Megapolis such as Mexico City, have atmospheric pollutants that interact with the humidity and solar radiation. The topography of this city promotes air stagnation, generating atmospheric pollutants and episodes of acid rain, a phenomenon well recorded since the end of the 1980s. However, little we know about how urban trees respond to acid rain in the city. Here we present how simulated acid rain causes anatomical and changes in photosynthetic pigments in two of the most abundant urban trees in Mexico City: Liquidambar styraciflua L. and Fraxinus uhdei (Wenz.) Lingelsh. We first described the leaf anatomy of both species. Then, we used one-year-old trees sprayed with sulfuric acid solutions at pH 2.5 and 3.8, and evaluated visible leaf damage, anatomical alterations, and chlorophyll contents. In both species, the pH 2.5 caused cuticle alterations and areas of total tissue destruction. L. styraciflua showed greater sensitivity, but we discuss some of the tolerance mechanisms. Finally, acid rain also reduced the chlorophyll contents. These results contribute toward a catalogue of urban tree species to describe pollution-induced damages, and the identification of tolerant species useful for short- and mid-term detection of environmental crisis, in cities with similar environmental conditions and urban tree composition.

Acidic soils have increased due to agricultural practices, climate factors, and the excessive use of nitrogen fertilizers to meet food demand. In these soils, aluminium (Al) is soluble and can be taken up by roots, but it is toxic to most plant species. Fagopyrum esculentum is able to adapt to acidic toxic aluminium conditions. Anatomical studies identifying novel potential cellular structures as sites of Al accumulation are currently lacking. This study provides an anatomical description of the cotyledons, revealing the presence of papillae and glandular trichomes at their margins. In seedlings treated with 100 μM Al, energy‐dispersive x‐ray spectroscopy (ESEM‐EDS) analysis of the cotyledons revealed that the margin has the highest concentration of Al. The margin containing the epidermal papillae was subjected to laser microdissection, and Al was quantified using mass spectrometry with an inductively coupled plasma source ICP‐MS and compared with the Al in the remaining leaf blades. The concentration of Al in the microdissected papillae was 3,460 mg Al kg⁻¹ Dry Weight (DW), whereas the blades contained only 1,390 mg Al kg⁻¹ DW. Moreover, histochemical tests for Al and total phenols in the epidermal papillae revealed that Al may be bound to phenolic compounds. Thus, this study demonstrated that the cotyledons of F. esculentum have epidermal papillae that can accumulate Al.

El aluminio (Al) es el tercer elemento más abundante en la corteza terrestre. Su forma química depende de los valores de pH del suelo. En suelos ácidos el Al se libera y solubiliza principalmente en la forma iónica de Al3+, la cual es tóxica para la mayoría de las plantas. Los principales efectos tóxicos del Al se observan en el ápice de la raíz, inhibiendo la división y elongación celular, lo que origina una raíz def iciente en la absorción de agua y nutrientes, dando como resultado la inhibición del crecimiento, y, por lo tanto, una disminución en la productividad de las plantas. Actualmente, el Al se encuentra disponible en suelos que no son naturalmente ácidos y se utilizan como tierras de cultivo. Esto ha generado una línea de investigación en relación con el efecto del Al en diferentes especies de plantas, por ejemplo, los sitios de acumulación y concentración en los diferentes órganos vegetales. En este contexto, el objetivo de la presente revisión es proporcionar una guía para seleccionar la técnica más adecuada que permita la localización y cuantif icación del Al en los diferentes órganos de las plantas que crecen en suelos ácidos. Para ello, primero se describen los fundamentos de las distintas técnicas para localizar y cuantif icar el Al en los órganos o tejidos vegetales y, con la f inalidad de integrar la información se proporciona una guía para recomendar la técnica más apropiada con base en algunas características de la(s) especie(s) a analizar. Profundizar en el estudio de los sitios de acumulación y las concentraciones de Al que las plantas pueden absorber, permitirá seleccionar cultivos tolerantes que pueden ser aprovechados para la producción agrícola o estudios de f itorremediación.

Anatomical insights from plant studies offer a unique way to understand the tissue-level adaptations that enable some species to develop aluminum (Al) tolerance. To conduct functional anatomy studies, methods are required that uphold both structural integrity and cellular chemical stability. Previous research on the Al-tolerant species in Fagopyrum esculentum has focused primarily on physiological mechanisms, leaving technical and structural gaps regarding its sequestration in tissues. This research presents a histochemical approach to elucidate Al compartmentalization in mature F. esculentum plants. Samples were preserved with a modified Zamboni fixative to avoid metal leaching before being embedded in glycol methacrylate (GMA). High-quality 12 μm sections were obtained. For anatomical description, Toluidine Blue O was utilized, while Chromazurol S (CAS) was employed for histochemistry. In addition, laser microdissection of the leaves and Al quantification by ICP-MS were performed. The results revealed a progressive acropetal gradient. The marginal papillae of the leaves exhibited a concentration of 4352 ± 0.5 mg Al*kg⁻¹ DW (1.6 times higher than the lamina fraction). This pattern shows that Al sequestration in this region is a permanent trait inherited from the developmental start. This study offers a replicable foundation for exploring metal compartmentalization and detoxification processes in F. esculentum and related metal-tolerant herbaceous plants.