How portulaca seedlings avoid their neighbours

Summary Portulaca oleracea L. seedlings do not develop in the direction of neighbours, even when these neighbours are small and distant. Neighbouring plants could be simulated by small rectangles of a plastic that resembled leaves in its spectral characteristics. Unlike seedlings, mature plants did not respond to objects that do not influence photosynthetic light. When light of equal intensity was received from all directions, Portulaca seedlings avoided the direction with higher far-red light. Portulaca is thus able to use spectral composition and direction of light as clues for the probability of the direction of future shade.     

The development of NAD(P)H-dependent and ferredoxin-dependent glutamate synthase in greening barley and pea leaves

The activity of NAD(P)H-dependent glutamate synthase (E.C. 1.4.1.14) has been demonstrated in extracts from etiolated shoots of pea (Pisum sativum L.) and barley (Hordeum vulgare L.). This activity does not significantly alter upon greening of the etiolated shoots, and is at a similar level in light-grown material. Ferredoxin-dependent glutamate synthase (E.C. 1.4.7.1) has low activity in etiolated shoots but increases rapidly on greening. In light grown leaves ferredoxin-dependent activity is 30–40-fold higher than NAD(P)H-dependent activity. It is not considered that the NAD(P)H-dependent glutamate synthase plays an important role in ammonia assimilation in the photosynthetic tissue of higher plants.     

<Emphasis Type="Italic">In vitro</Emphasis> micropropagation of four lupin species

The complete protocols for long-term micropropagation of some cultivars of four lupin species: Lupinus luteus, L. albus, L. angustifolius and L. mutabilis were elaborated. The shoots were regenerated in vitro via induction of axillary buds development. Plantlets were multiplicated on lowered salts MS-derived media containing BAP in diverse and generally low concentrations. Significant differences in regeneration capacity between species and cultivars were observed. The highest multiplication ratio revealed L. mutabilis and L. luteus. Regenerated shoots were rooted in vitro on low-salts MS-derived media with B5 vitamins. Media were supplemented with different auxins that affected roots formation of particular species and cultivars. Rooting ability of regenerated shoots decreased rapidly through in vitro culture. For that reason, grafting was applied as an alternative method of transfer of shoots to in vivo conditions. This method turned out to be successful for the majority of studied species and cultivars. Complete rooted or grafted plantlets were cultivated in pots with perlit in greenhouse. An erratum to this article is available at .     

Lupinus species differ in their requirements for iron

The effect of iron supply on the growth and nodulation ofLupinus angustifolius L. (Gungurru),Lupinus luteus L. (R-1171) andLupinus pilosus Murr. (P20957) was studied in acid solutions. Plants of the three species were grown together in the same solution and inoculated withBradyrhizobium (Lupinus) WU 425. Plants were then grown with or without applied NH₄NO₃. The lupin species differed greatly in their sensitivity to low iron concentrations in solution withL. pilosus being most tolerant andL. luteus most sensitive.L. pilosus had the highest iron concentration in tissues and had a higher ratio of iron concentration in the youngest fully expanded leaf blades (YEB) to that in roots than the other two species.L. luteus had higher iron concentrations in roots but lower iron concentration in YEB and shoots than didL. angustifolius. The requirements of internal iron for the maximal chlorophyll synthesis in YEB were 65 μg g^-1 forL. angustifolius andL. luteus, and 52 μg g^-1 forL. pilosus. In contrast to effects on growth, the three species had similar external iron requirements for nodule formation in roots and for maximal nitrogen concentrations in shoots. The results indicate that iron tolerant lupin species require lower internal and external iron supply and have a greater ability than sensitive species to translocate iron from roots to shoots.     

Callus and shoot formation in organ and tissue cultures of Hedera helix L., English ivy

When shoots of young plants of hemp (Cannabis sativa L.) and spinach (Spinacea oleracea L.) were cultured as cuttings and allowed to regenerate advenitious roots, ca. 80–85% became female (formed pistillate flowers) regardless of whether the leaves were left on the plants or were cut off (except for the 2–3 uppermost ones) after the beginning of adventitious-root formation. But when the leaves were cut off and the cuttings treated with gibberellic acid (GA₃, 25 mg/l) ca. 77–80% of the plants became male (formed staminate flowers). The result was quite similar when roots and leaves of young hemp plants were removed at the same time and the cuttings treated with GA₃. It is suggested that the leaves play an essential role in sex expression in hemp and spinach and that this role is related to gibberellin synthesis in the leaves.     

Comparison of carbonic anhydrase activity among various species of plantlets

During plant tissue culture, the culture container is small and sealed; the concentration of CO₂ in the microenvironment is relatively low. The plantlet growth is restrained for the shortage of CO₂ in the culture container. Carbonic anhydrase is a zinc-containing metalloenzyme that catalyzes the reversible conversion of bicarbonate to CO₂. The determination of carbonic anhydrase of leaves from Atractylodes lancea (thunb.) DC, Orychophragmus violaceus (L.) O.E. Schulz, Brassica juncea (L.) Czern.et Coss. cv. Luzhousileng, Brassica campestris L. cv. Chuanyou No.8, Brassica napus L cv. Oro, Brassica carinata Braun, Raphanus sativa L. var. raphanistroides Makino and their plantlets indicates that the carbonic anhydrase activity of leaves from both plantlets and fields varies from plant species to plant species, the carbonic anhydrase activity of leaves of Atractylodes lancea (thunb.) DC is the lowest among those plants, and the leaves of all plantlets are lower in carbonic anhydrase activity than the same species of plants from fields. The comparison of the growth rates of those plantlets shows that their relative growth rates are significantly different, plantlets of Atractylodes lancea have the slowest relative growth rate among those plants, and plantlets of Brassica juncea have the greatest relative growth rate. The relationship between RGR of plantlets and their CA activities is a significant linear function. It seems that there was certain correlation between carbonic anhydrase activities of plants and their growth rates. It suggests that in vitro, the greater the carbonic anhydrase activity of plantlet is, the higher its net photosynthetic rate, and the faster its growth rate. Those results offer a foundation to a rational medium choice in plant tissue culture.     

Competitive effects of the invasive shrub,Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings

Invasive plants are often associated with reduced cover of native plants, but rarely has competition between invasives and natives been assessed experimentally. The shrub Lonicera maackii, native to northeastern Asia, has invaded forests and old fields in numerous parts of eastern North America, and is associated with reduced tree seedling density in Ohio forests. A field experiment was conducted to test the effects of established L. maackii on the survival and growth of transplanted native tree species. The experiment examined above-ground competition (by removing L. maackii shoots) and below-ground competition (by trenching around transplanted seedlings). The effects of above-ground competition with L. maackii were generally more important than below-ground competition, though both were detected. Shoot treatment was the key determinant for the survival of all species except P. serotina, whereas trenching only enhanced survival for A. saccharum caged and P. serotina, and only in the shoot removal treatment. For the surviving seedlings, L. maackii shoot removal increased growth of A. saccharum seedlings protected with cages, but actually reduced the growth of unprotected Q. rubra and A. saccharum seedlings, indicating that L. maackii shoots confer some protection from deer browsing. Significant interactions between root and shoot treatment on Q. rubra growth parameters, specifically greatest growth in the shoot present & trenched treatment, is attributed to protection from deer browsing combined with release from below-ground competition. Despite this protective function of L. maackii shoots, the overall effect of this invasive shrub is increased mortality of native tree seedlings, suggesting it impacts the natural regeneration of secondary forests.     

The effect of monochromatic red light on ethylene production in leaves of Impatiens balsamina L. and other species

The effect of red and white light on ethylene production was investigated in several plant species. In most cases light inhibited ethylene production. However, stimulation or no effect were also observed in a few species. In those plants where light inhibited ethylene synthesis, the effect of red light was much stronger than that of white light.Both red and white light inhibited ethylene production in green and etiolated seedlings and green leaves of Impatiens balsamina L. The inhibitory effect of red light was stronger than that of white light and much more pronounced when the plants were pretreated with ACC. The effect of red light could be reversed by far-red light. These results suggest that light affects the ethylene forming enzyme (EFE) activity and that its action is mediated by phytochrome.     

Growth and mineral nutrition of six rapid-cycling Brassica species in response to seawater salinity

The growth of six rapid-cycling lines of Brassica species, B. napus, B. campestris, B. nigra, B. juncea, B. oleracea and B. carinata was inhibited by seawater salinity. Based on the change in dry matter reduction relative to the control at varying concentrations of salts (4, 8 and 12 dS m^-1), the relative salt tolerance of these species was evaluated. B. napus and B. carinata were the most tolerant and most sensitive species, respectively, while the other four species were moderately tolerant. The influence of seawater on the concentrations of 12 elements including macronutrients and micronutrients in the shoots of these Brassica plants was characterized to determine the relationship between nutritional disturbance and relative salt tolerance. It was found that seawater salinity had a significant effect on the concentrations of Ca, Mg, K, Cl, Na and total N in the shoots of these plants but only the change in Ca concentration was significantly related to the relative salt tolerance of these six rapid-cycling Brassica species according to a rank analysis of the data. This finding indicates that Ca may play a regulatory role in the responses of Brassica species to saline conditions.     

Effects of Short-term Red Radiation and Choline Compounds on Cytokinin Content, Chlorophyll Accumulation and Photomorphogenesis in Wheat Seedlings

Effects of choline compounds (2-chloroethyltrimethylammonium chloride and 2-ethyltrimethylammonium chloride) as well as red radiation (R) pulse on the dynamics of cytokinin changes, growth and chlorophyll (a + b) accumulation were studied during the growth and greening of etiolated wheat seedlings (Triticum aestivum L., var. Mironovskaya-808). The seedlings were grown for 120 h in the dark and then exposed for 72 h to white light. Pre-treatment of caryopses with cholines and pre-irradiation of etiolated seedlings with R inhibited elongation of both coleoptile and first leaf; but the same factors accelerated these growth responses when seedlings were exposed to white light. Chlorophyll (Chl) accumulation and the first leaf appearance from coleoptile were accelerated by the pre-treatments as well. Far-red radiation (FR) reversed all effects of R but choline pre-treatment eliminated partly R/FR photoreversibility. Two compounds with high cytokinin activity (tested on a fresh weight basis by the bioassay with Amaranthus caudatus L.) were found in shoots and first leaves. One of them had R_f, UV absorbance spectrum and the biological activity similar to N⁶-(Δ²-isopentenyl)adenosine. Another cytokinin-like substance was not identified with the used standards. Stimulation of greening by R pulse and cholines was accompanied with accelerated accumulation of both cytokinin-like substances. We conclude that the influence of R and cholines on the concentration of substances with cytokinin activities detected in the leaves might be involved in the stimulation of Chl accumulation.     

The adaptation of Dianthus carthusianorum L. (Caryophyllaceae) to growth on a zinc–lead heap in southern Poland

Plants of Dianthus carthusianorum from a calamine (zinc–lead) waste heap and from unpolluted stands were compared in the field and under controlled laboratory conditions. It was found that the waste-heap plants differed significantly from those in the normal population in respect to the following morphological traits: lower weight of aerial parts, shorter and narrower leaves, smaller number of leaves per plant. In combination with shorter, less numerous shoots, these features reduce the transpiration area of the plants. The general habit (predominance of forms with short and trailing shoots) of the waste-heap population points to adaptation to a xeric environment. Under controlled conditions all of the above traits were maintained through three successive generations. They are thus genetically controlled. Root tolerance tests showed that the waste-heap plants had higher tolerance to zinc and lead. These results indicate that strong selection processes have generated a clear ecotypical differentiation for heavy metal tolerance and drought tolerance in a zinc–lead-rich waste-heap population of D. carthusianorum (variety).     

Shade adaptation and shade tolerance in saplings of three Acer species from eastern North America

Summary Saplings of three, co-occurring maple species in a mature maple-beech forest differed in a suite of structural and physiological characters that separated the canopy species, Acer, saccharum, from the two subcanopy species, A. pensylvanicum and A. spicatum. Acer saccharum had both more dense wood and tougher and heavier but thinner leaves than the subcanopy species. Acer pensylvanicum had the largest, lightest leaves with high stomatal density and its canopy architecture was the most effective in terms of leaf display for light interception. Acer spicatum had weaker wood similar to that of A. pensylvanicum but also small, soft and relatively poorly displayed leaves. Both subcanopy species maintained marginally higher average rates of photosynthesis over the growing season in the understory environment. We consider juvenile A. saccharum only shade-tolerant, capable of persisting through long periods in the closed canopy until a gap occurs but not specifically adapted to the understory environment. Juvenile A. sacchrum appears to be constrained functionally by the requirements set by the canopy environment that adults will occupy. Characters such as high wood density are already expressed in the understory sapling; this investment in denser wood slows the growth of saplings, but is necessary for structural reasons in the adult. Juvenile A. saccaharum have morphological and photosynthetic characters better suited to gas exchange and extension growth under the increased photon flux densities in large forest gaps, characteristics that will also be advantageous in the sunlit canopy environment of adults.Both subcanopy maples appear to be more truly shade-adapted, although in somewhat different ways. Acer pensylvanicum has characteristics that enhance the potential for capture and utilization of sunflecks and is able to sustain higher growth rates than A. saccharum in the shaded subcanopy environment. Acer spicatum shares some shade-adapted features with A. pensylvanicum, and its habit of lateral spread through stem layering may confer an additional advantage in foraging for small light gaps.     

Chlorogenic acid as an antiherbivore defence of willows against leaf beetles

In the leaves of 13 Finnish willow species, the content of a phenolic, chlorogenic acid, was found to vary from 0 up to 18 mg g^–1 D.W. Effects of pure chlorogenic acid on insect feeding behaviour were tested using four common leaf beetle species which are in the field mainly found on willows with low-chlorogenic acid leaves. One species, Lochmaea capreae L., was invariably deterred by pure chlorogenic acid applied in naturally occurring concentrations on the willow leaves. Accordingly, in 2-choice laboratory feeding trials L. capreae was found to prefer low-chlorogenic acid leaves of four willow species over high-chlorogenic acid leaves of Salix pentandra L. and S. myrsinifolia Salisb. When presented on the leaves of S. phylicifolia L, pure chlorogenic acid inhibited also the feeding by Phratora polaris Sp.-Schn. Instead, chlorogenic acid had no significant effect on Ph. polaris when it was presented on the leaves of another willow S. cinerea L. In laboratory, Ph. polaris did not show general preference for willow species with low chlorogenic acid content in their leaves. Thus, the response of Ph. polaris to chlorogenic acid seems to depend on the plant species. Apparently variation in other traits such as leaf hairyness may easily override the potential effect of chlorogenic acid content on Ph. polaris. To two other leaf beetle species, Galerucella lineola F. and Plagiodera versicolora Laich., chlorogenic acid is an ineffective deterrent even at unnaturally high concentrations. In laboratory, G. lineola and P. versicolora did not prefer willows with low chlorogenic acid content in their leaves. Thus, among four studied leaf beetle species, only L. capreae seems to be clearly affected by this phenolic. Therefore, overall importance of chlorogenic acid as a defence against willow-feeding leaf beetles appears to be very limited.     

Sucrose and light effects on in vitro cultures of potato,chokecherry and saskatoon berry during low temperature storage

Cultures of potato (Solanum tuberosum) cv. Atlantic, chokecherry (Prunus virginiana L.) cv. Garrington and saskatoon berry (Amelancher alnifolia Nutt.) cv. Northline grown in vitro for 3 weeks at 24/22 °C, 16-h photoperiod, 150 μmol m⁻² s⁻¹ photosynthetic photon flux density (PPFD) mixed fluorescent/incandescent light were stored for 6, 9 and 12 weeks at 4 °C under 0 (darkness) and 3 μmol m⁻² s⁻¹ PPFD (690 nm red light continuous illumination). Growth regulators free MSMO medium either with or without 30 g l⁻¹ sucrose was used to store the cultures. All cultures retained capacity to re-grow after storage. Tested factors, sucrose, light and the length of the storage period had an impact on shoot quality and re-growth capacity of the cultures. For either light treatment sucrose was essential for the low temperature maintenance of vigorous stock plants of potato, if stored for over 6 weeks. Chokecherry and saskatoon cultures stored well without sucrose; although chokecherry benefited from sucrose in the storage medium when the stock cultures were kept at the low temperature for 12 weeks. Low light significantly improved quality of the stored potato cultures, but had very little effect on both chokecherry and saskatoon berry cultures. The woody plant cultures grew during storage, and the longer the stock plants were stored, the more vigorous cultures they generated. The results indicate that growers can successfully use their existing facilities, small refrigerators and coolers with low light intensity, set at 4 °C, for short term storage of potato, chokecherry and saskatoon berry cultures. The potato cultures, which are known to be sensitive to prolonged low temperature storage, should be frequently monitored and subcultured as required. On the other hand, the woody plant stock cultures do not require any special attention when kept at 4 °C and re-grow the most vigorous shoots if stored for at least 12 weeks. This revised version was published online in August 2006 with corrections to the Cover Date.     

Zinc phytoavailability after remediation in soils contaminated by sphalerite-containing pyritic sludge

Zinc can be toxic to plants growing on soils in areas of the Guadiamar River valley (southwestern Spain) affected by the spillage of pyritic sludge in April 1998. The shoots and the soil around the roots of two wild plants (viz. Amaranthus blitoides S. Wats., November 2000; and Xanthium strumarium L., June 2001) growing in the sludge-affected areas were sampled with the purpose of relating Zn phytoavailability to soil properties. The soils were calcareous and non-calcareous Entisols and Inceptisols which, after remediation, contained ploughed-in residual sludge and unevenly distributed industrial lime. Chemical extracts from the soils suggested that much of the sphalerite (ZnS) originally present in the sludge had weathered and Zn was partly bound to carbonates and Fe oxides, the total Zn concentration ranging from 37 to 2407 mg kg ^–1. To identify the soil properties that influenced Zn phytoavailability under controlled conditions, the soil samples (n=63) were homogenized and oilseed rape (Brassica napus var. Karola) was pot-grown on them in a growth chamber. The concentrations of Zn in oilseed rape shoots and roots were below phytotoxic levels, with mean ± standard deviation values of 142 ± 128 and 244 ± 328 mg kg ^–1 dry matter, respectively. Citrate/bicarbonate-extractable Zn in soil (Zn _cb) was found to be the best predictor for the Zn concentration in both shoots and roots. Also, the Zn _cb/Olsen P ratio exhibited a high predictive power for Zn in shoots as the likely result of the Zn-P interaction in soil. The shoot Zn concentration in the wild plants, generally lay below phytotoxic levels (the mean ± standard deviation values were 261 ± 255 and 200 ± 228 mg kg ^–1 dry matter for Amaranthus blitoides and Xanthium strumarium, respectively) and was not correlated with soil properties – by exception, there was slight correlation between the Zn concentration in Amaranthus blitoides and Zn _cb/Olsen P. Such a lack of correlation can be ascribed to the local small-scale soil heterogeneity caused by remediation practices. The Zn concentration in wild plants growing on CaCO ₃-poor soils was weakly correlated with Zn _cb/Olsen P; no similar correlation was found in CaCO ₃-rich soils, however. The wild plants growing on CaCO ₃-poor and CaCO ₃-rich soils differed little in Zn concentration; this suggests that further addition of lime to reduce Zn phytoavailability may be unjustified.     

草甘膦对入侵植物加拿大一枝黄花和伴生植物白茅光合特性的影响

入侵植物加拿大一枝黄花(Solidago canadensis)给许多地区带来了较大危害,目前常采用化学防除法进行防除,但除草剂防治入侵植物的同时难免会影响土著植物的生长。为探讨草甘膦对入侵植物与本地植物光合特性的影响,以加拿大一枝黄花及其伴生种白茅(Imperata cylindrica)为研究对象,采用盆栽控制试验方法,研究不同浓度草甘膦处理21后单种、混种加拿大一枝黄花和白茅的生长特征及光响应过程。结果表明:1)草甘膦显著抑制两种植物的生长。随处理浓度升高,加拿大一枝黄花的株高增长量不断减小、叶片枯萎率不断增加;白茅的分蘖死亡率、叶片枯萎率不断升高。白茅对草甘膦较敏感,0.6mL/L浓度下白茅先失绿,1.2mL/L下其分蘖死亡率、叶片枯萎率均超50%;1.8mL/L下加拿大一枝黄花叶片枯萎率超50%。施药后与单种相比,混种加拿大一枝黄花株高增长略快、叶片枯萎率略低,混种白茅分蘖死亡率及叶片枯萎率均较低,但单、混种之间差异不显著。种间关系显著影响白茅的分蘖数。2)随处理浓度递增,加拿大一枝黄花和白茅叶片净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)均不断降低,白茅下降更快。两个物种胞间CO_2浓度(C_i)的变化不同,随着浓度升高,单种加拿大一枝黄花C_i先下降而后上升,而混种时的C_i则不断下降;单、混种白茅C_i均上升。3)草甘膦显著影响加拿大一枝黄花和白茅最大净光合速率(P_(nmax))、光饱和点(LSP)和光补偿点(LCP);对两个物种暗呼吸速率(R_d)的影响不显著,对加拿大一枝黄花表观量子效率(AQY)的影响同样不显著,但显著影响白茅AQY。种植方式显著影响两个物种P_(nmax)、LSP以及白茅R_d和AQY。0.6mL/L草甘膦对混种加拿大一枝黄花和白茅P_(nmax)的影响要大于对单种植株的影响,随处理浓度上升,对不同种植方式下两种植物P_(nmax)的影响趋近。与本地种白茅相比,入侵植物加拿大一枝黄花具有更高的光合速率和生长速率;草甘膦显著降低两个物种的生长和光合作用,白茅对草甘膦处理更敏感。     

Transgenic peach plants (<Emphasis Type="Italic">Prunus persica</Emphasis> L.) produced by genetic transformation of embryo sections using the green fluorescent protein (GFP) as an <Emphasis Type="Italic">in vivo</Emphasis> marker

The main obstacle to genetic engineering of fruit tree species is the regeneration of transformed plantlets. Transformation events in peach (Prunus persica L.) have been reported using particle bombardment or Agrobacteriummediated transformation of immature embryos. However, the regeneration of plants from transgenic tissues is still difficult and the recovery of non-chimeric plants has not been reported to date. In this paper we describe an efficient, reliable transformation and regeneration system to produce transgenic peach plants using embryo sections of mature seeds as starting material. This represents an important advantage due to the availability of such material throughout the year. A. tumefaciens strain C58 (pMP90) containing the binary plasmid pBin19 was used as vector system for transformation. We used the Nospro-nptII-Noster cassette as a selectable marker and the CaMV35Spro-sgfp-CaMV35Ster cassette as a vital reporter gene coding for an improved version of the green fluorescent protein (sGFP). In vitro cultured embryo sections were Agrobacterium-cocultivated and, after selection, transgenic shoots were regenerated. Shoots that survived exhibited high-level of sGFP expression mainly visible in the young leaves of the apex. In vivo monitoring of GFP expression permitted an early, rapid and easy discrimination of both transgenic and escape buds. After elimination of escapes, transgenic shoots were rooted in vitro and the recovered plantlets were screened using PCR amplification. Southern analysis confirmed stable genomic integration of the sgfp transgene. The high levels of GFP expression were also maintained in the second generation of transgenic peach plants.     

The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

CO₂ exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA₃) at the concentration of 25 g/1 (GA-plants), and then grown under 17 W/m² blue light (B-plants) or 11 W/m² red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA₃ suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.     

Effects of simulated herbivory in three old field Compositae with different inflorescence architectures

The effects of simulated herbivory (early or late defoliation and cutting of the flowering shoot) on the growth and reproduction of three species of monocarpic composite forbs (Crepis pulchra, Picris hieracioides and C. foetida) with different inflorescence architectures were studied in experimental plots. For the three species studied, early defoliation had no significant effect on subsequent growth. In contrast, late defoliation, occurring at the start of the season of drought, had a negative effect on growth and reproduction in the two Crepis species, particularly C. foetida, but had less effect on P. hieracioides. Sexual biomass was more clearly affected by late defoliation than was vegetative biomass, although the effects differed markedly among species possibly as a result of differences in phenology. Clipping the flowering shoot removed about 3 times less biomass than late defoliation and had little effect on vegetative biomass. It had much greater effects on the sexual biomass in P. hieracioides and C. pulchra, and resulted in the production of many shoots sprouting from the rosette, allowing the treated plants to regain a vegetative biomass close to that of control plants. Clipping did however lead to the production of shorter shoots and a reduction in the number of capitula formed. In C. foetida, much branching occurred even when the main shoot was not cut; the architecture of individual plants was therefore only slightly changed by clipping the apical bud and the sexual biomass of this species was not affected by ablation of the flowering shoot. Overcompensation was found in only two families of C. pulchra for vegetative biomass. No over-compensation was found for sexual biomass, despite an increase in the number of flowering shoots in C. pulchra and P. hieracioides following clipping. However situations close to compensation for the vegetative biomass in the three species and in P. hieracioides for the sexual biomass were recorded. The response of the three study species to simulated herbivory were related to their architecture and to the time of defoliation.