Partitioning the Relative Contributions of Inorganic Plant Composition and Soil Characteristics to the Quality of Helichrysum italicum subsp. italicum (Roth) G. Don fil. Essential Oil

Composition of Helichrysum italicum subsp. italicum essential oil showed chemical variability according to vegetation cycle, environment, and geographic origins. In the present work, 48 individuals of this plant at different development stages and the corresponding root soils were sampled: i) 28 volatile components were identified and measured in essential oil by using GC and GC/MS; ii) ten elements from plants and soils have been estimated using colorimetry in continuous flux, flame atomic absorption spectrometry, or emission spectrometry (FAAS/FAES); iii) texture and acidity (real and potential) of soil samples were also reported. Relationships between the essential‐oil composition, the inorganic plant composition, and the soil characteristics (inorganic composition, texture, and acidity) have been established using multivariate analysis such as Principal Component Analysis (PCA) and partial Redundancy Analysis (RDA). This study demonstrates a high level of intraspecific differences in oil composition due to environmental factors and, more particularly, soil characteristics.     

The contact separation force of the fruit burrs from five plant taxa dispersing by epizoochory

Abstract

Many plant diaspores dispersing by epizoochory bear special structures, such as burrs with hooks, which are responsible for the mechanical interlocking with animal fur or feathers. The number, dimensions and distribution of the interlocking structures on the diaspore can strongly vary depending on the plant species. In this study, to evaluate the interlocking ability of distantly related plants having different diaspore morphologies, the contact separation force (CSF) of single burrs was measured in Arctium lappa, Bidens tripartita, Desmodium sp., Uncinia uncinata and Xanthium strumarium. This force is required to separate the single burr from interlocking with the loop. Usually in the experiment, the burr was broken after separation. The CSFs differed significantly, ranging from 7.07 to 820.94?mN, among the five taxa studied. Six morphometrical variables were measured from each burr and the correlations between the CSFs and these morphometrical variables were analyzed. We have shown that (1) the burr length, (2) the diameter of the distal part and (3) the hook span had significant influences on the CSF. The comparison between the CSF and the fruit weight indicated that single burrs of all taxa studied could bear at least 100-fold weight of the diaspore.     

Biological Control and Use of Adjuvants against Multiple Seeded Cocklebur (Xanthium strumarium) in Comparison with Several Other Cocklebur Types

Common cocklebur has several biotypes including multiple seeded cocklebur (MSC), NCC-TX, and NCC-MS. Alternaria helianthi applied at 2.5×10⁴ conidia mL^-1 in a 50% micro-emulsion of unrefined corn oil (MESUCO) or 0.2% Silwet L 77 caused 60-75% mortality on NCC-TX and MSC. Increasing the conidial concentration to 5×10⁴ mL^-1 increased mortality to 100% on MSC and NCC-TX, and 75% on NCC-MS. At 10×10⁴ conidia mL^-1, A. helianthi caused 100% mortality in all three biotypes. No mortality occurred in any biotype at inoculation rates of 2.5 and 5×10⁴ conidia mL^-1 when applied in water. Increasing the dew period from 0 to 12 h increased mortality from 0 to 100% on all three biotypes at a rate of 2.5×10⁴ conidia mL^-1 in Silwet and MESUCO. MSC appears to be the most sensitive biotype.     

Sesquiterpene lactone stereochemistry influences herbivore resistance and plant fitness in the field

Background and Aims

Stereochemical variation is widely known to influence the bioactivity of compounds in the context of pharmacology and pesticide science, but our understanding of its importance in mediating plant–herbivore interactions is limited, particularly in field settings. Similarly, sesquiterpene lactones are a broadly distributed class of putative defensive compounds, but little is known about their activities in the field.

Methods

Natural variation in sesquiterpene lactones of the common cocklebur, Xanthium strumarium (Asteraceae), was used in conjunction with a series of common garden experiments to examine relationships between stereochemical variation, herbivore damage and plant fitness.

Key Results

The stereochemistry of sesquiterpene lactone ring junctions helped to explain variation in plant herbivore resistance. Plants producing cis-fused sesquiterpene lactones experienced significantly higher damage than plants producing trans-fused sesquiterpene lactones. Experiments manipulating herbivore damage above and below ambient levels found that herbivore damage was negatively correlated with plant fitness. This pattern translated into significant fitness differences between chemotypes under ambient levels of herbivore attack, but not when attack was experimentally reduced via pesticide.

Conclusions

To our knowledge, this work represents only the second study to examine sesquiterpene lactones as defensive compounds in the field, the first to document herbivore-mediated natural selection on sesquiterpene lactone variation and the first to investigate the ecological significance of the stereochemistry of the lactone ring junction. The results indicate that subtle differences in stereochemistry may be a major determinant of the protective role of secondary metabolites and thus of plant fitness. As stereochemical variation is widespread in many groups of secondary metabolites, these findings suggest the possibility of dynamic evolutionary histories within the Asteraceae and other plant families showing extensive stereochemical variation.     

The role of weed invasion in controlling sand dune reactivation in abandoned fields in semi-arid Inner Mongolia, China

The growth of crops and invading weeds were examined at six sites under different cultivation conditions in semi-arid Inner Mongolia, where sand dune reactivation has been controlled by weed invasion. The soil moisture content was not sufficient for crop growth in over-cultivated farmland. The shortage of moisture in the soil suppresses the growth of both crops and weeds. Accordingly, farmers carry out weeding to maintain better soil moisture conditions for crop growth. Over-cultivated farmland is often abandoned when the crop yield decreases to an economically unprofitable level. If weed vegetation before abandonment remains, it becomes a core of vegetation expansion and recovers the entire soil surface. While weedy vegetation is lacking or has been grazed by livestock, sand dune reactivation occurs.     

蒙古苍耳核型分析

首次对蒙古苍耳染色体数目及核型进行了研究,结果表明,染色体数目２ｎ＝３６,核型公式为Ｋ（２ｎ）＝３６＝２６ｍ＋２ｍ（ｓａｔ）＋８ｓｍ．与苍耳的核型进行比较,认为蒙古苍耳的核型比苍耳的原始。     

Modification of phenotypic and functional gender in the monoecious Arum italicum (Araceae)

Other than studies on sex-labile Arisaema species, studies of gender patterns in Araceae are scarce. The modification of phenotypic and functional gender was investigated in three populations of the monoecious Arum italicum Miller. The probability of reproduction and the number of inflorescences produced increased with plant size, and flower number (total, male, staminodes, female, pistillodes) increased with both plant and inflorescence sizes. However, plant and inflorescence sizes were poor predictors of floral sex ratio (female to male flower ratio). In contrast, change in floral sex ratio towards increasing femaleness was found among inflorescences sequentially produced by a plant. This change could not be explained by either a decrease in inflorescence size or a change in the mating environment. Differences in functional gender did not appear to be related to plant size or stage in the flowering period. Instead, different patterns of functional gender were found between plants with different number of inflorescences. Multi-inflorescence plants showed a functional gender around 0.5, while plants with one inflorescence showed a more extreme functional gender (either male, female, or functionally sterile). Sex of flowers in this species did not seem to exhibit a phenotypic trade-off.     

Leaf nitrogen distribution in relation to leaf age and photon flux density in dominant and subordinate plants in dense stands of a dicotyledonous herb

We studied the effects of photon flux density (PFD) and leaf position, a measure of developmental age, on the distribution of nitrogen content per unit leaf area (N _area) in plants of different heights, in dense stands grown at two nitrogen availabilities and in solitary plants of the erect dicotyledonous herb Xanthium canadense. Taller more dominant plants received higher PFD levels and experienced a larger difference in relative PFD between their youngest and oldest leaves than shorter subordinate plants in the stands. Differences in PFD between leaves of solitary plants were assumed to be minimal and differences in leaf traits, found for these plants, could thus be mainly attributed to an effect of leaf position. In the solitary plants, N _area decreased with leaf position while in the plants from the stands it decreased with decreasing relative PFD, indicating both factors to be important in determining the distribution of N _area. Due to the effect of leaf position on N _area, leaves of subordinate plants had a higher N _area than older leaves of dominant plants which were at the same height or slightly higher in the canopy. Consequently, the N _area distribution patterns of individual plants plotted as a function of relative PFD were steeper, and probably closer to the optimal distribution which maximizes photosynthesis, than the average distribution in the stand. Leaves of subordinate plants had a lower mass per unit area (LMA) than those of dominant plants. In the dominant plants, LMA decreased with decreasing relative PFD (and with leaf position) while in the subordinate plants it increased. This surprising result for the subordinate plants can be explained by the fact that, during the course of a growing season, these plants became increasingly shaded and newer leaves were thus formed at progressively lower light availability. This indicates that LMA was strongly determined by the relative PFD at leaf formation and to a lesser extent by the current PFD. Leaf N content per unit mass (N _mass) was strongly determined by leaf position independent of relative PFD. This indicates that N _mass is strongly ontogenetically related to the leaf-aging process while changes in N _area, in response to PFD, were regulated through changes in LMA. Received: 11 May 1997 / Accepted: 9 September 1997     

Use of the Weibull model to describe inactivation of dry‐harvested conidia of different Penicillium species by ethanol vapours

Aims: This study aimed at modelling the effect of ethanol vapours, in the range 0·7–7·5 kPa, on the inactivation of dry‐harvested conidia of Penicillium chrysogenum, Penicillium digitatum and Penicillium italicum. Methods and Results: Survival curves were modelled by a Weibull model: log (N/N₀) = ?1/2·303 (t/α)^β. The shape parameter β was different from one in all cases, indicating that the classical first‐order kinetics approach is the exception rather than the rule. Survival curves exhibited upward concavity (β < 1) with the notable exception of P. chrysogenum at ethanol vapour pressures 0·7 and 1·5 kPa. The scale parameter α (h) varied greatly depending on the ethanol vapour pressure and on the species. Conclusions: For safety reasons, it is recommended not to exceed an ethanol vapour pressure of 3·3 kPa. At 2·8 kPa, more than 4 log₁₀ reductions in viable conidia were achieved for all the species after 24‐h exposure. Significance and Impact of the Study: Ethanol has GRAS status in the USA and represents an interesting alternative to fungicides. The effectiveness of ethanol vapours to inactivate dry‐harvested conidia of some Penicillium was demonstrated in this study.     

Effects of α-aminoisobutyric acid and D- and L-amino acids on ethylene production and content of 1-aminocyclopropane-1-carboxylic acid in cotyledonary segments of cocklebur seeds

In the cotyuledonary tissue of cocklebur ( Xanthium pennsylvanicum Wallr.) seeds, AIB (α- aminoisobutyric acid) inhibited not only the endogenous ethylene production but also the ACC (1-aminocyclopropane-1-carboxylic acid)-dependent and IAA-induced ones. The inhibition of the endogenous ethylene production by AIB was accompanied by the accumulation of ACC in the tissue. Thus AIB may act as a competitive inhibitor of the conversion of ACC to ethylene and thereby inhibit ethylene production. The promotion of ethylene production by D-isomers of some amino acids, such as phenylalanine, valine, threonine and methionine was accompained by and increse in the ACC content, the degree of which was similar to that of the stimulation of ethylene production. Moreover, these D-amino acids stimulated the conversion of exogenously applied ACC to ethylene. The corresponding L-isomers failed to produce these effects. It seems likely that D-amino-acid-stimulated ethylene production results from the increases of both the biosynthesis and degradation of ACC. Only for tryptophan did both D- and L-isomers cause an increase in ethylene production and in ACC content in the segments. The mechanism of stimulation of ethylene production by the tryptophen isomers is possibly due to their conversion to IAA in the cotyledonary tissue.