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 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The self-teaching hypothesis proposes that phonological recoding functions as a self-teaching mechanism enabling the learner to independently acquire an autonomous orthographic lexicon. Successful decoding encounters with novel letter strings provide opportunities to learn word-specific print-to-meaning connections. Although it may not play a central role in skilled word recognition, phonological recoding, by virtue of its self-teaching function, is regarded as critical to successful reading acquisition. This paper elaborates the self-teaching hypothesis proposed by Jorm and Share (1983), and reviews relevant evidence. Key features of phonological recoding include an item-based rather than stage-based role in development, the progressive "lexicalization" of the process of recoding, and the importance of phonological awareness and contextual information in resolving decoding ambiguity. Although phonological skills have been shown to be primary in reading acquisition, orthographic processing appears to be an important but secondary source of individual differences. This implies an asymmetrical pattern of dissociations in both developmental and acquired reading disorders. Strong relationships between word recognition, basic phonological processing abilities and phonemic awareness are also consistent with the self-teaching notion. Finally, it is noted that current models of word recognition (both PDP and dual-route) fail to address the quintessential problem of reading acquisition-independent generation of target pronunciations for novel orthographic strings.
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PMID:Phonological recoding and self-teaching: sine qua non of reading acquisition. 778 90

The yellow-green alga Trachydiscus minutus (Eustigmatophyceae, Heterocontophyta) was cultivated in a standard medium and under nitrogen- and phosphorus-starvation and its triacylglycerols were analyzed by RP-HPLC/MS-APCI. The molecular species of triacylglycerols included a total of 74 triacylglycerols having at least one polyunsaturated fatty acid. Polyunsaturated triacylglycerols were identified for the first time in a yellow-green alga. N-starvation brought about a nearly 50% drop in TAGs containing EPA, and also decreased TAGs containing ARA, while P-starvation had a sizable effect on those TAGs that contain two or three arachidonic acids. In four TAGs containing PUFA, i.e. EEE, EEA, EAA and AAA, N-starvation caused a rapid fivefold increase in ARA content and the ratio of TAGs containing ARA, i.e. AEE to AAA increased tenfold relative to control. Regioisomeric characterization of triacylglycerols containing palmitic, arachidonic (ARA) and eicosapentaenoic acids (EPA) showed that the proportion of positional isomers is affected by N- and P-starvation. N- and P-starvation also changed the ratio of symmetrical to asymmetrical TAGs. Positional isomers exhibited identical ratios of symmetrical and asymmetrical TAGs irrespective of the type of FAs. In control cultivation the major TAGs with a single PUFA were symmetrical ones (PEP or PAP) whose ratio to asymmetrical counterparts (PPE or PPA) was about 3:1, whereas N- and P-starvation yielded opposite ratios, 1:3-1:5. The control cultivation yielded ~90% asymmetrical TAGs with two PUFAs (i.e. PEE and PAA), whereas with N- and P-starvation the ratio of symmetrical to asymmetrical TAGs increased to 2:1 and 3:2, respectively.
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PMID:Effect of nitrogen and phosphorus starvation on the polyunsaturated triacylglycerol composition, including positional isomer distribution, in the alga Trachydiscus minutus. 2191 Dec 35

Structured triacylglycerols (TAGs) were isolated from nine cultivated strains of microalgae belonging to different taxonomic groups, i.e. Audouinella eugena, Balbiania investiens, Myrmecia bisecta, Nannochloropsis limnetica, Palmodictyon varium, Phaeodactylum tricornutum, Pseudochantransia sp., Thorea ramosissima, and Trachydiscus minutus. They were separated and isolated by means of NARP-LC/MS-APCI and chiral LC and the positional isomers and enantiomers of TAGs with two polyunsaturated, i.e. arachidonic (A) and eicosapentaenoic (E) acids and one saturated, i.e. palmitic acid (P) were identified. Algae that produce eicosapentaenoic acid were found to biosynthesize more asymmetrical TAGs, i.e. PPE or PEE, whereas algae which produced arachidonic acid give rise to symmetrical TAGs, i.e. PAP or APA, irrespective of their taxonomical classification. Nitrogen and phosphorus starvation consistently reversed the ratio of asymmetrical and symmetrical TAGs.
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PMID:Production of structured triacylglycerols from microalgae. 2483 34


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