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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tolerance to low oxygen availability is likely to be due to the interaction of several factors. Sugar availability is one of the elements required to support anaerobic metabolism. In cereal grains the availability of soluble sugars is limited, while starch is stored in large amounts. Degradation of starch under anoxia is therefore needed to avoid sugar starvation leading to rapid cell death. The striking difference in the ability to produce alpha-amylase when comparing the anoxia-tolerant rice (Oryza sativa L.) grains with grains of other cereals is not easily explained. Rice is able to respond to gibberellins under anoxia, but the response is too slow to explain the rapid production of alpha-amylase enzyme. In the present work we demonstrated that alpha-amylase production during the first 2 d after imbibition is mostly due to the activity of the Ramy3D gene, encoding for the G and H isoforms of alpha-amylase. The induction of Ramy3D transcription is likely to result from a low sugar content in the grains incubated under anoxia. The ability of rice embryos to sense sugars under anoxia is reported.
Ann Bot 2003 Jan
PMID:Sugar modulation of alpha-amylase genes under anoxia. 1250 35

A DNA fragment corresponding to part of an SNF1 (sucrose non-fermenting-1)-related protein kinase (SnRK1) transcript was amplified by a polymerase chain reaction (PCR) from a wheat (Triticum aestivum) endosperm cDNA library. It was used to construct a chimaeric gene, pUasSnRKN, comprising a ubiquitin promoter, the SnRK1 PCR product in the antisense orientation and the nopaline synthase (Nos) gene terminator. This construct was used in transient gene expression experiments in cultured wheat embryos together with a series of reporter gene constructs. These included the wheat alpha amylase gene alpha-Amy2 promoter with UidA (Gus) coding region (palpha2GT), rice actin promoter with Gus (pActIDGus), ubiquitin promoter with Gus (pAHC25) and actin promoter with green fluorescent protein (GFP) gene (pAct1Is-GFP1). All of the reporter genes were found to be active when bombarded into scutellae isolated from immature grains at 25 d post-anthesis and incubated on MS medium for 24 h prior to bombardment. However, co-bombardment of palpha2GT with equimolar amounts of pUasSnRKN resulted in no detectable Gus activity, indicating that the antisense SnRK1 construct repressed the alpha-Amy2 promoter. Co-bombardment with pUasSnRKN had no effect on the activity of the other promoters used in the study. A triple bombardment with palpha2GT, pAct1Is-GFP-1 and pUasSnRKN resulted in clear green fluorescence, indicating that the bombarded cells were still viable, but no Gus activity. RT-PCR analysis showed clearly that the antisense SnRK1 gene was expressing. Northern and RT-PCR analyses confirmed that SnRK1 and both alpha-amylase genes, alpha-Amy1 and alpha-Amy2, are expressed in cultured wheat embryos harvested from grain 25 d post-anthesis. Expression of alpha-Amy1 and alpha-Amy2 was up-regulated by sugar starvation.
J Exp Bot 2003 Feb
PMID:Antisense SNF1-related (SnRK1) protein kinase gene represses transient activity of an alpha-amylase (alpha-Amy2) gene promoter in cultured wheat embryos. 1255 17

Two-month-old tomato plants were submitted to day/night cycles and to prolonged darkness in order to investigate the physiological and biochemical response to sugar starvation in sink organs. Roots appeared particularly sensitive to the cessation of photosynthesis, as revealed by the reduction of the growth rate and the decline of the carbohydrate and protein content. Therefore, excised tomato roots were used as a model to deepen the characterization of sugar starvation symptoms. In excised roots, the endogenous sugars were rapidly exhausted and significant degradation of protein was observed. Glutamine and asparagine accounted for most of the nitrogen released by protein breakdown. Respiration declined and proliferation- and growth-associated genes were repressed soon after the beginning of the sugar depletion. Among the genes studied, only the gene encoding asparagine synthetase was strongly induced. All the starvation symptoms were reversible when the roots were resupplied with sugar. When the culture conditions deteriorated, the metabolic and molecular changes led to the triggering of apoptosis of the root cells.
J Exp Bot 2003 Apr
PMID:Physiological, biochemical and molecular analysis of sugar-starvation responses in tomato roots. 1265 65

Plants have evolved an array of responses that adapt their growth to conditions of limited phosphate (Pi) supply. These involve biochemical and developmental changes that improve Pi acquisition and recycling, and protect against the stress of Pi starvation. The induction of these responses requires a sophisticated regulatory system that integrates information on external and internal plant Pi status and the details of this regulatory system are only just beginning to be elucidated. In this review, the current knowledge of this regulatory system is summarized, the hallmark of which is the central role of transcription factor PHR1 in the co-ordinated regulation of many phosphate-starvation-responsive genes. The role of hormonal signalling is also described, including auxins, ethylene and, particularly, cytokinins in the regulation of Pi-starvation responses.
J Exp Bot 2004 Feb
PMID:The transcriptional control of plant responses to phosphate limitation. 1471 95

A genomics analysis on sulphur metabolism has been conducted at the level of transcriptomics and metabolomics. The analysis of these data after applying bioinformatic tools is to reveal novel findings. The findings are discussed and the knowledge obtained from comparable analyses on sulphur metabolism and other plant nutrient genomic studies is reviewed. The analysis of the response of the transcriptome and metabolome to sulphur deprivation in the growth medium provides a tool set for the analysis of comparable genomics studies of other nutrients. The goal of this 'sulphobolomics' (i.e. sulphur genomics and metabolome analysis) approach, and of other investigations, is to describe in a holistic way the biochemical, molecular, and physiological response of a plant to nutrient starvation, here sulphate, or, more generally, to alterations and imbalances in nutrient availability. Eventually, this analysis will provide a case study for a systems biology approach.
J Exp Bot 2004 Aug
PMID:Towards dissecting nutrient metabolism in plants: a systems biology case study on sulphur metabolism. 1520 39

Sulphate assimilation is an essential pathway being a source of reduced sulphur for various cellular processes and for the synthesis of glutathione, a major factor in plant stress defence. Many reports have shown that sulphate assimilation is well co-ordinated with the assimilation of nitrate and carbon. It has long been known that, during nitrate deficiency, sulphate assimilation is reduced and that the capacity to reduce nitrate is diminished in plants starved for sulphate. Only recently, however, was it shown that adenosine 5' phosphosulphate reductase (APR), the key enzyme of sulphate assimilation, is regulated by carbohydrates. In plants treated with sucrose or glucose APR was induced, whereas the activity was strongly reduced in plants grown in CO(2)-free air. The availability of cysteine is a crucial factor in glutathione synthesis, but an adequate supply of glutamate and glycine are also important. The molecular mechanisms for the co-ordination of S, N, and C assimilation are not known. O-acetylserine, a precursor of cysteine, was proposed to be the signal regulating sulphate assimilation, but most probably is not the outgoing signal to N and C metabolism. cDNA arrays revealed the induction of genes involved in auxin synthesis upon S-starvation, pointing to a possible role of phytohormones. Clearly, despite significant progress in understanding the regulation of sulphate assimilation and glutathione synthesis, their co-ordination with N and C metabolism achieved, and several potential signal molecules identified, present knowledge is still far from being sufficient.
J Exp Bot 2004 Aug
PMID:Control of sulphate assimilation and glutathione synthesis: interaction with N and C metabolism. 1528 42

Amino acids are regarded as the nitrogen 'currency' of plants. Amino acids can be taken up from the soil directly or synthesized from inorganic nitrogen, and then circulated in the plant via phloem and xylem. AtAAP3, a member of the Amino Acid Permease (AAP) family, is mainly expressed in root tissue, suggesting a potential role in the uptake and distribution of amino acids. To determine the spatial expression pattern of AAP3, promoter-reporter gene fusions were introduced into Arabidopsis. Histochemical analysis of AAP3 promoter-GUS expressing plants revealed that AAP3 is preferentially expressed in root phloem. Expression was also detected in stamens, in cotyledons, and in major veins of some mature leaves. GFP-AAP3 fusions and epitope-tagged AAP3 were used to confirm the tissue specificity and to determine the subcellular localization of AtAAP3. When overexpressed in yeast or plant protoplasts, the functional GFP-AAP3 fusion was localized in subcellular organelle-like structures, nuclear membrane, and plasma membrane. Epitope-tagged AAP3 confirmed its localization to the plasma membrane and nuclear membrane of the phloem, consistent with the promoter-GUS study. In addition, epitope-tagged AAP3 protein was localized in endodermal cells in root tips. The intracellular localization suggests trafficking or cycling of the transporter, similar to many metabolite transporters in yeast or mammals, for example, yeast amino acid permease GAP1. Despite the specific expression pattern, knock-out mutants did not show altered phenotypes under various conditions including N-starvation. Microarray analyses revealed that the expression profile of genes involved in amino acid metabolism did not change drastically, indicating potential compensation by other amino acid transporters.
J Exp Bot 2004 Oct
PMID:Root phloem-specific expression of the plasma membrane amino acid proton co-transporter AAP3. 1536 41

Lysine catabolism in plants is initiated by a bifunctional LKR/SDH (lysine-ketoglutarate reductase/saccharopine dehydrogenase) enzyme encoded by a single LKR/SDH gene. Yet, the AtLKR/SDH gene of Arabidopsis also encodes a second gene product, namely a monofunctional SDH. To elucidate the regulation of lysine catabolism in Arabidopsis through these two gene products of the AtLKR/SDH gene, an analysis was carried out on the effects of the hormones, abscisic acid and jasmonate, as well as various metabolic and stress signals, including lysine itself, on their mRNA and protein levels. The response of the two gene products to the various treatments was only partially co-ordinated, but the levels of the monofunctional SDH mRNA and protein were always in excess over their bifunctional LKR/SDH counterparts. These results suggest that lysine catabolism is regulated primarily by the first enzyme LKR, while the excess level of SDH enables efficient flux of lysine catabolism following the LKR step. Analysis of transgenic plants expressing beta-glucoronidase fusion constructs with the AtLKR/SDH and monofunctional AtSDH promoters demonstrated that transcriptional regulation contributes to the modulation of expression of the bifunctional LKR/SDH and monofunctional SDH gene products in response to hormonal and metabolic signals. To test whether the enhanced expression of the LKR/SDH gene under various hormonal and metabolic signals is correlated with enhanced lysine catabolism, wild-type Arabidopsis and a knockout mutant lacking lysine catabolism were exposed to abscisic acid and sugar starvation. Free lysine accumulated to significantly higher levels in this knockout mutant than in the wild-type plants.
J Exp Bot 2005 Feb
PMID:Regulation of lysine catabolism in Arabidopsis through concertedly regulated synthesis of the two distinct gene products of the composite AtLKR/SDH locus. 1556 7

Monitoring expression at the transcriptional level is an essential first step for the functional analysis of plant genes. Genes encoding proteins directly involved in sulphur metabolism constitute only a small fraction of all the genes affected by sulphur deficiency stress. Transcriptional responses to various periods of sulphur deprivation have been extensively studied in Arabidopsis thaliana; however, no corresponding data are available for Solanaceae sp. To address this problem, a subtractive library-based approach to search for tobacco genes regulated by a short-term sulphur starvation has been adopted. In this work, 38 genes were identified, of which 22 were regulated positively and 16 were regulated negatively. The transcript levels of the representative genes were monitored in four parts of the plants (mature and immature leaves, stems, and roots), which exhibited differential sulphur deficiency. Interestingly, some genes exhibit different regulation of expression in different parts of the plants. Database analysis allowed assignment of the potential function for many of the identified genes; however, the functions of a small number of genes strongly regulated by sulphur starvation remain unknown. The genes were grouped into nine functional categories, each including both up- and down-regulated genes. The possible links between the identified regulated genes and sulphur metabolism are considered, and compared where possible with expression patterns in Arabidopsis thaliana. Although no obvious regulatory genes were identified, the genes encoding proteins of unknown function remain as potential components of the regulatory processes.
J Exp Bot 2005 Jun
PMID:Using a suppression subtractive library-based approach to identify tobacco genes regulated in response to short-term sulphur deficit. 1583 8

Although the symptoms of magnesium deficiency are well documented in plants, the primary physiological effects of low Mg availability remain largely unknown. This paper describes the physiological responses of Mg starvation in Arabidopsis thaliana. Growth characteristics, Mg and sugar concentration, and photochemical performance were measured at regular intervals during the induction of Mg deficiency. These data show that Mg deficiency increased the sugar concentration and altered sucrose export from young source leaves before any noticeable effect on photosynthetic activity was seen. The decline in photosynthetic activity might be elicited by increased leaf sugar concentrations. Transcript levels of Cab2 (encoding a chlorophyll a/b protein) were lower in Mg-deficient plants before any obvious decrease in the chlorophyll concentration. These transcriptional data suggest that the reduction of chlorophyll is a response to sugar levels, rather than a lack of Mg atoms for chelating chlorophyll.
J Exp Bot 2005 Aug
PMID:Physiological characterization of Mg deficiency in Arabidopsis thaliana. 1598 14


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