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In the tropical region, the greatest challenge of the biomonitoring approach is to establish linear relationships between biomarkers measured in plants and pollutant concentrations, since the bioindicator responses can be intensified or restricted by climatic variations. In southeastern Brazil, there are two regions affected by air pollution, where the Atlantic Forest remains and should be preserved. Consequently, both areas have been monitored by biomonitoring procedures using standardized and tropical plants. The industrial complex settled in Cubatão is one of the world's most famous examples of environmental pollution and degradation, with consequent decline of the Atlantic Forest. An oil refinery is among the most polluting industries in the Cubatão region. The other region is located in the Metropolitan Region of Campinas (MRC). The MRC has been affected by high levels of air pollutants originated from road traffic and is responsible for over 80% of CO, NOx, and hydrocarbon emissions and develops industrial activities that emit about 70% of the particulate matter present in the region. Both regions are distinguished by the climate, despite the fact that they are only about 130 km far from each other. Several studies carried out by our group in these regions aimed to establish the best native tree species and respective potential biomarkers for future assessment of pollution effects on tropical Forests. We present a critical review about the efficiency of native species compared to standardized bioindicator plants considering antioxidant defense system, nutrient accumulation, and microscopic aspects when exposed to atmospheric pollutants and climate.

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Ozone (O 3) is an oxidative pollutant that causes visible foliar symptoms in sensitive plants. Importantly, cellular markers induced by physiological alterations, including oxidative burst (OB), hypersensitive response-like (HR-like) reactions, and accelerated cell senescence (ACS), precede these symptoms. Because little is known about the effects of ozone in tropical environments, we aimed to identify these cellular markers in Nicotiana tabacum, Ipomoea nil and Psidium guajava growing in an urban area of tropical Sao Paulo, Brazil, and describe the specific physiological alterations that trigger the development of visible symptoms. Cell wall wart-like protrusions, an OB cellular marker, and swelling of thylakoids and mitochondrial membranes, as well as accumulation of plastoglobuli, all markers of ACS, were cell markers common to all species studied. Cellular markers indicating HR-like reaction, as observed in the asymptomatic leaves of N. tabacum and I. nil, are precursors of future development of necrotic areas, featuring the visible symptoms. On the other hand, the main cause of visible symptoms in P. guajava appeared to be the accumulation of phenolic compounds in the mesophyll tissue, an ACS marker. Based on this line of evidence, these bioindicator plants growing in a tropical environment show the damaging effects of O 3 pollution, even before visible symptoms develop. Moreover, this damage can be detected through a distinct group of cellular markers.

No abstract