Differential regulation of alanine aminotransferase homologues by abiotic stresses in wheat (Triticum aestivum L.) seedlings

Wheat (Triticum aestivum L.) seedlings contain four alanine aminotransferase (AlaAT) homologues. Two of them encode AlaAT enzymes, whereas two homologues act as glumate:glyoxylate aminotransferase (GGAT). To address the function of the distinct AlaAT homologues a comparative examination of the changes in transcript level together with the enzyme activity and alanine and glutamate content in wheat seedlings subjected to low oxygen availability, nitrogen and light deficiency has been studied. Shoots of wheat seedlings were more tolerant to hypoxia than the roots as judging on the basis of enzyme activity and transcript level. Hypoxia induced AlaAT1 earlier in roots than in shoots, while AlaAT2 and GGAT were unaffected. The increase in AlaAT activity lagged behind the increase in alanine content. Nitrogen deficiency has little effect on the activity of GGAT. In contrast, lower activity of AlaAT and the level of mRNA for AlaAT1 and AlaAT2 in wheat seedlings growing on a nitrogen-free medium seems to indicate that AlaAT is regulated by the availability of nitrogen. Both AlaAT and GGAT activities were present in etiolated wheat seedlings but their activity was half of that observed in light-grown seedlings. Exposure of etiolated seedlings to light caused an increase in enzyme activities and up-regulated GGAT1. It is proposed that hypoxia-induced AlaAT1 and light-induced peroxisomal GGAT1 appears to be crucial for the regulation of energy availability in plants grown under unfavourable environmental conditions

In maize, two distinct ribulose 1,5-bisphosphate carboxylase/oxygenase activase transcripts have different day/night patterns of expression

Several cDNAs encoding ribulose-1,5-bisphosphate carboxylase/oxygenase activase (Rubisco activase, RCA) were isolated from a maize (Zea mays L.) leaf cDNA library. Although all the cDNAs encoded the same polypeptide, the RCA 0 isoform, they showed two different downstream-like elements (DST-like) at their 3' untranslated regions (UTRs). The Zmrca1 cDNAs had the subdomain I, and II and the Zmrca2 cDNAs, besides these subdomains, showed two repeats of the subdomain III. The presence of at least two different rca genes in the maize genome was demonstrated by Southern, and by PCR analysis using primers specific for the two cDNAs. Northern analysis with probes specific! for each gene showed that the Zmrca2 was expressed as a 1.8 kb transcript, the Zmrca1 corresponded to a 1.4 kb transcript, and a 1 kb band was a stable degradation product of one or both transcripts. Although both mRNAs showed cyclic variations during a day/night period, with their highest levels before dawn, the Zmrca2 transcript showed stronger changes than the Zmrca1 transcript, presenting a twofold larger highest to lowest RNA accumulation ratio than the Zmrca1 transcript, implying that they have different turnover rates. Our results suggest that post-transcriptional mechanisms, mediated by the DST-like element might be involved in the circadian expression of the maize rca transcripts. (C) 2004 Elsevier SAS. All rights reserved

Why are chlorinated pollutants so difficult to degrade aerobically? Redox stress limits 1,3-dichloroprop-1-ene metabolism by Pseudomonas pavonaceae

Chlorinated pollutants are hardly biodegradable under oxic conditions, but they can often be metabolized by anaerobic bacteria through organohalide respiration reactions. In an attempt to identify bottlenecks limiting aerobic catabolism of 1,3-dichloroprop-1-ene (1,3-DCP; a widely used organohalide) in Pseudomonas pavonaceae, the possible physiological restrictions for this process were surveyed. Flow cytometry and a bioluminescence reporter of metabolic state revealed that cells treated with 1,3-DCP experienced an intense stress that could be traced to the endogenous production of reactive oxygen species (ROS) during the metabolism of the compound. Cells exposed to 1,3-DCP also manifested increased levels of D-glucose-6-P 1-dehydrogenase activity (G6PDH, an enzyme key to the synthesis of reduced NADPH), observed under both glycolytic and gluconeogenic growth regimes. The increase in G6PDH activity, as well as cellular hydroperoxide levels, correlated with the generation of ROS. Additionally, the high G6PDH activity was paralleled by the accumulation of D-glucose-6-P, suggesting a metabolic flux shift that favours the production of NADPH. Thus, G6PDH and its cognate substrate seem to play an important role in P. pavonaceae under redox stress caused by 1,3-DCP, probably by increasing the rate of NADPH turnover. The data suggest that oxidative stress associated with the biodegradation of 1,3-DCP reflects a significant barrier for the evolution of aerobic pathways for chlorinated compounds, thereby allowing for the emergence of anaerobic counterparts.Fil: Nikel, Pablo Ivan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Universidad Nacional de San Martín. Instituto de Investigaciones Biotecnológicas; ArgentinaFil: Pérez Pantoja, Danilo. Consejo Superior de Investigaciones Científicas. Centro Nacional de Biotecnología; EspañaFil: de Lorenzo, Víctor. Consejo Superior de Investigaciones Científicas. Centro Nacional de Biotecnología; Españ

Dehydrins patterns in common bean exposed to drought and watered conditions

Drought is a major constraint for common bean (Phaseolus vulgaris L.) production in M�xico. Dehydrins are constitutive or stress-induced proteins related with a protective role of membranes and macromolecules against denaturation, thus preventing loss of their function. In this work, seed production and patterns of dehydrins accumulation in leaves and pods were evaluated in common bean cv. 'Otom�' subjected to drought, as compared with well-irrigated plants. Drought applied at pod formation and seed filling (SF) reduced yield up to 57 %. An antibody against a consensus sequence present in most dehydrins allowed for dehydrin identification. Two dehydrins of 82 and 73 kDA turned up both in leaves and pods throughout all the evaluated conditions. Presumably, both dehydrins are constitutive in the 'Otom�' cultivar. These dehydrins showed higher expression than controls in leaves after 6 d of drought at seedling and SF stages, and in pods 6 d after drought had started at SF. Increased expression might provide better protection during early stages of seedling and seed development. Increments on 63, 36 and 22 kDa dehydrin expression in pods at late SF might coincide with plant developmental programs, which prepare seed for desiccation. Dehydrins of 158, 54, 46, and 41 kDa were detected in pods 10 d after floral opening as a transient response to drought stress in SF. These results indicate dehydrins are relevant during plant development, as well as during drought stress

Dehydrins patterns in common bean exposed to drought and watered conditions

Drought is a major constraint for common bean (Phaseolus vulgaris L.) production in México. Dehydrins are constitutive or stress-induced proteins related with a protective role of membranes and macromolecules against denaturation, thus preventing loss of their function. In this work, seed production and patterns of dehydrins accumulation in leaves and pods were evaluated in common bean cv. 'Otomí' subjected to drought, as compared with well-irrigated plants. Drought applied at pod formation and seed filling (SF) reduced yield up to 57 %. An antibody against a consensus sequence present in most dehydrins allowed for dehydrin identification. Two dehydrins of 82 and 73 kDA turned up both in leaves and pods throughout all the evaluated conditions. Presumably, both dehydrins are constitutive in the 'Otomí' cultivar. These dehydrins showed higher expression than controls in leaves after 6 d of drought at seedling and SF stages, and in pods 6 d after drought had started at SF. Increased expression might provide better protection during early stages of seedling and seed development. Increments on 63, 36 and 22 kDa dehydrin expression in pods at late SF might coincide with plant developmental programs, which prepare seed for desiccation. Dehydrins of 158, 54, 46, and 41 kDa were detected in pods 10 d after floral opening as a transient response to drought stress in SF. These results indicate dehydrins are relevant during plant development, as well as during drought stress