Chemical and histochemical analysis of 'Quatre Saisons Blanc Mousseux', a Moss Rose of the Rosa x damascena group

BACKGROUND AND AIMS: Moss roses are old garden roses covered with a mossy growth on flower pedicel and calyx. This moss releases a pine-scented oleoresin that is very sticky and odoriferous. Rosa x centifolia 'muscosa' was the first moss rose to be obtained by bud-mutation but, interestingly, R. x damascena 'Quatre Saisons Blanc Mousseux' was the first repeat-blooming cultivar, thus interesting breeders. In the present study, the anatomy of these sports (i.e. bud-mutations) is characterized and the volatile organic compounds (VOCs) produced by the moss versus the petals are identified. They are compared between the two lines and their respective parents. METHODS: Anatomy of the moss is studied by environmental scanning electron microscopy and histochemical light microscopy. Sudan Red IV and Fluorol Yellow 088 are used to detect lipids, and 1-naphthol reaction with N,N-dimethyl-p-phenylenediamine to detect terpenes (Nadi reaction). Head-space or solid/liquid extraction followed by gas chromatography and mass spectrometry are used to identify VOCs in moss, trichomes and petals. KEY RESULTS: Moss of the two cultivars has the same structure with trichomes on other trichomes but not exactly the same VOCs. These VOCs are specific to the moss, with lots of terpenes. An identical VOC composition is found in leaves but not in petals. They are nearly the same in the moss mutants and in the respective wild types. CONCLUSIONS: Sepals of moss roses and their parents have a specific VOC pattern, different from that of the petals. The moss corresponds to a heterochronic mutation with trichomes developing on other trichomes. Such a mutation has probably appeared twice and independently in the two lines.     

Shaping the shoot: the relative contribution of cell number and cell shape to variations in internode length between parent and hybrid apple trees

Genetic control of plant size and shape is a promising perspective,particularly in fruit trees, in order to select desirable genotypes.A recent study on architectural traits in an apple progeny showedthat internode length was a highly heritable character. However,few studies have been devoted to internode cellular patterningin dicotyledonous stems, and the interplay between the two elementarycell processes that contribute to their length, i.e. cell divisionand elongation, is not fully understood. The present study aimedat unravelling their contributions in the genetic variationof internode length in a selection of F₁ and parent genotypesof apple tree, by exploring the number of cells and cell shapewithin mature internodes belonging to the main axes. The resultshighlighted that both the variables were homogeneous in samplescollected either along a sagital line or along the pith width,and suggest that cell lengthening was homogeneous during internodedevelopment. They allowed the total number of cells to be estimatedon the internode scale and opened up new perspectives for simplifyingtissue sampling procedures for further investigations. Differencesin internode length were observed between the genotypes, inparticular between the parents, and partly resulted from a compensationbetween cell number and cell length. However, genetic variationsin internode length primarily involved the number of cells,while cell length was more secondary. These results argue foran interplay between cellular and organismal control of internodeshape that may involve the rib meristem. Key words: Elongation, growth, histogenesis, Malusxdomestica Borkh, pith Received 2 January 2008; Revised 22 January 2008 Accepted 29 January 2008     

Antioxidant metabolism during acclimation of Begonia x erythrophylla to high light levels

This study examined the influence of high light levels on antioxidant metabolism and the photosynthetic properties of Begonia x erythrophylla leaves. The pigment composition of shaded leaves and those developing in full sunlight was typical of shade- and sun-leaves, respectively. After 28 d in full sunlight, the preformed leaves of shade plants transferred to full sunlight (transferred-leaves) showed photo-bleaching with lower Chl (a + b) content and Chl a : Chl b ratios than shade-leaves, with Chl (a + b) : carotenoid ratios not significantly different. The variable/maximal fluorescence (Fv/Fm) of sun-leaves was not significantly different from that of shade-leaves, but transferred-leaves had reduced Fv : Fm ratios. Light response curves for the electron transport rate (ETR), the oxidation state of photosystem II (qP) and non-photochemical quenching (NPQ) showed significant differences between the three leaf types, with transferred-leaves not able to acclimate completely to full sunlight, having lower ETR, qP and NPQ values at high light levels than sun-leaves. Transfer to full sunlight caused a rapid increase in H2O2 and lipid hyperoxides, and a slight increase in protein oxidation. Ascorbate and glutathione levels decreased rapidly, as did the size of the total glutathione pool and, in addition to the general oxidation of proteins, rapid decreases in both the initial and total activities of chloroplastic fructose-1,6-bisphosphatase and glyceraldehyde-3-phosphate dehydrogenase were observed. These results suggest that a more oxidizing cellular environment is the likely cause of the photo-bleaching observed upon transfer of shade-leaves to full sunlight. Acclimation of transferred-leaves to full sunlight involved gradual increases in the activities of enzymes involved in antioxidant metabolism, including superoxide dismutase, catalase, glutathione reductase, ascorbate peroxidase, dehydroascorbate reductase and monodehydroascorbate reductase, but the levels of these enzymes still remained at levels lower than those found in sun-leaves.     

Clarifying the effects of dwarfing rootstock on vegetative and reproductive growth during tree development: a study on apple trees

BACKGROUND AND AIMS: Despite the widespread use of dwarfing rootstocks in the fruit-tree industry, their impact on tree architectural development and possible role in the within-tree balance between growth and flowering are still poorly understood, in particular during the early years of growth. The present study addressed this question in apple trees, through a detailed analysis of shoot populations, i.e. both vegetative and flowering shoots, during tree development. METHODS: Architectural databases were constructed for trees of two cultivars that were either own-rooted or grafted on dwarfing rootstock. Within-tree shoot demographics and annual shoot characteristics, i.e. their dimensions, number of laterals and flowering, were observed from the first to the fifth year of growth and compared among scion/root system combinations. KEY RESULTS: Differences in axis demographics appeared among scion/root system combinations after the second year of growth. Differences were found (a) in the number of long axes and (b) the number of medium axes. Dwarfing rootstock reduced the total number of axes developed in a tree, and this reduction resulted from proportionally more medium axes and spurs than long axes. The life span of spurs was also shortened. These phenomena appeared after an increase in flowering that started in the second year of growth and involved both axillary and terminal positions. Flowering regularity was also increased in grafted trees. CONCLUSIONS: These results confirm that the number of long shoots and flowering potential depend on the cultivar. They indicate that tree architectural plasticity in response to its root system mainly derives from the number of medium shoots developed and follows priorities within the whole tree axis population. There was also evidence for dwarfing rootstock involvement in adjusting the flowering abundance and that differences in flowering occurrence take precedence over those regarding vegetative growth during tree development.     

Spatially quantitative control of the number of cotyledons in a clonal population of somatic embryos of hybrid larch Larix x leptoeuropaea

• Background and Aims Many conifer embryos, both in naturalseeds and in clonal populations of somatic embryos, displayvariability in the number of cotyledons. In hybrid larch, Larixx leptoeuropaea (synonymous with L. x marschlinsii Coaz), suchvariability has previously been reported in somatic embryos,together with a decrease in the average cotyledon number whenbenzyladenine (BA) is applied exogenously. Described here isa spatially quantitative study with the aim of throwing somelight on the way cotyledon number is determined, and hence themechanism of cotyledon formation. • Methods Stock cultures of embryogenic tissue were maintainedand later made embryogenically active by standard methods. Developmentthrough cotyledon formation was followed by optical microscopywith quantitative measurement of embryo diameter and numberof cotyledons. SEMs of representative stages and cotyledon numberswere done for purposes of illustration in this account. Existingmathematics of waveforms on a disc were cast into a form suitableto compare with the quantitative data. • Key Results The number of cotyledons is linearly relatedto the diameter of the apical surface of the embryo (which approximatesa circular disc) at the time of first appearance of the cotyledonprimordia. This linearity is a constant-spacing phenomenon betweenadjacent primordia. Addition of BA to the medium restricts therange of apical diameters without changing inter-cotyledon spacing.Slope/intercept ratio of the linear plot matches expectationfor initiation of cotyledon pattern as a harmonic waveform ona circular disc. • Conclusions The entire pattern of cotyledon primordiaarises as a single entity coordinated by a mechanism with wave-formingproperties. This is explicable by diverse mechanisms, especiallyeither mechanical buckling (‘biophysical’) or reaction–diffusionkinetics (‘physicochemical’).     

Induction of cambial reactivation by localized heating in a deciduous hardwood hybrid poplar (Populus sieboldii x P. grandidentata)

BACKGROUND AND AIMS: The timing of cambial reactivation plays an important role in the control of both the quantity and the quality of wood. The effect of localized heating on cambial reactivation in the main stem of a deciduous hardwood hybrid poplar (Populus sieboldii x P. grandidentata) was investigated. METHODS: Electric heating tape (20-22 degrees C) was wrapped at one side of the main stem of cloned hybrid poplar trees at breast height in winter. Small blocks were collected from both heated and non-heated control portions of the stem for sequential observations of cambial activity and for studies of the localization of storage starch around the cambium from dormancy to reactivation by light microscopy. KEY RESULTS: Cell division in phloem began earlier than cambial reactivation in locally heated portions of stems. Moreover, the cambial reactivation induced by localized heating occurred earlier than natural cambial reactivation. In heated stems, well-developed secondary xylem was produced that had almost the same structure as the natural xylem. When cambial reactivation was induced by heating, the buds of trees had not yet burst, indicating that there was no close temporal relationship between bud burst and cambial reactivation. In heated stems, the amount of storage starch decreased near the cambium upon reactivation of the cambium. After cambial reactivation, storage starch disappeared completely. Storage starch appeared again, near the cambium, during xylem differentiation in heated stems. CONCLUSIONS: The results suggest that, in deciduous diffuse-porous hardwood poplar growing in a temperate zone, the temperature in the stem is a limiting factor for reactivation of phloem and cambium. An increase in temperature might induce the conversion of storage starch to sucrose for the activation of cambial cell division and secondary xylem. Localized heating in poplar stems provides a useful experimental system for studies of cambial biology.     

Origin and development in vitro of shoot buds and somatic embryos from intact roots of Helianthus annuus x H. tuberosus

A variant clone of the tetraploid (2n = 4x = 68) interspecific hybrid Helianthus annuus x H. tuberosus derived by in vitro tissue culture showed a deviation from the usual pattern of organization of the plant body. This variant developed shoot-like structures and somatic embryos from intact adventitious roots of in vitro-grown plantlets. The morphogenetic structures were not normally able to differentiate complete plants. They did show cellular proliferation with the inception of additional secondary embryos, leaf-like structures and unorganized masses of callus. Nevertheless, some ectopic structures isolated from roots and transferred onto fresh basal medium without growth regulators were able to produce plantlets that exhibited the same phenotype as the original clone. Histological analyses demonstrate that they originate from cortical cells in association with the development of lateral root primordia.     

Perfect syncarpy in apple (Malus x domestica 'Summerland McIntosh') and its implications for pollination, seed distribution and fruit production (Rosaceae: Maloideae)

BACKGROUND AND AIMS: The gynoecium of the domestic apple, Malus x domestica, has been assumed to be imperfectly syncarpic, whereby pollination of each stigmatic surface can result in fertilization within only one of the five carpels. Despite its implied effect on fruit quantity and quality, the resulting influence of flower form on seed set and distribution within the apple fruit has seldom been investigated. Instead, poor fruit quality is usually attributed to problems with pollination, such as low bee numbers and/or ineffective pollinators within apple agro-ecosystems. The objective of this study was to determine the true nature of gynoecial structure and its influence on fruit production in the apple cultivar 'Summerland McIntosh'. METHODS: A stigma-excision method was used to determine the effects of uneven pollination among the five stigmas on fruit quantity (as measured by fruit set), and quality (seed number and distribution). In addition, flowers were examined microscopically to determine pollen tube pathways. KEY RESULTS: Fruit set, seed number, seed distribution, and the microscopic examination of flower gynoecial structure reported in this study indicated that the gynoecium of the cultivar Summerland McIntosh is perfectly syncarpic and not imperfectly syncarpic as previously thought. CONCLUSIONS: Pollination levels among the five stigmas need not be uniform to obtain full seed development within Summerland McIntosh fruit; even if one stigmatic surface is adequately pollinated, a full complement of seeds is likely. The importance of perfect syncarpy in recognizing true causes of poor fruit quality in apple is discussed.     

Nitrogen- and storage-affected carbohydrate partitioning in high-light-adapted Pelargonium cuttings in relation to survival and adventitious root formation under low light

BACKGROUND AND AIMS: The aim of this study was to determine the role of nitrogen- and storage-affected carbohydrate availability in rooting of pelargonium cuttings, focusing on the environmental conditions of stock plant cultivation at low latitudes, transport of cuttings, and rooting under the low light that prevails during the winter rooting period in Central European greenhouses. METHODS: Carbohydrate partitioning in high-light-adapted cuttings of the cultivar 'Isabell' was studied in relation to survival and adventitious root formation under low light. Effects of a graduated supply of mineral nitrogen to stock plants and of cutting storage were examined. KEY RESULTS: Nitrogen deficiency raised starch levels in excised cuttings, whereas the concentrations of glucose and total sugars in leaves and the basal stem were positively correlated with internal total nitrogen (Nt). Storage reduced starch to trace levels in all leaves, but sugar levels were only reduced in tissues of non-nitrogen deficient cuttings. Sugars accumulated in the leaf lamina of stored cuttings during the rooting period, whereas carbohydrates were simultaneously exhausted in all other cutting parts including the petioles, thereby promoting leaf senescence. The positive correlation between initial Nt and root number disappeared after storage. Irrespectively of storage, higher pre-rooting leaf glucose promoted subsequent sugar accumulation in the basal stem and final root number. The positive relationships between initial sugar levels in the stems with cutting survival and in leaves with root formation under low light were confirmed in a sample survey with 21 cultivars provided from different sources at low latitudes. CONCLUSIONS: The results indicate that adventitious rooting of pelargonium cuttings can be limited by the initial amount of nitrogen reserves. However, this relationship reveals only small plasticity and is superimposed by a predominant effect of carbohydrate availability that depends on the initial leaf sugar levels, when high-light adaptation and low current light conditions impair net carbon assimilation.     

A morphological and quantitative characterization of early floral development in apple (Malus x domestica Borkh.)

Apple is an important crop and a focus of research worldwide. However, some aspects of floral commitment and morphogenesis remain unclear. A detailed characterization of bourse shoot apex development was undertaken to provide a framework for future genetic, molecular and physiological studies. Eight morphologically distinct stages of shoot apex development, prior to winter dormancy, were defined. Based on measurements of meristem diameter, two stages of vegetative development were recognized. Vegetative meristems were flat, and either narrow (stage 0) or broad (stage 1). Pronounced doming of the apex marked stage 2. During stage 3, the domed meristem initiated four to six lateral floral meristems and subtending bracts before converting to a terminal floral meristem (stage 4). The terminal floral meristem proceeded directly with bractlet and sepal initiation, while lateral floral meristems initiated bractlets (stage 5). Sepal initiation began on the basal lateral flower (stage 6) and continued in an acropetal direction until all floral meristems had completed sepal initiation (stage 7). In this study, only stage 0 and stage 7 apices were observed in dormant buds, indicating that stages 1-6 are transient. The results suggest that broadening of the apex (stage 1) is the first morphological sign of commitment to flowering.     

Comparison of QTL controlling seedling vigour under different temperature conditions using recombinant inbred lines in rice (Oryza sativa)

BACKGROUND AND AIMS: Seedling vigour is one of the major determinants for stable stand establishment in rice (Oryza sativa), especially in a direct seeding cropping system. The objectives of this study were to identify superior alleles with consistent effects on seedling vigour across different temperature conditions and to investigate genotype x environmental temperature interactions for seedling vigour QTL. METHODS: A set of 282 F13 recombinant inbred lines (RILs) derived from a rice cross were assessed for four seedling vigour traits at three temperatures (25 degrees C, 20 degrees C and 15 degrees C). Using a linkage map with 198 marker loci, the main-effect QTL for the traits were mapped by composite interval mapping. KEY RESULTS: A total of 34 QTL for the four seedling vigour traits were identified. Of these QTL, the majority (82%) were clustered within five genomic regions, designated as QTL qSV-3-1, qSV-3-2, qSV-5, qSV-8-1 and qSV-8-2. All of these five QTL had small individual effects on the traits, explaining 3.1-15.8 % of the phenotypic variation with a mean of 7.3 %. QTL qSV-3-1, qSV-3-2 and qSV-8-1 showed almost consistent effects on the traits across all three temperatures while qSV-5 and qSV-8-2 had effects mainly at the 'normal' temperatures of 20 degrees C and 25 degrees C. Among the five QTL identified, all and four showed additive effects on shoot length and germination rate, respectively. The contributions of these five QTL to shoot length and germination rate were also much larger than those to the other two traits. CONCLUSIONS: A few of genomic regions (or QTL) were identified as showing effects on seedling vigour. For these QTL, significant genotype x environmental temperature interactions were found and these interactions appeared to be QTL-specific. Among the four seedling vigour traits measured, shoot length and germination rate could be used as relatively good indicators to evaluate the level of seedling vigour in rice.     

Apple dwarfing rootstocks and interstocks affect the type of growth units produced during the annual growth cycle: precocious transition to flowering affects the composition and vigour of annual shoots

Background and Aims: Precocious flowering in apple trees is often associated witha smaller tree size. The hypothesis was tested that floral evocationin axillary buds, induced by dwarfing rootstocks, reduces thevigour of annual shoots developing from these buds comparedwith shoots developing from vegetative buds. Methods: The experimental system provided a wide range of possible treevigour using ‘Royal Gala’ scions and M.9 (dwarfing)and MM.106 (non-dwarfing) as rootstocks and interstocks. Second-yearannual shoots were divided into growth units corresponding toperiods (flushes) of growth namely, vegetative spur, extensiongrowth unit, uninterrupted growth unit, floral growth unit (bourse)and extended bourse. The differences between the floral andvegetative shoots were quantified by the constituent growthunits produced. Key Results: The dwarfing influence was expressed, firstly, in reduced proportionsof shoots that contained at least one extension growth unitand secondly, in reduced proportions of bicyclic shoots (containingtwo extension growth units) and shoots with an uninterruptedgrowth unit. In treatments where floral shoots were present,they were markedly less vigorous than vegetative shoots withrespect to both measures. In treatments with M.9 rootstock,vegetative and floral shoots produced on average 0·52and 0·17 extension growth units, compared with 0·77extension growth units per shoot in the MM.106 rootstock treatment.Remarkably, the number of nodes per extension growth unit wasnot affected by the rootstock/interstock treatments. Conclusions: These results showed that rootstocks/interstocks affect thetype of growth units produced during the annual growth cycle,reducing the number of extension growth units, thus affectingthe composition and vigour of annual shoots. This effect isparticularly amplified by the transition to flowering inducedby dwarfing rootstocks. The division of annual shoot into growthunits will also be useful for measuring and modelling effectsof age on apple tree architecture.     

Modelling branching patterns on 1-year-old trunks of six apple cultivars

The structure resulting from branching on 1-year-old apple tree trunks was analysed in a set of apple cultivars with diverse branching and fruiting habits. Four different lateral types borne on successive nodes were observed when vegetative and flowering fates, as well as sylleptic and proleptic branching, were taken into account. The location and grouping of lateral types along the trunk were analysed for all cultivars, but are detailed for one cultivar only. This cultivar showed a succession of zones, each zone being characterized by its composition of lateral types. Statistical models-hidden semi-Markov chains-were built to take this structure into account and to characterize the cultivar's specific branching pattern. The models showed that most of the branching zones had a similar location in the different cultivars, even though zone composition and zone length differed among cultivars. On a more detailed scale, the nodes bearing a lateral, regardless of its type, were frequently followed by latent buds. The validity of the models and their biological interpretation are discussed with respect to parent shoot dynamics, hormonal gradients and competition between neighbouring buds.     

Evidence of natural hybridization and introgression between Vasconcellea species (Caricaceae) from southern Ecuador revealed by chloroplast, mitochondrial and nuclear DNA markers

BACKGROUND AND AIMS: Vasconcellea x heilbornii is believed to be of natural hybrid origin between V. cundinamarcensis and V. stipulata, and is often difficult to discriminate from V. stipulata on morphological grounds. The aim of this paper is to examine individuals of these three taxa and of individuals from the closely related species V. parviflora and V. weberbaueri, which all inhabit a hybrid zone in southern Ecuador. METHODS: Molecular data from mitochondrial, chloroplast and nuclear DNA from 61 individuals were analysed. KEY RESULTS: Molecular analysis confirmed occasional contemporary hybridization between V. stipulata, V. cundinamarcensis and V. x heilbornii and suggested the possible involvement of V. weberbaueri in the origin of V. x heilbornii. In addition, the molecular data indicated unidirectional introgression of the V. cundinamarcensis nuclear genome into that of V. stipulata. Several of the individuals examined with morphology similar to that of V. stipulata had genetic traces of hybridization with V. cundinamarcensis, which only seems to act as pollen donor in interspecific hybridization events. Molecular analyses also strongly suggested that most of the V. x heilbornii individuals are not F(1) hybrids but instead are progeny of repeated backcrosses with V. stipulata. CONCLUSIONS: The results of the present study point to the need for re-evaluation of natural populations of V. stipulata and V. x heilbornii. In general, this analysis demonstrates the complex patterns of genetic and morphological diversity found in natural plant hybrid zones.     

Hybridization and sexual reproduction in the invasive alien Fallopia (Polygonaceae) complex in Belgium

BACKGROUND AND AIMS: The knotweed complex, Fallopia spp. (Polygonaceae), belongs to the most troublesome invasive species in Europe and North America. Vegetative regeneration is widely recognized as the main mode of reproduction in the adventive regions. However, the contribution of sexual reproduction to the success of these invasive species has only been detailed for the British Isles. An examination was made as to how hybridization may influence the sexual reproduction of the complex in Belgium and to determine how it may contribute to the dispersal of the species. METHODS: Studies were made of floral biology, reproductive success, seed rain, seed bank, germination capacity, seedling survival and dispersal capacity in order to characterize the reproductive biology of the species. Moreover, chromosome counts and flow cytometry were used to assess the hybrid status of seedlings produced by sexual reproduction. KEY RESULTS: In the area investigated, extensive sexual reproduction by hybridization within the complex, including one horticultural species, was demonstrated. A small percentage of seeds may be dispersed outside the maternal clone (>16 m) allowing the formation of genetically differentiated individuals. Seed germination was possible even after a winter cold period. CONCLUSIONS: The extensive sexual reproduction by hybridization could further contribute to the dramatic invasive success of knotweeds in Belgium and should not be underestimated when considering control and management measures.     

Stomatal regulation of photosynthesis in apple leaves: evidence for different water-use strategies between two cultivars

BACKGROUND AND AIMS: Leaf responses to environmental conditions have been frequently described in fruit trees, but differences among cultivars have received little attention. This study shows that parameters of Farquhar's photosynthesis and Jarvis' stomatal conductance models differed between two apple cultivars, and examines the consequences of these differences for leaf water use efficiency. METHODS: Leaf stomatal conductance (g(sw)), net CO2 assimilation rate (A(n)), respiration (R(d)) and transpiration (E) were measured during summer in 8-year-old 'Braeburn' and 'Fuji' apple trees under well-watered field conditions. Parameters of Farquhar's and Jarvis' models were estimated, evaluated and then compared between cultivars. Leaf carbon isotope discrimination (delta(13)C) was measured at the end of the growing season. KEY RESULTS: A single positive relationship was established between V(Cmax) (maximum carboxylation rate) and N(a) (leaf nitrogen concentration per unit area), and between J(max) (maximum light-driven electron transport rate) and N(a). A higher leaf R(d) was observed in 'Fuji'. The g(sw) responded similarly to increasing irradiance and leaf temperature in both cultivars. g(sw) responded to lower vapour pressure deficit in 'Fuji' than in 'Braeburn'. Maximal conductance (g(swmax)) was significantly smaller and A(n) was more limited by g(sw) in 'Braeburn' than 'Fuji'. Lower g(sw), E and higher intrinsic water use efficiency were shown in 'Braeburn' and confirmed by smaller leaf delta(13)C compared with 'Fuji' leaves. CONCLUSIONS: The use of functional model parameters allowed comparison of the two cultivars and provided evidence of different water use 'strategies': 'Braeburn' was more conservative in water use than 'Fuji', due to stomatal limitation of A(n), higher intrinsic water use efficiency and lower delta(13)C. These physiological traits need to be considered in relation to climate adaptation, breeding of new cultivars and horticultural practice.