Amino acids play a central role in aphid-plant interactions. They are essential components of plant primary metabolism, function as precursors for the synthesis of defense-related specialized metabolites, and are major growth-limiting nutrients for aphids. To quantify changes in the free amino acid content of pepper (Capsicum annuum L.) leaves in response to green peach aphid (Myzus persicae Sulzer) feeding, plants were infested with a low (20 aphids/plant) or a high (200 aphids/plant) aphid density in time-course experiments ranging from 3 hours to 7 days. A parallel experiment was conducted with pepper plants that had been subjected to water stress. Factor Analysis of Mixed Data revealed a significant interaction of time x density in the free amino acid response of aphid-infested leaves. At low aphid density, M. persicae did not trigger a strong response in pepper leaves. Conversely, at high density, a large increase in total free amino acid content was observed and specific amino acids peaked at different times post-infestation. Comparing aphid-infested with water-stressed plants, most of the observed differences were quantitative. In particular, proline and hydroxyproline accumulated dramatically in response to water stress, but not in response to aphid infestation. Some additional differences and commonalities between the two stress treatments are discussed.

Animals eat different foods in proportions that yield a more favorable balance of nutrients. Despite known examples of these behaviors across different taxa, their ecological and physiological benefits remain unclear. We identified a surprising dietary shift that confers ecophysiological advantages in a dung beetle species. Thorectes lusitanicus, a Mediterranean ecosystem species adapted to eat semi-dry and dry dung (dung-fiber consumers) is also actively attracted to oak acorns, consuming and burying them. Acorn consumption appears to confer potential advantages over beetles that do not eat acorns: acorn-fed beetles showed important improvements in the fat body mass, hemolymph composition, and ovary development. During the reproductive period (October-December) beetles incorporating acorns into their diets should have greatly improved resistance to low-temperature conditions and improved ovarian development. In addition to enhancing the understanding of the relevance of dietary plasticity to the evolutionary biology of dung beetles, these results open the way to a more general understanding of the ecophysiological implications of differential dietary selection on the ecology and biogeography of these insects.

We have compared the ethylene and polyamine metabolism of senescing flowers from two cultivars of carnation (Dianthus caryophyllus L.), one showing climacteric (`Arthur') and the other non climacteric behavior (`Killer'). `Arthur' carnations showed the first symptoms of senescence at day 7, coinciding with maximum ethylene and CO <sub>2</sub> production, a peak in the ethylene-forming enzyme (EFE) activity, and a 7-fold increase in free ACC content in respect to the initial value. In `Killer' carnations, however, onset of senescence was 15 days after harvest, and no ethylene or CO ₂ peak was detected. The lack of ethylene production was due to a constantly low level of free ACC and a low EFE activity. Free polyamine distribution was similar in the two cultivars at the preclimacteric stage, with the spermidine content being about three times that of putrescine. But as senescence progressed, this situation was reversed in `Arthur' carnation, with a predominance of putrescine during the senescence, while it was maintained in `Killer', with no significant changes during senescence. No free spermine was found at any stage of senescence in either cultivar. Thus, a correlation exists between ACC level, distribution of polyamides, and longevity of cut carnation flowers. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).