奇甜蛋白基因在园艺作物中的表达

奇甜蛋白（thaumatin）是从非洲西部植物katemfe（Thaumatococcus daniellii Benth）中提取得到的几种关系相近的甜味蛋白的统称,其中最主要的为奇甜蛋白Ⅰ和奇甜蛋白Ⅱ。奇甜蛋白不仅甜度高,而且具有低热量、安全无毒以及不易诱发糖尿病等优点。因此,将奇甜蛋白基因转入园艺作物中并使之表达,用以提高可食部分的甜味,有其特别的研究意义。奇甜蛋白基因已先后在马铃薯、梨树、黄瓜、番茄等园艺作物得到表达,但仍有一些问题需要解决。现从奇甜蛋白基因的克隆、测序与表达,转基因果实的安全性检测,甜度的感官评价,甜味遗传特点以及奇甜蛋白抗真菌病害检验等几个方面综述了国内外研究进展,并对今后的研究提出了建议。     

Expression pattern of the pre-prothaumatin II gene under the control of the CaMV 35S promoter in transgenic cucumber (Cucumis sativus L.) flower buds and fruits

Thaumatin II is an extremely sweet-tasting protein produced by fruits of the West African shrubThaumatococcus daniellii Benth, so it can be used in biotechnology to improve the tastes of various plant products. This study is concerned with the spatial and temporal aspects of expression of the 35S-pre-prothaumatin II chimeric gene in flower buds and fruits of transgenic cucumber (Cucumis sativus L.) line 225. The activity of the 35S promoter in organs of line 225 was compared with its activity in 2 other transgenic lines. The accumulation of recombinant thaumatin varied spatially in flower bud tissues of transgenic lines. We found that these differences in the spatial accumulation of transgenic protein concerned the ovary of female buds and the perianth of male buds. In contrast to flower parts, recombinant thaumatin was found in nearly all parts of the young fruit from the transgenic plants. The pre-prothaumatin II gene expression was detected at a very early developmental stage in male buds, and its pattern was rather conserved as the buds aged. The expression of the transgene was also detected in vascular tissues of examined organs but was undetectable in pollen grains, in agreement with the generally held view that the CaMV 35S promoter is virtually silent in pollen. Immunocytochemical analyses of sections of control organs revealed endogenous homolog(s) of thaumatin when using polyclonal antisera, but not when using monoclonal antibodies for recombinant thaumatin detection in transgenic cucumber.     

Cloning of the thaumatin I cDNA and characterization of recombinant thaumatin I secreted by Pichia pastoris

Thaumatin is a sweet-tasting protein comprising a mixture of some variants. The major variants are thaumatins I and II. Although the amino acid sequence of thaumatin I was known and the nucleotide sequence of cDNA of thaumatin II was elucidated, the nucleotide sequence of thaumatin I has been controversial. We have cloned two thaumatin cDNAs from the fruit of Thaumatococcus daniellii Benth. One is the same nucleotide sequence as that of thaumatin II already reported, and the other is a novel nucleotide sequence. The amino acid sequence deduced from the novel cDNA was the same amino acid sequence as that of thaumatin I, the only exception being the residue at position 113 (Asp instead of Asn), indicating that the novel thaumatin cDNA is that for thaumatin I. This thaumatin I cDNA was transformed into Pichia pastoris X-33, and the recombinant thaumatin I expressed was purified and characterized. The threshold value of sweetness of the recombinant thaumatin I was the same as that of the plant thaumatin I, although several unexpected amino acid residues were attached to the N-terminal of the recombinant thaumatin I. These indicate that the N-terminal portion of thaumatin is not critical for the elicitation of sweetness.     

Mimosa pigra in eastern and southern Africa: Distribution and socio‐ecological impacts

The semiaquatic weed Mimosa pigra has negative impacts on biodiversity, fishing, crop and livestock production, and tourism in most places where it has been introduced, established and proliferated. Many of the ecological impacts are well known, but its impacts on rural livelihoods are less well documented, especially in Africa. We mapped the distribution of M. pigra in eastern and southern Africa, and then compared that with its potential distribution based on an ecoclimatic niche model. Household interviews were conducted to assess the impacts of this weed on local livelihoods. Mimosa pigra was found to be invasive in western Ethiopia, around the shores of Lake Victoria and Lake Tanganyika, and along the Tanzanian coastline, northern Malawi, parts of Mozambique and along the Kafue River and in the Barotse floodplain on the Zambezi River in Zambia. According to respondents living along the Kafue River floodplains in Zambia, it has a negative impact on biodiversity, wildlife, livestock, crop production, fishing and mobility. Dense stands prevented the movement of people and livestock, limiting access to croplands, grazing lands and fishing areas. Fish catches have been reduced and fishing equipment damaged. All respondents agreed that their livelihood options would be considerably enhanced if M. pigra was removed from the landscape. Based on its current and potential impact, we therefore recommend that an integrated management plan be developed and implemented, including the appropriate use of biological control agents to reduce the negative impacts of the weed.     

Cloning, expression and characterization of recombinant sweet-protein thaumatin II using the methylotrophic yeast Pichia pastoris

Thaumatin, an intensely sweet-tasting protein, was secreted by the methylotrophic yeast Pichia pastoris. The mature thaumatin II gene was directly cloned from Taq polymerase-amplified PCR products by using TA cloning methods and fused the pPIC9K expression vector that contains Saccharomyces cerevisiae prepro alpha-mating factor secretion signal. Several additional amino acid residues were introduced at both the N- and C-terminal ends by genetic modification to investigate the role of the terminal end region for elicitation of sweetness in the thaumatin molecule. The secondary and tertiary structures of purified recombinant thaumatin were almost identical to those of the plant thaumatin molecule. Recombinant thaumatin II elicited a sweet taste as native plant thaumatin II; its threshold value of sweetness to humans was around 50 nM, which is the same as that of plant thaumatin II. These results demonstrate that the functional expression of thaumatin II was attained by Pichia pastoris systems and that the N- and C-terminal regions of the thaumatin II molecule do not -play an important role in eliciting the sweet taste of thaumatin.     

Pollination efficiency and reproductive patterns in relation to local plant density,population size,and floral display in the rewarding Listera ovata (Orchidaceae)

Pollination efficiency and reproductive success vary strongly among populations of most animal‐pollinated plant species, depending on their size and local density, whereas individual plants within populations experience varying levels of reproductive output as a result of differences in floral display. Although most orchid species have been shown to be severely pollination limited, few studies have investigated the impact of the above‐mentioned factors on pollination success and reproduction, especially in rewarding species. In this study, the impact of population size, local density of flowering plants, and floral display on the rates of pollinia export and fruit production was investigated in 13 natural populations of the rewarding terrestrial orchid Listera ovata. In addition, an emasculation experiment was set up to examine how floral display and local density of flowering plants affected the relative importance of cross‐ vs. geitonogamous pollination in determining fruit set. In the studied populations, pollination efficiency, pollen removal, and fruit set increased with increasing population size until a threshold value of 30–40 flowering plants was reached, above which pollination efficiency and reproductive output decreased again. On average, plants with large floral displays showed higher proportional pollinia removal and fruit set compared with smaller plants. Fruit production was also significantly and positively related to local plant density, whereas emasculation did not affect the relationship between local plant density and fruit set, suggesting that geitonogamous pollination did not affect the outcome of female function. The results of this study are discussed in the light of the flowering mechanism of the species and its generalized pollination system. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 713–721.     

A historical review of research on the weaver ant Oecophylla in biological control

1 Although the weaver ant Oecophylla is the first written record of biological control, dating from 304 ad , there have been fewer than 70 scientific publications on this predator as a biological control agent in Asia, from the early 1970s onwards, and fewer than 25 in Africa. 2 Apart from crop‐specific ecological and perceptual factors, a historical review shows that political and market forces have also determined the extent to which Oecophylla was incorporated into research and development programmes. 3 In Africa, research on weaver ants in biological control concentrated on export crops, such as coconut and cocoa, whereas, in Asia and Australia, research focused on fruit and nut crops, primarily destined for domestic markets. 4 Increased evidence of pesticide inefficiency under tropical smallholder conditions, changing paradigm shifts in participatory research and a growing scientific interest in local knowledge in the early 1990s opened up new avenues for research on conservation biological control. 5 Lobbying and advocacy have been needed to ensure that Oecophylla was recognized as an effective biological control agent. 6 With an increased market demand for organic produce, holistic approaches such as conservation biological control, particularly the use of Oecophylla, are increasing in importance. 7 Multi‐stakeholder strategies for collaborative learning are proposed for a better control of major fruit, nut and timber tree pests in Africa, Asia and Australia.     

Fruit size and shape: Allometry at different taxonomic levels in bird-dispersed plants

Summary The likelihood that a plant's seeds will be dispersed by fruit-eating birds may depend upon the size and shape of its fruits. Assuming that elongate fruits can be swallowed more easily than spherical fruits of equal volume and that plant fitness is enhanced by seed dispersal by many individuals and species of birds, natural selection should favour increasing fruit elongation with increasing fruit size in bird-dispersed plants. According to this view, this allometric pattern would be adaptive. Alternatively, fruit shape in bird-dispersed plants may be constrained by development or phylogeny. To determine whether there was any evidence to support the adaptive allometry hypothesis, we examined allometric relationships between length and diameter in fruits and seeds in a group of neotropical bird-dispersed plant species. Using the major axis technique, we regressed ln(diameter) on ln(length) for fruits and seeds at various taxonomic levels: (1) within individual trees ofOcotea tenera (Lauraceae) (2) among 19 trees within a population ofO. tenera, as well as among pooled fruits from multiple trees within 20 other species in the Lauraceae, (3) among 25 sympatric species within a plant family (Lauraceae) and (4) among 167 species representing 63 angiosperm families within a plant community in Monteverde, Costa Rica. At most taxonomic levels, a tendency for fruit length to increase more rapidly than fruit diameter among fruits (negative allometry) occurred more frequently than expected by chance. Estimated slopes of the regressions of fruit length on fruit diameter were < 1 within 15 of the 19 individualO. tenera trees, among tree means withinO. tenera, among pooled fruits within 16 of the 20 other species in the Lauraceae, among species means within the Lauraceae and among means of all bird-dispersed species in the lower montane forests of Monteverde. Seed allometry showed similar patterns, although for both fruits and seeds the broad confidence intervals of the slopes estimated by major axis regression overlapped 1 in many cases. Among the 63 Monteverde family means, fruit length and diameter scaled isometrically. Based on measurements of ontogenetic changes in fruit shape in a single species,O. viridifolia, we found no evidence that negative allometry in fruit shape within the Lauraceae was an inevitable consequence of developmental constraints. Instead, increasing elongation of fruits and seeds in certain plant taxa is consistent with adaptation to gape-limited avian seed dispersers. Contrary results from vertebrate-dispersed species from Malawi and Spain may reflect differences between the New and Old World in plant taxa, seed dispersers or evolutionary history.     

Indigenous Medicine and Primary Health Care: The Importance of Lay Knowledge and Use of Medicinal Plants in Rural South Africa

Indigenous medicine is important to rural livelihoods, but lay knowledge and use of medicinal plants has not been extensively studied. Research in KwaZulu-Natal, South Africa, showed that medicinal plants were frequently used by villagers and contributed to their ability to cope with health problems. Knowledge of plants and household remedies was extensive and varied in that households often held different knowledge. Villagers mainly relied on common species, and were generally aware of alternative species for a certain ailment. People were flexible in their use of indigenous and western health care, which were both perceived as beneficial. Improved cooperation between health care systems could improve health standards. Extraction of medicinal plants has been described as unsustainable in the region—a situation not found in the study area. It is argued that conservation policies aimed to restrict access should be differential and potentially not include local consumption, since this may be ecologically unnecessary and entail local hardships.     

Structural investigation of the sweet-tasting proteins thaumatin and monellin by immunological studies

Rabbit antibodies were produced against thaumatin I, a sweet-tastingprotein from plant origin using the technique of double diffusionin agar. Cross-reactions were observed between these antibodiesand thaumatin I, monellin and chemically modified thaumatins.No cross-reaction was observed between the antibodies of thaumatinI and the not sweet-tasting iodinated monellin. This lack ofcross-reaction may be due to the fact that iodination splitsmonellin into its A and B chain, resulting in a disturbanceof the tertiary structure of the molecule. The appearance ofprecipitation lines from thaumatin I as well as from monellinin reaction with the antibodies of thaumatin in the immunodiffusionassay indicates that thaumatin and monellin are immunologicallyclosely related. An identical conformational antigenic determinantin both molecules is probably responsible for this relationship.It is tentatively concluded that the identical conformationaldeterminant coincides with the active site responsible for thesweet-taste sensation.     

Traditional Sustainable Harvesting Knowledge and Distribution of a Vulnerable Wild Medicinal Root (<Emphasis Type="Italic">A. pyrethrum</Emphasis> var. <Emphasis Type="Italic">pyrethrum</Emphasis>) in Ait M’hamed Valley,Morocco

This study examined traditional harvesting knowledge and practices, paired with field-based assessment of distribution of a vulnerable wild medicinal root, Anacyclus pyrethrum var. pyrethrum, in southern Morocco. Research included focus groups, qualitative interviews, and a survey of 38 collectors. Based on local knowledge, replanting trials were conducted and transects and plot-based assessments were used to examine distribution.Local collectors reported significant declines in A. pyrethrum var. pyrethrum populations, driven by poaching and premature (either before the root has become large enough or before the season of seed dispersal) harvesting in sites that cannot be protected from poaching, as well as grazing and tilling. Thirty sites, totaling approximately 30% of the region, were surveyed: A. pyrethrum var. pyrethrum was identified in only nine. In five sites, plot transects were used to determine plant density, revealing that plant density and the number of flowers and fruit per plant were significantly higher closest to habitation.This research contributes to the understanding and evaluation of the causes of over harvesting and factors that could help to protect this vulnerable species. We believe that there is significant room to build on local collector’s knowledge of harvesting and management of this important natural resource, with potential benefits for both local livelihoods and local ecosystems.     

Pollination and reproduction enhance the invasive potential of an early invader: the case of Lythrum salicaria (purple loosetrife) in South Africa

The potential of an alien plant to spread rapidly and colonize new habitat may be related to the mode of reproduction and the ability to attract pollinators. Most studies focus on widespread invasive plants, in which pollinators are rarely limiting. Here, we assess the ability of a recent invader in South Africa, the tristylous Lythrum salicaria to self-reproduce and whether this can explain the delay between introduction and spread. This study was conducted in one of the largest known populations (a total of 7 populations in South Africa) of L. salicaria in the Liesbeek river in the fynbos biome. We assessed the importance of pollinators and autonomous selfing in L. salicaria by comparing seed set between pollinator excluded and naturally pollinated flowers. Overall, 5 pollinators (4 native and 1 alien) were recorded with Cape honeybees and Africa Monarch butterflies the most prominent. Seed and fruit set were significantly higher in open pollinated flowers compared to pollinator excluded flowers. Also, seed and fruit set in pollinator excluded flowers were higher in long and medium morphs compared to short morphs. Germination was high for seeds from pollinator, but also from pollinator excluded treatments. This shows that L. salicaria in South Africa is self-compatible to some extent, but it is frequented by pollinators, significantly increasing seed production. Despite L. salicaria being tristylous, all 3 morphs are present in South Africa and with a huge seed production, this species has the potential to become a major invader of rivers and wetlands in South Africa.

     

A taxonomic,biogeographical and ecological overview of invasive woody plants

Abstract. Invasive plants are considered to be a major threat to the earth's biodiversity, but have not been sufficiently investigated. To address this problem a relational database on invasive woody plants has been set up. It is based on 2045 bibliographical references and contains records on 653 species representing 110 families. The families with the largest number of invasive species are: Rosaceae, Mimosaceae, Papilionaceae and Pinaceae. Out of 1060 recorded invasive events an equal number are reported from continents and oceanic islands. The highest number of invasive woody species are recorded from Europe, followed by the Pacific islands, North America, New Zealand, Australia, Indian Ocean islands and southern Africa. Included in these regions are areas which have fewer highly invasive species, e.g. islands on continental shelves, such as the British Isles. Although most invasions occur in disturbed habitats, most natural communities are susceptible to woody plant invasions. Data on species attributes are only available for a minority of species but indicate that invasive woody plant species may be either insect or wind-pollinated, have a wide array of fruit types, fruit and seed sizes, number of seeds per fruit and dispersal agents. The relative frequency of several attributes varies with the degree of invasiveness. Thus it is not yet possible to determine which set of attributes favours invasiveness and therefore it is difficult to make predictions.     

Genetic rescue by distant trees mitigates qualitative pollen limitation imposed by fine‐scale spatial genetic structure

Restricted seed dispersal frequently leads to fine‐scale spatial genetic structure (i.e., FSGS) within plant populations. Depending on its spatial extent and the mobility of pollinators, this inflated kinship at the immediate neighbourhood can critically impoverish pollen quality. Despite the common occurrence of positive FSGS within plant populations, our knowledge regarding the role of long‐distance pollination preventing reproductive failure is still limited. Using microsatellite markers, we examined the existence of positive FSGS in two low‐density populations of the tree Pyrus bourgaeana. We also designed controlled crosses among trees differing in their kinship to investigate the effects of increased local kinship on plant reproduction. We used six pollination treatments and fully monitored fruit production, fruit and seed weight, proportion of mature seeds per fruit, and seed germination. Our results revealed positive FSGS in both study populations and lower fruit initiation in flowers pollinated with pollen from highly‐genetically related individuals within the neighbourhood, with this trend intensifying as the fruit development progressed. Besides, open‐pollinated flowers exhibited lower performance compared to those pollinated by distant pollen donors, suggesting intense qualitative pollen limitation in natural populations. We found positive fine‐scale spatial genetic structure is translated into impoverished pollen quality from nearby pollen donors which negatively impacts the reproductive success of trees in low‐density populations. Under this scenario of intrapopulation genetic rescue by distant pollen donors, the relevance of highly‐mobile pollinators for connecting spatially and genetically distant patches of trees may be crucial to safeguarding population recruitment.     

Updated assessment of potential biopesticide options for managing fall armyworm (Spodoptera frugiperda) in Africa

The fall armyworm (FAW, Spodoptera frugiperda) has recently spread to many countries in Africa, the Near East, Asia and the Pacific. In sub-Saharan Africa (SSA), more than 300 million people depend on FAW’s preferred host plant, maize, as a staple crop. Hence, the spread of FAW in SSA has the potential to negatively affect livelihoods and food security. Many farmers have responded to FAW by increasing their use of synthetic pesticides, but these are not always used safely or effectively. More information on sustainable alternatives to high-risk synthetic pesticides is needed to inform decisions by farmers and policy makers. In a previous paper, the authors responded to this information need by identifying fifty biopesticides which had been registered for FAW management in one or more of 30 countries in FAWs native region and Africa. For each biopesticide identified, detailed profiles with information on their efficacy against FAW; associated human health and environmental hazards; their agronomic sustainability; and whether or not they are practical for use by smallholder farmers were developed Research for development (R4D) efforts is ongoing in Africa and Asia for development and use of biopesticides for FAW management. Hence, in this study the authors assessed the current state of knowledge and documented how information gaps have been filled (or not) since the previous paper was published. The authors found that for many biopesticides there is a growing body of information on their efficacy in the field in Africa and increased availability of commercialized products. They also note remaining information gaps, particularly the compatibility of the biopesticides with other recommended management practices, and cost-benefit analyses, important for developing and implementing sustainable IPM. An updated list of priority biopesticides for research, development and promotion is provided.     

Managing the natural capital of papyrus within riparian zones of Lake Victoria,Kenya

The harvesting of natural products such as papyrus (Cyperus papyrus L.), whether for subsistence value or for the production of commodities intended for sale at local markets, contributes to the well-being of riparian peoples around Lake Victoria, Kenya. Serious losses of papyrus wetlands across East Africa have been reported, most of which are attributed to increasing anthropogenic stressors. Recent studies have called for restoration of these wetlands, emphasizing the need for sustainable harvesting strategies to be put in place, although few have provided suggestions as to how this might happen in practical terms and, crucially, with the consent and active participation of local communities as key stakeholders. Here we explore the socioeconomic characteristics of livelihoods based on papyrus, presenting data generated from surveys, interviews and group discussions collected at multiple sites within the Nyando river basin, Kenya. Conceptualizing papyrus stands as living stocks of natural capital, we then outline our proposal for maintaining the provisioning services of this species, without compromising the critical ecohydrological functions of these swamps as land–water buffer zones. Finally we suggest how this approach might be adapted for wider dissemination around Lake Victoria and beyond, motivated by what we believe to be the first reported case of successful papyrus restoration by a local community.     

Invasive plants and their escape from root herbivory: a worldwide comparison of the root-feeding nematode communities of the dune grass <Emphasis Type="Italic">Ammophila arenaria</Emphasis> in natural and introduced ranges

Invasive plants generally have fewer aboveground pathogens and viruses in their introduced range than in their natural range, and they also have fewer pathogens than do similar plant species native to the introduced range. However, although plant abundance is strongly controlled by root herbivores and soil pathogens, there is very little knowledge on how invasive plants escape from belowground enemies. We therefore investigated if the general pattern for aboveground pathogens also applies to root-feeding nematodes and used the natural foredune grass Ammophila arenariaas a model. In the late 1800s, the European A. arenariawas introduced into southeast Australia (Tasmania), New Zealand, South Africa, and the west coast of the USA to be used for sand stabilization. In most of these regions, it has become a threat to native vegetation, because its excessive capacity to stabilize wind-blown sand has changed the geomorphology of coastal dunes. In stable dunes of most introduced regions, A. arenaria is more abundant and persists longer than in stabilized dunes of the natural range. We collected soil and root samples and used additional literature data to quantify the taxon richness of root-feeding nematodes on A.␣arenaria in its natural range and collected samples from the four major regions where it has been introduced. In most introduced regions A. arenaria did not have fewer root-feeding nematode taxa than the average number in its natural range, and native plant species did not have more nematode taxa than the introduced species. However, in the introduced range native plants had more feeding-specialist nematode taxa than A. arenaria and major feeding specialists (the sedentary endoparasitic cyst and root knot nematodes) were not found on A. arenaria in the southern hemisphere. We conclude that invasiveness of A. arenaria correlates with escape from feeding specialist nematodes, so that the pattern of escape from root-feeding nematodes is more alike escape from aboveground insect herbivores than escape from aboveground pathogens and viruses. In the natural range of A. arenaria, the number of specialist-feeding nematode taxa declines towards the margins. Growth experiments are needed to determine the relationship between nematode taxon diversity, abundance, and invasiveness of A. arenaria.     

The significance of the oil palm (Elaeis guineensis Jacq.) in the late Holocene environments of west and west central Africa: A further consideration

Abundant archaeological evidence of the occurrence of the endocarp of the oil palm,Elaeis guineensis, in the rain forest and woodland savanna zones of west and central Africa from about 5000 B.P. has shown the tree to be an important element in the subsistence economy of the region; its pollen also has been recorded in most of the regional terrestrial sediments studied so far. The distinct and consistently sudden and more marked increases in this pollen during the late Holocene when compared with the late Tertiary and late Pleistocene frequencies strongly indicate that the late Holocene upsurges were due to both natural and human factors favourable for the expansion of this heliophytic tree. Reasons are given for suggesting that upsurges in oil palm pollen during the late Holocene period in this region can be used as indices of plant cultivation. While the oil palm is known from early Tertiary deposits in west Africa, its earliest palynological record from terrestrial sediments in the west central part dates back only to the early Holocene. More palynological studies of Tertiary and Quaternary terrestrial cores are required to establish with more certainty the antiquity ofE. guineensis in west central Africa.     

Testing for ecological and genetic Allee effects in the invasive shrub Senna didymobotrya (Fabaceae)

For an introduced plant species to become invasive, it must be able to reproduce even in initially small populations. We tested for Allee effects (reduced reproductive performance of individuals in small populations) in the nonclonal, buzz-pollinated shrub Senna didymobotrya in its invasive range in South Africa. The species is self-compatible, but we found that in its invasive range in South Africa it requires pollinators to set seed. Nearly all stigmas (90%) received pollen, but natural fruit set was very low (3-20%). Pollen receipt and fruit set were not significantly correlated with population size. We thus found no evidence for an ecological Allee effect arising from pollen limitation in small populations. Offspring seedling performance, measured in terms of stem volume and leaf area, was also not significantly correlated with the number of plants in the source population, indicating that genetic Allee effects, such as inbreeding depression, are either absent or of such a small magnitude that they would be unlikely to limit further spread of S. didymobotrya in South Africa.