Characterization of the Key Aroma Compounds in Fresh Leaves of Garden Sage (Salvia officinalis L.) by Means of the Sensomics Approach: Influence of Drying and Storage and Comparison with Commercial Dried Sage

The overall aroma profiles of commercial dried sage differ significantly from the profile of macerated fresh leaves. To clarify changes in the key aroma compounds, first an aroma extract dilution analysis was applied on an extract/distillate prepared from the fresh leaves of Italian garden sage cultivated in a green house in Germany. Among the 39 aroma active compounds characterized, (Z)-3-hexenal, 1,8-cineol, borneol and eugenol showed the highest flavor dilution (FD) factors. Odorants identified with FD factors between 64 and 8192 were quantitated to calculate odor activity values (OAV; ratio of concentration to odor threshold). The highest OAVs were determined for myrcene, (Z)-3-hexenal, (1S,2R,4S)-borneol and 1,8-cineol. A mixture of 22 key reference aroma compounds in the same concentrations as determined in the fresh sage leaves successfully mimicked the overall aroma profile of the spice. To get insight into changes induced by drying, all key aroma compounds were quantitated in sage leaves from the same plant by drying at 50 °C. While all monoterpenes remained nearly unchanged during drying, in particular highly volatile compounds such as dimethyl sulfide or 2- and 3-methylbutanal were decreased. Almost a total loss occurred for 3-(methylthio)propanal, phenylacetaldehyde, and (Z)-3-hexenal. By contrast, storage of the dried leaves for 12 months at room temperature in the dark did not much effect the concentrations of selected key odorants, thus indicating that drying is the most important factor for the changes in aroma compounds. Sensory profiling of six commercial sage samples showed different aroma profiles, which also clearly differed from the profile of the sage dried in lab scale, which was rated to elicit the most typical sage aroma. In addition, the concentrations of selected key aroma compounds as well as the total amount of volatiles were clearly lower in all commercial samples.

SpitWorm, a Herbivorous Robot: Mechanical Leaf Wounding with Simultaneous Application of Salivary Components

Induction of jasmonate-mediated plant defense against insect herbivory is initiated by a combination of both mechanical wounding and chemical factors. In order to study both effects independently on plant defense induction, SpitWorm, a computer-controlled device which mimics the damage pattern of feeding insect larvae on leaves and, in addition, can apply oral secretions (OS) or other solutions to the 'biting site' during 'feeding,' was developed and evaluated. The amount of OS left by a Spodoptera littoralis larva during feeding on Phaseolus lunatus (lima bean) leaves was estimated by combining larval foregut volume, biting rate, and quantification of a fluorescent dye injected into the larvae's foregut prior to feeding. For providing OS amounts by SpitWorm equivalent to larval feeding, dilution and delivery rate were optimized. The effectiveness of SpitWorm was tested by comparing volatile organic compounds (VOC) emissions of P. lunatus leaves treated with either SpitWorm, MecWorm, or S. littoralis larvae. Identification and quantification of emitted VOCs revealed that SpitWorm induced a volatile bouquet that is qualitatively and quantitatively similar to herbivory. Additionally, RT-qPCR of four jasmonic acid responsive genes showed that SpitWorm, in contrast to MecWorm, induces the same regulation pattern as insect feeding. Thus, SpitWorm mimics insect herbivory almost identically to real larvae feeding.

Synthesis of 6-substituted 1-oxoindanoyl isoleucine conjugates and modeling studies with the COI1-JAZ co-receptor complex of lima bean

The conjugates of 6-substituted 1-oxoindanoyl carboxylic acids with L-isoleucine are mimics of the plant hormone (+)-7-iso-JA-L-Ile (3) that controls and regulates secondary metabolism and stress responses. In order to generate ligands that can be used as hormone-like compounds possessing different biological activities, an efficient and short synthesis of 6-bromo-1-oxoindane-4-carboxylic acid opens a general route to 6-Br-1-oxoindanoyl L-isoleucine conjugate (Br-In-L-Ile) (9a) as a key intermediate for several bioactive 6-halogen-In-L-Ile analogs (7a, 8a, 10a). The 6-ethynyl-In-L-Ile analog (11a) might be a valuable tool to localize macromolecular receptor molecules by click-chemistry. The activities of In-Ile derivatives were evaluated by assays inducing the release of volatile organic compounds (VOCs) in lima bean (Phaseolus lunatus). Each compound showed slightly different VOC induction patterns. To correlate such differences with structural features, modeling studies of In-Ile derivatives with COI-JAZa/b/c co-receptors of P. lunatus were performed. The modeling profits from the rigid backbone of the 1-oxoindanonoyl conjugates, which allows only well defined interactions with the receptor complex.

Poplar extrafloral nectaries: two types, two strategies of indirect defenses against herbivores

Many plant species grow extrafloral nectaries and produce nectar to attract carnivore arthropods as defenders against herbivores. Two nectary types that evolved with Populus trichocarpa (Ptr) and Populus tremula × Populus tremuloides (Ptt) were studied from their ecology down to the genes and molecules. Both nectary types strongly differ in morphology, nectar composition and mode of secretion, and defense strategy. In Ptt, nectaries represent constitutive organs with continuous merocrine nectar flow, nectary appearance, nectar production, and flow. In contrast, Ptr nectaries were found to be holocrine and inducible. Neither mechanical wounding nor the application of jasmonic acid, but infestation by sucking insects, induced Ptr nectar secretion. Thus, nectaries of Ptr and Ptt seem to answer the same threat by the use of different mechanisms.

Silencing jasmonate signalling and jasmonate-mediated defences reveals different survival strategies between two Nicotiana attenuata accessions

To determine the impact of genotypic variation in secondary metabolite production on antiherbivore resistance and plant fitness, we genetically silenced biosynthetic genes for nicotine, trypsin proteinase inhibitors (TPI), and jasmonate (JA) production in two accessions of Nicotiana attenuata: one from Utah (UT) which responds to herbivory with JA-induced nicotine and TPI production, and one from Arizona (AZ) which is TPI-deficient but also produces JA-induced nicotine. Transient silencing of JA biosynthesis increased Manduca sexta larval growth on wild type (WT) plants of both accessions, but not on TPI-deficient UT or nicotine-deficient AZ lines, demonstrating that JA-mediated resistance to M. sexta requires TPIs in the UT and nicotine in the naturally TPI-deficient AZ accession. When transplanted into a native UT population, AZ and UT plants, rendered equally able or unable to produce nicotine and TPIs by stable transformation, received significantly different levels of herbivory. Both accessions differed in their resistance depending on the type of herbivores: resistance to rare, voracious herbivores (Saltatoria and Mammalia) was greater in AZ than UT lines, and dependent on nicotine production, while resistance to small, abundant herbivores (Coleoptera and Thysanoptera) was greater in UT lines, and dependent on TPI production. AZ lines produced more flowers and seed capsules than UT lines independently of TPI production costs. This fitness advantage was lost when accessions did not produce nicotine. We conclude that these two accessions have developed different survival strategies and thus differ in the cost-benefit functions of their JA-mediated defences.