Functional properties of the Arabidopsis peptide transporters AtPTR1 and AtPTR5

The Arabidopsis di- and tripeptide transporters AtPTR1 and AtPTR5 were expressed in Xenopus laevis oocytes, and their selectivity and kinetic properties were determined by voltage clamping and by radioactive uptake. Dipeptide transport by AtPTR1 and AtPTR5 was found to be electrogenic and dependent on protons but not sodium. In the absence of dipeptides, both transporters showed proton-dependent leak currents that were inhibited by Phe-Ala (AtPTR5) and Phe-Ala, Trp-Ala, and Phe-Phe (AtPTR1). Phe-Ala was shown to reduce leak currents by binding to the substrate-binding site with a high apparent affinity. Inhibition of leak currents was only observed when the aromatic amino acids were present at the N-terminal position. AtPTR1 and AtPTR5 transport activity was voltage-dependent, and currents increased supralinearly with more negative membrane potentials and did not saturate. The voltage dependence of the apparent affinities differed between Ala-Ala, Ala-Lys, and Ala-Asp and was not conserved between the two transporters. The apparent affinity of AtPTR1 for these dipeptides was pH-dependent and decreased with decreasing proton concentration. In contrast to most proton-coupled transporters characterized so far, -I(max) increased at high pH, indicating that regulation of the transporter by pH overrides the importance of protons as co-substrate.     

Ethylene advances the transition from vegetative growth to flowering in Arabidopsis thaliana

The transition from vegetative growth to flowering is the most drastic change in plant development. In order to examine the involvement of ethylene in growth transition, we compared the development of ethylene-related mutants, eto1, etr1, ein2-1 and ein3-1, with the wild type (WT) in Arabidopsis thaliana. The ethylene sensitivity of two WT and the mutants is decreased in the following order: eto1 = WT < ein3-1 < ein2-1 = etr1-1. Bolting time was also delayed in nearly the same order: eto1 < WT < ein3-1 < ein2-1 < etr1. Leaf numbers increased according to the delay of bolting time, indicating that the delay of bolting time was caused by the delay of transition from vegetative to reproductive growth. Other growth parameters, including leaf area and number of flowers opening at the same time, increased in the same order, indicating that these changes were caused by a single factor, the amount of ethylene signal which was transferred though an ethylene signal transduction pathway. These results suggest that ethylene is involved in the transition from vegetative to reproductive growth in Arabidopsis thaliana.     

Flavonoid diversity and biosynthesis in seed of Arabidopsis thaliana

Functional characterization of genes involved in the flavonoid metabolism and its regulation requires in-depth analysis of flavonoid structure and composition of seed from the model plant Arabidopsis thaliana. Here, we report an analysis of the diverse and specific flavonoids that accumulate during seed development and maturation in wild types and mutants. Wild type seed contained more than 26 different flavonoids belonging to flavonols (mono and diglycosylated quercetin, kaempferol and isorhamnetin derivatives) and flavan-3-ols (epicatechin monomers and soluble procyanidin polymers with degrees of polymerization up to 9). Most of them are described for the first time in Arabidopsis. Interestingly, a novel group of four biflavonols that are dimers of quercetin-rhamnoside was also detected. Quercetin-3-O-rhamnoside (the major flavonoid), biflavonols, epicatechin and procyanidins accumulated in the seed coat in contrast to diglycosylated flavonols that were essentially observed in the embryo. Epicatechin, procyanidins and an additional quercetin-rhamnoside-hexoside derivative were synthesized in large quantities during seed development, whereas quercetin-3-O-rhamnoside displayed two peaks of accumulation. Finally, 11 mutants affected in known structural or regulatory functions of the pathway and their three corresponding wild types were also studied. Flavonoid profiles of the mutants were consistent with previous predictions based on genetic and molecular data. In addition, they also revealed the presence of new products in seed and underlined the plasticity of this metabolic pathway in the mutants.     

From seed to seed: the role of photoreceptors in Arabidopsis development

As sessile organisms, plants have evolved a multitude of developmental responses to cope with the ever-changing environmental conditions that challenge the plant throughout its life cycle. Of the many environmental cues that regulate plant development, light is probably the most important. From determining the developmental pattern of the emerging seedling, to influencing the organization of organelles to best maximize energy available for photosynthesis, light has dramatic effects on development during all stages of plant life. In plants, three classes of photoreceptors that mediate light perception have been characterized at the molecular level. The phytochromes recognize light in the red portion of the spectrum, while cryptochromes and phototropins perceive blue and UVA light. In this review, we discuss the different aspects of development that are regulated by these photoreceptors in the model plant species Arabidopsis thaliana and how the phytochromes, cryptochromes, and phototropins bring about changes in development seen in the growing plant.     

Expression and characterization of monocot rice cytosolic CuZnSOD protein in dicot Arabidopsis

Cytosolic CuZnSOD removes deleterious superoxides from plant cells. In order to understand its function better, we sought to express a monocot CuZnSODgene in transgenic Arabidopsis. We constructed a transgene usingthe CaMV 35S promoter to express a rice cytosolic CuZnSOD gene in Arabidopsis and generated over 200 transformants. A 16kD polypeptide, the same size as the native rice CuZnSOD polypeptide, was detected inthe transgenic Arabidopsis. Interestingly, two forms of riceCuZnSOD, rSODI and rSODII, having the same dimeric size, were detectedin the transgenic plants. rSODII protein was relatively abundant but hadlow specific activity. In contrast, rSODI protein was relatively rareand had high specific activity. Inter-conversion of rSODI and rSODIIcould be achieved by the addition and removal of copper ions into the purifiedrecombinant SOD and to the leaf extract of transgenic plants. Ouranalysis indicates that rSODI most likely corresponds to native riceCuZnSOD that has incorporated the Cu and Zn ions required for fullactivity, whereas the less active rSODII form may not have properlyincorporated the necessary copper ions.     

Glucose delays seed germination in<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

Here we report that glucose delays germination of Arabidopsis thaliana (L.) Heynh. seeds at concentrations below those known to inhibit early seedling development. This inhibition acts on embryo growth and is independent of hexokinase (HXK) function. Hormones and hormone inhibitors were applied to the germination media and several hormone biosynthesis and signalling mutants were tested on glucose media to investigate a possible role of abscisic acid (ABA), gibberellin and ethylene in the glucose-induced germination delay. Results indicate that the germination inhibition by glucose cannot be antagonized by ethylene or gibberellin and is independent of the HXK1/ABA/ABI4 signalling cascade. These findings suggest that there is a separate regulatory pathway independent of ABI2/ABI4/ABI5. Thus, in a relatively short time frame sugars utilize different signalling cascades to inhibit germination and post-germination growth, underlining the complexity of sugar responses.Abbreviations ABA Abscisic acid - ABI ABA insensitive - ACC 1-Aminocyclopropane-1-carboxylic acid - BR Brassinosteroid - CAB Chlorophyll a/b-binding protein - FUS3 Fusca3 - GA Gibberellin - GA ₃ Gibberellic acid - HXK Hexokinase - LEC1 Leafy cotyledon1 - RBCS Ribulose-1,5-bisphosphate carboxylase small subunit - WT Wild type     

Amino acids,polyamines and proteins during seed germination of two species of Dipterocarpaceae

Summary Amino acid, polyamine and protein concentrations in seeds and their evolution during seed germination of two dipterocarp species, Hopea odorata and Dipterocarpus alatus, were determined with the help of a multianalytical system. Glutamic acid and glutamine were the major amino compounds present. Hopea seeds also contain high levels of aspartic acid/asparagine, serine, threonine, arginine and alanine, while those of Dipterocarpus contain high levels of alanine, arginine and threonine. These species were quite different in their germination behavior and thus in their protein and amine metabolism rates. In Hopea, polyamines increased during the first 3 days of germination and reached a maximum by the 3rd day, 1 day before maximum germination rate. In Dipterocarpus polyamines reached their maximum at the 6th day while maximum germination rate is observed by the 7th day. This suggests that polyamine compounds could play a role in the early part of the germination process in Hopea and Dipterocarpus seeds. The possibility that control of polyamine biosynthesis could be used for the establishment of biochemical methods to improve seed storage and to control germination of these recalcitrant seeds is discussed.     

cDNA clones encoding Arabidopsis thaliana and Zea mays mitochondrial chaperonin HSP60 and gene expression during seed germination and heat shock

Mitochondria contain a nuclear-encoded heat shock protein, HSP60, which functions as a chaperonin in the post-translational assembly of multimeric proteins encoded by both nuclear and mitochondrial genes. We have isolated and sequenced full-length complementary DNAs coding for this mitochondrial chaperonin in Arabidopsis thaliana and Zea mays. Southern-blot analysis indicates the presence of a single hsp60 gene in the genome of A. thaliana. There is a high degree of homology at the predicted amino acid levels (43 to 60%) between plant HSP60s and their homologues in prokaryotes and other eukaryotes which indicates that these proteins must have similar evolutionarily conserved functions in all organisms. Northern- and western-blot analyses indicate that the expression of the hsp60 gene is developmentally regulated during seed germination. It is also heat-inducible. Developmental regulation of the (-subunit) of F₁-ATPase, an enzyme complex that is involved in the cyanide-sensitive mitochondrial electron transport system, indicates that imbibed embryos undergo rapid mitochondrial biogenesis through the early stages of germination. Based on the functional role of HSP60 in macromolecular assembly, these data collectively suggest that the presence of higher levels of HSP60 is necessary during active mitochondrial biogenesis, when the need for this protein is greatest in assisting the rapid assembly of the oligomeric protein structures.     

Photoregulation of germination in seed of transgenic lines of tobacco and Arabidopsis which express an introduced cDNA encoding phytochrome A or phytochrome B

Photoinduction and photoinhibition of germination in seed from a homozygous tobacco (Nicotiana tabacum L.) line containing an introduced oat phyA cDNA (encoding phytochrome A) is compared with that of isogenic wild-type (WT) tobacco. Under continuous irradiation by a light source with a low redfar-red (RFR) ratio the transgenic tobacco seed appeared to be less susceptible to photoinhibition of germination compared with WT seed. However, induction of germination following a short pulse by R (666 nm) was not enhanced in the genotype transformed by oat phyA cDNA compared with the WT; neither did germination of the transgenic tobacco seed show an increased sensitivity to saturating pulses of light of longer wavelengths (666–730 nm). In seeds of transgenic Arabidopsis thaliana (L.) Heynh. which contained an introduced phytochrome-B-encoding cDNA, levels of dark germination were enhanced, consistent with mediation of response by phytochrome B-P_fr. The germination behaviour of Arabidopsis genotypes wich contained an introduced cDNA encoding phytochrome A, however, did not significantly differ from that of the WT.Abbreviations ABO seed transformed with Arabidopsis phyB - cDNA; CaMV cauliflower mosaic virus - FR far-red light - P_fr far-red-absorbing form of phytochrome - P_tot total phytochrome - P_fr/P_tot phytochrome photoequilibrium - R red light - RBO seed transformed with rice phyB cDNA - RFR quantum ratio of red and far-red light - WL white light - WL + FR whitelight supplemented with far-red light - WT wild type The authors wish to thank R.D. Vierstra (Department of Horticulture, University of Wisconsin-Madison, USA) for providing the transgenic tobacco line, and M.T. Boylan, D. Wagner and P.H. Quail (U.C. Berkeley/USDA Plant Gene Expression Center, Albany, Calif. USA) for providing the transgenic Arabidopsis lines. The work presented in this paper was funded by grants from the Agricultural and Food Research Council (H.S., A.C.M., G.C.W.).     

Fluence-response curves and action spectra for promotion and inhibition of seed germination in wildtype and long-hypocotyl mutants of Arabidopsis thaliana L.

The fluence-response curves of wildtype and long-hypocotyl mutants of Arabidopsis thaliana L. for induction and inhibition of seed germination, expressed as percentage germination on probit scale against logarithm of fluence, are very different in shape. The mutants show reduced photoinhibition of hypocotyl growth in white light compared with wildtype, suggesting they are either mutated in phytochrome, the blue/UV-absorbing photosystem or some other red-absorbing photosystem. Calculations of the amount of the far-red-absorbing form of phytochrome (Pfr), by a given fluence have been made taking into account pre-existing Pfr in the seeds. This pre-existing Pfr can change dramatically the slope of a fluence-response curve. Other factors such as an overriding factor, stimulating germination by a non-phytochrome-related process, the total phytochrome content, the range of normal distribution of logarithm of Pfr requirement of individuals in the population and differential screening can influence the form and-or position of a fluence-response curve. Action spectra calculated for germination induction and for the inhibition of induction for the different genotypes are qualitatively the same, having peaks of effectiveness at 660 nm and 730 nm respectively. In the blue region of the spectrum very little activity is seen in comparison with that of red light. Differences in bandwidth of effectiveness for induction of germination are attributed to different amounts of screening pigments in the seed batches. The long-hypocotyl mutants therefore have a normal phytochrome system operative in the control of seed germination, by short-term irradiation and no other photosystem appears to be involved.Abbreviations and symbols FR far-red light - P phytochrome - Pfr far-red-absorbing form of P - Pr red-absorbing form of P - R red light - SD standard deviation of logarithm Pfr around - logarithm Pfr required for 50% germination - aparent molar conversion cross section - maximum Pfr/Ptot established by a given wave-length - ₀ initial Pfr     

Dynamics of vegetative cytoplasm during generative cell formation and pollen maturation inArabidopsis thaliana

Summary Ultrastructural changes of pollen cytoplasm during generative cell formation and pollen maturation inArabidopsis thaliana were studied. The pollen cytoplasm develops a complicated ultra-structure and changes dramatically during these stages. Lipid droplets increase after generative cell formation and their organization and distribution change with the developmental stage. Starch grains in amyloplasts increase in number and size during generative and sperm cell formation and decrease at pollen maturity. The shape and membrane system of mitochondria change only slightly. Dictyo-somes become very prominent, and numerous associated vesicles are observed during and after sperm cell formation. Endoplasmic reticulum appears extensively as stacks during sperm cell formation. Free and polyribosomes are abundant in the cytoplasm at all developmental stages although they appear denser at certain stages and in some areas. In mature pollen, all organelles are randomly distributed throughout the vegetative cytoplasm and numerous small particles appear. Organization and distribution of storage substances and appearance of these small particles during generative and sperm cell formation and pollen maturation are discussed.     

Allelopathic effects of sunflower extracts on mustard seed germination and seedling growth

The allelopathic potential of two cultivars of sunflower (Helianthus annuus L.) Lech and Ogrodowy was studied. Leaf aqueous extracts of sunflower at 2.5, 5, and 10 % (m/v) concentrations were applied to determine their effect on mustard (Sinapis alba) seed germination and seedlings growth under laboratory conditions. Increasing concentration of aqueous extracts of sunflower inhibited seed germination, up to almost complete failure of germination, observed in the presence of 10 % extract from sunflower cv. Ogrodowy. The decrease in germinability was well correlated with increased membrane deterioration, assayed as electrical conductivity and enhanced lipid peroxidation, detected as increased malondialdehyde content.     

鄱阳湖洲滩湿地植物生长和营养繁殖对水淹时长的响应

水淹时长是影响湿地植物分布的重要因素。在水情不断变化的背景下,鄱阳湖洲滩湿地植物种群和群落的变化规律还不清楚。为了探究淹水时长对鄱阳湖洲滩3种优势植物生长和繁殖的影响,并预测在水文发生剧烈变化后,3种优势植物分布的趋势,采用控制实验模拟了不同水淹时长(0、60、90、120、150 d和180 d)下鄱阳湖湿地3种优势植物(灰化薹草(Carex cinerascens)、南荻(Miscanthus lutarioriparius)和虉草(Phalaris arundinacea))的生长和繁殖情况。研究结果表明:1)南荻在水淹超过120 d后,存活率开始降低,水淹到达180 d完全死亡。而灰化薹草和虉草在淹水180 d后仍全部存活。表明南荻耐淹水的能力弱于其他两种植物。2)水淹显著降低灰化薹草的总生物量,并且总生物量随水淹时长的增加而逐渐降低。而短时间(小于150 d)的水淹没有对虉草总生物量产生显著影响。3)退水初期,灰化薹草的恢复生长趋向于地上部分,而虉草表现为地下和地下部分同步生长。该研究结果可以为预测水文情势变化下鄱阳湖湿地植物种群和群落的动态变化提供依据。     

黄梁木NcEXPA8基因提高拟南芥种子萌发速度的研究

为探究NcEXPA8基因的分子功能,该文以在黄梁木形成层区域中高表达的扩展蛋白基因NcEXPA8为研究对象,研究其在黄梁木种子萌发过程中的表达及其过表达对拟南芥种子萌发的影响。该文以黄梁木和拟南芥野生型(WT)(Col-0)种子以及转NcEXPA8基因的拟南芥T3代纯合体种子为实验材料,利用实时荧光定量RT-qPCR分析NcEXPA8基因在黄梁木种子萌发不同阶段的表达量,并分析NcEXPA8基因和拟南芥种子萌发内源相关基因在拟南芥WT和转基因不同株系萌发种子中的表达量,且对拟南芥WT种子和转基因T3代纯合体种子在不同处理和不同时间的萌发率进行比较。结果表明:NcEXPA8基因在黄梁木种子萌发不同阶段的表达量存在差异,在种壳破裂时表达量最高,随后降低。与拟南芥WT相比,过表达NcEXPA8基因不仅显著提高了种子的萌发速度,而且提高了对赤霉素的敏感性,降低了对脱落酸的敏感性,但未影响拟南芥内源相关结构基因的表达。该研究初步分析了黄梁木NcEXPA8基因在种子萌发中的功能,但其最终确定还需在黄梁木中进行验证。     

Developmental and gene expression analyses of a cotton naked seed mutant

Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Salinity effects on germination,growth, and seed production of the halophyte Cakile maritima

The growth ofEucalyptus regnans seedlings in forest soil is enhanced when it has been air-dried. In undried forest soil seedlings grow poorly and develop purple coloration in the foliage, indicating P deficiency. This paper reports the results of pot experiments designed to investigate the relationship between growth and P acquisition, ectomycorrhizal infection and age of seedlings grown in air-dried and undried soil. The effect on seedling growth of their inoculation with air-dried or undried soil or with ectomycorrhizal roots from plants growing in air-dried or undried soil was also investigated. Ectomycorrhizal root tips were detected in 3-week-oldE. regnans seedlings in both air-dried and undried soil, and from then on the frequency of ectomycorrhizal root tips increased rapidly. In air-dried soil, seedlings were fully ectomycorrhizal at 9 weeks, and the occurrence of maximum ectomycorrhizal infection coincided with enhanced P acquisition and the initiation of rapid seedling growth. In undried forest soil, seedling growth remained poor, even though the seedlings had well-developed ectomycorrhizae and the incidence of ectomycorrhizal root tips was the same as in air-dried soil. The dominant ectomycorrhizae in airdried soil were associated with an ascomycete fungus, whereas in undried, undisturbed soil they were commonly associated with basidiomycete fungi. Inoculation of sterile soil/sand mix with washed ectomycorrhizal roots from air-dried soil increased the P acquisition and growth of the seedlings significantly compared with controls, whereas ectomycorrhizal inocula from undried soil had no effect on seedling growth, although both inocula resulted in a similar incidence of ectomycorrhizal root tips. Similarly, addition of a small amount of air-dried soil into sterile soil/sand mix resulted in a significantly greater increase in the P content and dry weight of the seedlings, compared with the control, than addition of undried soil. In both treatments, the incidence of ectomycorrhial root tips was similar. As (i) the differentiation in seedling growth between air-dried and undried soil occurred after seedlings became ectomycorrhizal, (ii) the dominant ectomycorrhizae in air-dried soil were different from those in undried soil, and (iii) inocula from air-dried soil, but not from undried soil, stimulated seedling growth in sterile soil/sand mix, it is concluded that development of particular ectomycorrhizae may be involved in seedling growth stimulation and enhanced P acquisition associated with air drying of forest soil.