Differential Tolerance of Primary Metabolism of <i>Annona emarginata</i> (Schltdl.) H. Rainer to Water Stress Modulates Alkaloid Production

<i>Annona emarginata</i> produces alkaloids of ecological and pharmacological interest and is tolerant to water and biotic stress, so it is used as rootstock for other Annonaceae fruits. There are few reports in the literature on how contrasting water stress impacts the production of specialized metabolites in Annonaceae and how primary metabolism adjusts to support such production. The objective of this investigation was to evaluate how drought and flooding stress affect alkaloid concentration and the primary metabolism of young <i>A. emarginata</i> plants. Three water levels (flooding, field capacity, and drought) were studied at two moments (stress and recovery). Variables analyzed were gas exchange levels, chlorophyll <i>a</i> fluorescence, leaf sugars, total alkaloid content, alkaloid profile, and Liriodenine concentration. The photosynthetic metabolism of <i>A. emarginata</i> was affected by water stress, with plants having a greater ability to adapt to drought conditions than to flooding. During the drought, a reduction in photosynthetic efficiency with subsequent recovery, higher starch and trehalose concentrations in leaves, and total alkaloids in roots (480 µg.g⁻¹) were observed. Under flooding, there was a reduction in photochemical efficiency during stress, indicating damage to the photosynthetic apparatus, without reversal during the recovery period, as well as a higher concentration of total sugars, reducing sugars, sucrose, glucose, and fructose in leaves, and Liriodenine in roots (100 µg.g⁻¹), with a lower concentration of total alkaloids (90 µg.g⁻¹). It could be concluded that there is differential tolerance of <i>A. emarginata</i> to water stress, inducing the modulation of alkaloid production, while drought promotes a higher concentration of total alkaloids and flooding leads to an increase in the Liriodenine concentration.