The synthesis of small organic molecules, known as specialized or secondary metabolites, is one mechanism by which plants resist and tolerate biotic and abiotic stress. Many specialized metabolites are derived from the aromatic amino acids phenylalanine (Phe) and tyrosine (Tyr). In addition, the improved characterization of compounds derived from these amino acids could inform strategies for developing crops with greater resilience and improved traits for the biorefinery. Sorghum and other grasses possess phenylalanine ammonia-lyase (PAL) enzymes that generate cinnamic acid from Phe and bifunctional phenylalanine/tyrosine ammonia-lyase (PTAL) enzymes that generate cinnamic acid and p-coumaric acid from Phe and Tyr, respectively. Cinnamic acid can, in turn, be converted into p-coumaric acid by cinnamate 4-hydroxylase. Thus, Phe and Tyr are both precursors of common downstream products. Not all derivatives of Phe and Tyr are shared, however, and each can act as a precursor for unique metabolites. In this study, 13C isotopic-labeled precursors and the recently developed Precursor of Origin Determination in Untargeted Metabolomics (PODIUM) mass spectrometry (MS) analytical pipeline were used to identify over 600 MS features derived from Phe and Tyr in sorghum. These features comprised 20% of the MS signal collected by reverse-phase chromatography and detected through negative-ionization. Ninety percent of the labeled mass features were derived from both Phe and Tyr, although the proportional contribution of each precursor varied. In addition, the relative incorporation of Phe and Tyr varied between metabolites and tissues, suggesting the existence of multiple pools of p-coumaric acid that are fed by the two amino acids. Furthermore, Phe incorporation was greater for many known hydroxycinnamate esters and flavonoid glycosides. In contrast, mass features derived exclusively from Tyr were the most abundant in every tissue. The Phe- and Tyr-derived metabolite library was also utilized to retrospectively annotate soluble MS features in two brown midrib mutants (bmr6 and bmr12) identifying several MS features that change significantly in each mutant.
The SLC@ 96 carrier system has been developed to bring digital capability to the local loop network, and ultimately it may be a component of a completely integrated digital network. It uses two unique channel banks: one located in the central office to interface to the local switching machine, and the other located remotely in the vicinity of a group of subscribers. The SLC 96 carrier can provide, through the use of different channel units, message telephone service, coin service, special services, and data services. For digital transmission, it interfaces to standard Tllines or optical fibers. The design is patterned after the D4 channel bank, and many of D4 carrier's channel units can be used in the SLC 96 carrier system. The resultant system has the versatility to serve both rapidly growing metropolitan, as well as rural, areas. Features that provide highly reliable service and easy maintenance have been included in the design of the system.
The SLC*‐96 system is a digital subscriber carrier system that can carry up to 96 subscriber channels, when fully equipped, between a Central Office Terminal (cot) and a Remote Terminal (rt), using T1 digital lines. Typical economic applications are for expanding the service capability of existing cable plant or for new wire center deferral. Recent application studies show that SLC‐96 systems will be economically attractive in many permanent subscriber applications. In addition to Message Telephone Service (mts), the system can provide coin services, voice‐frequency special services, and digital data services. The SLC‐96 system is based on the transmission and physical format of the D4 system used for interoffice trunks. The system employs μ255 pulse code modulation (pcm) for voice transmission and, as a result, will allow the direct interface of the rt with a digital central office. Its maintenance features include channel and drop testing from a local test desk; single‐ended, active, T1 fault‐locating; automatic T1 line protection; extensive local and remote alarm displays; and outputs that can be transmitted to a remote operations center such as the Switching Control Center (scc). The channel and drop testing scheme requires a Pair Gain Test Controller (pgtc) to be installed in each wire center containing one or more SLC‐96 systems. Various other features that will enhance the application of the SLC‐96 system in the loop plant include extended range channel units, remote T1 line power feed, and a variety of RT enclosures.
The Fiber SLC' Carrier System is a repeaterless digital loop carrier that employs lightwave features for the transmission of voice and data from a telephone central office to a remote location. This paper describes the development and application of this 1.3-um LED/p-i-n based system. Experience with first applications is reported along with current developments intended to increase its capacity and bring digital capability close to the customer at the DS3 bit rate (44.736 Mbits/s). Services to the customer include DS1 port capability (1.544 Mbits/s), DS2 optical paths (6.312 MbitsJs), voice, and data.
The success of digital loop carrier depends not only on economic considerations, but also to a great extent on the ability of the operating companies to maintain, administer, and operate this technology. This paper discusses a generalized digital loop carrier operations plan and describes the SL~96 carrier system features that satisfy the requirements of the operations plan. A thorough explanation of the SLC 96 carrier maintenance features is included. The paper covers system maintenance philosophy, alarm structure, and line testing methodology. I. INTRODUCTIONOne of the most critical aspects in the design of a Digital Loop Carrier (DLC)* system is the maintenance and operational features. With the proper features, systems will be reliable, easy to maintain, and amenable to craftspeople. The SLC 96 carrier system was designed from the beginning with maintenance and operations in mind.' The design of the maintenance and operations features was based on a thorough understanding of the loop operations environment and how digital loop carrier can best be used within that environment.• AT&T Bell Laboratories. t AT&T Bell Laboratories; present affiliation Bell Communications Research, Inc.t Acronyms and abbreviations used in the text are defined at the back of the Journal.
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