RESUMEN
BACKGROUND AND AIMS: Despite general agreement regarding the adaptive importance of plasticity, evidence for the role of environmental resource availability in plants is scarce. In arid and semi-arid environments, the persistence and dominance of perennial species depends on their capacity to tolerate drought: tolerance could be given on one extreme by fixed traits and, on the other, by plastic traits. To understand drought tolerance of species it is necessary to know the plasticity of their water economy-related traits, i.e. the position in the fixed-plastic continuum. METHODS: Three conspicuous co-existing perennial grasses from a Patagonian steppe were grown under controlled conditions with four levels of steady-state water availability. Evaluated traits were divided into two groups. The first was associated with potential plant performance and correlated with fitness, and included above-ground biomass, total biomass, tillering and tiller density at harvest. The second group consisted of traits associated with mechanisms of plant adjustment to environmental changes and included root biomass, shoot/root ratio, tiller biomass, length of total elongated leaf, length of yellow tissue divided by time and ï¬nal length divided by the time taken to reach ï¬nal length. KEY RESULTS AND CONCLUSIONS: The most plastic species along this drought gradient was the most sensitive to drought, whereas the least plastic and slowest growing was the most tolerant. This negative relationship between tolerance and plasticity was true for fitness-related traits but was trait-dependent for underlying traits. Remarkably, the most tolerant species had the highest positive plasticity (i.e. opposite to the default response to stress) in an underlying trait, directly explaining its drought resistance: it increased absolute root biomass. The niche differentiation axis that allows the coexistence of species in this group of perennial dryland grasses, all limited by soil surface moisture, would be a functional one of fixed versus plastic responses.
Asunto(s)
Adaptación Fisiológica/fisiología , Sequías , Poaceae/fisiología , Argentina , Biomasa , Bromus/crecimiento & desarrollo , Bromus/fisiología , Fenotipo , Componentes Aéreos de las Plantas/fisiología , Raíces de Plantas/fisiología , Poa/crecimiento & desarrollo , Poa/fisiología , Poaceae/crecimiento & desarrollo , Suelo , Agua/metabolismoRESUMEN
We have previously reported the molecular characterization of a putative sucrose:fructan 6-fructosyltransferase (6-SFT) of Bromus pictus, a graminean species from Patagonia, tolerant to cold and drought. Here, this enzyme was functionally characterized by heterologous expression in Pichia pastoris and Nicotiana tabacum. Recombinant P. pastoris Bp6-SFT showed comparable characteristics to barley 6-SFT and an evident fructosyltransferase activity synthesizing bifurcose from sucrose and 1-kestotriose. Transgenic tobacco plants expressing Bp6-SFT, showed fructosyltransferase activity and fructan accumulation in leaves. Bp6-SFT plants exposed to freezing conditions showed a significantly lower electrolyte leakage in leaves compared to control plants, indicating less membrane damage. Concomitantly these transgenic plants resumed growth more rapidly than control ones. These results indicate that Bp6-SFT transgenic tobacco plants that accumulate fructan showed enhanced freezing tolerance compared to control plants.
Asunto(s)
Adaptación Fisiológica , Bromus/enzimología , Congelación , Hexosiltransferasas/metabolismo , Nicotiana/genética , Pichia/genética , Secuencia de Bases , Cromatografía por Intercambio Iónico , Cartilla de ADN , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
A computational study predicts a number of stable, unusual halogen- and hydrogen-bonded complexes involving FBr, NCH, and FH. Starting from the linear halogen-bonded FBr...NCH dimer, increasingly more stable complexes are obtained by the successive hydrogen bonding of one to three FH molecules to the lone pairs on the Br atom of FBr to form a trimer, tetramer, and pentamer. A hexamer is obtained from the pentamer by the bonding of FH to the F atom of FBr. The combined halogen and hydrogen bonding gives rise to a large computed zero-point corrected binding energy of 98 kJ/mol for the hexamer at the MP2/6-31++G(d,p) level of theory.
Asunto(s)
Bromus/química , Flúor/química , Simulación por Computador , Enlace de Hidrógeno , Sustancias Macromoleculares/química , Termodinámica , VibraciónRESUMEN
Fructans are fructose polymers synthesized in a wide range of species such as bacteria, fungi and plants. Fructans are synthesized by fructosyltransferases (FTs) and depolymerized by fructan exohydrolases (FEHs). Bromus pictus is a graminean decaploid species from the Patagonian region of Argentina, which accumulates large amounts of fructans even at temperate temperatures. The first gene isolated from B. pictus fructan metabolism was a putative sucrose:fructan 6-fructosyltransferase (6-SFT). Here, a complete cDNA of the first fructan exohydrolase (FEH) from B. pictus (Bp1-FEHa) was isolated using RT-PCR strategies. The Bp1-FEHa encoding gene is present as a single copy in B. pictus genome. Functional characterization in Pichia pastoris confirmed Bp1-FEHa is a fructan exohydrolase with predominant activity towards beta-(2-1) linkages. Its expression was analyzed in different leaf sections, showing the highest expression levels in the second section of the sheath and the tip of the blade. Bp1-FEHa expression was studied along with FEH and FT activities and fructan accumulation profile in response to chilling conditions during a 7-day time course experiment. Bp1-FEHa expression and FEH activity followed a similar pattern in response to low temperatures, especially in basal sections of the sheaths. In these sections the FEH and FT activities were particularly high and they were significantly correlated to fructan accumulation profile, along with cold treatment.
Asunto(s)
Adaptación Fisiológica , Bromus/enzimología , Bromus/genética , Frío , Glicósido Hidrolasas/genética , Secuencia de Aminoácidos , Southern Blotting , Clonación Molecular , Fructanos/metabolismo , Perfilación de la Expresión Génica , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Genes de Plantas/genética , Glicósido Hidrolasas/química , Hexosiltransferasas/genética , Hexosiltransferasas/metabolismo , Datos de Secuencia Molecular , Filogenia , Pichia , Hojas de la Planta/enzimología , Hojas de la Planta/genética , Proteínas Recombinantes/metabolismo , Alineación de SecuenciaRESUMEN
The fungi of genus Neotyphodium are systemic, constitutive, symbionts of grasses of subfamily Pooideae. In the southern hemisphere most of these asexual endophytes are the result of the hybridization between two sexual species, Epichlo" festucae and E. typhina, from the northern hemisphere. However the ancestral sexual species have not been detected in this region. Several grasses from Argentina are infected by Neotyphodium species. These endophytes are in general very similar macro- and micromorphologically and phylogenetically conform to species N. tembladerae. However the Neotyphodium spp. endophytes of some hosts, Bromus auleticus and Poa spicifomis var. spiciformis, have not been included in this species. In this work we studied the incidence and characterized the diversity of Neotyphodium species in populations of the native grass Bromus auleticus from Argentina. The incidence of endophytes was 100% in all populations investigated. Two groups of endophytes were differentiated by their morphologies, growth rates, conidial ontogenies and by relative resistance to the fungicide benomyl. Phylogenetic trees inferred from tefA and tubB intron sequences indicated that both N. tembladerae and the novel morphotype were hybrids of E. festucae and E. typhina, but the ancestral E. typhina genotype distinguished them. Isolates from plants that inhabit coastal dunes, xerophytic forests, savannahs and hills were similar morphologically and phylogenetically to N. tembladerae, whereas the endophytes from the humid pampa plains conformed to the novel group. We propose the endophyte of Bromus auleticus from humid pampas as a new species, Neotyphodium pampeanum.
Asunto(s)
Bromus/microbiología , Especiación Genética , Neotyphodium/clasificación , Filogenia , Argentina , ADN de Hongos/genética , ADN de Hongos/aislamiento & purificación , ADN Espaciador Ribosómico/análisis , ADN Espaciador Ribosómico/genética , Ecosistema , Variación Genética , Neotyphodium/citología , Neotyphodium/fisiología , Factor 1 de Elongación Peptídica/análisis , Factor 1 de Elongación Peptídica/genética , Análisis de Secuencia de ADN , Especificidad de la Especie , Esporas Fúngicas/citología , Simbiosis , Tubulina (Proteína)/análisis , Tubulina (Proteína)/genéticaRESUMEN
Fructans are fructose polymers synthesized from sucrose in the plant vacuole. They represent short- and long-term carbohydrate reserves and have been associated with abiotic stress tolerance in graminean species. We report the isolation and characterization of a putative sucrose:fructan 6-fructosyltransferase (6-SFT) gene from a Patagonian grass species, Bromus pictus, tolerant to drought and cold temperatures. Structural and functional analyses of this gene were performed by Southern and Northern blot. Sugar content, quality and fructosyltransferase activity were studied using HPAEC-PAD (high-pH anion-exchange chromatography with pulsed amperometric detection), enzymatic and colorimetric assays. The putative 6-SFT gene had all the conserved motifs of fructosyl-transferase and showed 90% identity at the amino acid level with other 6-SFTs from winter cereals. Expression studies, and determination of sugar content and fructosyl-transferase activity were performed on five sections of the leaf. Bp6-SFT was expressed predominantly in leaf bases, where fructosyltransferase activity and fructan content are higher. Bp6-SFT expression and accumulation of fructans showed different patterns in the evaluated leaf sections during a 7 d time course experiment under chilling treatment. The transcriptional pattern suggests that the B. pictus 6-SFT gene is highly expressed in basal leaf sections even under control temperate conditions, in contrast to previous reports in other graminean species. Low temperatures caused an increase in Bp6-SFT expression and fructan accumulation in leaf bases. This is the first study of the isolation and molecular characterization of a fructosyltransferase in a native species from the Patagonian region. Expression in heterologous systems will confirm the functionality, allowing future developments in generation of functional markers for assisted breeding or biotechnological applications.
Asunto(s)
Bromus/genética , Frío , Fructanos/biosíntesis , Hexosiltransferasas/metabolismo , Proteínas de Plantas/metabolismo , Secuencia de Aminoácidos , Bromus/enzimología , Clonación Molecular , ADN Complementario/genética , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Hexosiltransferasas/genética , Datos de Secuencia Molecular , Proteínas de Plantas/genética , ARN de Planta/genética , Alineación de Secuencia , Análisis de Secuencia de ADNRESUMEN
The subgenus Ceratochloa of the genus Bromus includes a number of closely related allopolyploid forms or species that present a difficult taxonomic problem. The present work combines data concerning chromosome length, heterochromatin distribution and nuclear genome size of different 6x, 8x and 12x accessions in this subgenus. Special attention is paid to the karyotype structure and genomic constitution of duodecaploid plants recently found in South America. Hexaploid lineages possess six almost indistinguishable genomes and a nuclear DNA content between 12.72 pg and 15.10 pg (mean 1Cx value = 2.32 pg), whereas octoploid lineages contain the same six genomes (AABBCC) plus two that are characterized by longer chromosomes and a greater DNA content (1Cx = 4.47 pg). Two duodecaploid accessions found in South America resemble each other and apparently differ from the North American duodecaploid B. arizonicus as regards chromosome size and nuclear DNA content (40.00 and 40.50 pg vs. 27.59 pg). These observations suggest that the South American duodecaploids represent a separate evolutionary lineage of the B. subgenus Ceratochloa, unrecognized heretofore.
Asunto(s)
Bromus/genética , Bandeo Cromosómico , Genoma de Planta , Citometría de Flujo , Heterocromatina , CariotipificaciónRESUMEN
BACKGROUND AND AIMS: Growth of grass species in temperate-humid regions is restricted by low temperatures. This study analyses the origin (intrinsic or size-mediated) and mechanisms (activity of individual meristems vs. number of active meristems) of differences between Bromus stamineus and Lolium perenne in the response of leaf elongation to moderately low temperatures. METHODS: Field experiments were conducted at Balcarce, Argentina over 2 years (2003 and 2004) using four cultivars, two of B. stamineus and two of L. perenne. Leaf elongation rate (LER) per tiller and of each growing leaf, number of growing leaves and total leaf length per tiller were measured on 15-20 tillers per cultivar, for 12 (2003) or 10 weeks (2004) during autumn and winter. KEY RESULTS: LER was faster in B. stamineus than in L. perenne. In part, this was related to size-mediated effects, as total leaf length per tiller correlated with LER and B. stamineus tillers were 71% larger than L. perenne tillers. However, accounting for size effects revealed intrinsic differences between species in their temperature response. These were based on the number of leaf meristems simultaneously active and not on the (maximum) rate at which individual leaves elongated. Species differences were greater at higher temperatures, being barely notable below 5 degrees C (air temperature). CONCLUSIONS: Bromus stamineus can sustain a higher LER per tiller than L. perenne at air temperatures > 6 degrees C. In the field, this effect would be compounded with time as higher elongation rates lead to greater tiller sizes.
Asunto(s)
Bromus/crecimiento & desarrollo , Lolium/crecimiento & desarrollo , Temperatura , Tamaño Corporal , Bromus/anatomía & histología , Lolium/anatomía & histología , Hojas de la Planta/anatomía & histología , Hojas de la Planta/crecimiento & desarrollo , Especificidad de la EspecieRESUMEN
Isolating the single effects and net balance of negative and positive species effects in complex interaction networks is a necessary step for understanding community dynamics. Facilitation and competition have both been found to operate in harsh environments, but their relative strength may be predicted to change along gradients of herbivory. Moreover, facilitation effects through habitat amelioration and protection from herbivory may act together determining the outcome of neighborhood plant-plant interactions. We tested the hypothesis that grazing pressure alters the balance of positive and negative interactions between palatable and unpalatable species by increasing the strength of positive indirect effects mediated by associational resistance to herbivory. We conducted a two-year factorial experiment in which distance (i.e., spatial association) from the nearest unpalatable neighbor (Stipa speciosa) and root competition were manipulated for two palatable grasses (Poa ligularis and Bromus pictus), at three levels of sheep grazing (none, moderate, and high) in a Patagonian steppe community. We found that grazing shifted the effect of Stipa on both palatable grasses, from negative (competition) in the absence of grazing to positive (facilitation) under increasing herbivore pressure. In ungrazed sites, belowground competition was the dominant interaction, as shown by a significant reduction in performance of palatable grasses transplanted near to Stipa tussocks. In grazed sites, biomass of palatable plants was greater near than far from Stipa regardless of competition treatment. Proximity to Stipa reduced the amount of herbivory suffered by palatable grasses, an indirect effect that was stronger under moderate than under intense grazing. Our results demonstrate that facilitation, resulting mainly from protection against herbivory, is the overriding effect produced by unpalatable neighbors on palatable grasses in this rangeland community. This finding challenges the common view that abiotic stress amelioration should be the predominant type of facilitation in arid environments and highlights the role of herbivory in modulating complex neighborhood plant interactions in grazing systems.