Legume nodulation: successful symbiosis through short- and long-distance signalling

Nodulation in legumes provides a major conduit of available nitrogen into the biosphere. The development of nitrogen-fixing nodules results from a symbiotic interaction between soil bacteria, commonly called rhizobia, and legume plants. Molecular genetic analysis in both model and agriculturally important legume species has resulted in the identification of a variety of genes that are essential for the establishment, maintenance and regulation of this symbiosis. Autoregulation of nodulation (AON) is a major internal process by which nodule numbers are controlled through prior nodulation events. Characterisation of AON-deficient mutants has revealed a novel systemic signal transduction pathway controlled by a receptor-like kinase. This review reports our present level of understanding on the short- and long-distance signalling networks controlling early nodulation events and AON.

Short root mutant of Lotus japonicus with a dramatically altered symbiotic phenotype

Legume plants carefully control the extent of nodulation in response to rhizobial infection. To examine the mechanism underlying this process we conducted a detailed analysis of the Lotus japonicus hypernodulating mutants, har1-1, 2 and 3 that define a new locus, HYPERNODULATION ABERRANT ROOT FORMATION (Har1), involved in root and symbiotic development. Mutations in the Har1 locus alter root architecture by inhibiting root elongation, diminishing root diameter and stimulating lateral root initiation. At the cellular level these developmental alterations are associated with changes in the position and duration of root cell growth and result in a premature differentiation of har1-1 mutant root. No significant differences between har1-1 mutant and wild-type plants were detected with respect to root growth responses to 1-aminocyclopropane1-carboxylic acid, the immediate precursor of ethylene, and auxin; however, cytokinin in the presence of AVG (aminoetoxyvinylglycine) was found to stimulate root elongation of the har1-1 mutant but not the wild-type. After inoculation with Mesorhizobium loti, the har1 mutant lines display an unusual hypernodulation (HNR) response, characterized by unrestricted nodulation (hypernodulation), and a concomitant drastic inhibition of root and shoot growth. These observations implicate a role for the Har1 locus in both symbiotic and non-symbiotic development of L. japonicus, and suggest that regulatory processes controlling nodule organogenesis and nodule number are integrated in an overall mechanism governing root growth and development.

Effects of copper on the photosynthesis of intact chloroplasts: interaction with manganese

Highly purified, intact chloroplasts were prepared from pea (Pisum sativum L.) and spinach (Spinacia oleracea L.) following an identical procedure, and were used to investigate the cupric cation inhibition on the photosynthetic activity. In both species, copper inhibition showed a similar inhibitor concentration that decreases the enzyme activity by 50% (IC(50) approximately 1.8 microM) and did not depend on the internal or external phosphate (Pi) concentration, indicating that copper did not interact with the Pi translocator. Fluorescence analysis suggested that the presence of copper did not facilitate photoinhibition, because there were no changes in maximal fluorescence (F(m)) nor in basal fluorescence (F(o)) of copper-treated samples. The electron transport through the photosystem II (PSII) was also not affected (operating efficiency of PSII-F'v/F'm similar in all conditions). Yet, under Cu(2+) stress, the proportion of open PSII reaction centers was dramatically decreased, and the first quinone acceptor (Q(A)) reoxidation was fully inhibited, as demonstrated by the constant photochemical quenching (q(P)) along experiment time. The quantum yield of PSII electron transport (Phi(PSII)) was also clearly affected by copper, and therefore reduced the photochemistry efficiency. Manganese, when added simultaneously with copper, delayed the inhibition, as measured by oxygen evolution and chlorophyll fluorescence, but neither reversed the copper effect when added to copper-inhibited plastids, nor prevented the inhibition of the Hill activity of isolated copper-treated thylakoids. Our results suggest that manganese competed with copper to penetrate the chloroplast envelope. This competition seems to be specific because other divalent cations e.g. magnesium and calcium, did not interfere with the copper action in intact chloroplasts. All results do suggest that, under these conditions, the stroma proteins, such as the Calvin-Benson cycle enzymes or others are the most probable first target for the Cu(2+) action, resulting in the total inhibition of chloroplast photosynthesis and in the consequent unbalanced rate of production and consumption of the reducing power.

Rotações de Culturas e Afolhamentos

A rotação de culturas é uma prática agronómica importante em todos os sistemas de agricultura. A alternância de culturas de espécies com características distintas ao nível morfológico (sistema radical), ciclo vegetativo (épocas distintas de sementeira e colheita) e ao nível da sua resistência a pragas e doenças, contribui para o aumento da melhoria das características físicas, químicas e biológicas dos solos. A rotação de culturas pode melhorar a estrutura do solo, quer pela introdução de matéria orgânica, quer pela porosidade biológica criada pelas raízes das culturas. O aumento da porosidade biológica conduzirá a uma maior infiltração da água no solo com consequência na redução do escoamento superficial e portanto, da erosão hídrica. O acréscimo da porosidade biológica no solo pelas raízes é de extrema importância, principalmente em sistemas de mobilização nula (sementeira directa). A utilização de plantas leguminosas, como por exemplo a Vicia sativa L. (vicia ou ervilhaca) a Lupinus luteus L.(tremocilha), o Cicer arietinum L. (grão-de-bico) a Pisum sativum L. (ervilha), etc., na rotação, favorecerá o incremento de azoto no solo, o qual será favorável ao crescimento das gramíneas com redução dos seus custos de produção. Outro aspecto extremamente importante da rotação de culturas prende-se com a melhor distribuição do parque de máquinas e da mão-de-obra ao longo do ano, fazendo-se alternar culturas com épocas de sementeira e de colheita diferentes, como por exemplo o Helianthus annuus L. (girassol) que é uma cultura de primavera-verão, o trigo mole (Triticum aestivum L.) e a cevada dística (Hordeum distichum L.) que são culturas de outono-inverno, etc.

Noves aportacions sobre agricultura i alimentació durant la primera edat del ferro a Catalunya: dades de l'assentament de Sant Jaume/Mas d'en Serrà (Alcanar, Montsià)

Els resultats de l'estudi arqueobotànic realitzat sobre diferents àmbits de l'assentament de Sant Jaume aporta noves dades al coneixement de la gestió dels recursos vegetals de la protohistòria del nordest peninsular. El registre arqueològic constata una certa homogeneïtzació en la funcionalitat dels àmbits, que s'interpreten com a magatzems en el pis superior i espais d'estabulació a l'inferior. L'àmbit millor representat és l'A4, que conserva com a fet singular un elevat nombre de restes de llavors i fruits amb molt bon estat de conservació. Els tàxons conreats més importants són la pisana (Triticum dicoccum) i les guixes i guixols (Lathyrus sativus i Lathyrus cicera), seguits d¿una menor proporció d'ordi vestit (Hordeum vulgare), blat nu (comú/dur) (Triticum aestivum/durum), pèsol (Pisum sativum), llentia (Lens culinaris) i erb (Vicia ervilia). D'altra banda, el registre arqueobotànic del pis inferior de l'àmbit A4 sembla posar en evidència la presència de l¿associació de pisana i guixa, destinada a l'alim.

Biochemical, physicochemical and molecular characterization of a genuine 2-Cys-peroxiredoxin purified from cowpea [Vigna unguiculata (L.) Walpers] leaves

Background: Peroxiredoxins have diverse functions in cellular defense-signaling pathways. 2-Cys-peroxiredoxins (2-Cys-Prx) reduce H2O2 and alkyl-hydroperoxide. This study describes the purification and characterization of a genuine 2-Cys-Prx from Vigna unguiculata (Vu-2-Cys-Prx). Methods: Vu-2-Cys-Prx was purified from leaves by ammonium sulfate fractionation, chitin affinity and ion exchange chromatography. Results: Vu-2-Cys-Prx reduces H2O2 using NADPH and DTT. Vu-2-Cys-Prx is a 44 kDa (SDS-PAGE)/46 kDa (exclusion chromatography) protein that appears as a 22 kDa molecule under reducing conditions, indicating that it is a homodimer linked intermolecularly by disulfide bonds and has a pI range of 4.56-4.72; its NH2-terminal sequence was similar to 2-Cys-Prx from Phaseolus vulgaris (96%) and Populus tricocarpa (96%). Analysis by ESI-Q-TOF MS/MS showed a molecular mass/pI of 28.622 kDa/5.18. Vu-2-Cys-Prx has 8% alpha-helix, 39% beta-sheet, 22% of turns and 31% of unordered forms. Vu-2-Cys-Prx was heat stable, has optimal activity at pH 7.0, and prevented plasmid DNA degradation. Atomic force microscopy shows that Vu-2-Cys-Prx oligomerized in decamers which might be associated with its molecular chaperone activity that prevented denaturation of insulin and citrate synthase. Its cDNA analysis showed that the redox-active Cys(52) residue and the amino acids Pro(45), Thr(49) and Arg(128) are conserved as in other 2-Cys-Prx. General significance: The biochemical and molecular features of Vu-2-Cys-Prx are similar to other members of 2-Cys-Prx family. To date, only one publication reported on the purification of native 2-Cys-Prx from leaves and the subsequent analysis by N-terminal Edman sequencing, which is crucial for construction of stromal recombinant 2-Cys-Prx proteins. (C) 2012 Elsevier B.V. All rights reserved.

Differential Expression of the S-Adenosyl-l-Methionine Synthase Genes during Pea Development1

Two genes coding for S-adenosyl-l-methionine synthase (SAMS, EC 2.5.1.6) were previously isolated from pea (Pisum sativum) ovaries. Both SAMS genes were highly homologous throughout their coding regions but showed a certain degree of sequence divergence within the 5′ and the 3′ untranslated regions. These regions have been used as gene-specific probes to analyze the differential expression of SAMS1 and SAMS2 genes in pea plants. The ribonuclease protection assay revealed different expression patterns for each individual gene. SAMS1 was strongly expressed in nearly all tissues, especially in roots. SAMS2 expression was weaker, reaching its highest level at the apex. Following pollination, SAMS1 was specifically up-regulated, whereas SAMS2 was expressed constitutively. The up-regulation of SAMS1 during ovary development was also observed in unpollinated ovaries treated with auxins. In unpollinated ovaries an increase in SAMS1 expression was observed as a consequence of ethylene production associated with the emasculation process. In senescing ovaries both SAMS1 and SAMS2 genes showed increased expression. Ethylene treatment of unpollinated ovaries led to an increase in the SAMS1 mRNA level. However, SAMS2 expression remained unchangeable after ethylene treatment, indicating that SAMS2 induction during ovary senescence was not ethylene dependent. SAMS mRNAs were localized by in situ hybridization at the endocarp of developing fruits and in the ovules of senescing ovaries. Our results indicate that the transcriptional regulation of SAMS genes is developmentally controlled in a specific way for each gene.

Identification of a major locus conferring resistance to powdery mildew (Erysiphe polygoni DC) in mungbean (Vigna radiata L. Wilczek) by QTL analysis

A major locus conferring resistance to the causal organism of powdery mildew, Erysiphe polygoni DC,, in mungbean (Vigna radiata L. Wilczek) was identified using QTL analysis with a population of 147 recombinant inbred individuals. The population was derived from a cross between 'Berken', a highly susceptible variety, and ATF 3640, a highly resistant line. To test for response to powdery mildew, F-7 and F-8 lines were inoculated by dispersing decaying mungbean leaves with residual conidia of E. polygoni amongst the young plants to create an artificial epidemic and assayed in a glasshouse facility. To generate a linkage map, 322 RFLP clones were tested against the two parents and 51 of these were selected to screen the mapping population. The 51 probes generated 52 mapped loci, which were used to construct a linkage map spanning 350 cM of the mungbean genome over 10 linkage groups. Using these markers, a single locus was identified that explained up to a maximum of 86% of the total variation in the resistance response to the pathogen.

Validation of non-fluorescent methods to reliably detect acrosomal and plasma membrane integrity of common marmoset (Callithrix jacchus) sperm

Simple, rapid and stable sperm evaluation methods which have been optimized for common marmoset (Callithrix jacchus) are critical for studies involving collection and evaluation of sperm in the field. This is particularly important for new species groups such as Callitrichidae where the sperm have been little studied. Of this family, C jacchus is the best known, and has been chosen as a model species for other members of the genus Callithrix. The fundamental evaluation parameters for sperm of any species are viability and acrosomal status. Semen samples were collected by penile vibratory stimulation. To evaluate sperm plasma membrane integrity, Eosin-Nigrosin was tested here for the common marmoset sperm to be used under field conditions. Further, a non-fluorescent stain for acrosome, the ""Simple"" stain, developed for domestic and wild cats, was tested on common marmoset sperm. This was compared with a fluorescent staining, Fluorescein isothiocyanate-Pisum sativum agglutinin (FITC-PSA), routinely used and validated for common marmoset at the German Primate Centre to evaluate acrosomal integrity. Results obtained with the ""Simple"" stain showed a marked differentiation between sperm with intact and non-intact acrosome both with and without ionophore treatment and closely correlated with results obtained with FITC-PSA. Temperature had no effect on the results with the ""Simple"" stain and the complete processing is simple enough to be carried out under field conditions. These findings indicated that the ""Simple"" stain and Eosin-Nigrosin provide rapid and accurate results for C. jacchus sperm and that those methods can be reliably used as field tools for sperm evaluation for this species. (c) 2008 Elsevier Inc. All rights reserved.

Do increases in xylem sap pH and/or ABA concentration mediate stomatal closure following nitrate deprivation?

Stomatal conductance (g(s)) of pepper (Capsicum annuum L.) plants decreased during the second photoperiod (day 2) after withholding nitrate (N). Stomatal closure of N-deprived plants was not associated with a decreased shoot water potential (Psi(shoot)); conversely Psi(shoot) was lower in N-supplied plants. N deprivation transiently (days 2 and 3) alkalized (0.2-0.3 pH units) xylem sap exuded from de-topped root systems under root pressure, and xylem sap expressed from excised shoots by pressurization. The ABA concentration of expressed sap increased 3-4-fold when measured on days 2 and 4. On day 2, leaves detached from N-deprived and N-supplied plants showed decreased transpiration rates when fed an alkaline (pH 7) artificial xylem (AX) solution, independent of the ABA concentration (10-100 nM) supplied. Thus changes in xylem sap composition following N deprivation can potentially close stomata. However, the lower transpiration rate of detached N-deprived leaves relative to N-supplied leaves shows that factors residing within N-deprived leaves also mediate stomatal closure, and that these factors assume greater importance as the duration of N deprivation increases.

New fluorescence parameters for monitoring photosynthesis in plants - 1. The effect of illumination on the fluorescence parameters of the JIP-test

Chlorophyll fluorescence measurements have a wide range of applications from basic understanding of photosynthesis functioning to plant environmental stress responses and direct assessments of plant health. The measured signal is the fluorescence intensity (expressed in relative units) and the most meaningful data are derived from the time dependent increase in fluorescence intensity achieved upon application of continuous bright light to a previously dark adapted sample. The fluorescence response changes over time and is termed the Kautsky curve or chlorophyll fluorescence transient. Recently, Strasser and Strasser (1995) formulated a group of fluorescence parameters, called the JIP-test, that quantify the stepwise flow of energy through Photosystem II, using input data from the fluorescence transient. The purpose of this study was to establish relationships between the biochemical reactions occurring in PS II and specific JIP-test parameters. This was approached using isolated systems that facilitated the addition of modifying agents, a PS II electron transport inhibitor, an electron acceptor and an uncoupler, whose effects on PS II activity are well documented in the literature. The alteration to PS II activity caused by each of these compounds could then be monitored through the JIP-test parameters and compared and contrasted with the literature. The known alteration in PS II activity of Chenopodium album atrazine resistant and sensitive biotypes was also used to gauge the effectiveness and sensitivity of the JIP-test. The information gained from the in vitro study was successfully applied to an in situ study. This is the first in a series of four papers. It shows that the trapping parameters of the JIP-test were most affected by illumination and that the reduction in trapping had a run-on effect to inhibit electron transport. When irradiance exposure proceeded to photoinhibition, the electron transport probability parameter was greatly reduced and dissipation significantly increased. These results illustrate the advantage of monitoring a number of fluorescence parameters over the use of just one, which is often the case when the F-V/F-M ratio is used.

Plantas de cobertura de solo como fonte de nitrogênio ao milho

Durante o período de 1990/94, foi realizado um trabalho na área experimental do Departamento de Solos da Universidade Federal de Santa Maria (RS), num Argissolo Vermelho distrófico arênico, para avaliar o potencial de algumas plantas de cobertura de solo no fornecimento de N ao milho no sistema plantio direto. O delineamento experimental foi o de blocos ao acaso, com parcelas subdivididas e quatro repetições. Nas parcelas principais, foram utilizadas, em cada inverno, as leguminosas ervilhaca comum (Vicia sativa L.), ervilha forrageira (Pisum sativum var. arvense (L.) Poir), chícharo (Lathyrus sativus L.) e tremoço azul (Lupinus angustifolius L.), a gramínea aveia preta (Avena strigosa Schieb.), além de um tratamento com pousio invernal (plantas invasoras). Nas subparcelas, foram aplicadas as doses de 0, 80 e 160 kg ha-1 de N no milho, na forma de uréia. Na média dos quatro anos, as duas espécies que produziram maior quantidade de matéria seca pela parte aérea foram o tremoço azul (5.228 kg ha-1) e a aveia preta (4.417 kg ha-1), seguidas do chícharo (3.047 kg ha-1), ervilha forrageira (2.754 kg ha-1), ervilhaca comum (2.527 kg ha-1) e plantas invasoras do pousio invernal (1.197 kg ha-1). Dentre as leguminosas, a espécie tremoço azul acumulou a maior quantidade de N na parte aérea (113,7 kg ha-1 de N). Os tratamentos que adicionaram menor quantidade de N ao solo pela fitomassa foram a aveia preta (41,7 kg ha-1 de N) e o pousio invernal (20,5 kg ha-1 de N). Aproximadamente, 60% do N acumulado na parte aérea das leguminosas foi liberado durante os primeiros 30 dias após o seu manejo. Na ausência de adubação nitrogenada, o rendimento de grãos de milho foi maior após as leguminosas do que após a aveia e o pousio invernal. As leguminosas diferiram entre si quanto ao potencial de fornecimento de N ao milho. Os maiores valores de equivalência em N mineral (EqN) foram obtidos com a ervilhaca (137 kg ha-1 de N) e com o tremoço (122 kg ha-1 de N), evidenciando a possibilidade de redução das quantidades de N mineral por aplicar no milho quando ele for cultivado em sucessão a estas duas leguminosas.

Fitomassa e decomposição de resíduos de plantas de cobertura puras e consorciadas

O cultivo de plantas de cobertura, no outono/inverno, na região do Planalto do Rio Grande Sul contribui para o sucesso do sistema plantio direto. No entanto, informações relativas à produção de fitomassa e decomposição de resíduos dessas espécies ainda são escassas para a região, sobretudo para espécies consorciadas. O experimento foi conduzido em Não-Me-Toque, RS, em um Latossolo Vermelho distrófico típico, avaliando-se nove tratamentos, sendo quatro constituídos por plantas de cobertura em culturas puras [centeio (Secale cereale L.), aveia-preta (Avena strigosa Schreb), ervilha forrageira (Pisum sativum subesp. arvense) e nabo forrageiro (Raphanus sativus L. var. oleiferus Metzg)] e cinco por consórcios [(centeio + ervilha forrageira, centeio + nabo forrageiro, aveia + nabo forrageiro, centeio + ervilhaca (Vicia sativa L.) e aveia + ervilhaca)]. A dinâmica de decomposição dos resíduos culturais das plantas de cobertura foi avaliada em bolsas de decomposição, as quais foram distribuídas na superfície do solo e coletadas aos sete, 14, 21, 28, 57, 117 e 164 dias. O consórcio entre leguminosas e crucífera com gramíneas resultou em maior produção de fitomassa em relação ao cultivo destas em culturas puras. O nitrogênio (N) acumulado na parte aérea dos consórcios formados por ervilha forrageira e nabo com centeio e aveia foi semelhante ao da leguminosa e da crucífera em culturas puras e superou em 220,4 % os valores de N observados para as gramíneas em culturas puras. Por meio do consórcio entre as espécies de cobertura foi possível reduzir a taxa de decomposição dos resíduos culturais, em comparação com as culturas puras da leguminosa e da crucífera.

ESTIMATIVA DO CONTEÚDO DE DNA DE DIFERENTES ACESSOS DE BANANEIRA: RELAÇÕES ENTRE NÍVEL DE PLOIDIA E GRUPOS GENÔMICOS

RESUMO A determinação do nível de ploidia é muito importante, principalmente em programas de melhoramento genético que envolvem poliploides, a fim de possibilitar a escolha adequada dos materiais vegetais com os quais se deseja trabalhar. A relação entre o conteúdo de DNA de acessos de bananeira e sua ploidia ainda permanece controversa na literatura; assim, o presente trabalho teve como objetivo avaliar o conteúdo de DNA de acessos de bananeira com diferentes níveis de ploidia. Foram avaliados sete acessos tetraploides, quatro triploides e quatro diploides. A determinação do conteúdo foi realizada pela técnica de citometria de fluxo. Foram trituradas entre 50-60 mg de folhas frescas, juntamente com o padrão interno (Pisum sativum) no tampão LB01, e, posteriormente, as amostras foram filtradas em gaze e filtro de 50 µm. Adicionaram-se 5 µL de RNase e 25 µL de iodeto de propídeo. Para cada amostra, foram analisados 10 mil núcleos, com três repetições. Os resultados obtidos para o conteúdo de DNA permitiram estimar o tamanho dos genomas A e B, sendo o primeiro cerca de 14% maior que o segundo. Os resultados apresentaram clara relação entre o conteúdo de DNA e o nível de ploidia dos materiais. O contéudo de DNA apresentou aumento médio de 30% nas cultivares diploides em relação às cultivares triploides avaliadas e de 25% nas cultivares triploides em relação às cultivares tetraploides. Apesar da diferença nos tamanhos dos genomas A e B, contribuições distintas desses dois genomas não foram diretamente relacionadas com alterações no conteúdo do DNA de cultivares tetraploides.