Assessing pollination quality on the bioactivity of medicinal plants

ASHWORTH, L.; CAMINA J.; USSEGLIO, V. L.; MARQUEZ, V.; DAMBOLENA, J. S.; ZYGADLO J.A.

Simposio; Simpósio Brasileiro de Polinização; 2022

Many animal-pollinated plant species are able toreproduce sexually by both selfing and outcrossing. Selfpollination may be mediated by pollinators or occurautonomously, in their absence. However, cross pollinationis feasible only through pollinators. The quality ofpollination (self/cross) affects the fitness of the progeny.Usually, selfed progeny has lower fitness than outcrossedprogeny, a phenomenon known as inbreeding depression.The chemical defenses of plants (i.e., the secondarymetabolites produced against herbivores and pathogens)are among the traits that can be negatively affected byinbreeding depression [1]. Medicinal plants have been usedby humans for centuries due to the beneficial effects ofsome of their secondary metabolites. Thus, changes inpollination quality (selfing vs outcrossing) may affect theproduction and composition of secondary metabolites ofplant progeny and therefore change the bioactivity ofmedicinal plants against pathogen microorganisms. Wehypothesize that selfed progeny has lower bioactivity thanthe outcrossed progeny.MethodsWe studied Lepechinia floribunda (Lamiaceae) amedicinal shrub native to south America. Its essential oils(EOs) have antibacterial and antiviral activities [2]. Bymanual pollination treatments, we produced selfed andoutcrossed progeny across three generations. Plants weregrown in greenhouses. The third generation of selfed (30plants) and outcrossed (30) plants was used to obtain EOsby hydrodistillation of the aerial part. The identification andquantification of EOs compounds were made by gaschromatography-mass and spectrometry. The bioactivity(bacteriostatic and bactericide effects) of the EOs fromselfed and outcrossed plants was tested against threebacterial species: Escherichia coli, Staphylococcus aureus(both Gram+), and Pseudomonas syringae (Gram-). Allstatistical analyses were conducted in R [3].Results and DiscussionThe EO of L. floribunda had higher abundance ofsesquiterpenes than monoterpenes. The chemicalqualitative composition of EOs was the same betweenoutcrossed and selfed plants (Jaccard`s diversity index=0).Outcrossed plants had higher abundance of oxygenatedmonoterpenes than selfed plants, higher negative value ofM index (Fig.1A). Moreover, outcrossed plants had higherabundance of oxygenated sesquiterpenes than hydrocarbonsesquiterpenes (S index negative in Fig. 1B), whereas,selfed plants had similar abundance of both kinds ofsesquiterpenes (Fig.1B). EOs from outcrossed plants hadhigher bacteriostatic effect than EOs from selfed onesagainst S. aureus (minimal inhibitory concentration:0.44±0.12; 0.70± 0.27 µl/ml, respectively), but nodifferences were found against E. coli. Both selfed andoutcrossed progeny had similar bactericide effects againstboth bacterial species. Neither bacteriostatic norbactericide effects were observed against P. syringae.Changes in EOs bioactivity were due to modifications inthe relative abundance of compounds and not to changes intheir composition. Our results support previous findings,terpenes would be more efficient against bacteria Gram +than Gram-[4].Figure 1 Relative abundances of terpene groups present inthe essential oil of Lepechinia floribunda A. M index: ln(relative abundance of hydrocarbons/oxygenatedmonoterpenes), and B: S index: ln (relative abundance ofhydrocarbons/oxygenated sesquiterpenes). C: outcrossed,S: selfed plants.ConclusionsOutcrossed progeny of a medicinal plant had higherantibacterial activity than progeny produced byautonomous selfing in absence of pollinators. We show forthe first time the importance of considering the pollinationquality effect on the bioactivity of a medicinal plant.