride-through fault without employing any other hardware modules. The paper introduces a double wavelet neural network controller which is appropriately tuned employing differential evolution. To validate the proposed controller module, a case study of wind farm with 1.5 MW wind turbines connected to a 25 kV distribution system exporting power to a 120 kV grid through a 30 km 25 kV feeder is carried out by simulation

Antimicrobial nature of specific compounds of Ampelomyces quisqualis identified from gas chromatography-mass spectrometry (GCMS) analysis and their mycoparasite nature against powdery mildew of grapes

Grapevine powdery mildew is the world's most important plant disease, and Ampelomyces frequently fight them. While it does not usually cause plant death, its major infections can result in significant production losses and severely impact wine quality. Fungicides are frequently used to control the disease, which can have long-term adverse effects on the ecosystem. As a result, alternative and environmentally friendly disease management approaches must be developed. The study aimed to reduce costly and toxic fungicide use by using Ampelomyces, a natural biofungicide, against various powdery mildew fungi. GC-MS analysis was also used to determine the antagonistic potential and efficacy of volatile organic chemicals produced by several Ampelomyces spp. against Erysiphe necator, which causes powdery mildew of grapes. The molecular characterization of A. quisqualis isolates based on using rDNA ITS region was also carried out and sequenced. GC-MS analysis identified various antimicrobial compounds, such as squalene (4.643%), octadecanoic acid (3.862%), tetradecanoic acid (3.600%), and 9,12-octadecadienoic acid (Z,Z) (1.451%). The least abundant compounds were 2-Hexadecanol, 1-Tricosanol, and 2-propenyl ester, with percentages of 0.485, 0.519, and 0.560, respectively. These bioactive compounds revealed by GC-MS analysis in crude extracts of A. quisqualis had a stronger antifungal and antibacterial activity against E. necator. As a result, using A. quisqualis to control the powdery mildew of grapes significantly reduced pathogen growth and disease incidence