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  • 1
    ISSN: 1573-1561
    Keywords: Phytoecdysteroid ; phytohormone ; phytosterol ; plant defense ; turnover ; Spinacia oleracea ; 20-hydroxyecdysone ; terpenoid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Using short (8-day) and long-term (28-day) experiments, we examined the stability of 20-hydroxyecdysone (20E) and the dominant phytosterols synthesized from a pulse of [2-14C]mevalonic acid ([14C]MVA) in hydroponically grown spinach (Spinacia oleracea). In the short-term experiment, plant dry mass and shoot 20E pools steadily increased. Root uptake of [14C]MVA resulted in the stable incorporation of 14C radiolabel into whole plant 20E pools, with no significant changes over time. Levels of free and saponifiable phytosterols increased in the shoots while 14C-labeled shoot phytosterols remained constant. Unexpectedly, both 14C-labeled and unlabeled pools of root phytosterols decreased over time. In the long-term experiment, plant dry mass and shoot 20E levels increased over time, while total 14C-labeled 20E pools remained constant. Both root and shoot phytosterol pools increased over time while the 14C incorporation in these pools remained constant. Together these experiments indicate that 20E in spinach is metabolically stabile and thus shares this characteristic with plant terpenoids of known defensive function. While little is known about phytosterol turnover in plants, our results suggest that phytosterols can indeed exist in a very dynamic state but may also be stable over time.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-1561
    Keywords: Bursera ; Burseraceae ; Blepharida ; Chrysomelidae ; monoterpenes ; chemical defense ; fecal shield ; insect defense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The genus Bursera produces resin stored in canals in the leaf. When leaves are damaged, some, but not all, species release abundant resin. Species of Blepharida are specialized herbivores of Bursera, and they exhibit variation in their counterdefensive behavior. Species feeding on resin-releasing plants cut the leaf veins before feeding, which often makes them more prone to predation. They also adorn their backs with their feces and may regurgitate and release an anal secretion when attacked or disturbed by predators. Species that feed on Bursera species that release no fluids do not sever the leaf veins prior to feeding, and they do not carry their feces on their backs. Instead, they face their predators, raise their heads in a "boxing-like" display, and rapidly swing their abdomens from side to side. We performed a comparative chemical analysis of the compounds found in Bursera schlechtendalii, a species that releases abundant resins, and B. biflora, a species that does not. We also analyzed the frass, enteric discharges, and larvae of the two species of Blepharida that feed on each of these plants. The compounds found in the body, feces, and discharges of the Blepharida species that adorns itself with feces match the chemical mixture of its host plant, suggesting that this beetle species can compensate its higher risk of predation by using the compounds present in the plant for defense. The chemical mixture of B. biflora is more complex and does not match the compounds found in the body or frass of its beetle herbivore, suggesting that the defensive strategy of this insect is behavioral and does not rely on its host's constituents.
    Type of Medium: Electronic Resource
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