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Query: UMLS:C0008272 (chlorosis)
 2,195 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To explore the role of rhizobitoxine in Bradyrhizobium-legume symbiosis, 11 rhizobitoxine mutants of B. japonicum USDA61 were isolated on the basis of their inability to synthesize the toxin in culture. Each mutant is prototrophic and symbiotically effective on soybean, cowpea, siratro, and Glycine soja. The rhizobitoxine mutants differ in their chlorosis phenotypes and rhizobitoxine production in planta. As expected, one group of mutant fail to make toxin in planta, resulting in the absence of chlorosis. Another group of mutants causes severe chlorosis on all cultivars of soybean tested. Surprisingly, this group of mutants makes more rhizobitoxine in soybean nodules than the wild-type strain does. This phenotype is only observed on soybean and not on other hosts such as cowpea, siratro, or G. soja. The remaining mutants all produce rhizobitoxine in planta but vary in the amount of toxin they produce and the severity of chlorosis they induce in soybean plants. Biochemical analysis of mutants demonstrates that one mutant is unable to synthesize serinol, a molecule hypothesized to be an intermediate in rhizobitoxine biosynthesis. By using these mutants, it was found that rhizobitoxine plays no apparent role in the nodulation of rj1 soybeans. Recently, it was found that inhibition of ethylene biosynthesis allows Rhizobium meliloti to overcome nitrate inhibition of nodule formation on alfalfa. Because rhizobitoxine also inhibits ethylene biosynthesis, we tested the ability of mutants which accumulate high levels of toxin in planta to overcome nitrate inhibition of nodule formation on soybean plants and found that the nodule formation induced by the wild type and that induced by mutant strains were equally suppressed in the presence of nitrate.
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PMID:Isolation and characterization of rhizobitoxine mutants of Bradyrhizobium japonicum. 131 77

Cyanobacteria acclimate to low temperature by desaturating their membrane lipids. Mutant strains of Synechococcus sp. PCC 7002 containing insertionally inactivated desA (Delta12 acyl-lipid desaturase) and desB (omega3 acyl-lipid desaturase) genes were produced, and their low-temperature susceptibility was characterized. The desA mutant synthesized no linoleic acid or alpha-linolenic acid, and the desB mutant did not produce alpha-linolenic acid. The desA mutant grew more slowly than the wild-type at 22 degrees C and could not grow at 15 degrees C. The desB mutant could not continuously grow at 15 degrees C, although no observable phenotype appeared at higher temperatures. It has been shown that expression of the desA gene occurs at 38 degrees C and is up-regulated at 22 degrees C, and that the desB gene is only expressed at 22 degrees C. These results indicate that the expression of the desA and desB genes occurs at higher temperatures than those at which a significant decline in physiological activities is caused by the absence of their products. The temperature dependency of photosynthesis was not affected by these mutations. Since chlorosis and inability to grow at 15 degrees C with nitrate was suppressed by the substitution of urea as a nitrogen source, it is very likely that the chilling susceptibility of the desaturase mutants is attributable to nutrient limitation.
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PMID:Alteration of low-temperature susceptibility of the cyanobacterium Synechococcus sp. PCC 7002 by genetic manipulation of membrane lipid unsaturation. 939 31

When deprived of essential nutrients, the non-diazotrophic cyanobacterium Synechococcus sp. strain PCC 7942 undergoes a proteolytic degradation of the phycobiliproteins, its major light-harvesting pigments. This process is known as chlorosis. This paper presents evidence that the degradation of phycobiliproteins is part of an acclimation process in which growing cells differentiate into non-pigmented cells able to endure long periods of starvation. The time course of degradation processes differs for various photosynthetic pigments, for photosystem I and photosystem II activities and is strongly influenced by the illumination and by the experimental conditions of nutrient deprivation. Under standard experimental conditions of combined nitrogen deprivation, three phases of the differentiation process can be defined. The first phase corresponds to the well-known phycobiliprotein degradation, in phase 2 the cells lose chlorophyll a prior to entering phase 3, the fully differentiated state, in which the cells are still able to regenerate pigmentation after the addition of nitrate to the culture. An analysis of the protein synthesis patterns by two-dimensional gel electrophoresis during nitrogen starvation indicates extensive differential gene expression, suggesting the operation of tight regulatory mechanisms.
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PMID:Nitrogen-starvation-induced chlorosis in Synechococcus PCC 7942: adaptation to long-term survival. 978 92

Type B strains of Rhizobium tropici induce severe foliar chlorosis when applied at planting to seeds of symbiotic host and non-host dicotyledonous plants. A Tn5-induced mutant, designated CT4812, or R. tropici strain CIAT899 that was unable to induce chlorosis was isolated. Cloning and sequencing of the DNA flanking the transposon in CT4812 revealed that the Tn5 insertion is located in a gene similar to glnD, which encodes uridylyltransferase/uridylyl-removing enzyme in enteric bacteria. Two marker-exchange mutants with insertions in glnD also failed to induce chlorosis in bean (Phaseolus vulgaris) plants. The 5'-most insertion in glnD (in mutant strain ME330) abolished the ability of R. tropici to utilize nitrate as a sole carbon source, whereas a mutation in glnD further downstream (in mutant strain ME245) did not have an obvious effect on nitrate utilization. A gene similar to the Salmonella typhimurium virulence gene mviN overlaps the 3' end of the R. tropici glnD homologue. A mutation in mviN had no effect on the ability of CIAT899 to induce chlorosis in bean plants. Therefore the glnD homologue, but not mviN, appears to be required for induction of chlorosis in plants by R. tropici strain CIAT899. A high nitrogen: carbon ratio in the rhizosphere of bean plants also prevented R. tropici from inducing chlorosis in bean plants. Mutations in either the glnD homologue or mviN had no significant effect on root nodule formation or acetylene reduction activity. A mutation in mviN eliminated motility in R. tropici. The sequence data, the inability of the glnD mutant to utilize nitrate, and the role of the R. tropici glnD gene in chlorosis induction in plants, a process that is nitrogen regulated, suggest that glnD plays a role in nitrogen sensing in R. tropici as its homologues do in other organisms.
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PMID:Mutants of Rhizobium tropici strain CIAT899 that do not induce chlorosis in plants. 978 10

In animals and yeast, voltage-dependent chloride channels of the CLC family play a role in basic cellular functions such as epithelial transport, plasma membrane excitability, and control of pH and membrane potential in intracellular compartments. To assess the function of CLCs in plants, we searched for CLC insertion mutants in a library of Arabidopsis lines transformed by Agrobacterium tumefaciens transferred DNA (T-DNA). Using a polymerase chain reaction-based screening procedure, an Arabidopsis line that carries a T-DNA insertion within the C-terminus of the AtCLC-a coding sequence was identified. Progeny from this plant line, clca-1, showed dramatically altered transcription of the AtCLC-a gene. Plants homozygous for the clca-1 mutation exhibited normal development and a morphology indistinguishable from the wild-type. However, their capacity to accumulate nitrate under conditions of nitrate excess was reduced in roots and shoots, by approximately 50%, while chloride, sulphate and phosphate levels were similar to the wild-type. In addition, the herbicide chlorate, an analogue of nitrate, induced a faster and more pronounced chlorosis in mutant plants. Hypersensitivity to chlorate as well as decreased nitrate levels co-segregated with the T-DNA insertion. They were found at various time points of the clca-1 life cycle, supporting the idea that AtCLC-a has a general role in the control of the nitrate status in Arabidopsis. Concordant with such a function, AtCLC-a mRNA was found in roots and shoots, and its levels rapidly increased in both tissues upon addition of nitrate but not ammonium to the culture medium. The specificity of AtCLC-a function with respect to nitrate is further supported by a similar free amino acid content in wild-type and clca-1 plants. Although the cellular localization of AtCLC-a remains unclear, our results suggest that AtCLC-a plays a role in controlling the intracellular nitrate status.
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PMID:Disruption of putative anion channel gene AtCLC-a in Arabidopsis suggests a role in the regulation of nitrate content. 1075 77

Legumes obtain a substantial portion of their nitrogen (N) from symbiotic N2 fixation in root nodules. The glutamine synthetase (GS, EC 6.3.1.2)/glutamate synthase (GOGAT) cycle is responsible for the initial N assimilation. This report describes the analysis of a transgenic alfalfa (Medicago sativa L.) line containing an antisense NADH-GOGAT (EC 1.4.1.14) under the control of the nodule-enhanced aspartate amino-transferase (AAT-2) promoter. In one transgenic line, NADH-GOGAT enzyme activity was reduced to approximately 50%, with a corresponding reduction in protein and mRNA. The transcript abundance for cytosolic GS, ferredoxin-dependent GOGAT (EC 1.4.7.1), AAT-2 (EC 2.6.1.1), asparagine synthase (EC 6.3.5.4), and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were unaffected, as were enzyme activities for AAT, PEPC and GS. Antisense NADH-GOGAT plants grown under symbiotic conditions were moderately chlorotic and reduced in growth and N content, even though symbiotic N2 fixation was not significantly reduced. The addition of nitrate relieved the chlorosis and restored growth and N content. Surprisingly, the antisense NADH-GOGAT plants were male sterile resulting from inviable pollen. A reduction in NADH-GOGAT enzyme activity and transcript abundance in the antisense plants was measured during the early stages of flower development. Inheritance of the transgene was stable and resulted in progeny with a range of NADH-GOGAT activity. These data indicate that NADH-GOGAT plays a critical role in the assimilation of symbiotically fixed N and during pollen development.
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PMID:Decreased NADH glutamate synthase activity in nodules and flowers of alfalfa (Medicago sativa L.) transformed with an antisense glutamate synthase transgene. 1093 93

Experiments have been carried out with field-grown pear trees to investigate the effect of iron chlorosis on the composition of the leaf apoplast. Iron deficiency was associated with an increase in the leaf apoplastic pH from the control values of 5.5-5.9 to 6.5-6.6, as judged from direct pH measurements in apoplastic fluid obtained by centrifugation and fluorescence of leaves incubated with 5-CF. The major organic acids found in leaf apoplastic fluid of iron-deficient and iron-sufficient pear leaves were malate, citrate and ascorbate. The total concentration of organic acids was 2.9 mM in the controls and increased to 5.5 mM in Fe-deficient leaves. The total apoplastic concentration of inorganic cations (Ca, K and Mg) increased with Fe deficiency from 15 to 20 mM. The total apoplastic concentration of inorganic anions (Cl-, NO3-, SO4(2-) and HPO4(2-)) did not change with Fe deficiency. Iron concentrations decreased from 4 to 1.6 microM with Fe deficiency. The major Fe species predicted to exist in the apoplast was [FeCitOH](-1) in both Fe-sufficient and deficient leaves. Organic acids in whole leaf homogenates increased from 20 to 40 nmol x m(-2) with Fe deficiency. The accumulation of organic anions in the Fe-deficient leaves does not appear to be associated to an increased C fixation in leaves, but rather it seems to be a consequence of C transport via xylem.
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PMID:Iron deficiency-associated changes in the composition of the leaf apoplastic fluid from field-grown pear (Pyrus communis L.) trees. 1145 9

Several levels of photosynthetic photon flux density (PPFD) were tested for effects on growth of 4 cultivars of lettuce (Lactuca sativa L.) under controlled-environment conditions. Growth of 'Salad Bowl', 'Bibb', and 'Ruby' was greater at 932 micromoles s-1 m-2 than at < or = 644 micromoles s-1 m-2 under a 16-hour photoperiod. Thirty mM NO3- or 5 mM NH4+ + 25 mM NO3- increased leaf dry weight while reducing leaf chlorosis in 'Salad Bowl' and 'Grand Rapids' relative to that with 15 mM NO3-, and reduced leaf purpling in 'Bibb' and 'Ruby' with little or no effect on yield. Continuous illumination with 455 or 918 micromoles s-1 m-2 stimulated yield of 'Salad Bowl' and 'Bibb' when 30 mM N as NH4+ + NO3- was used relative to that with 15 mM NO3-.
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PMID:Enhancement of lettuce yield by manipulation of light and nitrogen nutrition. 1154 84

It has been hypothesized that nitrate (NO(3)(-)) nutrition might induce iron (Fe) deficiency chlorosis by inactivation of Fe in the leaf apoplast (H.U. Kosegarten, B. Hoffmann, K. Mengel [1999] Plant Physiol 121: 1069-1079). To test this hypothesis, sunflower (Helianthus annuus L. cv Farnkasol) plants were grown in nutrient solutions supplied with various nitrogen (N) forms (NO(3)(-), NH(4)(+) and NH(4)NO(3)), with or without pH control by using pH buffers [2-(N-morpholino)ethanesulfonic acid or 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid]. It was shown that high pH in the nutrient solution restricted uptake and shoot translocation of Fe independently of N form and, therefore, induced Fe deficiency chlorosis at low Fe supply [1 micro M ferric ethylenediaminedi(O-hydroxyphenylacetic acid)]. Root NO(3)(-) supply (up to 40 mM) did not affect the relative distribution of Fe between leaf apoplast and symplast at constant low external pH of the root medium. Although perfusion of high pH-buffered solution (7.0) into the leaf apoplast restricted (59)Fe uptake rate as compared with low apoplastic solution pH (5.0 and 6.0, respectively), loading of NO(3)(-) (6 mM) showed no effect on (59)Fe uptake by the symplast of leaf cells. However, high light intensity strongly increased (59)Fe uptake, independently of apoplastic pH or of the presence of NO(3)(-) in the apoplastic solution. Finally, there are no indications in the present study that NO(3)(-) supply to roots results in the postulated inactivation of Fe in the leaf apoplast. It is concluded that NO(3)(-) nutrition results in Fe deficiency chlorosis exclusively by inhibited Fe acquisition by roots due to high pH at the root surface.
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PMID:Nitrate does not result in iron inactivation in the apoplast of sunflower leaves. 1285 12

In wild-type Nicotiana plumbaginifolia and other higher plants, nitrate reductase (NR) is rapidly inactivated/activated in response to dark/light transitions. Inactivation of NR is believed to be caused by phosphorylation at a special conserved regulatory Ser residue, Ser 521, and interactions with divalent cations and inhibitory 14-3-3 proteins. A transgenic N. plumbaginifolia line (S(521)) was constructed where the Ser 521 had been changed by site-directed mutagenesis into Asp. This mutation resulted in complete abolishment of inactivation in response to light/dark transitions or other treatments known to inactivate NR. During prolonged darkness, NR in wild-type plants is in the inactivated form, whereas NR in the S(521) line is always in the active form. Differences in degradation rate between NR from S(521) and lines with non-mutated NR were not found. Kinetic constants like Km values for NADH and NO3(-) were not changed, but a slightly different pH profile was observed for mutated NR as opposed to non-mutated NR. Under optimal growth conditions, the phenotype of the S(521) plants was not different from the wild type (WT). However, when plants were irrigated with high nitrate concentration, 150 mM, the transgenic plants accumulated nitrite in darkness, and young leaves showed chlorosis.
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PMID:Mutation of the regulatory phosphorylation site of tobacco nitrate reductase results in constitutive activation of the enzyme in vivo and nitrite accumulation. 1294 Sep 50


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