Every plant for himself; the effect of a phenolic monoterpene on germination and biomass of Thymus pulegioides and T. serpyllum

Thyme plants are known for their production of aromatic oils, whose main component is terpenes. The plants leach terpenes to their surroundings and thereby affect the seed germination and biomass of associated plants, but also potentially themselves. A variation in the dominant terpenes produced by thyme plants is found both within and among species. In Denmark two thyme species (Thymus pulegioides and T. serpyllum) are naturally occurring. The essential oil of T. pulegioides in Denmark is mainly dominated by one monoterpene; ‘carvacrol’. In contrast, the essential oil of T. serpyllum constitutes a mix of two–four different types of terpenes, both mono‐ and sesqui‐terpenes. As the effects of terpenes on plant performance can vary with the type of terpene, and in order to study species‐specific responses, we examined how the dominating T. pulegioides monoterpene ‘carvacrol’ affected germination and growth of both T. pulegioides and T. serpyllum. We compared the performance of seeds and seedlings of both thyme species on soil treated with carvacrol versus control soil. We found no effect of treatment on germination, but we detected a highly significant effect of treatment on seedling biomass. For both thyme species, seedling biomass was significantly higher on terpene soil compared to control soil, suggesting a general adaptation to the presence of terpenes in the soil for both thyme species. Moreover, while no difference in seedling biomass between species on control soil was found, T. pulegiodes seedlings were significantly larger than T. serpyllum when grown on soil treated with its ‘home’ terpene, suggesting an additional species specific response. Dividing the biomass into aboveground and root biomass showed that the increased biomass on terpene‐soil was due to increased aboveground biomass, whereas no difference in root biomass was detected among treatments and species. We discuss whether this response may be caused by an adaptation to a predictable terpene‐mediated alteration in nitrogen‐availability.     

Domestication of wild marigold (Tagetes minuta L.) as a potential economic crop in Western Himalaya and North Indian plains

Tagetes minuta L, syn.T. glandulifera Schrank grows wild in western Himalaya and is one of the important source of essential oils. The crop has been domesticated by our Institute not only in sub-temperate but also in subtropical zones and farmers have opted Tagetes minuta as an essential oil crop in their cropping system. Four cropping systems have been evolved based on variable sowing and harvesting times yielding varying quality of essential oil. All the four crop practices can be practised in sub-temperate regions while one crop practice is recommended for subtropical regions. Tagetes oil contains three major constituents of monoterpene ketones namely ocimenones E&Z, tagetones E&Z and dihydrotagetone and a hydrocarbon ocimene which are important base materials for synthesizing new aroma molecules.Tagetes oil of desired constituents can be produced by adopting selective crop practice based on experimental findings of present investigation. Ocimene rich crop can be harvested in winter (December–January), dihydrotagetone rich crop in autumn (October–November), tagetone rich crop in summer (June) and ocimenone rich crop can be harvested in short duration autumn–winter (December–January) and summer crops.     

垂序商陆繁殖期各器官锰富集规律及其对种子萌发的影响

通过室内盆栽实验,以锰超累积植物垂序商陆植株为材料,比较了不同供锰水平(0.005、0.1、1.0mmol/L)下种子成熟过程中各器官锰含量的动态变化及所产种子的萌发率,旨在了解高锰条件下垂序商陆在繁殖期体内锰富集规律及其对繁殖能力的影响。结果发现:(1)在垂序商陆种子成熟过程中,各处理组植株的根、茎、叶、果实中锰含量均随时间推移呈逐渐增加趋势,且植物器官中锰含量随环境中锰浓度升高而提高;种子内的锰含量变化规律在对照组和处理组之间不同,对照组(0.005mmol/L)先小幅下降后持续增加,而处理组(0.1与1.0mmol/L)则先持续增加,至末期出现不同程度的降低。(2)相同锰浓度环境条件下,种子成熟后期各器官锰含量均表现为种子茎根果实(包括种子)叶。(3)GC-MS分析表明果汁中有机酸主要成分为草酸与少量的2-羟基丙酸,有机酸的成分与含量在各组间无明显不同。(4)随锰浓度增加,种子中锰含量增加,而萌发率则逐渐降低,且各组间差异极显著。研究结果提示,垂序商陆植株各器官内锰积累量与环境中锰浓度密切相关,其在种子成熟过程中会对体内多余的锰在各器官进行合理分配,以减小锰富集带来的有害效应从而完成自身生命周期,并可能在种子成熟末期采取降低种子中锰的分配量来提高萌发率从而保证高繁殖能力,果浆的可溶性水环境及所含有机酸在繁殖期植株解锰毒中发挥了重要作用。     

Effects of enhanced UV-B radiation on the hormonal content of vegetative and reproductive tissues of two tomato cultivars and their relationships with reproductive characteristics

The effects of enhanced UV-B radiation on hormone changes in vegetative and reproductive tissues of tomato (Lycopersicon esculentum Mill.) and their relationships with reproductive characteristics were studied. Two cultivars, TongHui (TH) and XiaGuang (XG), were grown in the field for one growing season under ambient (Control), ambient plus 2.54 kJ m^–2 d^–1 (T1) or ambient plus 4.25 kJ m^–2 d^–1 (T2) of supplemental ultraviolet-B (280–320 nm). The number of open flowers increased significantly in the TH cultivar under T2 while it declined in the XG cultivar under T1. Although pollen germination from both cultivars was inhibited by UV-B treatment, fruit number was enhanced in the TH cultivar at both UV-B doses and in the XG cultivar at the low dose. On the other hand, seed size (dry weight) was reduced in the XG cultivar by both UV-B doses and in the TH cultivar at the low UV-B dose. The final germination rates of seeds from control and UV-B treated plants of both cultivars showed no significant differences (p > 0.05), while germination was delayed in the TH cultivar at both doses of UV-B and in the XG cultivar only for T2. To determine the mechanism of UV-B's effects on developmental processes, hormone concentrations in leaves, pistils and seeds were analyzed using ELISA on partially purified extracts. The results suggested that enhanced UV-B radiation induced hormone changes in both vegetative and reproductive tissues. The alteration of flower number may be associated with the changes of ZR in leaves under enhanced UV-B radiation and the delayed germination may due to the changes in seed ABA and GAs.     

入侵植物印加孔雀草在不同生境的种群构件生物量及其分配特征

印加孔雀草是中国西藏新近入侵种,其危害已初见端倪,但我国鲜有对其入侵机理的研究.为探究印加孔雀草在异质环境下的种群构件生物量及其分配特征,进一步深入了解其生存策略和易入侵生境.该研究在菜园、果园、路边、荒地和河滩等五种典型入侵生境内对其花果期的种群构件生物量进行了测定和分析,计算了表型可塑性指标值.结果表明:(1)印加...     

银杏叶萜内酯含量的变化及其与叶绿素荧光特性的关系

为探究银杏(Ginkgo biloba)叶萜类内酯含量和光合同化作用的关系,对其内酯含量和叶绿素荧光特性进行了研究。结果表明,不同采收时间银杏叶中白果内酯和银杏内酯含量有显著差异,总体上,5月份含量较低,此后逐渐升高,8月份达到高峰,然后快速下降,10月底最低;与此同时,银杏叶片的光合色素以及叶绿素荧光参数也呈现周期性变化。白果内酯以及萜内酯含量与叶绿素荧光参数Y(NPQ)之间呈极显著正相关关系,因此,可以通过银杏叶片的叶绿素荧光参数预测白果内酯和萜内酯含量。     

Differences in life‐cycle stage components between native and introduced ranges of five woody Fabaceae species

Understanding differences in the components of life‐cycle stages of species between their native and introduced ranges can provide insights into the process of species transitioning from introduction to naturalization and invasion. We examined reproductive variables of the germination (seed predation, seed viability, time to germination), seed output (crown projection, seed production, seed weight) and dispersal (seed weight, dispersal investment) stages of five woody Fabaceae species, comparing native and introduced ranges. We predicted that each species would differ in reproductive variables of at least one life‐cycle stage between their native and introduced ranges, thus allowing us to determine the life‐cycle stage most associated with invasion success in the introduced range. Acacia melanoxylon and Paraserianthes lophantha had reduced seed predation in their introduced ranges while P. lophantha also had higher seed viability indicating that the germination life‐cycle stage is most strongly associated with their invasion success in the introduced range. Only Acacia longifolia varied between ranges for the seed output stage due to larger plant size, greater seed production and smaller seed size in its introduced range. Similar to A. longifolia, Acacia cyclops had smaller seed size in its introduced range but did not have any other variable differences between ranges suggesting that the dispersal stage is best associated with its invasion success in the introduced range. Surprisingly, Acacia saligna was the only species without a clear life‐cycle stage difference between ranges despite it being one of the more invasive acacia species in Australia. Although we found clear differences in reproductive variables associated with life‐cycle stages between native and introduced ranges of these five species, these differences were largely species‐specific. This suggests that a species invasion strategy into a novel environment is complex and varies among species depending on the environmental context, phenotypic plasticity and genotypic variation in particular traits.     

The effect of fractionated Tagetes oil volatiles on aphid reproduction

The biological activity of essential oil volatiles from Tagetes minuta L. (Mexican marigold) against three aphid species was investigated in a series of laboratory experiments. The aphid species (Homoptera: Aphididae) studied were: Acyrthosiphon pisum (Harris) (pea aphid), Myzus persicae (Sulzer) (peach‐potato aphid), and Aulacorthum solani (Kaltenbach) (glasshouse and potato aphid). Tagetes minuta oil volatiles significantly reduced aphid reproduction (up to 100% after 5 days of exposure). The effect depended on the quantity of essential oil used, and varied with the aphid species tested. Pea aphids were the most susceptible. Tagetes minuta oil was fractionated by vacuum distillation. Fractions and three pure compounds (limonene, (Z)‐ocimene, and β‐caryophyllene) were tested using the same experimental technique. The chemical composition of the volatiles was investigated by headspace–solid phase microextraction–gas chromatography mass spectrometry (HS‐SPME‐GCMS), and the main constituents of the oil were identified. Overall, applied in equal quantity, fractions predominantly containing sesquiterpenes and oxygenated monoterpenoids were more effective in restricting aphid population growth than fractions predominantly containing monoterpenes. When tested as a pure compound, the sesquiterpene β‐caryophyllene produced a greater effect than the monoterpenes limonene and ocimene. The study demonstrates that T. minuta oil volatiles have potential for aphid control.     

印加孔雀草入侵生态风险评估及其管理措施

【目的】印加孔雀草为菊科一年生草本植物,原产南美洲,现已在我国多个地区发现,局部呈现生态危害。分析印加孔雀草生态适应性特点,可以有针对地提出其风险指标体系和判断标准,确定其危险级别。【方法】对印加孔雀草的分布、危害情况及生物学特性进行调查,定性分析其生态适应性特点,定量分析评估其生态风险,确定其危险级别。【结果】根据风险指标体系准则层的赋值,其中入侵性R_1为83,适应性R_2为88,扩散性R_3为65,危害性R_4为84,计算得出印加孔雀草风险值(R)=8061,属于具有危害性和侵入性的物种。【结论】印加孔雀草为具有危害性和侵入性的物种,应严格禁止引入。由于该植物已经传入我国,应采取必要的应急措施,开展检疫、监测和灭除,防止其传入其他还未发生的地区。     

Long-term responses of Melilotus segetalis to salinity. I. Growth and partitioning

Annual sweetclover plants [Melilotus segetalis (Brot) Ser.] were grown for a complete life cycle with and without saline (NaCl treatment of CE=15 dS m⁻¹). Growth and partitioning analyses were performed. Sequential harvests (every 15 d) during the life cycle, and separation of plant material into roots, stems, petioles, leaves and reproductive structures were carried out Salt treatment reduced growth during the early and middle stages of the life of the plant, but did not significantly affect RGR in the reproductive phase. The root–shoot allometric coefficient of salinized plants in the generative phase decreased more than in control plants. We suggest that salinity-induced growth reduction in M. segetalis was primarily a result of a lower unit leaf rate (ULR) despite an increased leaf area ratio (LAR). Earlier flowering, higher biomass allocation to shoot and greater reproductive investment, but similar relative growth rate (RGR), were some of the main characteristics of salt-stressed plants compared to controls during the reproductive phase, these apparently being associated with increased sink strength caused by developing flowers and fruits.     

Arbuscular mycorrhizal symbiosis increases host plant acceptance and population growth rates of the two-spotted spider mite <Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Most terrestrial plants live in symbiosis with arbuscular mycorrhizal (AM) fungi. Studies on the direct interaction between plants and mycorrhizal fungi are numerous whereas studies on the indirect interaction between such fungi and herbivores feeding on aboveground plant parts are scarce. We studied the impact of AM symbiosis on host plant choice and life history of an acarine surface piercing-sucking herbivore, the polyphagous two-spotted spider mite Tetranychus urticae. Experiments were performed on detached leaflets taken from common bean plants (Phaseolus vulgaris) colonized or not colonized by the AM fungus Glomus mosseae. T. urticae females were subjected to choice tests between leaves from mycorrhizal and non-mycorrhizal plants. Juvenile survival and development, adult female survival, oviposition rate and offspring sex ratio were measured in order to estimate the population growth parameters of T. urticae on either substrate. Moreover, we analyzed the macro- and micronutrient concentration of the aboveground plant parts. Adult T. urticae females preferentially resided and oviposited on mycorrhizal versus non-mycorrhizal leaflets. AM symbiosis significantly decreased embryonic development time and increased the overall oviposition rate as well as the proportion of female offspring produced during peak oviposition. Altogether, the improved life history parameters resulted in significant changes in net reproductive rate, intrinsic rate of increase, doubling time and finite rate of increase. Aboveground parts of colonized plants showed higher concentrations of P and K whereas Mn and Zn were both found at lower levels. This is the first study documenting the effect of AM symbiosis on the population growth rates of a herbivore, tracking the changes in life history characteristics throughout the life cycle. We discuss the AM-plant-herbivore interaction in relation to plant quality, herbivore feeding type and site and the evolutionary implications in a multi-trophic context.     

A Cambrian corynexochoid trilobite with only two thoracic segments

Discovery of articulated specimens of Vistoia? minuta Resser shows that species to be an isopygous corynexochoid trilobite with only two thoracic segments in the holaspid period. A new genus, Thoracocure, is proposed to include Vistoia? minuta Resser and Tonkinella idahoensis Resser, and concepts of those species are revised. Neoteny appears to be responsible for several holaspid characters of T. minuta. its holaspid size may be the smallest known for trilobites, and a pelagic mode of life is suggested. The combination of characters possessed by T. minuta requires revision of current concepts of the orders Agnostida and Corynexochida. As a related matter, it is proposed that the Miomera of Jaekel (1909) be suppressed as a subjective junior synonym of the Agnostida (nomen translatum Kobayashi, 1935) of Salter (1864).     

Interacting effects of warming and drought on regeneration and early growth of Acer pseudoplatanus and A. platanoides

Climate change is acting on several aspects of plant life cycles, including the sexual reproductive stage, which is considered amongst the most sensitive life‐cycle phases. In temperate forests, it is expected that climate change will lead to a compositional change in community structure due to changes in the dominance of currently more abundant forest tree species. Increasing our understanding of the effects of climate change on currently secondary tree species recruitment is therefore important to better understand and forecast population and community dynamics in forests. Here, we analyse the interactive effects of rising temperatures and soil moisture reduction on germination, seedling survival and early growth of two important secondary European tree species, Acer pseudoplatanus and A. platanoides. Additionally, we analyse the effect of the temperature experienced by the mother tree during seed production by collecting seeds of both species along a 2200‐km long latitudinal gradient. For most of the responses, A. platanoides showed higher sensitivity to the treatments applied, and especially to its joint manipulation, which for some variables resulted in additive effects while for others only partial compensation. In both species, germination and survival decreased with rising temperatures and/or soil moisture reduction while early growth decreased with declining soil moisture content. We conclude that although A. platanoides germination and survival were more affected after the applied treatments, its initial higher germination and larger seedlings might allow this species to be relatively more successful than A. pseudoplatanus in the face of climate change.     

Distribution Patterns,Species Assemblages and Habitat Selection of the Stoneflies (Plecoptera) from Two Mediterranean River Basins in Southern Spain

The stonefly distribution and its relationship with habitat changes, based on stream physico chemical features, were investigated in two Mediterranean river basins (Guadaira and Guadalete, S Spain). Plecopteran nymph distribution varied along an elevation gradient. Both stonefly species richness and species diversity increased with altitude. Stoneflies were able to tolerate a wide range of environmental conditions but were absent from low altitude sites, temporary streams with high salinity values and high water temperature. A total of 13 stonefly species were found in the study area, from which Tyrrhenoleuctra minuta (Klapálek ) and Protonemura sp. were dominant. The most widespread species were Nemoura lacustris and Capnioneura mitis. Three distinct species assemblages were observed according to their distribution patterns, but with similar environmental preferences. Capnioneura petitpierreae and T. minuta showed preferences to low altitude sites, whereas C. mitis and N. lacustris were found throughout all sites. T. minuta and N. lacustris inhabited permanent and temporary sites, while the same species and C. mitis also were found in semipermanent streams. Temporally, most stoneflies were caught during winter (85.9%), especially at the low altitude sites.     

Foliar terpenoids in Tsuga species and the fecundity of scale insects

Summary The relationship between the reproductive success of two Japanese scale insects, Fiorinia externa Ferris and Nuculaspis tsugae (Marlatt) (Homoptera: Diaspididae) and the concentrations of 15 terpenoids in needles of Tsuga sieboldii, the Japanese host, and T. canadensis, the North American host, was investigated during 1981 and 1982 in a field plot of 8-year-old trees in New Haven, CT, USA. Both scales produced significantly more eggs per female on T. sieboldii than on T. canadensis. Stepwise multiple regression analyses indicated that the variation in fecundity within both scales was strongly associated with variation in the terpenoid profile between tree species.General patterns of phytochemical variation between the two Tsuga species based on differences in the concentration of terpenoids having similar chemical structures were revealed by the multivariate statistical technique, principal components analysis. The volatile leaf oil profile of T. sieboldii was relatively richer in terpene alcohols, while that of T. canadensis was relatively richer in terpene hydrocarbons and terpene acetates. The individual terpenoids were then assigned to one of five groups based on chemical structure and regression analyses were repeated; fecundity of both scales increased with increasing concentration of terpenoid alcohols. Fecundity of F. externa was negatively associated with the relative concentration of acyclic terpenes but the opposite was true for N. tsugae. Analysis of foliar terpenoids may provide a basis for predicting the relative susceptibility of Tsuga species to attack by F. externa and N. tsugae.     

Differences in polypeptide expression in thermoinhibited and germinating achenes of Tagetes minuta L.

When imbibed at their optimum germination temperature of25°C, achenes of Tagetes minutaL.germinate over a period of 48 h. At a temperature of36°C, the achenes become thermoinhibited and do notgerminate. This elevated temperature does not harm the achenes, however, and assoon as the temperature is reduced below 35°C,germination occurs, but is spread over a reduced period of only 24h. The polypeptide patterns of germinating and thermoinhibitedachenes were compared, to test whether thermoinhibition is the result ofdifferential gene expression or repression. Ten polypeptides which weredifferentially expressed in thermoinhibited achenes were observed. Thesepolypeptides were all extremely specific to thermoinhibited achenes anddeclinedrapidly when the incubation temperature was decreased, in a manner whichcorrelated with the increase in germinability of the achenes. The tightlyregulated nature of the expression of these polypeptides suggests thatthermoinhibition in T. minuta may be under positivecontrol. These proteins may therefore result in the prevention of radicleemergence at unfavourable temperatures.     

Chemical Composition and Allelopathic Potential of Essential Oils from Tipuana tipu (Benth.) Kuntze Cultivated in Tunisia

In Tunisia, Tipuana tipu (Benth .) Kuntze is an exotic tree, which was introduced many years ago and planted as ornamental street, garden, and park tree. The present work reported, for the first time, the chemical composition and evaluates the allelopathic effect of the hydrodistilled essential oils of the different parts of this tree, viz., roots, stems, leaves, flowers, and pods gathered in the area of Sousse, a coastal region, in the East of Tunisia. In total, 86 compounds representing 89.9 – 94.9% of the whole oil composition, were identified in these oils by GC‐FID and GC/MS analyses. The root essential oil was clearly distinguished for its high content in sesquiterpene hydrocarbons (β‐caryophyllene, 1 (44); 24.1% and germacrene D, 2 (53); 20.0%), while those obtained from pods, leaves, stems, and flowers were dominated by non‐terpene hydrocarbons. The most important ones were n‐tetradecane (41, 16.3%, pod oil), 1,7‐dimethylnaphthalene (43, 15.6%, leaf oil), and n‐octadecane (77, 13.1%, stem oil). The leaf oil was rich in the apocarotene (E)‐β‐ionone ( 4 (54); 33.8%), and the oil obtained from flowers was characterized by hexahydrofarnesylacetone ( 5 (81); 19.9%) and methyl hexadecanoate (83, 10.2%). Principal component and hierarchical cluster analyses separated the five essential oils into three groups and two subgroups, each characterized by the major oil constituents. Contact tests showed that the germination of lettuce seeds was totally inhibited by the root essential oil tested at 1 mg/ml. The inhibitory effect on the shoot and root elongation varied from ?1.6% to ?32.4%, and from ?2.5% to ?64.4%, respectively.     

Fitness implications of late bud break and time of burning in Lannea edulis (Sond.) Engl. (Anacardiaceae)

Many woody plants of savannas have massive underground parts (“lignotubers”) and diminutive aboveground parts with phenologies that are triggered by fire. Lannea edulis (Anacardiaceae) represents this life form and is widely distributed in south central Africa. The phenology of L. edulis was monitored on 42 permanently marked shoots over a 3-year period, from 2002 to 2004, and under three fire treatments (early and middle dry season burning, and fire protection) to determine whether (i) fire affected time of bud break and (ii) time of fruit ripening affected seed germination. Statistical analyses revealed that shoot reproductive status and fire treatments significantly affected time of bud break and the lag between bud break and leaf production. Shoot reproductive status explained 27% (P<0.001) while the interaction between reproductive status and fire treatments explained 34% (P<0.0001) of the variation in time at bud break. The appearance of the first leaf was delayed by 4 weeks in reproductive shoots compared with vegetative shoots. Shoot reproductive status explained 28% (P<0.0001) of the variation in the lag between bud break and appearance of the first leaf suggesting the existence of resource competition between reproduction and vegetative growth. However, reproductive status and fire treatments did not affect shoot size and leaves produced because replacement shoots after dieback due to fire were as long as shoots surviving from previous years due to insignificant annual shoot extension among the latter. There was high autocorrelation in the germination rate of seed-lots with seeds from fruits ripening early having a significantly higher germination rate (47% in 2002 and 89% in 2004) than those from fruits ripening later (3% in 2002 and 53% in 2004). Since time at bud break and fruit ripening were linked, it is proposed that late bud break results in reduced fitness in L. edulis because of reduced seed germination rate. Early and late dry season fires that delay bud break and destroy reproductive structures, respectively, also reduce this measure of fitness.     

On the life history ofTurnerella mertensiana (Rhodophyta,Gigartinales)

Turnerella (Gigartinales) withT. mertensiana known from northern Japan was studied to determine its life history. Carpospores cultured from foliose female plants gave rise on germination to crustose plants containing tetrasporangia, as noted previously inT. pennyi from the Atlantic. The crusts were slow to develop and required 3–5 years to achieve reproductive maturity. Tetraspores liberated in culturedT. mertensiana gave rise on germination eventually to thalli similar to gametophyticT. mertensiana. Thus this species may be said to adhere to the pattern of life history in which a large, foliose gametophyte alternates with a small crustose tetrasporophyte. The erect filaments of the small sporophytes branch laterally and tetrasporangial mother cells are found there, exemplifying an unusual method for crustose species to produce tetrasporangia.     

Growth and Development in Arabidopsis thaliana through an Entire Life Cycle under Simulated Microgravity Conditions on a Clinostat

Arabidopsis thaliana ecotype Columbia and Landsberg erecta were studied. Horizontal clinorotation affected little germination of seeds, growth and development of rosette leaves and roots during early vegetative growth stage, and the onset of the bolting of inflorescence axis and flower formation in reproductive growth stage, although it suppressed elongation of inflorescence axes. The clinorotation substantially reduced the numbers of siliques and seeds in Landsberg erecta, and completely inhibited seed production in Columbia. Seeds produced in Landsberg erecta on the clinostat were capable of germinating and developing rosette leaves normally on the ground. On the other hand, growth of pin-formed mutant (pin/pin) of Arabidopsis ecotype Enkheim, which has a unique structure of inflorescence axis with no flower and extremely low levels of auxin polar transport activity, was inhibited and the seedlings frequently died during vegetative stage on the clinostat. Seed formation and inflorescence growth of the seedlings with normal shape (pin/+ or +/+) were also suppressed on the clinostat. These results suggest that the growth and development of Arabidopsis, especially in reproductive growth stage, is suppressed under simulated microgravity conditions on a clinostat. To complete the life cycle probably seems to be quite difficult, although it is possible in some ecotypes. Received 18 June 1999/ Accepted in revised form 27 August 1999