Differential regulation of trichome formation on the adaxial and abaxial leaf surfaces by gibberellins and photoperiod in Arabidopsis thaliana (L.) Heynh

In wild-type (WT) Columbia and Landsberg erecta ecotypes of Arabidopsis thaliana (L.) Heynh., trichomes are present on the adaxial surfaces of all rosette leaves but are absent from the abaxial surfaces of the first-formed leaves. We have determined that both long-day (LD) photoperiod and gibberellin (GA) stimulate trichome formation. WT plants grown in LD conditions produce the first abaxial trichome on earlier leaves than plants grown in short-day (SD) conditions. Photoperiod sensitivity of abaxial trichome formation on WT plants develops gradually over time, reaching the maximum sensitivity about 24 d after germination. Application of gibberellic acid to WT plants growing in SD conditions accelerates the onset of abaxial trichomes. Conversely, application of 20 to 80 mg L-1 paclobutrazol, a GA biosynthesis inhibitor, to wild-type plants suppresses trichome initiation on the abaxial epidermis. The GA-deficient mutants ga1-5 and ga4-1 and the GA-insensitive mutant gai-1 exhibit delayed onset of abaxial trichomes when grown in LD conditions. The null mutant ga1-3 produces completely glabrous leaves when grown in SD conditions. Application of gibberellic acid to glabrous ga1-3 plants consistently induces earlier formation of trichomes on the adaxial epidermis than on the abaxial epidermis, demonstrating a difference between the adaxial and abaxial surfaces in their response to GA with regard to trichome formation.     

Effect of aluminum on cytoplasmic Ca2+ homeostasis in root hairs of Arabidopsis thaliana (L.)

Aluminum inhibition of root growth is a major world agricultural problem where the cause of toxicity has been linked to changes in cellular calcium homeostasis. Therefore, the effect of aluminum ions (Al) on changes in cytoplasmic free calcium concentration ([Ca2+]c) was followed in root hairs of wild-type, Al-sensitive and Al-resistant mutants of Arabidopsis thaliana (L.) Heynh. Generally, Al exposure resulted in prolonged elevations in tip-localized [Ca2+]c in both wild-type and Al-sensitive root hairs. However, these Al-induced increases in [Ca2+]c were not tightly correlated with growth inhibition, occurring up to 15 min after Al had induced growth to stop. Also, in 32% of root hairs examined growth stopped without a detectable change in [Ca2+]c. In contrast, Al-resistant mutants showed little growth inhibition in response to AlCl3 exposure and in no case was a change in [Ca2+]c observed. Of the other externally applied stresses tested (oxidative and mechanical stress), both were found to inhibit root hair growth, but only oxidative stress (H2O2, 10 microM) caused a prolonged rise in [Ca2+]c similar to that induced by Al. Again this increase occurred after growth had been inhibited. The lack of a tight correlation between Al exposure, growth inhibition and altered [Ca2+]c dynamics suggests that although exposure of root hairs to toxic levels of Al causes an alteration in cellular Ca2+ homeostasis, this may not be a required event for Al toxicity. The elevation in [Ca2+]c induced by Al also strongly suggests that the phytotoxic action of Al in root hairs is not through blockage of Ca2(+)-permeable channels required for Ca2+ influx into the cytoplasm.     

Pressure regulation of the electrical properties of growing Arabidopsis thaliana L. root hairs

Actively growing Arabidopsis thaliana L. (Columbia wild type) root hairs were used to examine the interplay between cell turgor pressure and electrical properties of the cell: membrane potential, conductance, cell-to-cell coupling, and input resistance. Pressure was directly modulated using a pressure probe or indirectly by changing the extracellular osmolarity. Direct modulation of pressure in the range of 0 to about 15 x 10(5) Pa (normal turgor pressure was 6.8 +/- 2.0 x 10(5) Pa, n = 29) did not affect the membrane potential, conductance, coupling, or input resistance. Indirect modulation of turgor pressure by adding (hyperosmotic) or removing (hypo-osmotic) 200 mM mannitol/sorbitol affected the potential and conductance but not cell-to-cell coupling. Hypo-osmotic treatment depolarized the potential about 40 mV from an initial potential of about -190 mV and increased membrane conductance, consistent with an increase in anion efflux from the cell. Hyperosmotic treatment hyperpolarized the cell about 25 mV from the same initial potential and decreased conductance, consistent with a decline in cation influx. The results are likely due to the presence of an "osmo-sensor," rather than a "turgor-sensor," regulating the cell's response to osmotic stress.     

Isolation and characterization of a cDNA encoding Arabidopsis thaliana mevalonate kinase by genetic complementation in yeast

A 1.64-kb cDNA encoding an Arabidopsis thaliana mevalonate kinase (MK) was cloned by complementation of the erg 12-1 mutation affecting MK in the yeast Saccharomyces cerevisiae, and the nucleotide sequence was determined. The longest open reading frame encodes a protein of 378 amino acids (aa) with a predicted molecular mass of 40,650 Da. A striking feature of the cDNA sequence is a long 5' untranslated region (322 bp). The deduced aa sequence reveals that the plant enzyme shows strong similarities to the yeast and mammalian enzymes, especially the strong hydrophobicity percentage and several conserved regions. Southern analysis suggests that probably only one locus exists in the A. thaliana genome.     

A serine/threonine protein kinase gene isolated by an in vivo binding procedure using the Arabidopsis floral homeotic gene product, AGAMOUS

During the course of characterizing fragments bound to an Arabidopsis floral protein AGAMOUS in vivo, a gene encoding a putative serine/threonine protein kinase was found on one of the fragments. The deduced 426 amino acid residues of the gene, named APK2a, are 65% identical to a previously reported Arabidopsis serine/threonine protein kinase, APK1a. The gene is composed of 6 exons and maps at 10 cM from the upper end of chromosome 1. Northern hybridization experiments indicated that the gene is strongly expressed in leaves, moderately in roots, and very weakly in flowers. Further in situ analysis of the expression in floral buds showed that the APK2a gene is expressed at pedicels, is not expressed at the floral organ primordia of wild type floral buds, but is moderately expressed in the floral organ primordia of the agamous mutant. In vitro binding assay suggest that the AGAMOUS protein binds to a sequence similar to, but different from, the known MADS-binding consensus sequences, the CArG box, located 3' downstream of the APK2a gene. These results suggest that APK2a expression is negatively regulated by the AG protein. A close homologue of the APK2a gene, named APK2b, was also isolated from the Arabidopsis cDNA library. The expression pattern of the APK2b gene differs from that of APK2a. It is strongly expressed in leaves, moderately in flowers, and weakly in roots.     

A modified autonomous En transposon in maize (Zea mays L.) elicits a differential response of reporter alleles

Transposable elements in maize are composed of a defined molecular structure that includes coding sequences, determiners of functionality and ordered terminal motifs that provide binding sites for transposase proteins. Alterations in these components change the phenotypic expression of unstable genes with transposon inserts. The molecular basis for the altered timing and frequency of transposition as determined by the size and number of spots on kernels or stripes on leaves has generally been described for defective inserts in genes. Most differential patterns can be ascribed to alterations in the terminal motifs of the reporter allele structure that supplies a substrate (terminal inverted repeat motifs) for transposase activity. For autonomously functioning alleles, the explanations for changes in phenotype are not so clear. In this report, an En-related element identified as F-En is described that shares with En the recognition of a specific defective element cl(mr)888104 but differs from En in that this F-En element does not recognize the canonical cl(mr) elements that are recognized by En. Evidence is provided suggesting that F-En does not recognize other En/Spm-related defective elements, some of whose sequences are known. This modified En arose from a cl-m autonomously mutating En allele.     

Characterization of DNA sequences encoding a novel isoform of the 55 kDa B regulatory subunit of the type 2A protein serine/threonine phosphatase of Arabidopsis thaliana

We have identified a novel gene (AtB beta) encoding a previously uncharacterized isoform of the B regulatory subunit of the type 2A serine/threonine protein phosphatase (PP2A) of Arabidopsis, and show that mRNA derived from the AtB beta gene accumulates in all Arabidopsis organs. In addition, we examined the expression of the three genes encoding the A regulatory subunit of Arabidopsis PP2A and show these genes are expressed in all organs as well. Taken together, our results suggest a myriad of PP2A subunit combinations, possibly with distinct substrate specificities, may occur within each Arabidopsis cell.     

A dominant-negative cyclin D1 mutant prevents nuclear import of cyclin-dependent kinase 4 (CDK4) and its phosphorylation by CDK-activating kinase

Cyclins contain two characteristic cyclin folds, each consisting of five alpha-helical bundles, which are connected to one another by a short linker peptide. The first repeat makes direct contact with cyclin-dependent kinase (CDK) subunits in assembled holoenzyme complexes, whereas the second does not contribute directly to the CDK interface. Although threonine 156 in mouse cyclin D1 is predicted to lie at the carboxyl terminus of the linker peptide that separates the two cyclin folds and is buried within the cyclin subunit, mutation of this residue to alanine has profound effects on the behavior of the derived cyclin D1-CDK4 complexes. CDK4 in complexes with mutant cyclin D1 (T156A or T156E but not T156S) is not phosphorylated by recombinant CDK-activating kinase (CAK) in vitro, fails to undergo activating T-loop phosphorylation in vivo, and remains catalytically inactive and unable to phosphorylate the retinoblastoma protein. Moreover, when it is ectopically overexpressed in mammalian cells, cyclin D1 (T156A) assembles with CDK4 in the cytoplasm but is not imported into the cell nucleus. CAK phosphorylation is not required for nuclear transport of cyclin D1-CDK4 complexes, because complexes containing wild-type cyclin D1 and a CDK4 (T172A) mutant lacking the CAK phosphorylation site are efficiently imported. In contrast, enforced overexpression of the CDK inhibitor p21Cip1 together with mutant cyclin D1 (T156A)-CDK4 complexes enhanced their nuclear localization. These results suggest that cyclin D1 (T156A or T156E) forms abortive complexes with CDK4 that prevent recognition by CAK and by other cellular factors that are required for their nuclear localization. These properties enable ectopically overexpressed cyclin D1 (T156A), or a more stable T156A/T286A double mutant that is resistant to ubiquitination, to compete with endogenous cyclin D1 in mammalian cells, thereby mobilizing CDK4 into cytoplasmic, catalytically inactive complexes and dominantly inhibiting the ability of transfected NIH 3T3 fibroblasts to enter S phase.     

Repeated DNA sequences isolated by microdissection. I. Karyotyping of barley (Hordeum vulgare L.)

We report on microdissection, cloning and sequence, and Southern and fluorescence in situ hybridization (FISH) analysis of one moderately and one highly amplified repetitive DNA element, pHvMWG2314 and pHvMWG2315, respectively, isolated from barley (Hordeum vulgare L.) chromosome arm 3HL. The pHvMWG2315 sequence hybridizes to all 14 telomeric or subtelomeric regions of the barley chromosomes as determined by FISH. The 50 different hybridization sites that include intercalary signals allow the discrimination of all 14 chromosome arms and the construction of a kariotype of barley. The tandemly repeated subtelomeric element of 331 bp exists in all Triticeae species tested (H. vulgare, Agropyron elongatum, Secale cereale, Triticum tauschii, T. turgidum, and T. aestivum). It is AT rich (66%), exibits 84% sequence homology to subfragments of the D genome ?specific? 1-kb element pAs1 of T. tauscii and 75% homology to interspersed genome-specific DNA sequence pHcKB6 from H. chilence. The repetitive sequence pHvMWG2314 is moderately amplified in barley and highly amplified in hexaploid wheat. The in situ experiments revealed no distinct signals on barley chromosomes, indicating a dispersed character for the sequence. The significance of the results for the identification of chromosomes and chromosome aberrations in FISH experiments are discussed.     

Interaction of a receptor tyrosine kinase, EGF-R, with caveolins. Caveolin binding negatively regulates tyrosine and serine/threonine kinase activities

Caveolin, a 21-24-kDa integral membrane protein, is a principal component of caveolae membranes. We and others have suggested that caveolin functions as a scaffolding protein to organize and concentrate certain caveolin-interacting signaling molecules within caveolae membranes. In this regard, it has been shown that a 20-amino acid membrane-proximal region of the cytosolic NH2-terminal domain of caveolin is sufficient to mediate the interaction of caveolin with signaling proteins, namely G-proteins, Src-like kinases, eNOS, and H-Ras. This caveolin-derived protein domain has been termed the caveolin-scaffolding domain. Binding of the caveolin-scaffolding domain functionally suppresses the activity of G-protein alpha subunits, eNOS, and Src-like kinases, suggesting that caveolin binding may also play a negative regulatory role in signal transduction. Here, we report the direct interaction of caveolin with a growth factor receptor, EGF-R, a known caveolae-associated receptor tyrosine kinase. Two consensus caveolin binding motifs have been previously defined using phage display technology. One of these motifs is present within the conserved kinase domains of most known receptor tyrosine kinases (termed region IX). We now show that this caveolin binding motif within the kinase domain of the EGF-R can mediate the interaction of the EGF-R with the scaffolding domains of caveolins 1 and 3 but not with caveolin 2. In addition, the scaffolding domains of caveolins 1 and 3 both functionally inhibit the autophosphorylation of the EGF-R kinase in vitro. Importantly, this caveolin-mediated inhibition of the EGF-R kinase could be prevented by the addition of an EGF-R-derived peptide that (i) contains a well conserved caveolin binding motif and (ii) is located within the kinase domain of the EGF-R and most known receptor tyrosine kinases. Similar results were obtained with protein kinase C, a serine/threonine kinase, suggesting that caveolin may function as a general kinase inhibitor. The implications of our results are discussed within the context of caveolae-mediated signal transduction. In this regard, caveolae-coupled signaling might explain how linear signaling pathways can branch and interconnect extensively, forming a signaling module or network.     

A UV-sensitive mutant of Arabidopsis defective in the repair of pyrimidine-pyrimidinone(6-4) dimers

Plants are continually subjected to ultraviolet-B (UV-B) irradiation (290 to 320 nanometers) as a component of sunlight, which induces a variety of types of damage to the plant DNA. Repair of the two major DNA photoproducts was analyzed in wild-type Arabidopsis thaliana and in a mutant derivative whose growth was sensitive to UV-B radiation. In wild-type seedlings, repair of cyclobutane pyrimidine dimers occurred more slowly in the dark than in the light; repair of this photoproduct was not affected in the mutant. Repair, in the dark, of pyrimidine-pyrimidinone(6-4) dimers was defective in the UV-sensitive mutant.     

秩次分析法对谷子品种区试产量性能评价的有效性分析

[目的]研究秩次分析法在评价谷子[Setaria italica (L.) Beauv.]品种区试产量性能评价中的有效性.[方法]以2007、2008年国家谷子品种区域试验(西北春谷区组)晚熟组区试资料为例,用秩次分析法评价农作物品种区域试验的产量结果.[结果]用秩次分析法评价农作物品种区域试验可以解决不均衡试验的区试资料给联合方差分析带来的困难,对参试品种作出比较客观公正的评价.[结论]秩次分析法能较准确地评价谷子品种的产量性能.     

Establishment of a series of alien monosomic addition lines of Japanese bunching onion (Allium fistulosum L.) with extra chromosomes from shallot (A. cepa L. aggregatum group)

We performed an oral tolerance test for potassium metabisulfite in 33 patients and discovered sulfite intolerance in 9. These 9 patients had rhinitis including 7 with asthma. Alcoholic beverages, especially champagne, were the triggering factors the most frequently found for respiratory manifestations. Alcoholic beverages triggered bronchial or nasal reactions in 7 patients out of 9 (rhinitis in 7, asthma in 2). As in a large number of published cases, sulfite intolerance was evidenced by respiratory manifestations in our patients. Exceptional anaphylactic reactions have also been reported. Respiratory intolerance to sulfites in uncommon. A nasal or bronchial reaction occurring within minutes following ingestion of alcoholic beverages is highly suggestive of sulfite intolerance as is the development of acute asthma after administration of sulfite-containing drugs. Diagnosis is confirmed by oral tolerance tests versus placebo. The only effective preventive measure is to eliminate food and drugs containing sulfites. Such measures are justified to prevent acute episodes of asthma.     

豹斑毒鹅膏菌毒素粗品对黄粉虫的毒性研究

[目的]探讨豹斑毒鹅膏菌毒素粗品对黄粉虫的毒性.[方法]测定了5种大型真菌子实体及毒素粗品对黄粉虫的毒杀活性,并对筛选出的豹斑毒鹅膏菌进行了致死效应研究.[结果]随着豹斑毒鹅膏菌毒素粗品浓度的增大,防治效果越来越明显.当豹斑毒鹅膏菌毒素粗品浓度为17.5 mg/ml时,黄粉虫死亡率为93.3%,效果显著.[结论]豹斑毒鹅膏菌毒素粗品对黄粉虫有较显著的毒杀作用.     

A genetic system involving superoxide causes F1 necrosis in wheat (T. aestivum L.)

A genetic system in wheat is described in which F1 produced by crossing a drought tolerant cultivar C306 and high yielding cultivar WL711 exhibits leaf necrosis leading to the death of the plant. The mechanism underlying hybrid necrosis is not yet known. The hybrid exhibited a higher level of superoxide anion compared to the healthy leaves of parents at similar developmental stages. This increase in superoxide generation preceded necrotic lesion formation and displayed a gradient from the leaf tip to base. The leaf tip where necrotic lesions make their first appearance exhibited a higher level of superoxide compared to the base. Superoxide anion thus appears to play a vital role in necrosis of leaves in F1 hybrid. This genetic system can be a model system for understanding cell death in higher plants.     

Characterization of early induced genes in Arabidopsis thaliana responding to bacterial inoculation: identification of centrin and of a novel protein with two regions related to kinase domains

It is well known that significant differences exist in the anthropometric data of different races and ethnic groups. This is a cross-sectional study on segmental bone length based on 3,647 Chinese children of equal sex distribution aged 3-18 years. The measurements included standing height, weight, arm span, foot length, and segmental bone length of the humerus, radius, ulna, and tibia. A normality growth chart of all the measured parameters was constructed. Statistical analysis of the results showed a very high linear correlation of height with arm span, foot length, and segmental bone lengths with a correlation coefficient of 0.96-0.99 for both sexes. No differences were found between the right and left side of all the segmental bone lengths. These Chinese children were found to have a proportional limb segmental length relative to the trunk.     

High efficiency transformation of maize (Zea mays L.) mediated by Agrobacterium tumefaciens

Transformants of maize inbred A188 were efficiently produced from immature embryos cocultivated with Agrobacterium tumefaciens that carried "super-binary" vectors. Frequencies of transformation (independent transgenic plants/embryos) were between 5% and 30%. Almost all transformants were normal in morphology, and more than 70% were fertile. Stable integration, expression, and inheritance of the transgenes were confirmed by molecular and genetic analysis. Between one and three copies of the transgenes were integrated with little rearrangement, and the boundaries of T-DNA were similar to those in transgenic dicotyledons and rice. F1 hybrids between A188 and five other inbreds were transformed at low frequencies.