Annonaceae aporphine alkaloids, of which liriodenine is the most abundant, have not been extensively studied from a biological standpoint. The goal of this study was to investigate the role of liriodenine in antimicrobial defense during early developmental stages in Annona diversifolia. The fungi Rhizopus stolonifer and Aspergillus glaucus, which are responsible for seed deterioration, were isolated during imbibition, and their antifungal activity was determined by diffusion, macrodilution, and metabolic inhibition assays using purifi ed liriodenine and alkaloid extracts obtained from embryos, radicles, and roots at early developmental stages. The presence of liriodenine in extracts was quantifi ed by high-performance liquid chromatography. Purifi ed liriodenine and alkaloidal extracts inhibited both fungi, and there was a positive relationship between extract activity and amount of liriodenine contained therein. The quantity of liriodenine present in extracts suggests its importance in controlling other phytopathogens.

Annonaceous acetogenins (ACGs) are molecules with carbon numbers C35-C37, usually with tetrahydrofuran and tetrahydropyran rings and one terminal γ-lactone (usually α,β-unsaturated), in a large aliphatic chain that is varyingly hydroxylated, acetoxylated or ketonized. ACGs have ecological functions as insecticides and are pharmacologically promising due to their cytotoxic and antitumoral properties. They are found in the seeds, leaves, roots, flowers and fruits of annonaceous plants and can be detected during isolation via thin-layer chromatography using Kedde's reagent, which reacts with the unsaturated lactone. This chapter describes the location in situ of ACGs in fresh sections of annonaceous seeds using Kedde's reagent.The acetogenins are located in the idioblasts, in the endosperm and in the embryonic axis during differentiation. This method can aid in the detection of ACGs with a terminal unsaturated γ-lactone in organs and tissues.

Acetogenins (ACGs) are bioactive compounds with cytotoxic properties in different cell lines. They are antitumoural, antiparasitic, antimalarial, insecticidal, antimicrobial, anti-fungal and antibacterial. These secondary metabolites function in plant defence and are found in specific organelles and specific cells, thereby preventing toxicity to the plant itself and permitting site-specific defence. The aim of this work was to histochemically determine the in situ localisation of ACGs in the endosperm of Annona macroprophyllata seeds using Kedde’s reagent. Additionally, the co-localisation of ACGs with other storage molecules was analysed. The seeds were analysed after 6 and 10 days of imbibition, when 1 or 2 cm of the radicle had emerged and metabolism was fully established. The seeds were then transversally cut in half at the midline and processed using different histological and histochemical techniques. Positive reactions with Kedde’s reagent were only observed in fresh, unfixed sections that were preserved in water, and staining was found only in the large cells (the idioblasts) at the periphery of the endosperm. The ACGs’ positive reaction with Sudan III corroborated their lipid nature. Paraffin sections stained with Naphthol Blue Black showed reactions in the endosperm parenchyma cells and stained the proteoplasts blue, indicating that they might correspond to storage sites for albumin-like proteins. Lugol’s iodine, which is similar in chemical composition to Wagner’s reagent, caused a golden brown reaction product in the cytoplasm of the idioblasts, which may indicate the presence of alkaloids.Based on these results, we propose that Kedde’s reagent is an appropriate histochemical stain for detecting ACGs in situ in idioblasts and that idioblasts store ACGs and probably alkaloids. ACGs that are located in idioblasts found in restricted, peripheral areas of the endosperm could serve as a barrier that protects the seeds against insects and pathogen attack.

Currently, the Annonaceae family is characterised by the production of acetogenins (ACGs), and also by the biosynthesis of alkaloids, primarily benzylisoquinolines derived from tyrosine. The objective of this study was to confirm the presence of alkaloids and acetogenins in the idioblasts of the endosperm and the embryonic axis of A. macroprophyllata seeds in germination. The Dragendorff, Dittmar, Ellram, and Lugol reagents were used to test for alkaloids, and Kedde’s reagent was used to determine the presence of acetogenins in fresh sections of the endosperm and embryonic axis of seeds after twelve days of germination. A positive reaction was observed for all the reagents, and the presence of alkaloids and acetogenins was confirmed in the idioblasts of the endosperm and those involved in the differentiation of the embryonic axis of the developing seedling. We concluded that the idioblasts store both metabolites, acetogenins and alkaloids. Beginning at differentiation, the idioblasts of the embryonic axis simultaneously biosynthesise acetogenins and alkaloids that are characteristic of the species during the development of the seedling. The method used here can be applied to histochemically confirm the presence of acetogenins and alkaloids in tissues and structures of the plant in different stages of its life cycle.

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