Micromorphological and phytochemical survey of Ballota acetabulosa (L.) Benth

Abstract Within the Open Science project entitled ‘Botanic Garden, factory of molecules’, a multidisciplinary study approach was applied to Ballota acetabulosa (L.) Benth., at the Ghirardi Botanic Garden (Toscolano Maderno, BS, Italy). Micromorphological and histochemical investigations were performed on the secreting structures of the vegetative and reproductive organs under light, fuorescence and electronic microscopy. Concurrently the characterization of the volatiles spontaneously emitted from leaves and flowers were examined. Four trichome morphotypes were identified: peltate and short‐stalked, medium‐stalked and long‐stalked capitate trichomes, each with a specific distribution pattern. The histochemical analysis was confirmed using ultrastructural observations, with the peltates and long‐stalked capitates as the main sites responsible for terpene production. The head‐space characterization revealed that sesquiterpene hydrocarbons dominated both in leaves and flowers, with γ‐muurolene, β‐caryophyllene and (E)‐nerolidol as the most abundant compounds. Moreover, a comparison with literature data concerning the ecological roles of the main compounds suggested their dominant roles in defence, both at the leaf and flower level. Hence, we correlated the trichome morphotypes with the production of secondary metabolites in an attempt to link these data to their potential ecological roles. Finally, we made the obtained scientific knowledge available to visitors of the Botanic Garden through the realization of new labelling dedicated to B. acetabulosa that highlights the ‘invisible’, microscopic features of the plant.


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The peltates were made of a basal cell, a stalk cell, and a large secretory head of 8 cells arranged 193 in a single disc. They were localized on the whole plant epidermis, being scarce on leaves and 194 prevailing on the sepal abaxial surfaces (Figure 1 a-f).

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Three different types of capitate trichome were found: short-stalked consisting of a basal cell, a 196 stalk cell, and a round 2-4-celled head, mainly located along the veinal system of the whole 197 plant, especially on the leaf and the corolla abaxial sides (Figure 1 a-

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The observed non-glandular hairs were of two different types: simple, multicellular, uniseriate 203 with distinct articulation between the cells (Figure 1 a-

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In the long capitates, the simultaneous occurrence of lipidic, polysaccharidic, and phenolic

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In detail, 34 and 21 compounds were identified in the foliar and floral profiles, respectively 232 ( Table 3).

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were the most abundant. The remaining exclusive compounds accounted for percentages lower 244 than 2.0% or in traces (<0.1%).

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Sesquiterpene hydrocarbons represented the main compound class in the floral profile,

Scientific dissemination
The scientific results reported in the "Micromorphological investigation" and "Phytochemical

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The long capitate hairs were scarce on leaves and numerous on the calyx abaxial side.

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In mature trichomes, Golgi bodies and RER occurred occasionally, while the most striking

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Although it was detected as a common compound, its larger relative abundance in the leaves 358 allowed us to hypothesize a more marked repellent action at the vegetative organs level.

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Regarding the other common compounds, the attractive-repulsive action of β-caryophyllene (

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In addition, (E)-geranyl acetone (26)  to the species, but information is lacking on these topics.

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Finally, our study, that originated and takes place at the Ghirardi Botanic Garden, converged towards the fruition of the research products by the general public, following a new approach to 391 the dissemination of scientific data that is increasingly appreciated in literature (Giuliani et al.