Roots, shoots and reproduction: sexual dimorphism in size and costs of reproductive allocation in an annual herb

Females tend to be smaller than males in woody dioecious plant species, but they tend to be larger in herbs. The smaller size of females in woody species has been attributed to higher reproductive costs, yet no satisfactory explanation has been provided for their larger size in herbs. Because herbs have higher nitrogen concentrations in their tissues than woody plants, and because pollen is particularly rich in nitrogen, we predicted that male growth would be more compromised by reproduction than female growth. To test this hypothesis, we conducted three experiments on the annual dioecious herb Mercurialis annua. First, we compared the timing of reproduction between males and females and found that males started flowering earlier than females; early flowering is expected to compromise growth more than later flowering. Second, we compared plants allowed to flower with those prevented from flowering by experimental debudding and found that males incurred a higher reproductive cost than females in terms of both biomass and, particularly, nitrogen. Third, we grew plants under varying levels of nitrogen availability and found that although sexual size dimorphism was unaffected by nitrogen, females, but not males, decreased their relative allocation to both roots and reproduction under high nitrogen availability. We propose that males deal with the high cost of pollen production in terms of nitrogen by allocating biomass to nitrogen-harvesting roots, whereas females pay for carbon-rich seeds and fruits by investing in photosynthetic organs. Sexual dimorphism would thus seem to be the outcome of allocation to above- versus below-ground sinks that supply resources (carbon versus nitrogen) limiting the female and male reproduction differentially.     

Sucrose/cytokinin interaction in Sinapis alba at floral induction: a shoot-to-root-to-shoot physiological loop

In plants of Sinapis alba induced to flower by exposure to a single long day (LD), previous work demonstrated that the movement of a shoot-to-root signal early during the photoextension period of the LD was essential for flowering. Interrupting this movement by bark ringing (girdling) of the stem inhibited the floral response of plants to the LD. In the present work we show that (a) the girdling treatment decreases the soluble sugar level in the roots of induced plants, and (b) the inhibitory effect on the floral response caused by girdling can be completely overcome by supplying the roots with sucrose directly at appropriate times. Thus, we demonstrate that sucrose moving in the phloem is the shoot-to-root signal essential for flowering. We have also found that one of the major effects of the extra-sucrose on the roots is to stimulate the root-to-shoot movement of [9R]Z, the predominant cytokinin of the xylem sap in Sinapis . The importance of this upward movement of [9R]Z for flowering is indicated by the observation that (a) the floral response to the LD is inhibited by growing plants in an atmosphere saturated with water (impairing upward movement of xylem sap) during the LD itself, and (b) the inhibitory effect on the floral response caused by girdling, which markedly reduces [9R]Z export from roots, is relieved by direct application of BA, a cytokinin, to the apex. Other possible effects of the shoot-derived sucrose on roots in relation to flowering are also discussed. Our results show that a shoot-to-root-to-shoot physiological loop is essential for flowering in intact Sinapis plants.     

The impacts of flowering phenology on the reproductive success of the narrow endemic Nouelia insignis Franch. (Asteraceae)

Nouelia insignis Franch. (Asteraceae) is a short, narrow endemic and endangered tree, growing with a natural population in the dry and hot valley of the Jinsha River in the southwest area of China. In this work, flowering phenology (time and duration), floral biology, visit frequency and behavior of pollinators, and pollination characteristics were studied based on investigation in the field and analysis in the laboratory with the help of a stereomicroscope, and the relationship between seed setting rate and reproductive traits, as well as the relationship between flowering time and rainfall before flowering, was tested using the method of general linear regression model. The results showed that natural population of N. insignis exhibited high flowering synchrony with relatively stable flowering duration, and the flowering time fluctuated greatly depending on the rainfall 5 months before flowering. The pollination of N. insignis required pollinators, and insect activities played a very important role in the pollination process. However, lack of the pollinators was not a limitation for reproductive fitness in N. insignis, although the number of pollinators was small and the frequency of visits was low. In addition, no pollen limitation was found during pollination. The average seed setting rate of N. insignis in the natural condition was only 1.52%–3.73%, and it was generally affected by changes in flowering phenology between years and had a higher seed set in early flowering year. The annual variation of seed set might be related to the annual variations of stamen and pistil functions, such as changes of pollen viability and stigma receptivity, which were closely related to flowering time. The results of this study are of value for further conservation actions on natural population of this threatened endemic plant.     

Cabomba as a model for studies of early angiosperm evolution

BACKGROUND: The angiosperms, or flowering plants, diversified in the Cretaceous to dominate almost all terrestrial environments. Molecular phylogenetic studies indicate that the orders Amborellales, Nymphaeales and Austrobaileyales, collectively termed the ANA grade, diverged as separate lineages from a remaining angiosperm clade at a very early stage in flowering plant evolution. By comparing these early diverging lineages, it is possible to infer the possible morphology and ecology of the last common ancestor of the extant angiosperms, and this analysis can now be extended to try to deduce the developmental mechanisms that were present in early flowering plants. However, not all species in the ANA grade form convenient molecular-genetic models. SCOPE: The present study reviews the genus Cabomba (Nymphaeales), which shows a range of features that make it potentially useful as a genetic model. We focus on characters that have probably been conserved since the last common ancestor of the extant flowering plants. To facilitate the use of Cabomba as a molecular model, we describe methods for its cultivation to flowering in the laboratory, a novel Cabomba flower expressed sequence tag database, a well-adapted in situ hybridization protocol and a measurement of the nuclear genome size of C. caroliniana. We discuss the features required for species to become tractable models, and discuss the relative merits of Cabomba and other ANA-grade angiosperms in molecular-genetic studies aimed at understanding the origin of the flowering plants.     

Phenology and phenotypic natural selection on the flowering time of a deceit-pollinated tropical orchid, Myrmecophila christinae

BACKGROUND AND AIMS: Flowering phenology is described and the effect of flowering time on pollination success is evaluated in the deceit-pollinated tropical orchid, Myrmecophila christinae. It was expected that, due to this species' deceit pollination strategy and low observed pollinator visit rate, there would be a higher probability of natural selection events favouring individuals flowering away from the population flowering peak. METHODS: The study covers two consecutive years and four populations of M. christinae located along the north coast of the Yucatán Peninsula. For phenological and pollination success data, a total of 110 individuals were monitored weekly in 1998, and 83 individuals in 1999, during all the flowering and fruiting season. KEY RESULTS: The results showed significant differences in the probability of donating and receiving pollen throughout the flowering season. The probability of receiving or donating pollen increased the further an individual flowering was from the flowering peak. Regression analysis showed directional and disruptive phenotypic natural selection gradients, suggesting the presence of selection events unfavourable to flowering during flowering peak, for both male success (pollen removal) and female success (fruit production). However, the intensity and significance of the natural selection events varied between populations from year to year. The variation between seasons and populations was apparently due to variations in the density of reproductive individuals in each population and each season. CONCLUSIONS: As in other deceit-pollinated orchids, natural selection in M. christinae favours individuals flowering early or late in relation to population peak flowering. However, results also suggested a fluctuating regime of selective events act on flowering time of M. christinae.     

NEMA, a functional-structural model of nitrogen economy within wheat culms after flowering. II. Evaluation and sensitivity analysis

Background and Aims

Simulating nitrogen economy in crop plants requires formalizing the interactions between soil nitrogen availability, root nitrogen acquisition, distribution between vegetative organs and remobilization towards grains. This study evaluates and analyses the functional–structural and mechanistic model of nitrogen economy, NEMA (Nitrogen Economy Model within plant Architecture), developed for winter wheat (Triticum aestivum) after flowering.

Methods

NEMA was calibrated for field plants under three nitrogen fertilization treatments at flowering. Model behaviour was investigated and sensitivity to parameter values was analysed.

Key Results

Nitrogen content of all photosynthetic organs and in particular nitrogen vertical distribution along the stem and remobilization patterns in response to fertilization were simulated accurately by the model, from Rubisco turnover modulated by light intercepted by the organ and a mobile nitrogen pool. This pool proved to be a reliable indicator of plant nitrogen status, allowing efficient regulation of nitrogen acquisition by roots, remobilization from vegetative organs and accumulation in grains in response to nitrogen treatments. In our simulations, root capacity to import carbon, rather than carbon availability, limited nitrogen acquisition and ultimately nitrogen accumulation in grains, while Rubisco turnover intensity mostly affected dry matter accumulation in grains.

Conclusions

NEMA enabled interpretation of several key patterns usually observed in field conditions and the identification of plausible processes limiting for grain yield, protein content and root nitrogen acquisition that could be targets for plant breeding; however, further understanding requires more mechanistic formalization of carbon metabolism. Its strong physiological basis and its realistic behaviour support its use to gain insights into nitrogen economy after flowering.     

Evolution of unusual morphologies in Lentibulariaceae (bladderworts and allies) and Podostemaceae (river-weeds): a pictorial report at the interface of developmental biology and morphological diversification

Background Various groups of flowering plants reveal profound (‘saltational’) changes of their bauplans (architectural rules) as compared with related taxa. These plants are known as morphological misfits that appear as rather large morphological deviations from the norm. Some of them emerged as morphological key innovations (perhaps ‘hopeful monsters’) that gave rise to new evolutionary lines of organisms, based on (major) genetic changes.Scope This pictorial report places emphasis on released bauplans as typical for bladderworts (Utricularia, approx. 230 secies, Lentibulariaceae) and river-weeds (Podostemaceae, three subfamilies, approx. 54 genera, approx. 310 species). Bladderworts (Utricularia) are carnivorous, possessing sucking traps. They live as submerged aquatics (except for their flowers), as humid terrestrials or as epiphytes. Most Podostemaceae are restricted to rocks in tropical river-rapids and waterfalls. They survive as submerged haptophytes in these extreme habitats during the rainy season, emerging with their flowers afterwards. The recent scientific progress in developmental biology and evolutionary history of both Lentibulariaceae and Podostemaceae is summarized.Conclusions Lentibulariaceae and Podostemaceae follow structural rules that are different from but related to those of more typical flowering plants. The roots, stems and leaves – as still distinguishable in related flowering plants – are blurred (‘fuzzy’). However, both families have stable floral bauplans. The developmental switches to unusual vegetative morphologies facilitated rather than prevented the evolution of species diversity in both families. The lack of one-to-one correspondence between structural categories and gene expression may have arisen from the re-use of existing genetic resources in novel contexts. Understanding what developmental patterns are followed in Lentibulariaceae and Podostemaceae is a necessary prerequisite to discover the genetic alterations that led to the evolution of these atypical plants. Future molecular genetic work on morphological misfits such as bladderworts and river-weeds will provide insight into developmental and evolutionary aspects of more typical vascular plants.     

基于数字标本探究绿绒蒿属植物花期的变化

近年来,随着全球气温的明显升高,气候变化引起的全球变暖受到人们的广泛关注.气候变暖会使植物物候发生改变,花期的变化能够直观地反映出植物对周围环境的适应,尤其是高山植物对气候变化更为敏感,因此探究高山植物的花期更具有代表性.为了解植物在气候变暖背景下花期的变化特征,并制定出合理的植物保护措施,该文以典型的高山植物绿绒蒿属...     

In vivo and in vitro flowering response of chicory (Cichorium intybus L.): influence of plant age and vernalization

Chicory plants (Cichorium intybus L. var foliosum cv Flash) were tested with and without a 4-week-long cold treatment for in vivo and in vitro flowering potential every 2 weeks during the growing season. One hundred percent of the plants harvested 112 days or later after sowing and then vernalized flowered in vivo. In vitro, no vernalization was needed to initiate flowering-stems on chicory explants taken from roots of 100 days old and older. 5-Azacytidine, a DNA demethylation agent, increased the flowering percentage on explants from young, vernalized roots but could not induce more than 15% flowering on young, nonvernalized roots. The greater flowering potential of chicory root explants in vitro when compared to plants of the same age tested in vivo was clearly established. This result suggests that some negative control on flowering was removed when root explants were excised and the main plant body discarded. Received: 31 August 1998 / Revision received: 27 October 1998 / Accepted: 10 November 1998     

Ontogenetic Changes in the Level of Ureides and Enzymes of their Metabolism in Various Plant Parts of Pigeonpea (Cajanus cajan)

Levels of allantoin and allantoic acid in shoots, roots, nodulesand leaves of pigeonpea plant, in general, followed the patternof acetylene reduction in nodules, increasing progressivelyfrom 15 days after sowing (DAS) and attaining peaks at 75 DASand 60 DAS, respectively, except in shoots where their contentsevinced maximum values at pod-setting (90 DAS). Activity ofGS in nodules and shoots reached a maximum at 60 DAS and 75DAS, respectively. However, in leaves and roots, the enzymeshowed a biphasic behaviour with peaks at days 60 and 105 inleaves and at days 75 and 105 in roots. GDH activity in nodulespeaked at 60 DAS, whereas, in leaves and roots, the maximumactivity was observed at flowering (75 DAS). Uricase was presentonly in nodules with peak activity at flowering. Allantoinaseactivity again peaked at flowering, where nodules had maximumactivity followed by leaves, roots and shoots. Urease couldbe detected in all the organs with maximum activity at 60 DASin leaves followed by roots and nodules. Except uricase, allthe enzymes reported above were also present in reproductivestructures. Compared to GS, GDH was more active both in flowerbuds and developing pods. Seeds, compared to podwalls, containedhigher activities of GDH, allantoinase and urease at day 105.Only allantoin could be detected in seeds and podwalls at day105. Key words: Cajanus cajan, Allantoin, Allantoic acid, Nitrogenase, Glutamine synthetase, Glutamate dehydrogenase, Uricase, Allantoinase, Urease, Development     

Correlation between Long-Day Flowering and Root Elongation in Pharbitis nil, Sfrain Kidachi

Long-day flowering of Pharbitis nil, dwarf strain Kidachi, at20?C was greatly influenced by the size of the culture vesseland the number of plants per vessel. The smaller the vessel,the greater the flowering response. The volume of nutrient solutionper plant was not decisive for long-day flowering. For instance,plants cultured singly in 200-ml beakers flowered, but thosecultured in 5,000-ml vessels (33?26?11.5 cm, 48 plants per vessel)did not, even though there was only about 100 ml of nutrientsolution per plant. Long-day flowering was always accompaniedby the suppression of root elongation, but not by a decreasein the dry weight of roots or shoots, or in the rate at whichthe leaf primordia appeared (plastochrone). Aeration of thenutrient solution or culture in vermiculite promoted root elongationeven in small vessels, thereby inhibiting long-day flowering.Thus the suppression of root elongation seems to be necessaryfor long-day flowering. Removal of the roots or cotyledons;however, suppressed long-day flowering even when root elongationwas inhibited by culture in small vessels. When plants werecultured at 24?C, suppression of root elongation (culture ina small vessel) did not induce long-day flowering; but, short-daytreatment induced flowering without suppressing root elongation. (Received April 19, 1982; Accepted June 24, 1982)     

Herbarium records identify sensitivity of flowering phenology of eucalypts to climate: Implications for species response to climate change

Flowering phenology is very sensitive to climate and with increasing global warming the flowering time of plants is shifting to earlier or later dates. Changes in flowering times may affect species reproductive success, associated phenological events, species synchrony, and community composition. Long‐term data on phenological events can provide key insights into the impacts of climate on phenology. For Australia, however, limited data availability restricts our ability to assess the impacts of climate change on plant phenology. To address this limitation other data sources must be explored such as the use of herbarium specimens to conduct studies on flowering phenology. This study uses herbarium specimens for investigating the flowering phenology of five dominant and commercially important Eucalyptus species of south‐eastern Australia and the consequences of climate variability and change on flowering phenology. Relative to precipitation and air humidity, mean temperature of the preceding 3 months was the most influential factor on the flowering time for all species. In response to a temperature increment of 1°C, a shift in the timing of flowering of 14.1–14.9 days was predicted for E. microcarpa and E. tricarpa while delays in flowering of 11.3–15.5 days were found for E. obliqua, E. radiata and E. polyanthemos. Eucalyptus polyanthemos exhibited the greatest sensitivity to climatic variables. The study demonstrates that herbarium data can be used to detect climatic signals on flowering phenology for species with a long flowering duration, such as eucalypts. The robust relationship identified between temperature and flowering phenology indicates that shifts in flowering times will occur under predicted climate change which may affect reproductive success, fitness, plant communities and ecosystems.     

Interaction du photopériodisme et des effets de la zéatine, du saccharose et de ľeau dans la floraison du Chenopodium polyspermum

Interaction of photoperiodism and zeatin, sucrose and water effects on the flowering of Chenopodium polyspermum Root removal in Chenopodium polyspermum, a quatitative short-day plant, enhances flowering under non-inductive conditions. Presence of roots may be mimicked by zeatin applications on buds. Induction of flowering by short days may be counteracted by applications of zeatin, and appearance of flowers depends on the balance between number of inductive short days and zeatin quantity applied. Sucrose added in the culture medium or applied on buds acts as zeatin. Applications of water on buds may also delay flowering. These results show the plurifactorial regulation of the floral development of this plant. The relations between the non-specificity of the induction and the specificity of the morphogenetic response are discussed.     

Temporal and intraclonal variation of flowering and pseudovivipary in Poa bulbosa

Background and Aims

Versatility in the reproductive development of pseudoviviparous grasses in response to growth conditions is an intriguing reproduction strategy. To better understand this strategy, this study examined variation in flowering and pseudovivipary among populations, co-occurring clones within populations, and among tillers in individual clones of Poa bulbosa, a summer-dormant geophytic grass that reproduces sexually by seed, and asexually by basal tiller bulbs and bulbils formed in proliferated panicles.

Methods

Clones were collected from 17 populations across a rainfall gradient. Patterns of reproduction were monitored for 11 years in a common garden experiment and related to interannual differences in climatic conditions. Intraclonal variation in flowering and pseudovivipary was studied in a phytotron, under daylengths marginal for flowering induction.

Key Results

Clones showed large temporal variability in their reproductive behaviour. They flowered in some years but not in others, produced normal or proliferated panicles in different years, or became dormant without flowering. Proliferating clones did not show a distinct time sequence of flowering and proliferation across years. Populations differed in incidence of flowering and proliferation. The proportion of flowering clones increased with decreasing rainfall at the site of population origin, but no consistent relationship was found between flowering and precipitation in the common garden experiment across years. In contrast, flowering decreased at higher temperatures during early growth stages after bulb sprouting. Pulses of soil fertilization greatly increased the proportion of flowering clones and panicle production. High intraclonal tiller heterogeneity was observed, as shown by the divergent developmental fates of daughter plants arising from bulbs from the same parent clone and grown under similar conditions. Panicle proliferation was enhanced by non-inductive 8 h short days, while marginally inductive 12 h days promoted normal panicles.

Conclusions

Interannual variation in flowering and proliferation in P. bulbosa clones was attributed to differences in the onset of the rainy season, resulting in different daylength and temperature conditions during the early stages of growth, during which induction of flowering and dormancy occurs.     

Fatty acid changes in Hibiscus esculentus tissues during growth

Lipids were isolated from roots, stems, cotyledons, leaves, buds, flowers, pods and seeds of okra (Hibiscus esculentus) at different stages of plant growth from germination to seed formation and their fatty acid compositions analysed. The lipid contents of roots and stems were 1–3%, cotyledons 3.7–9%, leaves 2.5–5.1% and seeds 2.2–20.2%. Palmitic, linoleic and linolenic were the main fatty acids present in all tissues at all stages, but their relative proportions varied. Cyclopropene fatty acids (CFA) were present at some stages in roots and seeds. In the roots their formation coincided with bud formation (35 days after sowing) and their content reached a maximum (12.8%) seven days after flowering. CFA were present in maturing seeds from 31 days after flowering and occurred as dihydro derivatives throughout. Dihydro derivatives of the CFA were absent in all other tissues. Heptadecenoic acid was present (0.4–1.3%) in root lipids at all stages and in the stem lipids (0.4–1.2%) in the initial stages and after flowering.     

Inhibition of flower induction on in vitro chicory root explants by hydroponic forcing pretreatment of roots

Fragments of vernalized chicory roots (Cichorium intybus L.) cultured in vitro under continuous light flower almost 100%. When chicory roots were placed in hydroponic forcing before in vitro culture, flowering percentage was reduced by half. The build-up of inhibition during 3 weeks of hydroponic forcing was studied in detail. The third week, in which growth of the chicory head is the strongest, was especially important in the inhibition process. When the root apex was eliminated during hydroponic forcing, flowering inhibition in vitro was weaker. The same observation was made when adventitious roots, developed during hydroponic forcing, were removed. The photoperiodic conditions during hydroponic forcing had no influence on the build-up of inhibition. It is suggested that activity of the apex and, possibly, of the adventitious roots during hydroponic forcing cause the flowering inhibition on chicory root fragments in vitro.     

栽培条叶龙胆根中龙胆苦苷含量差异的研究

采用高效液相色谱法,测定栽培条叶龙胆根中龙胆苦苷的含量,结果表明:花末期(9月3日)龙胆苦苷含量高于果期(9月18日)和枯萎期(10月10日);同一根系中二龄根的含量显著高于一龄根;有性后代个体之间龙胆苦苷含量差异显著,对条叶龙胆进行高含量育种研究是可行的。     

Analysis of a Juvenile-like Condition Affecting Flowering in the Black Currant (Ribes nigrum)

Rooted shoots of the black currant with fewer than 20 nodes,taken from mature bushes, cannot be induced to initiate flowersby short-day treatment. This ‘juvenile’ conditionhas been shown to be unrelated to ‘size’ attributes,such as leaf area, but is associated with the proximity of theshoot tips to the roots. Aerial rooting on long ‘mature’shoots prevents flower initiation. Gibberellic acid applicationprevents flowering in mature shoots, as do high levels of IBA.Cytokinins have no effect. Abscisic acid and CCC applicationgave some promotion of flowering in long shoots in long-day,but did not overcome the ‘juvenility’ of short shoots.Gibberellin assay reveals activity in the roots and lower partsof stems, while none could be detected in the tops of long shoots.It is suggested that the correlation between shoot length andgibberellin activity may be decisive in determining juvenilityin the black currant and possibly other species.     

Uptake and distribution of root-applied or foliar-applied 65Zn after flowering in aerobic rice

We investigated the uptake and distribution of zinc (Zn) either applied to the roots or to the leaves in rice during grain development. Plants of two aerobic rice cultivars were grown in a nutrient solution with either sufficient Zn or surplus Zn. Root treatment with 1 week‘s supply of both ⁶⁵Zn and unlabelled Zn was started at flowering or 15 days after flowering (DAF). Foliar treatment with ⁶⁵Zn applied to the flag leaf or to senescent leaves was carried out at flowering. When ⁶⁵Zn was applied to roots, plants continued to take up Zn after flowering, even beyond 15 DAF, irrespective of cultivar and Zn nutritional status of the plants. During the 1 week of supply of both ⁶⁵Zn and unlabelled Zn, which either started at flowering or 15 DAF, the absorbed ⁶⁵Zn was mainly distributed to roots, stem and grains. Little ⁶⁵Zn was allocated to the leaves. Following a week of ⁶⁵Zn supply directly after flowering, under sufficient Zn or surplus Zn, the proportions of total ⁶⁵Zn uptake allocated to the grains continued to change during grain filling (9–33%). This Zn mainly came from the roots but under sufficient Zn supply also from the stem. With ⁶⁵Zn applied to leaves (either the flag leaf or the lowest senescent leaf), both cultivars showed similar Zn distribution within the plants. About 45–50% of the ⁶⁵Zn absorbed was transported out of the ⁶⁵Zn‐treated leaf. From that Zn, more than 90% was translocated to other vegetative organs; little was partitioned to the panicle parts and even less to the grains. These results suggest that in rice plants grown under sufficient or surplus Zn supply, most of the Zn accumulated in the grains originates from uptake by roots after flowering and not from Zn remobilisation from leaves.