Fructosyl transferase and hydrolase activities in rhizophores and tuberous roots upon growth of Polymnia sonchifolia (Asteraceae)

The underground reserve organs of yacon (Polymnia sonchifolia Poep. Endl.), similarly to other economically important Asteraceae, accumulate more than 60%, on a DW basis, of inulin type β(2‐1) fructans, mainly oligomers (GF2–GF16). Although sucrose:sucrose 1‐fructosyl transferase (1‐SST), fructan:fructan 1‐fructosyl transferase (1‐FFT) and fructan 1‐exohydrolase (1‐FEH) were properly described and characterized from a number of plant species, detailed information about their activities in different organs during development are rather scarce in the literature. In the present work 1‐SST, 1‐FFT and 1‐FEH activities were measured monthly in rhizophores and tuberous roots of yacon plants during their complete growth cycle under field conditions. Results showed that 1‐SST activity in rhizophores was always higher than 1‐FFT activity and increased up to 8 months of cultivation, decreasing to initial values at the end of the growth period. In the tuberous roots 1‐SST activity was also higher than 1‐FFT but varied differently. The higher values were found at the beginning of tuberization (3‐month‐old plants) and at the flowering phase (7‐month‐old plants). Results also showed that synthesizing activities in yacon plants were always higher in rhizophores than in the tuberous roots, while hydrolysing activity predominated in the latter, mainly when 1‐kestose and nystose were used as substrates. 1‐FEH from yacon plants showed low efficiency when commercial inulin from Helianthus tuberosus was utilized as substrate. The analysis of the enzymatic activities performed during growth of yacon clearly indicated the most appropriate source organ and phase of development to obtain the highest enzymatic activities for purification purposes and for the production of fructo‐oligosaccharides (FOS). Furthermore, the results suggested that the relative levels of activities of 1‐SST, 1‐FFT and 1‐FEH could be involved in the chain length distribution of the fructan molecules found in rhizophores and in tuberous roots of this species.     

In vitro culture and fructan production by Vernonia herbacea (Asteraceae)

Vernonia herbacea is a native species from the Brazilian Cerrado that accumulates about 80 % of inulin-type fructans in the underground reserve organs, the rhizophores. This work aimed at establishing a protocol for in vitro culture of V. herbacea, using seeds (achenes) and leaf discs as explants. Following germination and seedling growth, stem nodes from 6-month-old in vitro germinated plants were isolated and incubated on culture medium free of growth regulators for plant propagation and rhizophore formation. Fructan content and composition were evaluated in leaves, stems, roots and rhizophores from plants grown in vitro and compared with those of greenhouse-grown plants, in order to evaluate inulin production in vitro. Fructan contents of aerial organs and roots from in vitro plants were higher, compared with greenhouse plants, while in rhizophores, the opposite was observed. High performance anion exchange chromatography/pulsed amperometric detection profiles revealed the presence of the inulin homologous series in the aerial organs exclusively for in vitro plants, while in roots and rhizophores, this series was detected in plants grown in both conditions. These results indicate a modification in the source/sink ratio, leading to changes in the distribution of carbohydrates in in vitro plants. The leaf disc cultures on medium supplemented with indole-3-butyric acid induced the formation of roots (0.24, 0.49 µM) and friable callus (2.46 µM), while 6-benzylaminopurine (from 1.1 through 4.43 µM) induced compact callus. However, no shoot formation was observed. The use of seeds allowed the establishment of a protocol for in vitro culture and provides a model system for a better understanding of fructan metabolism in V. herbacea.     

Genetic diversity and structure of populations in Pilosocereus gounellei (F.A.C.Weber ex K.Schum.) (Cactaceae) in the Caatinga biome as revealed by heterologous microsatellite primers

Microsatellite transferability was used as a method to examine the genetic diversity and structure of populations in Pilosocereus gounellei seedling samples that have potential to implement effective restoration strategies for degraded and disturbed areas of the Caatinga biome. Genomic DNA was extracted from 85 seedlings obtained from fruit collected from plants growing in native areas in the Brazilian states of Piaui (PI), Rio Grande do Norte (RN), and Bahia (BA). Six microsatellite primers were polymorphic. AMOVA showed higher genetic variation within (72%) than among (28%) the samples from the three states. The high level of similarity between the seedlings from PI, BA, and RN indicated that samples collected at any of the three sites can be used to represent the genetic diversity of the species. Seeds of plants from the three States are recommended as samples for germplasm banks and/or the production of plantlets to i) plant in areas of strategic reserves for forage, ii) deploy new cultivation areas, iii) restore degraded areas in the semi-arid Northeast, and iv) maintain ecological reserve banks and fodder with genetically divergent plants.     

Icacina oliviformis (Icacinaceae): A close look at an underexploited food plant. III. Ecology and production

Data are presented on the ecology and production ofIcacina oliviformis (Poiret) Raynal in natural stands in northern Central African Republic. The species grows on a variety of soils and in numerous plant communities. It is fire adapted, and thrives when burned in the early dry season. The plant is primarily bee pollinated and has a number of pests that infest the stems and young fruits. Plant densities are high, with a maximum of ca. 5345 plants/ha in the study sites. Standing tuberous root biomass can be considerable, with a maximum of ca. 19904 kg/ha for the study sites. Seed yield in the sample sites was relatively low with a maximum of ca. 214 kg/ha. With proper management, yields of both seed and tuberous roots could be substantially increased.     

Morphological changes and resource allocation of Zizania latifolia (Griseb.) Stapf in response to different submergence depth and duration

Plants around ponds, rivers and lakes are subjected to long-term partial or complete submergence. When they are flooded, water level affects the plants simultaneously with duration of submergence. Separate and interactive effects of water level and duration on the growth of the herbaceous perennial Zizania latifolia (Poaceae) were investigated by exposing the plants in greenhouse water tanks to submergence in different water depths and for different time-spans. The plants exhibited great shoot elongation upon submergence and prolonged flood duration, and the basal tiller number of the species decreased with higher water levels. Submergence treatment advanced the flowering date and increased the inflorescence number. Plant total biomass did not differ among all the treatments, while the root:shoot ratio decreased with increased water level, prolonged duration of submergence and their interaction. The high plasticity in morphology and shifts in reproductive strategy and biomass allocation enabled the Zizania plants to survive the compound effect of flooding height and duration. This may explain the occurrence of this species in habitats subjected to long-term flooding. The results obtained in this experiment will contribute to understanding the impact of flooding dynamics on plants and the ways of adaptation responses to prolonged waterlogging.     

Effects of elevated CO2 concentration and water deficit on fructan metabolism in Viguiera discolor Baker

Elevated [CO₂] is suggested to mitigate the negative effects of water stress in plants; however responses vary among species. Fructans are recognised as protective compounds against drought and other stresses, as well as having a role as reserve carbohydrates. We analysed the combined effects of elevated [CO₂] and water deficit on fructan metabolism in the Cerrado species Viguiera discolor Baker. Plants were cultivated for 18 days in open‐top chambers (OTC) under ambient (～380 ppm), and high (～760 ppm) [CO₂]. In each OTC, plants were submitted to three treatments: (i) daily watering (control), (ii) withholding water (WS) for 18 days and (iii) re‐watering (RW) on day 11. Analyses were performed at time 0 and days 5, 8, 11, 15 and 18. High [CO₂] increased photosynthesis in control plants and increased water use efficiency in WS plants. The decline in soil water content was more distinct in WS 760 (WS under 760 ppm), although the leaf and tuberous root water status was similar to WS 380 plants (WS under 380 ppm). Regarding fructan active enzymes, 1‐SST activity decreased in WS plants in both CO₂ concentrations, a result consistent with the decline in photosynthesis and, consequently, in substrate availability. Under WS and both [CO₂] treatments, 1‐FFT and 1‐FEH seemed to act in combination to generate osmotically active compounds and thus overcome water deficit. The proportion of hexoses to sucrose, 1‐kestose and nystose (SKN) was higher in WS plants. In WS 760, this increase was higher than in WS 380, and was not accompanied by decreases in SKN at the beginning of the treatment, as observed in WS 380 plants. These results suggest that the higher [CO₂] in the atmosphere contributed to maintain, for a longer period, the pool of hexoses and of low DP fructans, favouring the maintenance of the water status and plant survival under drought.     

Seasonal changes in the amount of carbohydrate and crude protein in the rhizome ofMiscanthus sacchariflorus

In the herbaceous perennials, seasonal changes in the amount of reserve substances play an important role in the production processes of whole plants. Mutohet al. (1968) indirectly estimated the amount of reserve substances stored in the rhizome ofMiscanthus sacchariflorus by measuring the bulk density of the rhizome, and found aarked seasonal changes. In the present study seasonal changes in the carbohydrate and crude protein content of the rhizome were determined and the results obtained were compared with the changes in the total amount of reserve substances estimated by means of changes in the bulk density. A good parallel seasonal relationship was confirmed between the amount of consumable carbohydrate determined chemically and the quantity of reserve substances estimated from the changes in bulk density. The total yields of carbohydrate and crude protein were ca. 75% of the available reserve substances estimated from the changes of bulk density for the old rhizomes and ca. 65% for the new rhizomes in the middle of December.     

Morpho‐anatomical diversity of the underground systems of Arrojadoa (Cactaceae), an endemic Brazilian genus

Members of Arrojadoa exhibit a variety of underground structures that can originate from roots or stems. Although the development of underground structures of stem origin in Arrojadoa represents a unique trait among Cactaceae of eastern Brazil, no detailed reports on the morphological diversity of such structures are available. The present morpho‐anatomical study of the underground systems of Arrojadoa has demonstrated that a single species can exhibit one or more structural types, such as single or branched stem tubers, short thick stems and/or long subterranean stems, thick and fleshy contractile roots and normal fibrous roots. Various morpho‐anatomical structures relating to the underground storage systems in Arrojadoa spp. have also been observed, including thick contractile roots consisting mainly of secondary xylem formed by fibrous wood with wide‐band tracheids (WBTs) and underground stems with a wide cortical region and WBTs‐type wood. Based on the evidence presented, we suggest that such traits, together with the occurrence of contractile roots associated with underground stems, are important adaptive strategies for the survival of the plants during seasonal drought in areas of cerrado (savannah), campo rupestre (rocky uplands) and caatinga (dry thorny scrubland). © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 108–128.     

Water relations and gas exchange in Coespeletia moritziana (Sch. Bip) Cuatrec., a giant rosette species of the high tropical Andes

Giant rosettes are ones of the most striking features of the vegetation in the high tropical Andes, with Coespeletia moritziana reaching the highest altitudes up to 4,600 m a.s.l. Different from other giant rosettes, this species grows on rock outcrops with poorly developed soils and where water availability may be limited. Two questions are addressed in this study: How does this species respond in terms of water relations to maintain favorable gas-exchange conditions? Considering that adult plants rely on a water-reserving central pith, how do early stages respond to this environment??s extreme conditions? Water relations and gas-exchange studies were carried out on juveniles, intermediate and adult C. moritziana plants during wet and dry seasons in Páramo de Piedras Blancas at 4,200 m a.s.l. Adult plants maintained higher leaf water potentials (??_L) during the wet season, however, no differences between stages were found for the dry season. Minimum dry season ??_L were never near the turgor loss point in any of the stages. Juveniles show a more strict stomatal control during the dry season to maintain a favorable water status. Net photosynthesis significantly decreased in intermediate and juvenile stages from wet to dry seasons. Our results suggest that C. moritziana resists more extreme conditions compared to other Andean giant rosettes     

Cell ultrastructure and fatty acid composition of lipids in vegetative organs of <Emphasis Type="Italic">Chenopodium album</Emphasis> L. under salt stress conditions

White goosefoot plants (Chenopodium album L. of the family Chenopodiaceae) grown at various NaCl concentrations (3–350 mM) in the nutrient solution were used to study the cell ultrastructure as well as the qualitative and quantitative composition of fatty acids in the lipids of vegetative organs. In addition, the biomass of Ch. album vegetative organs, the water content, and the concentrations of K⁺, Na⁺, and Cl^– were determined. The growth rates of plants raised at NaCl concentrations up to 200–250 mM were the same as for the control plants grown at 3 mM NaCl; the growth parameters remained rather high even at NaCl concentrations of 300–350 mM. The water content in Ch. album organs remained high at all NaCl concentrations tested. Analysis of the ionic status of Ch. album revealed a comparatively high K⁺ content in plant organs. At low NaCl concentrations in the nutrient solution, K⁺ ions were the dominant contributors to the osmolarity (the total concentration of osmotically active substances) and, consequently, to the lowered cell water potential in leaves and roots. As the concentration of NaCl was increased, the plant organs accumulated larger amounts of Na⁺ and Cl^–, and the contribution of these ion species to osmolarity became increasingly noticeable. At 300–350 mM NaCl the contribution of Na⁺ and Cl^– to osmolarity was comparable to that of K⁺. An electron microscopy study of Ch. album cells revealed that, apart from the usual response to salinity manifested in typical ultrastructural changes of chloroplasts, mitochondria, and the cytosol, the salinity response comprised the enhanced formation of endocytic structures and exosomes and stimulation of autophagy. It is supposed that activation of these processes is related to the removal from the cytoplasm of toxic substances and the cell structures impaired by salt stress conditions. The qualitative and quantitative composition of fatty acids in the lipids of Ch. album organs was hardly affected by NaCl level. These findings are consistent with the high salt tolerance of Ch. album, manifested specifically in retention of growth functions under wide-range variations of NaCl concentration in the nutrient solution and in maintenance of K⁺, Na⁺, and Cl^– content in organs at a constant level characteristic of untreated plants.     

Xylem embolism refilling and resilience against drought-induced mortality in woody plants: processes and trade-offs

Understanding which species are able to recover from drought, under what conditions, and the mechanistic processes involved, will facilitate predictions of plant mortality in response to global change. In response to drought, some species die because of embolism-induced hydraulic failure, whilst others are able to avoid mortality and recover, following rehydration. Several tree species have evolved strategies to avoid embolism, whereas others tolerate high embolism rates but can recover their hydraulic functioning upon drought relief. Here, we focus on structures and processes that might allow some plants to recover from drought stress via embolism reversal. We provide insights into how embolism repair may have evolved, anatomical and physiological features that facilitate this process, and describe possible trade-offs and related costs. Recent controversies on methods used for estimating embolism formation/repair are also discussed, providing some methodological suggestions. Although controversial, embolism repair processes are apparently based on the activity of phloem and ray/axial parenchyma. The mechanism is energetically demanding, and the costs to plants include metabolism and transport of soluble sugars, water and inorganic ions. We propose that embolism repair should be considered as a possible component of a ‘hydraulic efficiency-safety’ spectrum. We also advance a framework for vegetation models, describing how vulnerability curves may change in hydrodynamic model formulations for plants that recover from embolism.     

Patterns of intraspecific trait variation along an aridity gradient suggest both drought escape and drought tolerance strategies in an invasive herb

Background and AimsIn water-limited landscapes, some plants build structures that enable them to survive with minimal water (drought resistance). Instead of making structures that allow survival through times of water limitation, annual plants may invoke a drought escape strategy where they complete growth and reproduction when water is available. Drought escape and resistance each require a unique combination of traits and therefore plants are likely to have a suite of trait values that are consistent with a single drought response strategy. In environments where conditions are variable, plants may additionally evolve phenotypically plastic trait responses to water availability. Invasive annual species commonly occur in arid and semi-arid environments and many will be subject to reduced water availability associated with climate change. Assessing intraspecific trait variation across environmental gradients is a valuable tool for understanding how invasive plants establish and persist in arid environments.MethodsIn this study, we used a common garden experiment with two levels of water availability to determine how traits related to carbon assimilation, water use, biomass allocation and flowering phenology vary in California wild radish populations across an aridity gradient.Key ResultsWe found that populations from arid environments have rapid flowering and increased allocation to root biomass, traits associated with both drought escape and tolerance. Early flowering was associated with higher leaf nitrogen concentration and lower leaf mass per area, traits associated with high resource acquisition. While trait values varied across low- and high-water treatments, these shifts were consistent across populations, indicating no differential plasticity across the aridity gradient.ConclusionsWhile previous studies have suggested that drought escape and drought resistance are mutually exclusive drought response strategies, our findings suggest that invasive annuals may employ both strategies to succeed in novel semi-arid environments. As many regions are expected to become more arid in the future, investigations of intraspecific trait variation within low water environments help to inform our understanding of potential evolutionary responses to increased aridity in invasive species.     

Potential contribution to the invasion process of different reproductive strategies of two invasive roses

The type of reproductive system may be an important trait for the establishment and maintenance of populations of invasive plant species in new areas, as it can influence their demography and genetics. We studied the breeding system of two exotic invasive species, Rosa rubiginosa and R. canina, in a natural reserve in Argentina, using a combination of pollination experiments. We asked how the different reproductive modes of these species affect the quantity and quality of the fruits and seed produced. Our results show that both invasive rose species have an array of reproductive strategies, and that they are able to invade without pollinators, as they can produce seeds in the same quantity and quality through wind-pollination, self-pollination, and apomixis. Such lack of dependence on pollinators and pollination for reproduction should enhance colonization into new areas, suggesting the need of intensive monitoring of spread and dispersal. Considering that both species are successful invaders in the region, our results are in line with Baker’s rule, which posits that plants capable of uniparental reproduction are more likely to invade new areas.     

Not only the butterflies: managing ants on road verges to benefit Phengaris (Maculinea) butterflies

Obligate myrmecophilic butterfly species, such as Phengaris (Maculinea) teleius and P. nausithous, have narrow habitat requirements. Living as a caterpillar in the nests of the ant species Myrmica scabrinodis and M. rubra, respectively, they can only survive on sites with both host ants and the host plant Great Burnet Sanguisorba officinalis. After having been reintroduced into a nature reserve in the Netherlands in 1990, both butterfly species expanded their distribution to linear landscape elements such as road verges and ditch edges outside this reserve. As additional habitat of both butterfly species, vegetation management of these landscape elements became important. Our results show that a management beneficial for Phengaris butterflies should aim to increase the nest density of Myrmica species, at the same time reducing the density of nests of the competitor Lasius niger or at least keeping them at a low density. Unfavourable grassland management under which L. niger thrives, includes not mowing or flail-cutting the grass, or depositing dredgings along the side of the ditch. Management favourable for the two Myrmica species differs, demanding some flexibility if both species are to benefit. M. scabrinodis is best supported with early mowing of the road verge vegetation or late mowing in the nature reserve, both of which result in an open vegetation and warm microclimate. In contrast, the nest sites of M. rubra should be left undisturbed during the summer, and mown in late autumn. Mowing of butterfly habitat should be avoided between mid-June and mid-September as this would remove the flowerheads of the Sanguisorba plants, on which the butterflies lay their eggs.     

THE ANNUAL CARBOHYDRATE CYCLE OF ALPINE PLANTS AS RELATED TO GROWTH

Mooney, H. A., and W. D. Billings. (Duke U., Durham, N. C.) The annual carbohydrate cycle of alpine plants as related to growth. Amer. Jour. Bot. 47(7): 594–598. Illus. 1960.—Analyses were made of the carbohydrate content of roots, rhizomes, and shoots of certain plants in the alpine tundra region of the Medicine Bow Mountains, Wyoming, from the beginning of one growing season until the start of the following one. Principal species investigated were Saxifraga rhomboidea, Polygonum bistortoides, and Geum turbinatum. Results were correlated with phenological events as observed in the field. Growth of these plants was found to be very rapid, commencing in some instances under a cover of old snow. The underground organs contained relatively large amounts of carbohydrate reserves. A great part of this stored carbohydrate was utilized in growth prior to snowmelt and during the grand period of shoot growth immediately following snowmelt. In Polygonum, 50% of the rhizome reserves was used in a 1-wk. period in early growth. Except for this short period of rapid depletion in rhizomes and roots during early growth, high carbohydrate levels were maintained both in the shoot and in the underground organs during most of the growing season. Generally, the lowest carbohydrate reserve level in both root and shoot occurred before flowering, a relatively high level was maintained in the shoot from flowering until after fruiting, while peak storage in underground parts was reached at the start of fall dormancy. The carbohydrate cycle in these alpine plants is quite similar to that in certain arctic plants.     

Specialised host-use and phenophase tracking in restio leafhoppers (Cicadellidae: Cephalelini) in the Cape Floristic Region

The Cape Floristic Region (CFR) has exceptionally high plant diversity, but because there are so few studies on insect diversity and diet breadth, little is known about the relationship between plant and insect diversity. One possibility is that plant and insect diversity in the CFR are linked through host specialisation. Alternatively, the nutrient-poor soils of the CFR may favour generalist feeding strategies with insects tracking the favourable phenophases of a variety of host plants. We studied Cephalelus, a genus of leafhoppers apparently specialised on the Restionaceae, a diverse and dominant plant family in the CFR. We examined patterns of Cephalelus host association at a single site during a 24 month field survey to determine whether Cephalelus diversity is related to the partitioning of host plant or temporal niches; or whether Cephalelus tracks the most nutritive phenophases of restios by temporal host-switching. Seven Cephalelus species were recorded which varied in their seasonal abundance patterns. The majority of these species exhibited specialised host use on different Restionaceae species, with the exception of C. pickeri. This species specialised on two host plants. The populations of two dominant species, C. pickeri and C.uncinatus, tracked the phenology of their primary host plants but not of the Restionaceae in general. To conclude; we find no evidence for host-switching or generalism in Cephalelus. Instead, they appear to be host-specialised, suggesting coupling between their diversity and that of their host plants; the Restionaceae in the CFR.     

Diet and seed dispersal by five marsupials (Didelphimorphia: Didelphidae) in a Brazilian cerrado reserve

The food habits and seed dispersal promoted by five didelphid marsupials, were investigated through fecal analysis in a cerrado reserve located in the central part of the Espinhaço mountain range in Minas Gerais state, southeastern Brazil. The studied species presented a remarkable constancy in their diets and just for C. philander a seasonal change in diet seems to be present with a high consumption of fruits during the wetter season. Arthropods such as hymenopterans, coleopterans and homopterans were the main food resource detected but seeds belonging to pioneer plants were found with high frequencies in samples of all didelphids. Fruits of pioneer plants belonging to the families Melastomataceae (Clidemia urceolata and Miconia holocericea) and Rubiaceae (Psychotria barbiflora and P. capitata) present high germination rates and were among the mostly consumed. In spite of the differences observed in food preferences, all of the didelphids studied must be considered effective seed dispersers of pioneer plants.     

Construction of a supF-based system for detection of mutations in the chromosomal DNA of Arabidopsis

The factors maintaining genomic integrity, which have been studied in detail in other species, have yet to be investigated in plants. Recent progress in gene-silencing technology has made it possible to produce transgenic plants with loss-of-function phenotypes for the effective analysis of these factors, even with the high redundancy of genes in plants. Therefore, a mutation-detection system for plants is necessary to estimate the biological function of a target gene for mutation frequencies and spectra. Here, we reported the development of a novel system to analyze mutations in the chromosomal DNA of plants. The supF gene of E. coli was used as a target for the mutation because it was possible to detect all mutational base changes. Based on the plasmid pTN30, which carries supF, we constructed a binary Ti vector for its introduction to Arabidopsis genomes. The system was validated by measuring mutations in both non-treated and mutagen-treated transgenic plants. DNA fragments including pTN30 were rescued from the plants, and introduced into E. coli KS40/pOF105 to isolate the supF mutant clones conferring both nalidixic acid and streptomycin resistance on transformants. We found that the mutation frequency was approximately three times higher with the ethyl methanesulfonate (EMS) treatment than without it and G:C to A:T transitions dominated, which was the most reasonable mutation induced by EMS. These results show that this system allowed for the rapid analysis of mutations in plants, and may be useful for analyzing plant genes related to the functions of genomic stability and monitoring environmental genotoxic substances.     

Cloning and characterization of a tuberous root-specific promoter from cassava (Manihot esculenta Crantz)

In order to obtain a tuberous root-specific promoter to be used in the transformation of cassava, a 1,728 bp sequence containing the cassava granule-bound starch synthase (GBSSI) promoter was isolated. The sequence proved to contain light- and sugar-responsive cis elements. Part of this sequence (1,167 bp) was cloned into binary vectors to drive expression of the firefly luciferase gene. Cassava cultivar Adira 4 was transformed with this construct or a control construct in which the luciferase gene was cloned behind the 35S promoter. Luciferase activity was measured in leaves, stems, roots and tuberous roots. As expected, the 35S promoter induced luciferase activity in all organs at similar levels, whereas the GBSSI promoter showed very low expression in leaves, stems and roots, but very high expression in tuberous roots. These results show that the cassava GBSSI promoter is an excellent candidate to achieve tuberous root-specific expression in cassava.