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Stem Length (stem + length)

Distribution by Scientific Domains

Life Sciences	68%

Distribution within Life Sciences

Ecology & Organismal Biology	36%

Selected Abstracts

Diversity and food quality properties of farmers' varieties of sorghum from Bénin

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2006
AP Polycarpe Kayodé
Abstract Farmers' varieties of sorghum from three communities in different regions of northern Bénin were analysed for their food quality and agro-morphological properties, and also for their genetic diversity using amplified fragment length polymorphism (AFLP). Farmers' varieties of sorghum differed greatly with respect to their morphology and agronomic and food traits. Most of the varieties had long (>200 cm) stems (87%), loose panicles (79%) and a red or pink colour (52%). Most were susceptible to drought (54%) and to attacks by striga (79%), insects (99%) and birds (77%). Farmers evaluated the quality of the seeds for preparing porridges as being high for 60% of the varieties and 26% of the varieties were regarded as suitable for making beverages. Late-maturing, large-seeded, red or pink varieties are preferred by farmers for porridges and beverages. Gene diversity among varieties within regions, as measured by neutral markers, was similar for the three regions (0.211,0.240). However, across regions the short (<150 cm) stem varieties showed relatively high genetic diversity compared with long or medium stem varieties (0.378 vs 0.184,0.216 for long,medium stem varieties). Genetic differentiation (Fst) among regions and among stem lengths of varieties was significant and ranged between 0.086 and 0.135. Grain colour, stem length and panicle shape varied significantly with the region/stem length and correlated with the genetic differentiation of regions. No relationship could be detected between the genetic differentiation of the varieties and their food quality as expressed by the farmers. Implications of the findings for crop conservation and breeding are discussed. Copyright © 2006 Society of Chemical Industry [source]

Effects of moisture, nitrogen, grass competition and simulated browsing on the survival and growth of Acacia karroo seedlings

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
Keletso Mopipi
Abstract The effects of irrigation, nitrogen fertilization, grass competition and clipping were investigated for one growing season at the research farm of the University of Fort Hare in the Eastern Cape Province of South Africa. The aim of the experiment was to assess the short-term performance of Acacia karroo seedlings under different environmental conditions and the implications of such factors on the long-term recruitment of plant species in savanna rangelands. There were no significant treatment effects on the survival of A. karroo seedlings. Using stem length and basal diameter as growth parameters, it was observed that irrigation enhanced both variables, while nitrogen fertilization did not have any significant effects. Clipping, grass competition and their interaction greatly suppressed the growth of the seedlings. Clipping increased the mean stem length when they were irrigated and fertilized. Control and fertilized plants had the highest stem length in the absence of grass competition, while grass competition combined with clipping resulted in the lowest stem length in both irrigated and nonirrigated plants. It was concluded that in the presence of grass competition, controlled browsing could be a viable solution to the problem of bush encroachment in savanna rangelands. Résumé Les effets de l'irrigation, d'une fertilisation à l'azote, de la compétition avec l'herbe et de la taille ont étéétudiés pendant une saison de croissance dans la ferme expérimentale de l'Université de Fort Hare, dans la Province du Cap oriental, en Afrique du Sud. Le but de l'expérience était d'évaluer les performances à court terme de jeunes plants d'Acacia karroo dans différentes conditions expérimentales, et les implications de ces facteurs sur le recrutement à long terme d'espèces végétales dans des pâturages de savane. Il n'y a pas eu d'effet significatif des traitements sur la survie des plants d'A. karroo. En utilisant la longueur des troncs et le diamètre de la base comme indicateurs de croissance, on a observé que l'irrigation augmentait les deux variables, alors que la fertilisation à l'azote n'avait aucun effet significatif. La taille, la compétition avec l'herbe et leur interaction supprimait fortement la croissance des jeunes plants. La taille augmentait la longueur moyenne des troncs lorsqu'ils étaient irrigués et fertilisés. Les plants témoins et les plants fertilisés avaient les troncs les plus longs en absence de toute compétition avec des herbes, alors que cette dernière, combinée avec la taille, aboutissait à la longueur la plus petite des troncs, chez les plants irrigués ou non. On en a conclu qu'en cas de compétition avec des herbes, un pâturage contrôlé pourrait être une solution viable au problème de l'envahissement des broussailles dans les pâturages de savane. [source]

Effects of global change on a sub-Arctic heath: effects of enhanced UV-B radiation and increased summer precipitation

JOURNAL OF ECOLOGY, Issue 2 2001
Gareth K. Phoenix
Summary 1The responses of sub-Arctic heathland vegetation to enhanced UV-B radiation and increased summer precipitation over 7 years were investigated in a field experiment in northern Sweden. 2Growth, phenology and reproduction of the dominant dwarf shrubs Vaccinium myrtillus, V. uliginosum, V. vitis-idaea and Empetrum hermaphroditum were studied after 5,7 years of manipulation and retrospective analyses were used to assess growth responses in earlier years. Leaf tissue N and P and 13C natural abundances were determined for V. myrtillus and E. hermaphroditum. Growth responses were also assessed for the moss Hylocomium splendens. 3The deciduous V. myrtillus showed reduced growth, increased leaf thickness and increased flowering and berry production under enhanced UV-B in some years. V. uliginosum, V. vitis-idaea, E. hermaphroditum and H. splendens were, in general, tolerant of UV-B. 4Increased precipitation affected growth only in the evergreen species: stem length and branching were sometimes stimulated in E. hermaphroditum, whereas V. vitis-idaea showed reduced branching. 5Precipitation also increased leaf thickness in V. uliginosum and reduced flowering and berry production in V. myrtillus. 6In the interactions that occurred between enhanced UV-B radiation and increased summer precipitation, combining the two treatments often negated any effect that either may have had separately. The effect of concurrent increases on this ecosystem is therefore likely to be much less than if either occurred singly. 7Enhanced UV-B and increased summer precipitation appeared not to effect dwarf shrub abundances during the first 5 years of the experiment, suggesting that overall this heath may be more tolerant of these environmental changes than previously thought. [source]

Sensitivity to Abscisic Acid Modulates Positive Interactions between Arabidopsis thaliana Individuals

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2010
Hao Zhang
The ability of abscisic acid (ABA) to modulate positive interactions between Arabidopsis thaliana individuals under salinity stress was investigated using abi1-1 (insensitive to ABA), era1-2 (hypersensitive to ABA) mutant and wild type plants. The results showed that sensitivity to ABA affects relative interaction intensity (RII) between Arabidopsis thaliana individuals. The neighbor removal experiments also confirmed the role of phenotypic responses in linking plant-plant interactions and sensitivity to ABA. For abi1-1 mutants, the absolute value differences between neighbor removal and control of stem length, root length, leaf area, leaf thickness, flower density, above biomass/belowground biomass (A/U), photosynthetic rate, stomatal conductance, leaf water content and water-use efficiency were smaller than those of the wild type, while for era1-2 mutants, these absolute value differences were larger than those of the wild type. Thus, it is suggested that positive interactions between Arabidopsis thaliana individuals are at least partly modulated by different sensitivity to ABA through different physiological and phenotypic plasticity. [source]

Diversity and food quality properties of farmers' varieties of sorghum from Bénin

Seed size and response to rainfall patterns in annual grasslands: 16 years of permanent plot data

JOURNAL OF VEGETATION SCIENCE, Issue 1 2009
B. Peco
Abstract Question: Are seed size and plant size linked to species responses to inter-annual variations in rainfall and rainfall distribution during the growing season in annual grasslands? Location: A 16-year data set on species abundance in permanent plots 15 km north of Madrid in a Quercus ilex subsp. ballota dehesa. Methods: At species level, a GLM was used to analyse the effects of various rainfall indices (total autumn rainfall, early autumn rainfall and spring drought) on species abundance residuals with respect to time and topography. We also assessed the importance of seed size and plant size in the species responses at community level using species as data points. Seed mass and maximum stem length were used as surrogates for seed size and plant size, respectively. Results: Seed mass and plant size may explain some of the fluctuations in the floristic composition of annual species associated with autumn rainfall patterns. Species that are more abundant in dry autumns have greater seed mass than those species that are more abundant in wet autumns. Early autumn rainfall seems to favour larger plants. Conclusions: Our empirical results support the hypothesis that autumn rainfall patterns affect the relative establishment capacity of small and large seedlings in annual species. [source]

Spatial patterns of microsite colonisation on two young lava flows on Mount Hekla, Iceland

JOURNAL OF VEGETATION SCIENCE, Issue 2 2008
N.A. Cutler
Abstract Questions: How does vegetation first establish on newly-formed lava substrates? Do very small (cm) and meso-scale (m) variations in the physical environment influence this process and subsequent vegetation development? Location: Mount Hekla, southern Iceland (64°00' N, 19°40' W). Methods: Data on vegetation structure and the incidence of ,safe sites' suitable for colonisation were collected from high and low points on the surfaces of lava flows emplaced during the 1991 and 2000 A.D. eruptions of Mount Hekla. Effects of flow age and meso-topographic position on vegetation structure (moss cover, patch density, stem length) were assessed by two-way analyses of variance. The distributions of colonisation events and available safe sites were analysed using point pattern techniques. Results: Rapid colonisation of the lava surface was observed, despite stressful environmental conditions. The 1991 and 2000 flows differed significantly in vegetation structure, but there were no significant differences in moss cover, patch density and stem length between ,high' and ,low' sites. Conclusions: Colonisation events are invariably associated with small-scale irregularities on the surface of the lava. The colonisation process appears to be spatially random. Development of the moss ,carpet' proceeds by vertical thickening and lateral growth and coalescence of moss patches that establish in ,safe sites'. This process is rapid, with close to 100% of available safe sites exploited within 20 years. Topographic position makes no difference to the very early stages of vegetation development and cannot be used to ,forecast' the later stages of development. [source]

Xanthomonas citri: breaking the surface

MOLECULAR PLANT PATHOLOGY, Issue 3 2003
Asha M. Brunings
SUMMARY Taxonomy: Bacteria; Proteobacteria, Gammaproteobacteria; Xanthomonadales; Xanthomonadaceae, Xanthomonas. Microbiological properties: Gram-negative, obligately aerobic, straight rods, motile by a single polar flagellum, yellow pigment. Related species:X. campestris , X. axonopodis , X. oryzae , X. albilineans . Host range: Affects Rutaceous plants, primarily Citrus spp., Fortunella spp., and Poncirus spp., world-wide. Quarantined pathogen in many countries. Economically important hosts are cultivated orange, grapefruit, lime, lemon, pomelo and citrus rootstock. Disease symptoms: On leaves, first appearance is as oily looking, 2,10 mm, similarly sized, circular spots, usually on the abaxial surface. On leaves, stems, thorns and fruit, circular lesions become raised and blister-like, growing into white or yellow spongy pustules. These pustules then darken and thicken into a light tan to brown corky canker, which is rough to the touch. On stems, pustules may coalesce to split the epidermis along the stem length, and occasionally girdling of young stems may occur. Older lesions on leaves and fruit tend to have more elevated margins and are at times surrounded by a yellow chlorotic halo (that may disappear) and a sunken centre. Sunken craters are especially noticeable on fruit, but the lesions do not penetrate far into the rind. Defoliation and premature abscission of affected fruit occurs on heavily infected trees. Useful websites: ; [source]

Density-Induced Plant Size Reduction and Size Inequalities in Ethylene-Sensing and Ethylene-Insensitive Tobacco

PLANT BIOLOGY, Issue 2 2004
R. Pierik
Abstract: Plant competition for light is a commonly occurring phenomenon in natural and agricultural vegetations. It is typically size-asymmetric, meaning that slightly larger individuals receive a disproportionate share of the light, leaving a limited amount of light for the initially smaller individuals. As a result, size inequalities of such stands increase with competition intensity. A plant's ability to respond morphologically to the presence of neighbour plants with enhanced shoot elongation, the so-called shade avoidance response, acts against the development of size inequalities. This has been shown experimentally with transgenic plants that cannot sense neighbours and, therefore, show no shade avoidance responses. Stands of such transgenic plants showed a much stronger development of size inequalities at high plant densities than did wild type (WT) stands. However, the transgenic plants used in these experiments displayed severely hampered growth rates and virtually no response to neighbours. In order to more precisely study the impact of this phenotypic plasticity on size inequality development, experiments required plants that have normal growth rates and reduced, but not absent, shade avoidance responses. We made use of an ethylene-insensitive, transgenic tobacco genotype (Tetr) that has wild type growth rates and moderately reduced shade avoidance responses to neighbours. Here, we show that the development of size inequalities in monocultures of these plants is not affected unambiguously different from wild type monocultures. Plots of Tetr plants developed higher inequalities for stem length than did WT, but monocultures of the two genotypes had identical CV (Coefficient of Variance) values for shoot biomass that increased with plant density. Therefore, even though reduced shade avoidance capacities led to the expected higher size inequalities for stem length, this does not necessarily lead to increased size inequalities for shoot biomass. [source]

Stable expression of AtGA2ox1 in a low-input turfgrass (Paspalum notatum Flugge) reduces bioactive gibberellin levels and improves turf quality under field conditions

PLANT BIOTECHNOLOGY JOURNAL, Issue 6 2007
Mrinalini Agharkar
Summary Bahiagrass (Paspalum notatum Flugge) is a prime candidate for molecular improvement of turf quality. Its persistence and low input characteristics made it the dominant utility turfgrass along highways in the south-eastern USA. However, the comparatively poor turf quality due to reduced turf density and prolific production of unsightly inflorescences currently limits the widespread use of bahiagrass as residential turf. Alteration of endogenous gibberellin (GA) levels by application of growth regulators or transgenic strategies has modified plant architecture in several crops. GA catabolizing AtGA2ox1 was subcloned under the control of the constitutive maize ubiquitin promoter and Nos 3'UTR. A minimal AtGA2ox1 expression cassette lacking vector backbone sequences was stably introduced into apomictic bahiagrass by biolistic gene transfer as confirmed by Southern blot analysis. Expression of AtGA2ox1 in bahiagrass as indicated by reverse transcription,polymerase chain reaction and Northern blot analysis resulted in a significant reduction of endogenous bioactive GA1 levels compared to wild type. Interestingly, transgenic plants displayed an increased number of vegetative tillers which correlated with the level of AtGA2ox1 expression and enhanced turf density under field conditions. This indicates that GAs contribute to signalling the outgrowth of axillary buds in this perennial grass. Transgenic plants also showed decreased stem length and delayed flowering under controlled environment and field conditions. Consequently, turf quality following weekly mowing was improved in transgenic bahiagrass. Transgene expression and phenotype were transmitted to seed progeny. Argentine bahiagrass produces seeds asexually by apomixis, which reduces the risk of unintended transgene dispersal by pollen and results in uniform progeny. [source]

Optimization of an siRNA-expression system with an improved hairpin and its significant suppressive effects in mammalian cells

THE JOURNAL OF GENE MEDICINE, Issue 7 2004
Makoto Miyagishi
Abstract Background RNA interference (RNAi) is a phenomenon in which expression of an individual gene can be specifically silenced by introducing a double-stranded RNA, one complementary to the gene, into cells. This phenomenon can be observed in mammalian cells when small interfering RNAs (siRNAs) are used, and is receiving attention as the most powerful tool for reverse genetics in the post genome era. Several groups have developed vector-based siRNA-expression systems that can induce RNAi in living cells. Methods We describe here a comparative analysis of various siRNA-expression systems, in which we examined the effects of stem length, loop sequence and insertion of mutation(s) and/or bulges in the stem sequence on silencing effects and on the stability of the vectors. Results As a result of the comparative analysis, we determined the following optimized siRNA-expression system: U6 promoter-driven hairpin-type dsRNA with 21-nt stem length, three to four mutations in the sense strand only, and the optimized 9-nt loop sequence, derived from microRNA. Moreover, we demonstrate that the siRNA-expression system with a tetracycline-regulated U6 promoter(s) could have the potential to control RNAi in cells, and that the HIV vector-mediated transfer of an siRNA-expression cassette into cells resulted in efficient silencing of a target gene at a multiplicity of infection as low as five. Conclusion The mutated hairpin siRNAs and their genetically stable coding vectors could be very useful for gene knockdown experiments, and could further benefit gene therapy using RNAi. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Counteractive biomass allocation responses to drought and damage in the perennial herb Convolvulus demissus

AUSTRAL ECOLOGY, Issue 5 2010
IVÁN M. QUEZADA
Abstract Herbivory and water shortage are key ecological factors affecting plant performance. While plant compensatory responses to herbivory include reallocation of biomass from below-ground to above-ground structures, plant responses to reduced soil moisture involve increased biomass allocation to roots and a reduction in the number and size of leaves. In a greenhouse study we evaluated the effects of experimental drought and leaf damage on biomass allocation in Convolvulus demissus (Convolvulaceae), a perennial herb distributed in central Chile, where it experiences summer drought typical of Mediterranean ecosystems and defoliation by leaf beetles and livestock. The number of leaves and internode length were unaffected by the experimental treatments. The rest of plant traits showed interaction of effects. We detected that drought counteracted some plant responses to damage. Thus, only in the control watering environment was it observed that damaged plants produced more stems, even after correcting for main stem length (index of architecture). In the cases of shoot : root ratio, relative shoot biomass and relative root biomass we found that the damage treatment counteracted plant responses to drought. Thus, while undamaged plants under water shortage showed a significant increase in root relative biomass and a significant reduction in both shoot : root ratio and relative shoot biomass, none of these responses to drought was observed in damaged plants. Total plant biomass increased in response to simulated herbivory, apparently due to greater shoot size, and in response to drought, presumably due to greater root size. However, damaged plants under experimental drought had the same total biomass as control plants. Overall, our results showed counteractive biomass allocation responses to drought and damage in C. demissus. Further research must address the fitness consequences under field conditions of the patterns found. This would be of particular importance because both current and expected climatic trends for central Chile indicate increased aridity. [source]

Growth responses of African savanna trees implicate atmospheric [CO2] as a driver of past and current changes in savanna tree cover

AUSTRAL ECOLOGY, Issue 4 2010
BARNEY S. KGOPE
Abstract Atmospheric CO2 has more than doubled since the last glacial maximum (LGM) and could double again within this century, largely due to anthropogenic activity. It has been suggested that low [CO2] contributed to reduced tree cover in savanna and grassland biomes at LGM, and that increasing [CO2] over the last century promoted increases in woody plants in these ecosystems over the past few decades. Despite the implications of this idea for understanding global carbon cycle dynamics and key global role of the savanna biome, there are still very few experimental studies quantifying the effects of CO2 on tree growth and demography in savannas and grasslands. In this paper we present photosynthetic, growth and carbon allocation responses of African savanna trees (Acacia karroo and Acacia nilotica) and a C4 grass, Themeda triandra, exposed to a gradient of CO2 concentrations from 180 (typical of LGM) to 1000 µmol mol,1 in open-top chambers in a glasshouse as a first empirical test of this idea. Photosynthesis, total stem length, total stem diameter, shoot dry weight and root dry weight of the acacias increased significantly across the CO2 gradient, saturating at higher CO2 concentrations. After clipping to simulate fire, plants showed an even greater response in total stem length, total stem diameter and shoot dry weight, signalling the importance of re-sprouting following disturbances such as fire or herbivory in savanna systems. Root starch (per unit root mass and total root starch per plant) increased steeply along the CO2 gradient, explaining the re-sprouting response. In contrast to the strong response of tree seedlings to the CO2 gradient, grass productivity showed little variation, even at low CO2 concentrations. These results suggest that CO2 has significant direct effects on tree recruitment in grassy ecosystems, influencing the ability of trees to recover from fire damage and herbivory. Fire and herbivore regimes that were effective in controlling tree increases in grassy ecosystems could thus be much less effective in a CO2 -rich world, but field-based tests are needed to confirm this suggestion. [source]