Rosette Plants Research Articles

Role of absorption and translocation in the mechanism of glyphosate resistance in horseweed (Conyza canadensis)

Abstract Greenhouse and laboratory experiments were conducted to investigate mechanisms of glyphosate resistance in horseweed populations from Mississippi, Arkansas, Delaware, and Tennessee. A nondestructive leaf-dip bioassay was developed to confirm resistance and susceptibility in individual test plants. A single leaf was excised from each plant, and the petiole and bottom one-fourth of leaf was dipped in a 600 mg ae L−1 glyphosate solution for 2 d followed by visually estimating the injury on a scale of 0 to 10. Plants were classified as resistant (R) if the score was 2 to 3 and susceptible (S) if the score was 5 to 6. 14C-glyphosate solution was applied on the adaxial surface of a fully expanded leaf of the second whorl of four-whorl rosette plants. Plants were harvested 48 h after treatment and radioactivity was determined in treated leaf, other leaves, crown, and roots. Absorption of 14C-glyphosate was similar (47 to 54%) between R and S plants from within and among the four states, suggesting absor...

REMARKS ON THE NEW WORLD PSEUDOSCORPION GENERA PARAWITHIUS AND VICTORWITHIUS, WITH A NEW GENUS BEARING A REMARKABLE STERNAL MODIFICATION (PSEUDOSCORPIONES, WITHIIDAE)

Abstract The withiid genus Parawithius Chamberlin is rediagnosed, based upon a detailed examination of the type species, P. nobilis (With) from Colombia, which is redescribed and illustrated. The subgenus Parawithius (Victorwithius) Feio is returned to full generic level. Cystowithius, a new genus of Withiidae, is described from high elevation localities in central and South America for four species: Cystowithius smithersi new species (type species) from Ecuador, C. ecuadoricus (Beier) new combination, from Ecuador and Peru, C. colombicus new species from Colombia, and C. chamberlini new species from Mexico and Guatemala. Males of Cystowithius are highly unusual due to the presence of sternal invaginations, a feature that has not been previously observed in pseudoscorpions. Populations of Cystowithius smithersi occur within the leaf sheaths of the giant rosette plant Espeletia pycnophylla var. angelensis (Compositae).

Arabidopsis Cys2/His2-type zinc-finger proteins function as transcription repressors under drought, cold, and high-salinity stress conditions.

ZPT2-related proteins that have two canonical Cys-2/His-2-type zinc-finger motifs in their molecules are members of a family of plant transcription factors. To characterize the role of this type of protein, we analyzed the function of Arabidopsis L. Heynh. genes encoding four different ZPT2-related proteins (AZF1, AZF2, AZF3, and STZ). Gel-shift analysis showed that the AZFs and STZ bind to A(G/C)T repeats within an EP2 sequence, known as a target sequence of some petunia (Petunia hybrida) ZPT2 proteins. Transient expression analysis using synthetic green fluorescent protein fusion genes indicated that the AZFs and STZ are preferentially localized to the nucleus. These four ZPT2-related proteins were shown to act as transcriptional repressors that down-regulate the transactivation activity of other transcription factors. RNA gel-blot analysis showed that expression of AZF2 and STZ was strongly induced by dehydration, high-salt and cold stresses, and abscisic acid treatment. Histochemical analysis of beta-glucuronidase activities driven by the AZF2 or STZ promoters revealed that both genes are induced in leaves rather than roots of rosette plants by the stresses. Transgenic Arabidopsis overexpressing STZ showed growth retardation and tolerance to drought stress. These results suggest that AZF2 and STZ function as transcriptional repressors to increase stress tolerance following growth retardation.

Reduced Glutathione is a Novel Regulator of Vernalization-Induced Bolting in the Rosette Plant Eustoma grandiflorum

The transition from the vegetative rosette stage to the reproductive growth stage (bolting) in the rosette plant Eustoma grandiflorum has a strict requirement for vernalization, a treatment that causes oxidative stress. Since we have shown that reduced glutathione (GSH) and its biosynthesis are associated with bolting in another rosette plant Arabidopsis thaliana, we here investigated whether a similar mechanism governs the vernalization-induced bolting of E. grandiflorum. Addition of GSH or its precursor cysteine, instead of vernalization, induced bolting but other thiols, dithiothreitol and 2-mercaptoethanol, did not. The inductive effect of vernalization on bolting was nullified by addition of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, without decreasing the plant growth rate. BSO-mediated inhibition of bolting was reversed by addition of GSH but not by cysteine. These indicate that vernalization-induced bolting involves GSH biosynthesis and is specifically regulated by GSH. Plant GSH increased during the early vernalization period along with the activity of gamma-glutamylcysteine synthetase that catalyzes the first step of GSH biosynthesis, although there was little change in amounts of GSH precursor thiols, cysteine and gamma-glutamylcysteine. These findings strongly suggest that vernalization stimulates GSH synthesis and synthesized GSH specifically determines the bolting time of E. grandiflorum.

Temporal changes in local spatial structure of late‐successional species: establishment of an Andean caulescent rosette plant

Summary 1 We analyse successional changes in local spatial structure of populations of a dominant late-successional species ( Espeletia schultzii ) in the high tropical Andes. 2 Spatial maps of plants of E. schultzii and important features of their environment were recorded at early (year 3) and middle (year 8) stages of succession after agricultural disturbance, and in non-cultivated paramo. 3 Spatial covariance functions were calculated from the maps to provide information on the changing ‘plant-eye’s view’ of seedlings and adults during succession, and on the coupling of spatial structure to dynamics of successional communities. 4 Seedlings of E. schultzii appeared at high densities shortly after agricultural disturbance ceased. Spatial aggregation, which among seedlings was strongest in later stages of succession, was absent among adults, suggesting greater mortality within aggregations of conspecifics plays a part in regulating population dynamics. 5 Early in succession, seedlings of E. schultzii were slightly segregated from the dominant early successional species, Rumex acetosella . By year 8 of succession, R. acetosella was strongly segregated from adults of E. schultzii , but not from seedlings. This suggests that competitive exclusion caused by asymmetric competition may contribute to decline in early successional species. 6 Spatial sorting in relation to abiotic factors was most evident in the mature paramo, with E. schultzii adults occurring on steeper slopes and on less stony ground. E. schultzii adults here were also segregated from Hypericum laricifolium , the other dominant species. 7 The coupling of local spatial structure to community dynamics may have profound effects on succession. In particular, the development of interspecific segregation could contribute to the continued coexistence of early and late successional species throughout succession.

갯쑥부쟁이(Heteropappus hispidus (Thunb.))의 감마방사선 감수성과 M1 세대 형질변동 특징

제주도에서 자생하는 갯쑥부쟁이(Heteropappus hispidus (Thunb.))에 감마선을 10, 20, 40, 80, 120, 160, 200, 300, 400 Gy 수준으로 나누어서 조사한 뒤 발아율 및 발아 30일 후의 본엽 출현율, <TEX>$LD_{50}$</TEX>, 본엽길이, 줄기부분의 안토시아닌 색소 형성 유무, 생육 60일 후의 로젯형 엽, multi-shoot 형성율, 초장, 개화 결실률 등의 주요 양적형질들을 생존개체를 대상으로 실시하였다. 120Gy 까지의 발아율은 88.5%로 대조구와 큰 차이를 보이지 않았으나 160Gy 이상에서부터는 급격히 감소하여 치사선량(<TEX>$LD_{50}$</TEX>)은 160 Gy 범위 정도였다. 또한, 본엽 출현율과 그 길이는 조사선량이 높아질수록 억제되었다. 안토시아닌 색소 형성은 조사선량이 높을수록 대조구 2%에서 30%로 높아졌으며 로젯형도 고선량 처리구에서 발생하였다. Multi-shooting은 80Gy 이상일 때부터 나타났으며 multi-shooting을 형성하는 개체들은 초장은 짧고 줄기는 가늘게 다발형으로 자라는 특성이 있어서 만일 형질이 고정된다면 화분 관상용 개체로 선발하기에 적합하였다. 특히, 조사선량이 증가됨에 따라서 안토시아닌 색소 형성, 로젯형 개체, multi-shoot등의 개체가 많이 출현되었는데 이는 돌연변이 유기의 선발지표가 될 수 있을 것으로 보인다. The seeds of naturally growing Heteropappus hispidus (Thunb.) were treated by nine different doses (0, 10, 20, 40, 80, 120, 160, 200, 300, 400 Gy) of gamma rays to investigate their germination rate and to quantity the characteristics of their germinated plants as like as leaf appearance and length, the formation rate of anthocyanin color in stem 30 days after germination, the formation rate of rosette leaf and multi-shoot, the flowering and seed-bearing, and shoot length. The germination rate at least up to 120Gy was not greatly affected but was rapidly decreased at over 160Gy. It seemed that lethal dose (<TEX>$LD_{50}$</TEX>) of germination was 160Gy. The leaf appearance and growth was also inhibited, but the formation rate of anthocyanin color in the flower stem was enhanced up to 30% with dose. The rosette plants were observed in plants irradiated with higher than 40Gy. Multi-shoots were developed over 80Gy. For a short shoot length and bundle of thin stem, it was considered that they can be selected as the potential pot flower plants, through genetic fixation. In particular, it was suggested that the formation of anthocyanin color in flower stem, rosette and multi-shoot plants induced by the high dose of gamma rays could be utilized as the morphological markers for the mutant selection of Heteropappus hispidus (Thunb.).

Freezing avoidance mechanisms in juveniles of giant rosette plants of the genus Espeletia

Along soil–air gradients in tropical high mountains, plants growing at soil level tolerate frost while those growing well above ground, including all species in the genus Espeletia, use freezing avoidance mechanisms to survive low nighttime temperatures. The question that arises and the objective of this work were: What are the low temperature resistance mechanisms in giant rosettes when they are within the juvenile stages, i.e. closer to the ground? Juveniles of Espeletia spicata and Espeletia timotensis, dominant plants of the high Venezuelan Andes, were chosen for this study. To determine resistance mechanisms for these species, air and leaf temperatures were recorded in the field in 24 h cycles, while thermal analysis and injury temperature were determined in the laboratory. Both E. spicata and E. timotensis juveniles depend on avoidance mechanisms through a high supercooling capacity, permitting leaves to resist low nighttime temperatures. Minimum leaf temperatures were –4.9 and –5.1 °C, for E. spicata and E. timotensis, respectively, occurring during the dry season. Ice formation occurred at –14.3 and –15.3 °C for E. spicata and E. timotensis, respectively. Injury occurred at approximately –15 °C in both species. Low temperature resistance mechanisms in juveniles are similar to those in adult plants.

Influence of substrate on the distribution of the Hawaiian Silversword ( Argyroxiphium sandwicense DC.) in Haleakala (Maui, HI)

The spatial patterns of the Hawaiian silversword ( Argyroxiphium sandwicense DC.) were studied in Haleakala (Maui, HI). The silversword is a “giant” rosette plant nearly brought to extinction by human impact and goat browsing during the 1920s, but stern protection has resulted in the resurgence of plant populations. Silversword regeneration is occurring vigorously in soils with surficial layers of volcaniclastic fragments. Ten sites with sizable silversword populations and the associated substrates were examined in Haleakala's crater between 2175 and 2755 m. At each site, the population structure of 100 plants was determined along wandering-quarter transects, which limit sampling bias. Substrates where rosettes were rooted and the size of the biggest stone fragments upslope and downslope from the plant's base were determined. Volcaniclastic substrates were examined with photographs along 12-m-long transverse transects. Fine-debris samples (gravel and pebbles) were analyzed by mechanical sifting of surficial fragments gathered from 15×15 cm miniplots. Volcaniclastic fragments in silversword areas have different sources. (i) Most were ejected during eruptions yielding pyroclastic materials (ash to blocks) that built cinder cones on Haleakala's crater. (ii) On steep slopes, weathering of (olivine alkali) basalt outcrops and subsequent mass wasting of rock fragments contributed a mantle of clasts to slopes below. (iii) On some cinder cones, welded spatter was produced during late eruptive stages; this coalesced into ruff-like agglutinate layers around crater rims, called Pohaku-o-Hanalei (“wreath of stones”). Agglutinate deposits weather gradually, supplying clasts that roll downhill and accumulate on cone flanks. (iv) On weathered aa lava flows, stone fragments and rocky crags abound along eroding lava-flow ridges, associated with vegetation; but the intervening troughs, covered with fine ash and cinder, remain bare. Silversword population structures indicate healthy regeneration. All populations display a typical pattern of decreasing silversword numbers with increasing size (=age). Nearly 65% of the rosettes are rooted near cobbles (5–10 cm long) or pebbles (2.5–5 cm), and ∼23% grow at the base of blocks (>10 cm) or outcrops; 9% of the plants are on gravel (<2.5 cm), but only 1% have germinated on sandy soil without granules or stones; 2% of the silverswords grow on organic litter of dead rosettes. Plants on six sites showed noticeable differences in clast size between their upslope and downslope sides; particles are significantly larger upslope from rosettes. This suggests that successful seedlings germinate below clasts, which deflect finer downslope-moving sediment, thus protecting young plants from burial by descending debris. Statistical tests indicate a few blocks above plants may have been stopped by adult rosettes. Such a relationship underscores the dynamic nature of steep cinder and rubble (talus) slopes, regularly affected by dry debris slides, frost creep, and other mass-wasting processes. Slope instability is also evinced by (i) common bending and deformation of silversword roots—particularly in seedlings—which trail upslope; (ii) pronounced downhill tilting and asymmetry of tall rosettes on steep gradients; (iii) presence of accumulated fine-debris steps (9.9–13.8 cm thick) upslope from plants and blocks; (iv) ubiquitous fine-earth flags exposed below embedded blocks, which intercept descending debris and deflect it laterally; (v) widespread miniature sorted stripes.

Rosetted siblings in F2 of a cross in pomegranate (Punica granatum L.) can be useful model for rosetting investigations

Environmentally and developmentally controlled rosette formation is welldocumented in certain crop species. But this report describes a geneticallyinduced rosetting observed in pomegranate (Punica granatum L.).Rosette genotypes were detected at a frequency of 0.12 in the F2 familiesof cv. Ganesh and a recessive rosette mutant clone of cv. Kabul Yellow. Therosetted seedlings had leaves almost touching the ground at emergence, whichwere closely set on a thick, compressed stem with narrow inter-nodes andinactive subapical meristem. They were similar in some certain respects tothe naturally occurring rosetting noticed in lettuce, spinach and lisianthus.The occurrence of rosette type was attributed to a recessive mutant gene ofKabul Yellow and was ascribed the gene symbol rg (rosette growth) whichwas found to alter a host of morphological traits in rosette siblings innursery and field. The foliage colour, pink of Ganesh and yellow of KabulYellow, served as visual marker in distinguishing segregating progeny intopink/yellow normal and rosette types in the nursery. A monogenic segregationin F2 for pink and yellow was evident both in normal and rosette siblings.When a single gene mutation for rosetting was considered a large portion ofthe rosette progeny in F2 was found missing. This has been explained on thebasis of two conditional lethal genes operating in rosette individuals.Moreover, the F2 and BC1 seeds had very low seed fertility indicatingthat F1 possibly carried heavy load of lethal genes. On transplantation,the rosette mutants started to grow tall and erect, like spinach, but had acompact habit with restricted branching and exhibited early leaf senescence,leaving a crown of bushy growth at the tip of almost naked, brittle shoots.Rosettes differed significantly from normal siblings for all the morphologicalcharacteristics studied. The normal progenies flowered and set fruits within13 months, the rosette ones almost failed to do so even after growing for 38months, although they showed relatively loose rosetting than in the nursery.However, one seedling produced 3 small flowers with rudimentary ovary.Moreover, it was observed that the rosette plants had a tendency to regressto normal state, since 9 out of the 31 rosette progeny produced axilary shootsthat had normal stem and leaf attributes. The individuals with both normal androsette shoots should serve the same purpose in research work, as do perfect isogeniclines. Based on the frequency at which the normal shoots appeared the role ofcryptic transposable elements (TEs) was suspected rather than back mutation.Rosette siblings with altered morphology reported here can be secured inabundant number along with the contrasting normal siblings by raising theF2, which provide a good opportunity to gain an insight in the control ofvarious plant developmental processes. Besides, it can be viewed as a valuablemodel system for fundamental research on physiological, biochemical andmolecular genetical bases of rosetting in crop plants.

A saponin correlated with variable resistance of Barbarea vulgaris to the diamondback moth Plutella xylostella.

Two types of Barbarea vulgaris var. arcuata, the G-type and the P-type, differed in resistance to larvae of the diamondback moth (DBM) Platella xylostella. Rosette plants of the G-type were fully resistant to the DBM when grown in a greenhouse or collected in the summer season, but leaves collected during the late fall were less resistant, as previously found for flea beetle resistance. The P-type was always susceptible. Extracts of resistant leaflets inhibited larval growth in a bioassay, and a growth-inhibiting fraction was isolated by activity-guided fractionation. A triterpenoid saponin (1) was isolated from this fraction and identified as 3-O-beta-cellobiosyloleanolic acid from spectroscopic data and analysis of hydrolysis products. The decrease in resistance of the G-type in the fall was correlated with a decrease in the level of 1, from 0.6-0.9 to < 0.2 micromol/g dry wt. Compound 1 was not detected in the susceptible P-type. We conclude that 1 is correlated with the variable resistance of B. vulgaris foliage to the DBM.

Morphology and ontogenesis of Lambornella trichoglossa nov. spec., a new tetrahymenid ciliate (Protozoa, Ciliophora) from Brasilian tank bromeliads (Bromeliaceae)

This is the second of a series of papers describing the morphology and ontogenesis of new ciliates occurring in the cisterns of tank bromeliads, a group of rosette plants of tropical America, entrapping rainwater between the coalescing leaf axils. The new species described here was discovered in the tanks of ground bromeliads from the east coast (Mata Atlantica) of Brazil, South America, and in tank bromeliads of the Dominican Republic, Caribbean Sea. Its morphology and ontogenesis were investigated on cultivated specimens, using live observation, silver impregnation, and scanning electron microscopy. Morphologically, the new ciliate resembles the tetrahymenine genus Lambornella , while the habit is different in that it does not parasitize and produce cuticular cysts on mosquito larvae. Thus, it could be considered as representative of a new genus. Likewise, the Brazilian and Dominican populations are probably not conspecific. Basically, Lambornella trichoglossa nov. spec. has a tetrahymenid somatic and oral ciliary pattern with characteristics likely diagnostic for the, unfortunately, still insufficiently described type species of Lambornella , viz., an increased number (8) of postoral kineties, a spatulate preoral suture, a curved adoral membranelle 1, a sigmoidal membranelle 2, loop-like intrameridional silverlines, and a synchronous replacement of the parental oral apparatus during cell division, a conspicuous ontogenetic feature. Lambornella trichoglossa differs from the two described congeners mainly by the large size (200 × 50 m vs. 100 × 50 m), the fusiform to claviform shape (vs. ovoidal), the location of the contractile vacuole (near mid-body vs. posterior body third), a 25 m long caudal cilium (vs. lacking), and the arrangement of adoral membranelle 2 (directed to right vs. left). Considering that L. trichoglossa has not been found in Europe, though it is a large, conspicuous ciliate, it might be restricted to South America or Gondwana.

Endemic ciliates (Protozoa, Ciliophora) from tank bromeliads (Bromeliaceae): a combined morphological, molecular, and ecological study

Bromeliads are mainly epiphytic rosette plants occurring only in Central and South America. They collect rain water and particulate materials in tanks (cisterns) formed by the coalescing leaf axils. These tanks form an extensive, highly compartmentalized water and humus body above the ground and are inhabited by many ordinary and endemic organisms. We discovered at least 10 new ciliate species in the tanks of about 15 bromelian species from the Dominican Republic, Ecuador, and Brazil. Since there are 2000–3000 bromelian species with very different lifestyles, they are likely to contain hundreds of novel ciliate species. Two of the new species described here are real “flagships”, that is, they have such a large size that they would have been found in Europe, if they were there. Consequently, these species must have a restricted geographical distribution, disproving the old hypothesis that microscopic organisms are cosmopolitan. Also the smaller ciliates described here represent new genera and families, arguing for a long-lasting, independent evolution driven by ecological constraints and spatial isolation. Almost half of the new species can switch from bacteriophagous, microstome morphs to a predatory, macrostome lifestyle, likely due to the strong competition in these peculiar habitats. The high morphological and ecological diversity of tank bromeliad ciliates is only partially recovered by small-subunit (18S) ribosomal RNA (rRNA) gene sequences.

The plant family Asteraceae: 4 Interesting growth forms and economic importance

The plant family Asteraceae contains a wealth of different and interesting growth forms like annual or perennial herbs, dwarf shrubs, shrubs, trees, climbers, succulents, aquatic plants, rosette plants, cushion plants, ericoid, prostrate, grass-like and spinescent. The leaves also exhibit numerous different shapes and characters, e.g. alternate, opposite, fascicled, sessile, petiolate, simple, entire, dentate, lobed or pinnate, compound, with three to five main veins, reduced or absent, glabrous or densely hairy on upper or lower surface. Sometimes latex is present and some plants are aromatic. Certain members of the family are also economically important; some are edible or used as medicine while others are poisonous, some are utilised as grazing but others are weeds, and the wood of some was used in the past.

GAI homologues in the Hawaiian silversword alliance (Asteraceae-Madiinae): molecular evolution of growth regulators in a rapidly diversifying plant lineage.

Accelerated evolution of regulatory genes has been proposed as an explanation for decoupled rates of morphological and molecular evolution. The Hawaiian silversword alliance (Asteraceae-Madiinae) has evolved drastic differences in growth form, including rosette plants, cushion plants, shrubs, and trees, since its origin approximately 6 MYA. We have isolated genes in the DELLA subfamily of putative growth regulators from 13 taxa of Hawaiian and North American Madiinae. The Hawaiian taxa contain two copies of DaGAI that form separate clades within the Madiinae, consistent with an allotetraploid origin for the silversword alliance. DaGAI retains conserved features that have previously been identified in DELLA genes. Selective constraint in the Hawaiian DaGAI copies remains strong in spite of rapid growth form divergence in the silversword alliance, although the constraint was somewhat relaxed in the Hawaiian copies relative to the North American lineages. We failed to detect evidence for positive selection on individual codons. Notably, selective constraint remained especially strong in the gibberellin-responsive DELLA region for which the gene subfamily is named, which is truncated or deleted in all identified dwarf mutants in GAI homologues in different angiosperm species. In contrast with the coding region, however, approximately 900 bp of the upstream flanking region shows variable rates and patterns of evolution, which might reflect positive selection on regulatory regions.

Gene expression of 5- epi-aristolochene synthase and formation of capsidiol in roots of Nicotiana attenuata and N. sylvestris

Three new copies of a sesquiterpenoid synthase gene encoding 5- epi-aristolochene synthase ( EAS) were cloned as cDNAs from Nicotiana attenuata and functionally characterized after expression of the recombinant enzymes in E. coli. Differential patterns of EAS gene expression and formation of the antimicrobial sesquiterpenoid capsidiol were found in roots and shoots of two species of Nicotiana. EAS is expressed constitutively in roots of N. attenuata and N. sylvestris corresponding with constitutive capsidiol formation in roots. Constitutive expression of EAS and capsidiol accumulation were not detectable in shoots of rosette plants of N. attenuata, but accumulation of terpene synthase transcripts could be induced in shoots by feeding of the tobacco hornworm, Manduca sexta. Constitutive expression of EAS has not been previously reported from N. tabacum, where capsidiol is known as an elicitor- and pathogen-inducible phytoalexin. It is conceivable that capsidiol contributes not only to an inducible defense against pathogens, but also to a constitutive defense in an organ-specific manner in some species of Nicotiana.

Rosette scrub occurrence and fog availability in arid mountains of Mexico

Abstract. Large succulent leaf rosettes are a characteristic life form in many deserts. In certain areas they become the dominant life form, creating a vegetation type indicated as rosette scrub. The large number of rosette species suggests a close relationship between form and environment. Rosettes are excellent harvesters of low‐intensity rains and fogs. We propose that some rosette‐dominated formations of the Mexican mountains, namely the montane rosette scrub, occur in altitudinal belts around mountains where fog is abundant. We sampled four altitudinal gradients in mountains with different flora recording the abundance and richness of plants. At one site, the Tehuacán Valley, we also measured the quantity of fog along the gradient, below, above and in the rosette scrub for one year. We found that the abundance and richness of succulent rosette species are strongly associated with altitude, showing maximum values in the well‐defined elevational belts where the montane rosette scrub occurs. Other life forms, such as stem succulent cacti or woody shrubs, do not show this mid‐elevation pattern. The altitudinal ranges where the montane rosette scrub occurs usually coincide with areas where clouds and fog form. Our micrometeorological measurements indicate that rosette plants growing within a cloud belt can increase their water supply by 10–100% by harvesting fog. Outside these belts fog harvest is negligible. Desert rosettes constitute one of the most common fog‐harvesting growth forms.

Differential genetic variation in adaptive strategies to a common environmental signal in Arabidopsis accessions: phytochrome‐mediated shade avoidance

AbstractShade avoidance is a syndrome of plastic responses to light signals encountered in crowded plant communities and is a crucial component of competitive strategy in higher plants. The responses are mediated via signal perception by specific members of the phytochrome family of photoreceptors, which detect the relative proportions of red (R) and far‐red (FR) radiation within dense communities. We analysed two aspects of shade avoidance, the acceleration of flowering and the enhancement of elongation growth, displayed by more than 100 accessions of Arabidopsis thaliana (Heyn.) in response to FR‐proximity signals. Both traits showed wide variation between accessions, which was unrelated to the latitude of the location of original collection. Flowering acceleration is a major feature of shade avoidance in rosette plants such as Arabidopsis, and most accessions showed dramatic responses, but several were identified as being recalcitrant to the proximity signal. These accessions are likely to be informative in the analysis of quantitative variation in shade avoidance. Hypocotyl elongation, treated here as an indicator of elongation growth responses, also varied widely amongst accessions. The variations in flowering acceleration and elongation were not correlated, indicating that microevolution in the downstream pathways from signal perception has occurred separately.

Rosette scrub occurrence and fog availability in arid mountains of Mexico

Abstract. Large succulent leaf rosettes are a characteristic life form in many deserts. In certain areas they become the dominant life form, creating a vegetation type indicated as rosette scrub. The large number of rosette species suggests a close relationship between form and environment. Rosettes are excellent harvesters of low-intensity rains and fogs. We propose that some rosette-dominated formations of the Mexican mountains, namely the montane rosette scrub, occur in altitudinal belts around mountains where fog is abundant. We sampled four altitudinal gradients in mountains with different flora recording the abundance and richness of plants. At one site, the Tehuacán Valley, we also measured the quantity of fog along the gradient, below, above and in the rosette scrub for one year. We found that the abundance and richness of succulent rosette species are strongly associated with altitude, showing maximum values in the well-defined elevational belts where the montane rosette scrub occurs. Other life forms, such as stem succulent cacti or woody shrubs, do not show this mid-elevation pattern. The altitudinal ranges where the montane rosette scrub occurs usually coincide with areas where clouds and fog form. Our micrometeorological measurements indicate that rosette plants growing within a cloud belt can increase their water supply by 10–100% by harvesting fog. Outside these belts fog harvest is negligible. Desert rosettes constitute one of the most common fog-harvesting growth forms.

Flowering on time: genes that regulate the floral transition. Workshop on the molecular basis of flowering time control.

The workshop was held at the John Innes Centre, Norwich, UK, July 11–14, 2001. http://www.jic.bbsrc.ac.uk/events/embo/. Workshop Administrator: Dee Rawsthorne, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, Norfolk, UK (Tel: +44 1603 450527; Fax: +44 1603 450025; E‐mail: dee.rawsthorne@bbsrc.ac.uk). ![][1] Successful sexual reproduction in plants depends on the recognition of favourable environmental conditions and the integration of that information with endogenous developmental cues. Flowering in higher plants involves the transition of a vegetative meristem, producing leaves and stems, into a floral meristem, producing flowers. Most of our understanding of the regulation of the floral transition has been developed in the past 10 years using molecular genetic approaches in the model plant Arabidopsis thaliana , a rosette plant in which the initiation of flowering is followed by the elongation of the main stem. The two main environmental factors that promote flowering in Arabidopsis are long days (Figure 1) and exposure to low temperatures (vernalization). Genetic and physiological analysis of flowering time in Arabidopsis has led to the identification of a large number of flowering‐time genes (>80) that regulate flowering time in response to environmental and endogenous cues (reviewed by Simpson et al ., 1999). Regulation occurs through a complex network of genetic pathways, with two main pathways mediating environmental responses (the long‐day and vernalization pathways) and two pathways that function independently of environmental cues: the autonomous pathway, which promotes flowering under all conditions, and the gibberellin (GA) pathway, which is needed for flowering under non‐inductive short‐day conditions. These pathways converge in the induction of floral meristem identity genes and the floral transition (Figure 2). Many flowering‐time genes have been cloned recently, and the primary aim of the EMBO workshop in Norwich, and this report, was to highlight the most recent advances in our understanding of the molecular mechanisms regulating … [1]: /embed/graphic-1.gif

ADAPTIVE EVOLUTION OF PLASTIC FORAGING RESPONSES IN A CLONAL PLANT

Stoloniferous rosette plants may show horizontal and vertical foraging responses, such as changes in branching frequency, stolon internode length, leaf length, and height growth of stolons. To study whether such plastic foraging responses constitute an adaptation to het- erogeneity in competition, we studied genetic variation in and fitness consequences of plastic foraging responses in the stoloniferous lake-shore plant Ranunculus reptans. Because plastic foraging responses are likely to have been more strongly selected for in heterogeneous envi- ronments, we used 15 genotypes from competitive, heterogeneous microhabitats and 15 from competition-free, homogeneous microhabitats from Lake Constance (central Europe). We planted vegetatively propagated rosettes of the 30 genotypes (totaling 236 rosettes) into a greenhouse environment with spatially heterogeneous competition. Four replicates of each genotype were planted into the competition-free halves of experimental trays, and four other replicates into the halves with the naturally co-occurring grass Agrostis stolonifera. We found significant variation among genotypes in vertical and horizontal foraging responses. In line with the hypothesis of adaptive plasticity, genotypes from the competitive heterogeneous microhabitats more strongly increased the vertical angle of the first stolon internode (126%) and the specific stolon length (166%) in response to competition than genotypes from the competition-free homogeneous microhabitats. Moreover, we found that genotypes that were more plastic in the vertical angle of the first stolon internode, stolon height, and specific internode length produced more rosettes and flowers than less plastic genotypes (all selection gradients for plasticity . 0.316). Our findings strongly suggest that plastic foraging responses constitute an adaptation to environmental heterogeneity, at least in the stoloniferous R. reptans.