Title : Leaf anatomy and histochemistry of Piper species from the Colombian Andes
Abstract:
The genus Piper (Piperaceae) comprises more than 2,000 pantropical species and represents one of the most diverse lineages of basal angiosperms. Species of Piper produce a remarkable diversity of specialized metabolites, including volatile terpenes, phenylpropanoids, amides, piperolides, lignans, neolignans, and flavonoids. This compounds mediate chemical defense and pollinator/disperser attraction, and exhibit anti-inflammatory, antimicrobial, antitumor, and antioxidant activities. Their production is modulated by environmental factors, organ type, developmental stage, tissue type, and the presence of specialized secretory cells. Consequently, Integrated anatomical and histochemical studies of Piper organs provide valuable insights into both taxonomically informative characters and the tissue-level localization of specialized metabolites. Despite their ecological and economic importance, the anatomy of Piper species from the northern Colombian Andes (Boyacá and Cundinamarca) remains poorly documented. This study characterized quantitative and categorical anatomical traits, along with histochemical features, of the leaf blade in 17 Piper species from Boyacá and Cundinamarca. Leaf blades from the third node, in the basal third of wild shrubs, were fixed in FAA and processed using standard histological protocols (dehydration, paraffin embedding, 5–8 µm sections, staining with acidified Astra blue and basic fuchsin). Characters of the dermal, ground and vascular tissues were recorded, with particular emphasis on secretory structures, including oil cells associated with epidermis, hypodermis, parenchyma and vascular bundles. Histochemical analyses of fresh material were performed to detect terpenes (NADI reagent), phenolics (ferric chloride and potassium dichromate), flavonoids (aluminum chloride), and tannins (vanillin). Anatomical data were analyzed using principal component analysis, revealing distinct patterns of secretory tissue differentiation among species. Piper fusagasuganum was distinguished by a markedly higher abundance and larger size of secretory cells in the vascular bundles and parenchyma of the midrib, suggesting an enhanced capacity for metabolite accumulation in central vein tissues. In contrast, P. reticulatum exhibited more numerous and larger size of secretory cells in the adaxial hypodermis and abaxial epidermis, together with thicker palisade parenchyma, reflecting distinct investment in dermal secretory tissue and photosynthetic parenchyma. P. peltatum showed comparatively low development of these traits, while species such as P. grande, P. aequale, P. aduncum, and P. auritum displayed more homogeneous anatomical patterns without pronounced tissue specialization. These findings identify anatomical characters of potential taxonomic value associated with the distribution and morphology of secretory structures and provide a framework for future studies on the environmental and developmental regulation of specialized metabolite production in Piper. This research was funded by the Colombian General System of Royalties (Sistema General de Regalías, under project BPIN 2023000100058), and by the "Convocatoria para el Apoyo al Desarrollo de Tesis de Posgrado (Maestría de Investigación y Doctorado) de la Facultad de Ciencias Sede Bogotá de la Universidad Nacional de Colombia 2025, Modalidad 1" (Call for Support of Graduate Thesis Development, Universidad Nacional de Colombia, 2025), Código Hermes 66084. Research involving Colombian biodiversity was conducted under Genetic Resource Access Contract No. 121 (22 January 2016), and Amendment (Otrosí) No. 21, entered into between the Ministry of Environment and Sustainable Development and the Universidad Nacional de Colombia.
