Prickly poppies can get pricklier: ontogenetic patterns in the induction of physical defense traits.

Plant ontogeny is a common source of variation in defense and herbivory. Yet, few studies have investigated how the induction of physical defense traits changes across plant ontogeny. Physical defense traits are costly to produce, and thus, it was predicted that induction as a cost-saving strategy would be particularly favorable for seedlings, leading to ontogenetic declines in the inducibility of these traits. We tested for induction of three different physical defense traits (prickles, latex and leaf toughness) in response to mechanical defoliation and jasmonic acid application using prickly poppies (Argemone glauca and A. mexicana, Papaveraceae) as a model system. Genetic variation in the induction of physical defenses was tested using maternal sib-ships sampled from multiple populations. Both species induced higher densities of laminar prickles, although the magnitude of induction was much higher in the endemic Hawaiian prickly poppy, A. glauca, than in the cosmopolitan A. mexicana. The magnitude of prickle induction was also higher in young compared to older juvenile plant stages in A. glauca, demonstrating a strong role of ontogeny. Neither latex exudation nor leaf toughness was induced in either species. Although significant genetic variation was detected within and among populations for constitutive expression of physical defense traits in Argemone, there was no evidence for genetic variation in the induction of these traits. This study provides the first evidence for the induction of physical defenses in prickly poppies, emphasizing how an ontogenetically explicit framework can reveal new insights into plant defense. Moreover, this study illustrates how sister species comparisons between island vs. continental plants can provide new insights into plant functional and evolutionary ecology, highlighting a fruitful area for future research on more species pairs.

Fusarium oxysporum homogenates and jasmonate induce limited sanguinarine accumulation in Argemone mexicana cell cultures.

In vitro cultures of Argemone mexicana (Papaveraceae) were induced from leaves of mature plants. Sanguinarine, a benzophenanthridine, was the main alkaloid in the cultures, even in the absence of inducers of secondary metabolism. The accumulation of this metabolite was increased by adding methyl jasmonate and fungal elicitors, although in a limited fashion in comparison to other sanguinarine-producing species. Evidence of a transport mechanism, which may be related to the magnitude of the response, was obtained based on the fluorescent properties of bezophenathridines in the elicited cultures.