Co-Pt alloys were studied in detail by a corrosion test under phosphoric acid fuel cell (PAFC) conditions on the well-defined crystallographic structures for a typical combination of the alloy catalysts used in PAFCs, examining the long-life stabilities of the structures and the catalytic activities for O2 electroreduction. The ordered (O) and disordered (D) alloys at the same particle sizes can be obtained by heat-treating the mother alloy in different temperature sequences. The O-alloy exhibits a specific activity, an electrocatalytic activity based on the catalyst surface area, L35 times higher than the D-alloy before the corrosion test, but shows less activity (0.73 times) after the corrosion test, due to a higher degradation (47%) in the O-alloy activity as compared with that of the D-alloy (1%). It was found that the Co atoms on particle surfaces of both alloys dissolve easily in the acid. This is followed by a second slow dissolution from inside the alloy particles probably due to the protective action by a monolayer thickness of Pt remaining on the alloy surfaces, but the loss of Co in the second stage dissolution for the O-alloy is higher by several percentage points compared to that of the D-alloy. It was also found that the Pt content does not change on the catalyst support even after 50 h of corrosion test, but the pure Pt phase is formed in the corrosion product, where the phase for the O-alloy grows faster than that for the D-alloy with corrosion time. Based on these results, obtained by chemical, x-ray diffraction, and transmission electron microscopy with energy dispersive spectroscopy analyses, the corrosion for Pt alloy catalysts is clearly explained, i.e., after the dissolution

When subjected to salt stress or drought, some vascular plants such as barley respond with an increased accumulation of the osmoprotectant glycine betaine (betaine), being the last step of betaine synthesis catalyzed by betaine aldehyde dehydrogenase (BADH). We report here cloning and characterization of BADH cDNA from barley, a monocot, and the expression pattern of a BADH transcript. An open reading frame of 1515 bp encoded a protein which showed high homology to BADH enzymes present in other plants (spinach and sugar-beet) and in Escherichia coli. Transgenic tobacco plants harboring the clone expressed high levels of both BADH protein and its enzymatic activity. Northern blot analyses indicated that BADH mRNA levels increased almost 8-fold and 2-fold, respectively, in leaves and roots of barley plants grown in high-salt conditions, and that these levels decreased upon release of the stress, whereas they did not decrease under continuous salt stress. BADH transcripts also accumulate in response to water stress or drought, indicating a common response of the plant to osmotic changes that affect its water status. The addition of abscisic acid (ABA) to plants during growth also increased the levels of BADH transcripts dramatically, although the response was delayed when compared to that found for salt-stressed plants. Removal of plant roots before transferring the plants to high-salt conditions reduced only slightly the accumulation of BADH transcripts in the leaves.

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SummaryBetaine aldehyde dehydrogenase (BADH) catalyzes the last step in the plant biosynthetic pathway that leads to glycinebetaine. Rice plants (Oryza sativa L.}, albeit considered a typical non-glycinebetaine accumulating species, have been found to express this enzyme at low levels. This observation evokes an interest in phylogenic evolution of the enzyme in the plant kingdom. It is reported here that rice plants possess the ability to take up exogenously added betaine aldehyde through the roots and convert it to glycinebetaine, resulting in an enhanced salttolerance of the plants. A gene encoding a putative BADH from the rice genome was also cloned and sequenced. The gene was found to contain 14 introns, and the overall nucleotide sequence of the coding region is c. 78% identical to that of the barley BADH cDNA. Cloning of a partial BADH cDNA from rice was accomplished by reverse transcription-polymerase chain reaction (RT-PCR). The nucleotide sequence of the cloned fragment was found to be identical to the corresponding exon regions of the rice genomic BADH gene. The deduced amino acid sequences of rice and barley BADH both contain a C-terminal tripeptide SKL, a signal known to target preproteins to microbodies. This localization was confirmed by an immuno-gold labeling study of transgenic tobacco harboring barley cDNA, which showed BADH protein inside peroxisomes. Northern blot analysis revealed that the level of BADH mRNA is salt-inducible.

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